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Article

Zinc(II) Iodide Complexes with Redox-Active α-Diimine Ligands: Synthesis, Structure, Spectroscopic and Electrochemical Properties

by
Dmitriy S. Yambulatov
*,
Natalia V. Gogoleva
,
Ivan V. Smolyaninov
,
Vladimir A. Bushuev
,
Anna A. Tychinina
,
Alexandra S. Samulionis
,
Julia K. Voronina
,
Ivan V. Skabitsky
,
Sergey S. Shapovalov
,
Stanislav A. Nikolaevskii
and
Mikhail A. Kiskin
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky prosp., 119991 Moscow, Russia
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(11), 967; https://doi.org/10.3390/cryst15110967
Submission received: 27 October 2025 / Revised: 7 November 2025 / Accepted: 7 November 2025 / Published: 10 November 2025
(This article belongs to the Special Issue Transition Metal Complexes with Heterocyclic Ligands: Structural Insights, Biological Potential, and Computational Perspectives)
Browse Figures
Versions Notes

Abstract

Reactions of anhydrous Zn(II) iodides with redox-active 1,4-diaza-1,3-butadiene (DAD) and its bis(imino)acenaphtene (BIAN) derivatives in absolute acetonitrile yielded a series of new complexes: [(Mes-DAD)ZnI2] (1), [(dpp-DAD)ZnI2] (2), and [(dpp-BIAN)ZnI2] (3). Single crystals of all compounds were obtained, and their molecular structures were unambiguously determined by X-ray diffraction analysis. Purity of bulk samples in solid state was confirmed by PXRD. Stability of the complexes in solution was investigated by means of UV-Vis and NMR spectroscopy. Cyclic voltammetry revealed two or three quasi-reversible reduction waves in the cathodic region for complexes 1–3. The ability of 3 to accept up to three electrons highlights the potential of these compounds as electrocatalysts for reductive transformations.

1. Introduction

The redox activity in metal complexes is not limited to the metal center; organic ligands can also exhibit accessible non-innocent behavior. Among them, α-diimine systems, particularly 1,4-diaza-1,3-butadienes (DADs) and acenaphthene-1,2-diimines (BIANs), have become prominent scaffolds in modern organometallic chemistry. Their key feature is the presence of lone electron pairs on the nitrogen atoms of the diimine moiety, enabling chelation to a metal center. Upon coordination, these ligands can persist in their neutral form or undergo reversible reduction (Scheme 1). DAD ligands can be reduced to stable radical-anionic or dianionic states [1,2,3,4], while the extended π-system of BIANs allows for even more extensive electron uptake, forming mono-, di-, tri-, and tetraanionic species [5].
The coordination of α-diimine ligands to metal center induces significant changes in their spectral and structural parameters, enabling comprehensive characterization through non-destructive analytical techniques. The electronic state of these ligands can be effectively studied by various methods: EPR spectroscopy for radical-anionic species, NMR for diamagnetic compounds, and magnetochemical measurements for assessing the ligand reduction state. Structural evolution accompanies electron transfer, as evidenced by X-ray crystallographic data [5,6] (Table 1).
Further reduction of the diimine fragment leads to characteristic bond length alterations, i.e., C–N bonds elongate while C–C bonds shorten, transitioning from double to single bond character. Furthermore, the electronic state of coordinated diimines is reflected in strong, characteristic C-N vibration frequencies in IR spectra (Table 2) [7,8,9].
While the exact positions of these bands may be influenced by the nature of the R-substituents, the metal center, and coordinating solvents, they consistently fall within ranges that are characteristic of the ligand’s reduction state. Furthermore, the reduction of dpp-BIAN is accompanied by distinct color changes in solution, which serve as a useful visual indicator of the ligand’s electronic state and facilitate real-time monitoring of the synthesis [10].
Redox-active α-diimine ligands, particularly DADs, are highly versatile building blocks in coordination chemistry due to their tunable electronic properties. The extensive conjugation in their π-system, combined with the ability to modify nitrogen substituents, allows for precise control over their steric profile, electron-donor/acceptor character, and redox potentials [1,3,11,12]. This versatility translates into a wide range of applications for their metal complexes. They serve as key components in catalytic systems [13,14,15,16,17,18], act as potent one-electron oxidants, and can stabilize unusual oxidation states in lanthanides [4,9,19,20]. Their intriguing electronic properties also lead to phenomena such as charge-transfer [21,22,23] and single-molecule magnetism [24,25,26,27]. Beyond classical N,N’-chelation [28,29,30], these ligands can also form rare bridging or chelating-bridging coordination modes, although such examples are less common [31,32,33,34]. Furthermore, their reactivity extends to facilitating C–C bond formation in the coordination sphere of nickel [27] and imparting anticancer activity in platinum(II) complexes [35]. As exemplified by anthracene-functionalized diimine complexes, diimine systems can undergo specific and irreversible photochemical reactions, such as cycloreversion, upon exposure to UV light [36]. Coordination compounds incorporating diimine ligands demonstrate significant potential as photoresponsive materials.
Moreover, zinc, as a metal center, offers a high extreme ultraviolet (EUV) absorption cross-section [37], which is crucial for the next-generation lithography operating at 13.5 nm. This intrinsic property, combined with the ability to form well-defined molecular clusters (such as Zn-oxo clusters), allows for the creation of photoresists with enhanced sensitivity and reduced line-edge roughness (LER). The structural versatility of zinc coordination compounds enables precise tuning of their solubility and photoreactivity through rational ligand design, making them outstanding candidates for high-resolution negative photoresists in advanced semiconductor manufacturing [38,39]. As demonstrated in Sn-oxo cluster systems, the diffusion of highly mobile radicals like butyl species can lead to pattern blur and a loss of critical dimension control [40,41]. In this context, redox-active diimine ligands offer a unique advantage. Their ability to act as efficient electron scavengers can quench uncontrolled radical chain reactions, effectively acting as “radical sinks” that confine the exposure event and enhance lithographic precision. This inherent radical regulation mechanism, combined with the high EUV absorption of the metal center, positions zinc diimine complexes as a promising platform for designing advanced negative-tone photoresists that intrinsically balance sensitivity and resolution. On the other hand, the iodine atom also exhibits a high atomic photoabsorption cross-section [37], which also indicates the prospects for using complexes based on metal iodides as highly sensitive resists for photolithography applications.
As stated above redox-active α-diimine ligands are well-known for their ability to undergo reversible, stepwise reduction, accepting up to two electrons to form stable radical-anionic and dianionic states. This capacity can be even greater for specific types, such as dpp-BIAN, which can accommodate up to four electrons. The electrochemical properties of both metal-free diazadienes and their complexes with various d-block metals have been extensively studied. In contrast, the redox behavior of zinc(II) iodide complexes with these ligands remains largely unexplored. Herein, we report a systematic investigation of the electrochemical properties of a series of Zn(II) diimine complexes, filling this gap in the literature. In addition, the [(dpp-DAD)ZnCl2] (4) complex, previously obtained [42] but structurally uncharacterized, was used in this study. This compound was included in this work due to a comparison of the structures and electrochemical characteristics of new zinc iodide-based compounds.

2. Results and Discussion

2.1. Synthesis and Characterization [(Mes-DAD)ZnI2] (1), [(Dpp-DAD)ZnI2] (2), [(Dpp-BIAN)ZnI2] (3)

Three novel Zn(II) diimine complexes were prepared in high yields (60–95%) via the reaction of anhydrous Zn(II) iodides with redox-active 1,4-diaza-1,3-butadiene derivatives in absolute acetonitrile under an inert atmosphere (Scheme 2). Heating the reaction mixtures in a sealed ampoules induced a color change to yellow or orange-red, with crystalline products forming upon cooling. Isolation involved simple decantation and washing with mother solution media. It was found that strict adherence to anhydrous and anaerobic conditions is imperative, as exposure to air or moisture promoted side reactions and amorphous products, significantly reducing yields.
The coordination of the α-diimine ligands to the zinc center in complexes 1–3 is clearly evidenced by their IR spectra (see Supplementary Information). A defining feature is the observed shift in the C=N stretching vibrations to lower wavenumbers—to 1596 cm−1 (1), 1586 cm−1 (2), and 1662 cm−1 (3)—compared to the free ligands (approx. 1620 cm−1 for DADs and 1671–1642 cm−1 for dpp-BIAN) [1,28]. This consistent shift is a characteristic signature of coordination through both nitrogen atoms of the diimine moiety [43].
The solubility of 1 in CDCl3 is extremely low, and the compound’s signals in the 1H spectrum are difficult to detect. Coordination with zinc iodide results in a shift in the ortho-methyl group signal (2.45 ppm, see Supplementary Information for discussed NMR spectra) compared to the free ligand (2.17 ppm) [44]. The proton signals of the diimine fragment are also shifted downfield (8.28 and 8.11 ppm in the complex and free ligand, respectively). Dissolution in d6-DMSO results in a reaction accompanied by a color change to yellow and the formation of a yellow precipitate. The 1H spectrum of the solution contains signals virtually identical to the signals of the free ligand in d6-DMSO.
For ligands containing 2,6-diisopropylphenyl substituents, hindered rotation about the N-dpp bond makes the methyl groups nonequivalent. For the 2, the signal of methyl groups observed as one broadened signal near the coalescence point centered at 1.27 ppm. As for 3, complex formation leads to a downfield shift in the diimine proton signals (8.24 and 8.10 ppm in the complex and the free ligand) [45].
For 3 1H и 1H–1H EXSY spectra show no evidence of exchange between nonequivalent methyl groups suggesting totally hindered rotation about N–Ar bonds. The signals in the 1H spectrum of the complex are shifted downfield compared to the ligand [46], with a particularly strong shift (0.42 ppm) for the CH groups of the isopropyl substituents. In addition to the ligand signals, the spectrum also contains a signal of solvate acetonitrile. Assignments of CH group resonances in the 13C spectrum were made by using 1H13C-HSQC spectroscopy. Notably, the BIAN carbons located farthest from the coordination site exhibit the second greatest downfield shift upon coordination (3.4 ppm) after imine carbon (4.7 ppm). In contrast to most of the signals, the ipso-aryl carbons are shifted upfield by at least 2.7 ppm upon complex formation.

2.2. Crystal Structures of 1–4

Compounds 1, 2 and 4 crystallize in the monoclinic crystal system C2/c, and the complex 4 crystallizes as a solvate with one MeCN molecule in the orthorhombic space group Pbca. All studied compounds are mononuclear, in which zinc atom coordinates one chelate ligand and two halogen atoms (Figure 1). The molecules of complexes 1, 2 and 4 are symmetrical and the two-fold axis passes through the metal atom, through the center of the C1–C1 bond and between two halogen atoms. The main bond lengths and angles for 1–4 are given in Table 3. Coordination environment of metal atoms ZnN2 × 2 (X = Cl, I) in 1–4 correspond to tetrahedral, which is confirmed by the analysis of the τ4 parameter (Table 3; τ4 = [360 − (β + α)/141°], where α and β are two largest valence angles at the central coordination atom and θ = 109.5° is a tetrahedral angle; τ4 = 1 corresponds to a tetrahedron, τ4 = 0 corresponds to a square) [47]. The Zn–X bonds are equal to the known values for previously reported zinc complexes with α-diimine ligands (Zn–I 2.525–2.563 Å [48,49,50,51]; Zn–Cl 2.179–2.229 Å [52,53,54,55]). The Zn-N bond lengths for DAD ligands are similar to those known (Zn–N 2.067–2.109 Å), but in the case of the BIAN ligand, an elongation of this bond is observed (Zn–N 2.079–2.116 Å) [55]. The C–N and C–C bonds in the chelate units confirms a double bond character for C–N and indicates the neutral form of DAD and BIAN ligands [5,6]. In all complexes, the phenyl part is orthogonal to the chelate ring, which is a result of the steric effect caused by the methyl and isopropyl substituents in the phenyl group.
Intermolecular non-covalent contacts C(Me)–H…π (Table 4) in the crystal of 1 promote the packing of the molecules into a supramolecular layer in the ab plane (Figure 2a). The molecular structure of 3 is stabilized by intramolecular C(BIAN)–H…π(Ph) contacts between two H atoms of acenaphthenequinone and two phenyl fragments. In the crystal, the molecules of 3 are linked into a supramolecular chain along the b axis via C(Ph)–H…π(Ph) contacts (Figure 2c). In addition, the solvate molecule MeCN forms non-covalent C(Me)–H…π(Ph) and N…π(BIAN) interactions with aromatic rings of the complex (Table 3).
In 2 and 4, the π…π contacts between the phenyl fragments of adjacent molecules of the complex can be classified as weak, since the distances between the centroids are 4.048(4) Å for 2 and 4.035(2) Å for 4, but since the interplanar distance is about 3.527(3) for 2 and 3.321(1) Å for 4. As a result, this leads to the formation of a supramolecular layer along the ab plane (Figure 2b).

2.3. Photophysical Properties of 1–3 in Solution and Solid State

The photoabsorption spectra of free DAD and BIAN ligands and their Zn complexes in MeCN solution are shown in Figure 3. Free DAD ligands and their Zn complexes exhibit two photoabsorption bands. The relatively broad band (λ = ∼255 nm) in the range from 200 to 300 nm is due to the π–π* transition occurring from the Ph moieties. The other broad band (λ = ∼359 nm for dpp-DAD and 1 and ∼355 nm for Mes-DAD and 2) in the range from 300 to 450 nm is due to the intraligand charge transfer (ILCT) between the Ph moieties and the α-diimine moiety. The free dpp-BIAN ligand exhibits two broad, intense bands with peaks at 272 and 309 nm, the latter with a shoulder at 325 nm attributed to the π–π* transition, and weak bands at 350, 370, and 410 nm (ILCT). The π–π* bands 3 showed a bathochromic shift to 312 nm, an increase in intensity at 325 nm, and broad weak peak in the range from 370 to 500 nm.
The solid-state UV-Vis diffuse reflection–photoabsorption spectra of the free DADs and dpp-BIAN ligands and 1–3 are shown in Figure 4. All compounds exhibit low-intensity bands in the range of 200–270 nm and broad bands in the range of 270 to 600 nm. The transition from dpp-DAD (λmax = 388 nm, in the range of 270–480 nm) to 1 is accompanied by a bathochromic shift by 5 nm and the appearance of a new band at 429 nm with shoulders at ~490 and ~530 nm. The Mes-DAD ligand in the solid state has one broad band at 408 nm (the range of 270–510 nm) as well as complex 2 reveals a band at 396 nm with shoulders at ~350, ~430, ~460 and ~490 nm. The free Dpp-BIAN show broad band in the range of 270–570 nm with a maximum at 420 nm and a shoulder at 380 nm, while photoabsorption 3 has three peaks 352, 397 and 413 nm.
Based on the spectral characteristics of the complexes in solutions, it can be concluded that the photoabsorbing properties of 1 and 2 are close, and the addition of an acenaphthene moiety to the ligand in case 3 leads to the appearance of a band at 320 nm and a bathochromic shift in the bands associated with ILCT to the blue region. In the solid state, complexation leads to a broadening of the photoabsorption region, which may be due to non-covalent intermolecular interactions of aromatic fragments.

2.4. Cyclic Voltammetry of Obtained Complexes

The electrochemical properties of zinc iodide complexes with redox-active ligands were studied by cyclic voltammetry in acetonitrile using a GC working electrode (Table 5).
The investigated complexes undergo both reduction and oxidation within the considered potential range. In the cathodic region, zinc complexes with DAD ligands are reduced via two consecutive, one-electron, quasi-reversible stages (Figure 5).
The current ratio values indicate the formation of relatively stable mono- and dianionic species of the complexes during the timescale of the CV experiment. The peaks observed on the CV curves correspond to changes in the oxidation state of the coordinated redox-active ligand. Throughout the potential sweep, no electrochemical activity of the metal is detected. Under analogous conditions, the zinc iodide electroreduction proceeds irreversibly at −1.1 V with an anodic adsorptive peak corresponding to the reoxidation of zero-valent metal appearing at −0.4 V on the CV back scan (See Supporting Information), which is in good agreement with previously obtained data [57]. The reversibility of the first cathodic step decreases upon extending the potential scan range to −1.9 V and generating the corresponding dianionic complex. The observed electrochemical behavior suggests the occurrence of a rapid chemical reaction following the second electron transfer. The general scheme of the redox transformations for the complexes with DAD ligands can be represented as follows (Scheme 3):
Coordination of redox-active ligands to zinc(II) iodide results in a significant anodic shift in their reduction potentials by 1.27 and 1.32 V, respectively, compared to the free diimines [35]. An analogous potential drift was also observed when quinonoid ligands were employed [58]. Furthermore, compared to 4, the substitution of the chloride anion with iodide also facilitates a shift in the Ered11/2 to more positive values, along with a partial stabilization of the doubly reduced form of the 2 complex. The mechanism of electroreduction is also altered: for 4, the second reduction step is irreversible and is accompanied by the reduction of the zinc ion to its zero-valent state [56], whereas for 2, the second peak is quasi-reversible and the reoxidation anodic peak is not observed on the CV reverse scan (Figure 5).
In the case of the BIAN compound (3), three quasi-reversible cathodic reduction peaks are observed on the CV curves (Figure 6).
The results are consistent with the electrochemical behavior of the free BIAN ligand, for which three cathodic redox stages were also observed, corresponding to the formation of the mono-, di-, and trianion radical species [59]. The current ratio for the first and second cathodic stages indicate the formation of relatively stable mono- and dianionic complexes containing the reduced form of the ligand. The decrease in the Ia/Ic ratio for the second redox transition and the appearance of an anodic peak (−0.03 V) on the CV reverse scan upon extending the potential sweep range to −1.7 V (Figure 6(2)) suggest the possibility of a rapid chemical reaction following the second electron transfer. The reoxidation peak current intensity increases upon generating the trianionic form of the complex in the near-electrode region. This behavior can be rationalized by the high basicity of the generated di- and trianionic species, which are capable of interacting with trace water in the solvent. It is important to note that the metal center does not participate in these electrode processes, in contrast to previously studied iron complexes [59,60].
As with the first two complexes, the reduction potentials of 3 are significantly shifted anodically compared to the free ligand [59]: upon coordination, the potential of the first cathodic stage shifts to more positive values by 1.0 V, while the second and third stages shift by approximately 0.7 V. In the anodic region, all complexes under consideration exhibit a single, irreversible, multi-electron process at 0.73–0.74 V, independent of the ligand type (See Supporting Information). The electrochemical oxidation of ZnI2 in the MeCN/CH2Cl2 solvent mixture proceeds via an irreversible one-electron step at a potential of 0.86 V. For the previously discussed chloride complexes of platinum(II) and zinc(II) with analogous DAD ligands, no electrochemical activity was observed in the anodic region up to 1.8 V; therefore, it can be postulated that the observed peak corresponds to Zn–I bond cleavage.

3. Materials and Methods

3.1. General Remarks

All synthetic and product isolation procedures were performed under an inert atmosphere using standard Schlenk techniques due to the hygroscopic nature of zinc(II) iodide precursors. Anhydrous acetonitrile was prepared by drying over phosphorus(V) oxide, followed by storage over 3 Å molecular sieves, and was distilled in vacuo immediately prior to use. Zinc(II) iodide was synthesized in situ from elemental zinc and iodine in acetonitrile within a glass ampoule equipped with a Teflon valve under heating. The diimine ligands (Mes-DAD, dpp-DAD, dpp-BIAN) were prepared according to previously reported literature procedures [61,62]. The reactions were carried out in sealed, thick-walled glass ampoules under low pressure. This allowed the reaction mixture to be heated above the boiling point of the solvent, allowing for the processes to be observed with the naked eye. Heating the reaction mixture above the boiling point leads to the formation of a supersaturated solution and the formation of product crystals. The zinc(II) chloride complex (4) with dpp-DAD ligand was obtained according to a previously described method [42].
The phase purity of the bulk polycrystalline samples 1–3 was confirmed by powder X-ray diffraction analysis (PXRD). The experimental patterns show excellent agreement with the simulations obtained from single-crystal X-ray diffraction data (See Supporting Information), indicating the absence of crystalline or amorphous impurities. Notably, the PXRD measurements were performed on samples exposed to air, with no special precautions taken to exclude moisture or oxygen. The close match between the theoretical and experimental diffractograms further demonstrates the stability of these zinc complexes in the solid state under ambient atmospheric conditions.
The main crystallographic parameters and refinement details of compounds 1–4 are listed in Table 6. Other data on the equipment used to record the spectra and conduct the research are described in the Supplementary Materials.

3.2. Synthesis of 1–3

Compounds 1–3 were prepared according similar procedures: equivalent ligand amount (1 mmol) was added to zinc diiodide (1 mmol) prepared in situ in absolute acetonitrile from iodine (0.254 g, 1 mmol) and an excess of zinc metal. The color of the reaction mixture instantly became orange (1, 3) or yellow (2). Crystallization from acetonitrile gave crystals amenable for SC X-RAY analysis.
1: Yield, 0.367 g (60%). Anal. calcd for C20H24I2N2Zn (%): C, 39.28; H, 3.96; N, 4.58. Found (%): C, 38.9; H, 3.91; N, 4.48. IR (ATR, ν, cm−1): 3033 w, 2967 m, 2915 m, 2856 m, 2744 w, 2722 w, 2408 w, 1772 w, 1730 w, 1642 m, 1596 m, 1579 m, 1472 s, 1455 s, 1383 w, 1354 vs, 1309 m, 1203 vs, 1146 s, 1026 s, 962 m, 920 m, 895 m, 846 vs, 816 m, 723 w, 580 s, 522 m, 505 m, 477 w. 1H NMR (300 MHz, CDCl3) δ 8.28 (s, 2H, NCH), 6.99 (s, 4H, CHMes), 2.45 (s, 12H, o-Me), 2.32 (s, 6H p-Me). 1H NMR (300 MHz, DMSO-d6) δ 8.09 (s, 2H, NCH), 6.91 (s, 4H, CHMes), 2.23 (s, 6H, o-Me), 2.08 (s, 12H, p-Me).
2: Yield, 0.640 g (92%). Anal. calcd for C26H36I2N2Zn (%): C, 44.88; H, 5.21; N, 4.03. Found (%): 44.71; H, 5.11; N, 3.94. IR (ATR, ν, cm−1): 3062 w, 3026 w, 2964 vs, 2926 s, 2866 m, 1643 w, 1586 m, 1460 vs, 1382 m, 1354 m, 1326 m, 1256 m, 1179 s, 1106 s, 1041 s, 939 m, 896 m, 847 w, 793 m, 744 s, 637 w, 590 w, 529 w, 435 s. 1H NMR (300 MHz, CDCl3) δ 8.24 (s, 2H, NCH), 7.40–7.28 (m, 6H, CHAr), 3.30 (sept, J = 6.7 Hz, 4H, CH), 1.27 (near coalescence, 12H, Me)
3: Yield, 0.818 g (95%). Anal. calcd for C38H43I2N3Zn (%): C, 53.01; H, 5.03; N, 4.88. Found (%): C, 52.93; H, 4.99; N, 4.76. IR (ATR, ν, cm−1): 3062 w, 2962 s, 2923 m, 2905 m, 2883 w, 2866 w, 2287 w, 2250 w, 1662 m, 1626 s, 1597 m, 1585 m, 1489 w, 1464 w, 1435 w, 1421 w, 1382 w, 1364 w, 1353 w, 1322 m, 1290 s, 1260 s, 1222 w, 1205 w, 1186 w, 1128 s, 1087 s, 1052 s, 1040 s, 1015 vs, 972 w, 951 w, 936 w, 927 w, 914 w, 865 w, 853 w, 833 m, 800 vs, 780 s, 757 s, 738 w, 715 w, 695 w, 672 w, 658 w, 629 w, 610 m, 587 w, 576 w, 542 m, 513 w, 487 w, 468 w, 451 w, 440 w, 425 w. 1H NMR (300 MHz, CDCl3) δ 8.13 (d, J = 8.3 Hz, 2H, H6), 7.53 (pst, J = 8.1 Hz, 2H, H5), 7.51–7.38 (m, 6H, H15–17), 6.58 (d, J = 7.4 Hz, 2H, H4), 3.45 (hept, J = 6.7 Hz, 4H, CHMe2), 2.01 (s, 3H, MeCN), 1.36 (d, J = 6.6 Hz, 12H, CHMe2), 0.81 (d, J = 6.8 Hz, 12H, CHMe2). 13C NMR (75 MHz, CDCl3) δ 165.42, 144.61, 140.62, 139.71, 132.72(C6), 131.05, 128.97(C5), 128.58, 127.28(C4), 126.01, 125.32(C15), 29.56(CHMe2), 25.86(CHMe2), 25.06(CHMe2), 2.10(MeCN).

4. Conclusions

Thus, three new mononuclear molecular iodide zinc compounds with redox-active diimine ligands were obtained. Their composition and phase purity were confirmed by a combination of elemental analysis, NMR data in solution, UV-Vis spectroscopy for solutions and solid-state samples, as well as PXRD. According to the analysis of their crystal structure, it was shown that the packing of complexes with DAD and BIAN derivatives is due to weak intermolecular contacts C–H…π or π…π. According to the analysis of X-ray structural data and IR spectroscopy, all ligands are in neutral form. For the investigated complexes, the cathodic region is characterized by either two or three quasi-reversible reduction stages, depending on the specific ligand type, which correspond to changes in the oxidation state of the redox-active organic fragment. A key common feature for all complexes is the redox-inertness of the metal center within the studied cathodic potential window. The demonstrated ability to accept up to three electrons, as observed for 3, indicates the potential utility of these compounds as electrocatalysts for reductive transformations.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst15110967/s1, Figure S1: IR spectrum of 1; Figure S2: IR spectrum of 2; Figure S3: IR spectrum of 3; Figure S4: Cyclic voltammograms of 2 (CH3CN, C = 2 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1); Figure S5: Cyclic voltammograms of ZnI2 oxidation (MeCN/CH2Cl2 (v/v = 1:1), C = 3 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1); Figure S6: Cyclic voltammograms of ZnI2 reduction (MeCN/CH2Cl2 (v/v = 1:1), C = 3 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1); Figure S7: The experimental (blue line) and calculated (red line) powder patterns for 1 and their difference (grey curve). Ticks indicated calculated positions of the peaks; Figure S8: The experimental (blue line) and calculated (red line) powder patterns for 2 and their difference (grey curve). Ticks indicated calculated positions of the peaks; Figure S9: The experimental (blue line) and calculated (red line) powder patterns for 3 and their difference (grey curve). Ticks indicated calculated positions of the peaks; Figure S10: 1H NMR spectrum of Mes-DAD ligand (300 MHz, DMSO-d6, 295 K); Figure S11: 1H NMR spectrum of 1 (the signals correspond to the free ligand) (300 MHz, DMSO-d6, 295 K); Figure S12: 1H NMR spectrum of 1 (300 MHz, CDCl3, 295 K); Figure S13: 1H NMR spectrum of 2 (300 MHz, CDCl3, 295 K); Figure S14: 1H NMR spectrum of 3 (300 MHz, CDCl3, 295 K); Figure S15: 13C{1H} NMR spectrum of 3 (75 MHz, CDCl3, 295 K); Figure S16: 1H–1H COSY-DQF NMR spectrum of 3 (300 MHz, CDCl3, 295 K); Figure S17: 1H–1H NOESY NMR spectrum of 3 (300 MHz, CDCl3, 295 K); Figure S18: 1H–13C HSQC NMR spectrum of 3 (300/75 MHz, CDCl3, 295 K) [63,64,65,66].

Author Contributions

Conceptualization, D.S.Y.; investigation and IR spectroscopy, V.A.B., A.A.T. and D.S.Y.; X-ray analysis, M.A.K. and J.K.V.; investigation and NMR spectroscopy, I.V.S. (Ivan V. Smolyaninov), I.V.S. (Ivan V. Skabitsky) and S.S.S.; XRPD-analysis, N.V.G.; absorption spectroscopy N.V.G., A.S.S. and V.A.B.; writing—original draft preparation, D.S.Y.; writing—review and editing, D.S.Y., S.A.N. and M.A.K.; project administration, M.A.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the Russian Science Foundation (project 25-73-20065), https://rscf.ru/project/25-73-20065 (accessed on 27 October 2025).

Data Availability Statement

The structure parameters of the obtained compound were deposited into the Cambridge Structural Database (CCDC No. 2496700-2496703 for 1–4, respectively) deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk/data_request/cif (accessed on 19 October 2025).

Acknowledgments

This work was partially performed using the equipment of the Joint Research Centre of the Kurnakov Institute of General and Inorganic Chemistry of the Russian Academy of Sciences. The authors express their gratitude to Sergei Kottsov for recording the diffuse reflectance spectra.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Koten, G.; Van Vrieze, K. 1,4-Diaza-1,3-Butadiene (α-Diimine) Ligands: Their Coordination Modes and the Reactivity of Their Metal Complexes. In Advances in Organometallic Chemistry; Academic Press: Cambridge, MA, USA, 1982; Volume 21, pp. 151–239. ISSN 0065-3055. [Google Scholar]
  2. Vrieze, K. Advances in the Chemistry of Heterodiene Metal Complexes. J. Organomet. Chem. 1986, 300, 307–326. [Google Scholar] [CrossRef]
  3. Mealli, C.; Ienco, A.; Phillips, A.D.; Galindo, A. A Critical Review of Electronic Effects in Enediamido and α-Diimino Complexes of the Group 4 Metals. Eur. J. Inorg. Chem. 2007, 2007, 2556–2568. [Google Scholar] [CrossRef]
  4. Panda, T.K.; Kaneko, H.; Michel, O.; Pal, K.; Tsurugi, H.; Törnroos, K.W.; Anwander, R.; Mashima, K. Dianion and Monoanion Ligation of 1,4-Diaza-1,3-Butadiene to Barium, Strontium, and Calcium. Organometallics 2012, 31, 3178–3184. [Google Scholar] [CrossRef]
  5. Fedushkin, I.L.; Skatova, A.A.; Chudakova, V.A.; Fukin, G.K. Four-Step Reduction of Dpp-Bian with Sodium Metal: Crystal Structures of the Sodium Salts of the Mono-, Di-, Tri- and Tetraanions of Dpp-Bian. Angew. Chem. Int. Ed. 2003, 42, 3294–3298. [Google Scholar] [CrossRef] [PubMed]
  6. Muresan, N.; Weyhermüller, T.; Wieghardt, K. Neutral Bis(1,4-Diaza-1,3-Butadiene)Nickel Complexes and Their Corresponding Monocations: Molecular and Electronic Structures. A Combined Experimental and Density Functional Theoretical Study. Dalton Trans. 2007, 39, 4390–4398. [Google Scholar] [CrossRef]
  7. Fedushkin, I.L.; Maslova, O.V.; Hummert, M.; Schumann, H. One-and Two-Electron-Transfer Reactions of (Dpp-Bian)Sm(Dme)3. Inorg. Chem. 2010, 49, 2901–2910. [Google Scholar] [CrossRef]
  8. Pott, T.; Jutzi, P.; Kaim, W.; Schoeller, W.W.; Neumann, B.; Stammler, A.; Stammler, H.G.; Wanner, M. Reactivity of “GaI” toward N-Substituted 1,4-Diazabuta-1,3-Dienes: Synthesis and Characterization of Gallium Heterocycles Containing Paramagnetic Diazabutadiene Monoanions. Organometallics 2002, 21, 3169–3172. [Google Scholar] [CrossRef]
  9. Trifonov, A.A.; Borovkov, I.A.; Fedorova, E.A.; Fukin, G.K.; Larionova, J.; Druzhkov, N.O.; Cherkasov, V.K. Ytterbocenes as One- and Two-Electron Reductants in Their Reactions with Diazadienes: YbIII Mixed-Ligand Bent-Sandwich Complexes Containing a Dianion of Diazabutadiene. Chem. Eur. J. 2007, 13, 4981–4987. [Google Scholar] [CrossRef]
  10. Fedushkin, I.L.; Maslova, O.V.; Baranov, E.V.; Shavyrin, A.S. Redox Isomerism in the Lanthanide Complex [(Dpp-Bian)Yb(DME)(μ-Br)]2 (Dpp-Bian) 1,2-Bis[(2,6-Diisopropylphenyl)Imino]Acenaphthene). Inorg. Chem. 2009, 48, 2355–2357. [Google Scholar] [CrossRef]
  11. Trifonov, A.A. Reactions of Ytterbocenes with Diimines: Steric Manipulation of Reductive Reactivity. Eur. J. Inorg. Chem. 2007, 2007, 3151–3167. [Google Scholar] [CrossRef]
  12. Nikolaevskaya, E.N.; Druzhkov, N.O.; Syroeshkin, M.A.; Egorov, M.P. Chemistry of Diazadiene Type Ligands with Extra Coordination Groups. Prospects of Reactivity. Coord. Chem. Rev. 2020, 417, 213353. [Google Scholar] [CrossRef]
  13. Lima, G.; Nunes, E.; Dantas, R.; Simone, C.; Meneghetti, M.; Meneghetti, S. Catalytic Behaviors of CoII and MnII Compounds Bearing α-Diimine Ligands for Oxidative Polymerization or Drying Oils. J. Braz. Chem. Soc. 2018, 29, 412–418. [Google Scholar] [CrossRef]
  14. Crossetti, G.L.; Dias, M.L.; Queiroz, B.T.; Silva, L.P.; Ziglio, C.M.; Bomfim, J.A.S.; Filgueiras, C.A.L. Ethylene Polymerization with Imine and Phosphine Nickel Complexes Containing Isothiocyanate. Appl. Organomet. Chem. 2004, 18, 331–336. [Google Scholar] [CrossRef]
  15. Bart, S.C.; Hawrelak, E.J.; Lobkovsky, E.; Chirik, P.J. Low-Valent α-Diimine Iron Complexes for Catalytic Olefin Hydrogenation. Organometallics 2005, 24, 5518–5527. [Google Scholar] [CrossRef]
  16. Palmer, W.N.; Diao, T.; Pappas, I.; Chirik, P.J. High-Activity Cobalt Catalysts for Alkene Hydroboration with Electronically Responsive Terpyridine and α-Diimine Ligands. ACS Catal. 2015, 5, 622–626. [Google Scholar] [CrossRef]
  17. Braconi, E.; Götzinger, A.C.; Cramer, N. Enantioselective Iron-Catalyzed Cross-[4+4]-Cycloaddition of 1,3-Dienes Provides Chiral Cyclooctadienes. J. Am. Chem. Soc. 2020, 142, 19819–19824. [Google Scholar] [CrossRef]
  18. Nishiyama, H.; Ikeda, H.; Saito, T.; Kriegel, B.; Tsurugi, H.; Arnold, J.; Mashima, K. Structural and Electronic Noninnocence of α-Diimine Ligands on Niobium for Reductive C–Cl Bond Activation and Catalytic Radical Addition Reactions. J. Am. Chem. Soc. 2017, 139, 6494–6505. [Google Scholar] [CrossRef] [PubMed]
  19. Duraisamy, R.; Liebing, P.; Harmgarth, N.; Lorenz, V.; Hilfert, L.; Busse, S.; Engelhardt, F.; Edelmann, F.T. The Manifold Structural Chemistry of Alkali Metal Enediamide Complexes. Eur. J. Inorg. Chem. 2019, 2019, 3343–3351. [Google Scholar] [CrossRef]
  20. Duraisamy, R.; Liebing, P.; Harmgarth, N.; Lorenz, V.; Hilfert, L.; Feneberg, M.; Goldhahn, R.; Engelhardt, F.; Edelmann, F.T. Rubidium and Cesium Enediamide Complexes Derived from Bulky 1,4-Diazadienes. ACS Omega 2020, 5, 19061–19069. [Google Scholar] [CrossRef]
  21. Pashanova, K.I.; Lazarev, N.M.; Zolotukhin, A.A.; Kovylina, T.A.; Petrov, B.I.; Piskunov, A.V. Thermal Behavior of the “α-Diimine-NiII-Catecholate” Chromophores. ChemistrySelect 2024, 9, e202304536. [Google Scholar] [CrossRef]
  22. Klimashevskaya, A.V.; Arsenyeva, K.V.; Maleeva, A.V.; Druzhkov, N.O.; Arsenyev, M.V.; Cherkasov, A.V.; Yakushev, I.A.; Aysin, R.R.; Piskunov, A.V. Donor-Acceptor Tin(IV) Complexes with α-Diimine and Catecholate Ligands. Eur. J. Inorg. Chem. 2023, 26, e202300540. [Google Scholar] [CrossRef]
  23. Pashanova, K.I.; Ershova, I.V.; Yakushev, I.A.; Meshcheryakova, I.N.; Arsenyev, M.V.; Piskunov, A.V. Intramolecular Charge Transfer in Bulky “Diazabutadiene-M(II)-Catecholate” Chromophores (M = Ni, Co): A Role of a Molecular Geometry. Polyhedron 2023, 243, 116527. [Google Scholar] [CrossRef]
  24. Wang, P.; Saber, M.R.; VanNatta, P.E.; Yap, G.P.A.; Popescu, C.V.; Scarborough, C.C.; Kieber-Emmons, M.T.; Dunbar, K.R.; Riordan, C.G. Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(Thioether)–Iron Complexes Containing Redox-Active α-Diimine Ligands. Inorg. Chem. 2021, 60, 6480–6491. [Google Scholar] [CrossRef]
  25. Liu, B.-C.; Ge, N.; Zhai, Y.-Q.; Zhang, T.; Ding, Y.-S.; Zheng, Y.-Z. An Imido Ligand Significantly Enhances the Effective Energy Barrier of Dysprosium(Iii) Single-Molecule Magnets. Chem. Commun. 2019, 55, 9355–9358. [Google Scholar] [CrossRef]
  26. Long, J.; Shestakov, B.G.; Liu, D.; Chibotaru, L.F.; Guari, Y.; Cherkasov, A.V.; Fukin, G.K.; Trifonov, A.A.; Larionova, J. An Organolanthanide(III) Single-Molecule Magnet with an Axial Crystal-Field: Influence of the Raman Process over the Slow Relaxation. Chem. Commun. 2017, 53, 4706–4709. [Google Scholar] [CrossRef] [PubMed]
  27. Bubnov, M.P.; Cherkasov, V.K.; Teplova, I.A.; Druzhkov, N.O.; Grishin, I.D.; Baranov, E.V.; Bogomyakov, A.S.; Abakumov, G.A. Novel Dioxolene Nickel Complexes with Sterically Hindered Diazabutadienes. Coupling of Aza-Ligands Coordinated to Nickel. Dalton Trans. 2019, 48, 10516–10525. [Google Scholar] [CrossRef]
  28. Yambulatov, D.S.; Nikolaevskii, S.A.; Babeshkin, K.A.; Efimov, N.N.; Kiskin, M.A.; Eremenko, I.L. Synthesis, Structure, and Magnetic Properties of the Cobalt(Ii) Iodide Complex with 1,4-Diazabuta-1,3-Diene Ligand. Russ. Chem. Bull. 2021, 70, 2390–2396. [Google Scholar] [CrossRef]
  29. Petrov, P.A.; Sukhikh, T.S.; Piryazev, D.A.; Virovets, A.V.; Konchenko, S.N. Syntheses and Structures of the Cobalt, Nickel, and Zinc Complexes with 1,4-Diaza-1,3-Butadiene Ligands. Russ. J. Coord. Chem. 2013, 39, 11–22. [Google Scholar] [CrossRef]
  30. Petrov, P.A.; Konchenko, S.N.; Nadolinny, V.A. A New Approach to the Synthesis of Gallium(III) Complexes with α-Diimine Ligands in the Radical Anion Form. Russ. J. Coord. Chem. 2014, 40, 885–890. [Google Scholar] [CrossRef]
  31. Richter, B.; Scholz, J.; Sieler, J.; Thiele, K.-H. Dad Compounds of Niobium and Tantalum: Examples of the Structural Flexibility of Dad Ligands. Angew. Chem. Int. Ed. Engl. 1996, 34, 2649–2651. [Google Scholar] [CrossRef]
  32. Zoet, R.; van Koten, G.; Muller, F.; Vrieze, K.; van Wijnkoop, M.; Goubitz, K.; van Halen, C.J.G.; Stam, C.H. Synthesis of Heterodinuclear FeRu(CO)6(R-DAB(6e))(R-DAB=RN=C(H)C(H)=NR) Part XV. Comparison of the Reactivities of Heterodinuclear FeRu(CO)6(R-DAB(6e)) and Homodinuclear Analogues M2(CO)6(R-DAB(6e)) (M = Fe, Ru). Single-Crystal x-Ray Structures of FeRu(CO)6(i-Pr-DAB(6e)) and FeRu(CO)5(i-Pr-DAB(4e))(C3H4). Inorg. Chim. Acta 1988, 149, 193–208. [Google Scholar] [CrossRef]
  33. Dieck, H.T.; Klaus, J. Diazadien-Rhodium-Komplexe: III. Konformationsstabilität Durch Rhodium(I) ··· H-C-Wechselwirkungen. Festkörper- Und Lösungsstruktur von [(1,5-Cod)RhCl]2(μ-Dad). J. Organomet. Chem. 1983, 246, 301–308. [Google Scholar] [CrossRef]
  34. Shen, L.; Zhao, Y.; Luo, Q.; Li, Q.-S.; Liu, B.; Redshaw, C.; Wu, B.; Yang, X.-J. Cyclotrimerization of Alkynes Catalyzed by a Self-Supported Cyclic Tri-Nuclear Nickel(0) Complex with α-Diimine Ligands. Dalton Trans. 2019, 48, 4643–4649. [Google Scholar] [CrossRef]
  35. Yambulatov, D.S.; Lutsenko, I.A.; Nikolaevskii, S.A.; Petrov, P.A.; Smolyaninov, I.V.; Malyants, I.K.; Shender, V.O.; Kiskin, M.A.; Sidorov, A.A.; Berberova, N.T.; et al. Diimine Cisplatin Derivatives: Synthesis, Structure, Cyclic Voltammetry and Cytotoxicity. Molecules 2022, 27, 8565. [Google Scholar] [CrossRef] [PubMed]
  36. Trouts, T.D.; Tyson, D.S.; Pohl, R.; Kozlov, D.V.; Waldron, A.G.; Castellano, F.N. Dinuclear Metal-Organic Material for Binary Optical Recording. Adv. Funct. Mater. 2003, 13, 398–402. [Google Scholar] [CrossRef]
  37. CXRO. X-Ray Properties of the Elements. 1995. Available online: http://www.cxro.lbl.gov (accessed on 27 October 2025).
  38. Luo, C.; Xu, C.; Lv, L.; Li, H.; Huang, X.; Liu, W. Review of Recent Advances in Inorganic Photoresists. RSC Adv. 2020, 10, 8385–8395. [Google Scholar] [CrossRef]
  39. Wang, D.; Xu, R.; Zhou, D.; Zhao, J.; Zhang, J.; Chen, P.; Peng, X. Zn-Ti Oxo Cluster Photoresists for EUV Lithography: Cluster Structure and Lithographic Performance. Chem. Eng. J. 2024, 493, 152315. [Google Scholar] [CrossRef]
  40. Chen, H.; Huang, X.; Zhao, Y.; Zhao, J.; Chen, P.; Peng, X. Balancing Sensitivity and Resolution by Feedback Regulation of Free Radicals from Sn-C Bonds in Tin-Oxygen Clusters EBL Photoresist. Sci. China Mater. 2024, 67, 3142–3150. [Google Scholar] [CrossRef]
  41. Chen, H.; Peng, Y.; Fu, H.; Han, F.; Shi, G.; Luo, F.; Zhao, J.; Zhou, D.; Chen, P.; Peng, X. Effect of Free Radicals on Irradiation Chemistry of a Double-Coordination Organotin (Sn4) Photoresist by Adjusting Alkyl Ligands. CCS Chem. 2024, 6, 2044–2053. [Google Scholar] [CrossRef]
  42. Abakumov, G.A.; Cherkasov, V.K.; Piskunov, A.V.; Trofimova, O.Y.; Romanenko, G.V. Activating Complex Formation in the Diazabutadiene-Zinc Halide System. Dokl. Chem. 2010, 434, 237–240. [Google Scholar] [CrossRef]
  43. Beloglazkina, E.K.; Yudin, I.V.; Majouga, A.G.; Moiseeva, A.A.; Tursina, A.I.; Zyk, N.V. Synthesis and Electrochemical Study of 2-(2-Pyridyl)Benzothiazole Complexes with Transition Metals (CoII, NiII, and CuII). Molecular Structure of Aquabis[2-(2-Pyridyl)Benzothiazole]Copper(II) Diperchlorate. Russ. Chem. Bull. 2006, 55, 1803–1809. [Google Scholar] [CrossRef]
  44. Kim, J.H.; Mertens, R.T.; Agarwal, A.; Parkin, S.; Berger, G.; Awuah, S.G. Direct Intramolecular Carbon(Sp2)-Nitrogen(Sp2) Reductive Elimination from Gold(Iii). Dalton Trans. 2019, 48, 6273–6282. [Google Scholar] [CrossRef]
  45. Nolte, C.; Mayer, P.; Straub, B.F. Isolation of a Copper(I) Triazolide: A “Click” Intermediate. Angew. Chem.-Int. Ed. 2007, 46, 2101–2103. [Google Scholar] [CrossRef]
  46. El-Ayaan, U.; Abdel-Aziz, A.A.-M. Synthesis, Antimicrobial Activity and Molecular Modeling of Cobalt and Nickel Complexes Containing the Bulky Ligand: Bis[N-(2,6-Diisopropylphenyl)Imino] Acenaphthene. Eur. J. Med. Chem. 2005, 40, 1214–1221. [Google Scholar] [CrossRef]
  47. Yang, L.; Powell, D.R.; Houser, R.P. Structural Variation in Copper(I) Complexes with Pyridylmethylamide Ligands: Structural Analysis with a New Four-Coordinate Geometry Index, Τ4. J. Chem. Soc. Dalton Trans. 2007, 9, 955–964. [Google Scholar] [CrossRef]
  48. Zhong, Y.; Wu, Y.; Mei, D.; Wen, S.; Doert, T. Synthesis, Crystal Structures and Luminescent Properties of Three Layered Zinc Complexes: Zn(1,10-Phen)MI2 (m = 1, 2) and Zn2(1,10-Phen)2C2O4Br2 (Phen = Phenanthroline). J. Mol. Struct. 2022, 1265, 133489. [Google Scholar] [CrossRef]
  49. Zhao, X.-S.; Luo, J.-S.; Tian, Y.-P. {9-Hexyl-2-[2-Phenyl-6-(Pyridin-2-Yl) Pyridin-4-Yl]-9H-Carbazole} Diiodidozinc. Struct. Rep. 2013, 69, m553. [Google Scholar] [CrossRef]
  50. Khalaji, A.D.; Grivani, G.; Akerdi, S.J.; Stoeckli-Evans, H.; Das, D. Synthesis, Spectroscopic and Thermal Studies of Zinc(II) Complexes with the Symmetrical Bidentate Schiff-Base Ligand (2,3-MeO-Ba) 2en: Crystal Structure of Zn((2,3-MeO-Ba) 2en)I2. J. Chem. Crystallogr. 2012, 42, 83–88. [Google Scholar] [CrossRef]
  51. Seebacher, J.; Ji, M.; Vahrenkamp, H. (Neocuproin)Zinc Thiolates: Attempts at Modeling Cobalamin-Independent Methionine Synthase. Eur. J. Inorg. Chem. 2004, 2004, 409–417. [Google Scholar] [CrossRef]
  52. Fumoto, T.; Tanaka, R.; Ooyama, Y. Aggregation-Induced Emission of a Bis(Imino)Acenaphthene Zinc Complex with Tetraphenylethene Units. Dalton Trans. 2023, 52, 5047–5055. [Google Scholar] [CrossRef]
  53. Evans, D.A.; Lee, L.M.; Vargas-Baca, I.; Cowley, A.H. Photophysical Tuning of the Aggregation-Induced Emission of a Series of Para-Substituted Aryl Bis(Imino)Acenaphthene Zinc Complexes. Dalton Trans. 2015, 44, 11984–11996. [Google Scholar] [CrossRef]
  54. Dong, Y.W.; Fan, R.Q.; Chen, W.; Zhang, H.J.; Song, Y.; Du, X.; Wang, P.; Wei, L.G.; Yang, Y.L. Luminescence Properties of a Zn(II) Supramolecular Framework: Easily Tunable Optical Properties by Variation of the Alkyl Substitution of (E)-N-(Pyridine-2-Ylethylidyne)Arylamine Ligands. RSC Adv. 2016, 6, 110422–110432. [Google Scholar] [CrossRef]
  55. Evans, D.A.; Lee, L.M.; Vargas-Baca, I.; Cowley, A.H. Aggregation-Induced Emission of Bis(Imino)Acenaphthene Zinc Complexes: Photophysical Tuning via Methylation of the Flanking Aryl Substituents. Organometallics 2015, 34, 2422–2428. [Google Scholar] [CrossRef]
  56. Poddel’sky, A.I.; Smolyaninov, I.V.; Druzhkov, N.O.; Fukin, G.K. Heterometallic Antimony(V)-Zinc and Antimony(V)-Copper Complexes Comprising Catecholate and Diazadiene as Redox Active Centers. J. Organomet. Chem. 2021, 952, 121994. [Google Scholar] [CrossRef]
  57. Brooks, A.C.; Basore, K.; Bernhard, S. Photon-Driven Reduction of Zn2+ to Zn Metal. Inorg. Chem. 2013, 52, 5794–5800. [Google Scholar] [CrossRef]
  58. Ershova, I.V.; Meshcheryakova, I.N.; Trofimova, O.Y.; Pashanova, K.I.; Arsenyeva, K.V.; Khamaletdinova, N.M.; Smolyaninov, I.V.; Arsenyev, M.V.; Cherkasov, A.V.; Piskunov, A.V. Complexes of Metal Halides with Unreduced O-(Imino)Quinones. Inorg. Chem. 2021, 60, 12309–12322. [Google Scholar] [CrossRef] [PubMed]
  59. Khrizanforova, V.V.; Morozov, V.I.; Khrizanforov, M.N.; Lukoyanov, A.N.; Kataeva, O.N.; Fedushkin, I.L.; Budnikova, Y.H. Iron Complexes of BIANs: Redox Trends and Electrocatalysis of Hydrogen Evolution. Polyhedron 2018, 154, 77–82. [Google Scholar] [CrossRef]
  60. Yambulatov, D.S.; Nikolaevskii, S.A.; Kiskin, M.A.; Kholin, K.V.; Khrizanforov, M.N.; Budnikova, Y.G.; Babeshkin, K.A.; Efimov, N.N.; Goloveshkin, A.S.; Imshennik, V.K.; et al. Generation of a Hetero Spin Complex from Iron(II) Iodide with Redox Active Acenaphthene-1,2-Diimine. Molecules 2021, 26, 2998. [Google Scholar] [CrossRef]
  61. Paulovicova, A.; El-Ayaan, U.; Shibayama, K.; Morita, T.; Fukuda, Y. Mixed-Ligand Copper(II) Complexes with the Rigid Bidentate Bis (N-Arylimino) Acenaphthene Ligand: Synthesis, Spectroscopic-, and X-Ray Structural Characterization. Eur. J. Inorg. Chem. 2001, 2001, 2641–2646. [Google Scholar] [CrossRef]
  62. Bantreil, X.; Nolan, S.P. Synthesis of N-Heterocyclic Carbene Ligands and Derived Ruthenium Olefin Metathesis Catalysts. Nat. Protoc. 2011, 6, 69–77. [Google Scholar] [CrossRef] [PubMed]
  63. Sheldrick, G.M. SADABS; Bruker AXS Inc.: Madison, WI, USA, 1997. [Google Scholar]
  64. Sheldrick, G.M. Crystal Structure Refinement with SHELXL. Acta Crystallogr. Sect. C. 2015, 71, 3–8. [Google Scholar] [CrossRef] [PubMed]
  65. Dolomanov, O.V.; Bourhis, L.J.; Gildea, R.J.; Howard, J.A.K.; Puschmann, H. OLEX2: A Complete Structure Solution, Refinement and Analysis Program. J. Appl. Crystallogr. 2009, 42, 339–341. [Google Scholar] [CrossRef]
  66. TOPAS Software, version 4.2; Bruker AXS: Karlsruhe, Germany, 2009.
Crystals 15 00967 sch001
Scheme 1. 1,2-diimines reversible reduction ability (Red is the diimine part in the radical-anionic form, blue—dianionic).
Scheme 1. 1,2-diimines reversible reduction ability (Red is the diimine part in the radical-anionic form, blue—dianionic).
Crystals 15 00967 sch001
Crystals 15 00967 sch002
Scheme 2. Synthesis pathway of the obtained compounds.
Scheme 2. Synthesis pathway of the obtained compounds.
Crystals 15 00967 sch002
Crystals 15 00967 g001aCrystals 15 00967 g001b
Figure 1. Molecular structure of 1–4 (a–d) (for 3, H atoms and solvate molecule are omitted; for all, thermal ellipsoids with 30% probability).
Figure 1. Molecular structure of 1–4 (a–d) (for 3, H atoms and solvate molecule are omitted; for all, thermal ellipsoids with 30% probability).
Crystals 15 00967 g001aCrystals 15 00967 g001b
Crystals 15 00967 g002aCrystals 15 00967 g002b
Figure 2. Fragments of the crystal packing for 1 (a), 2 (b) and 3 (c) (dashed lines correspond to the C–H···π (for 1 and 3) and π…π (for 2) contacts).
Figure 2. Fragments of the crystal packing for 1 (a), 2 (b) and 3 (c) (dashed lines correspond to the C–H···π (for 1 and 3) and π…π (for 2) contacts).
Crystals 15 00967 g002aCrystals 15 00967 g002b
Crystals 15 00967 g003
Figure 3. UV-Vis absorption spectra of Dpp-DAD, Mes-DAD, Dpp-BIAN and 1–3 in MeCN solution (C = 10−4 M, RT).
Figure 3. UV-Vis absorption spectra of Dpp-DAD, Mes-DAD, Dpp-BIAN and 1–3 in MeCN solution (C = 10−4 M, RT).
Crystals 15 00967 g003
Crystals 15 00967 g004
Figure 4. Solid-state UV-Vis diffuse reflection absorption spectra of Dpp-DAD, Mes-DAD, Dpp-BIAN and 1–3 (RT).
Figure 4. Solid-state UV-Vis diffuse reflection absorption spectra of Dpp-DAD, Mes-DAD, Dpp-BIAN and 1–3 (RT).
Crystals 15 00967 g004
Crystals 15 00967 g005
Figure 5. Cyclic voltammograms of 2: the potential switch from 0.0 to −1.9 V (curve 1); the potential switch from 0.0 to −0.7 V (curve 2) (CH3CN, C = 2 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1).
Figure 5. Cyclic voltammograms of 2: the potential switch from 0.0 to −1.9 V (curve 1); the potential switch from 0.0 to −0.7 V (curve 2) (CH3CN, C = 2 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1).
Crystals 15 00967 g005
Crystals 15 00967 sch003
Scheme 3. Two successive electrochemical oxidation stages for DAD complexes (Red is the diimine part in the radical-anionic form, blue—dianionic).
Scheme 3. Two successive electrochemical oxidation stages for DAD complexes (Red is the diimine part in the radical-anionic form, blue—dianionic).
Crystals 15 00967 sch003
Crystals 15 00967 g006
Figure 6. Cyclic voltammograms of 3: the potential switch from 0.0 to −0.8 V (curve 1); the potential switch from 0.0 to −1.7 V (curve 2); the potential switch from 0.0 to −2.1 V (curve 3) (CH3CN, C = 2 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1).
Figure 6. Cyclic voltammograms of 3: the potential switch from 0.0 to −0.8 V (curve 1); the potential switch from 0.0 to −1.7 V (curve 2); the potential switch from 0.0 to −2.1 V (curve 3) (CH3CN, C = 2 mmol, 0.1 M TBAP, scan rate 200 mV∙s−1).
Crystals 15 00967 g006
Table 1. Bond lengths (Å) of the diimine fragment of α-diimines depending on the reduction state of the ligand, Ar = 2,6-diisopropylphenyl (dpp) [5,6].
Table 1. Bond lengths (Å) of the diimine fragment of α-diimines depending on the reduction state of the ligand, Ar = 2,6-diisopropylphenyl (dpp) [5,6].
Ligand Form/BondFree LigandMonoanionicDianionic
(Ar-BIAN)0(Ar-DAD)0(Ar-BIAN)−(Ar-DAD)−(Ar-BIAN)2−(Ar-DAD)2−
C–N, av.1.281.291.331.341.391.40
C–C1.531.471.451.381.401.36
Table 2. Vibration frequencies (cm−1) of the bonds of the α-diimine fragment, Ar′ = 2,4,6-trimethylphenyl (Mes) [7,8,9].
Table 2. Vibration frequencies (cm−1) of the bonds of the α-diimine fragment, Ar′ = 2,4,6-trimethylphenyl (Mes) [7,8,9].
Ligand Form/BondFree LigandMonoanionicDianionic
(Ar-BIAN)0(Ar′-DAD)0(Ar-BIAN)−(Ar′-DAD)−(Ar-BIAN)2−(Ar′-DAD)2−
C–N1671, 1652, 164216201500–15501500–155013101300–1350
Table 3. Selected distances and angles for 1–4.
Table 3. Selected distances and angles for 1–4.
Complex/Parameters1234
Zn–X2.5419(4)2.5285(9)2.4691(8), 2.5213(7)2.1977(9)
Zn–N2.099(2)2.094(6)2.141(4), 2.154(4)2.085(2)
N=Cimine1.267(4)1.270(11)1.291(6), 1.291(6)1.263(4)
N–Car1.449(3)1.451(9)1.463(6), 1.468(6)1.449(3)
Cimine–Cimine1.475(6)1.481(17)1.532(6)1.486(5)
Zn–N–Cimine111.58(19)112.2(5)110.7(3), 111.7(3)112.57(18)
Zn–N–Car129.89(18)128.7(5)130.1(3), 130.7(3)128.32(18)
N–Zn–N79.63(13)79.5(3)79.81(15)79.34(12)
N–Zn–X112.06(7), 116.16(7)113.25(16), 114.71(17)111.31(11)–117.41(10)113.10(7), 114.59(8)
X–Zn–X115.79 (2)116.20(6)112.66(3)116.63(5)
N–Cimine–Cimine–N002.0(6)0
Cimine–N–CAr–Corto86.7(4)90.3(9)82.4(6), 87.9(6)90.0(4)
τ40.9050.9160.8890.913
Table 4. Parameters of C–H···π-interactions in crystal of 1 and 3 (Cgi is the centroid of the phenyl ring; C/H···Cg is the distance from the centroid to the atom, H–Perp is the shortest distance from the H atom to the ring plane, γ is the angle between the Cgi–H vector and the normal to the i-plane, C–H···Cg is the angle).
Table 4. Parameters of C–H···π-interactions in crystal of 1 and 3 (Cgi is the centroid of the phenyl ring; C/H···Cg is the distance from the centroid to the atom, H–Perp is the shortest distance from the H atom to the ring plane, γ is the angle between the Cgi–H vector and the normal to the i-plane, C–H···Cg is the angle).
Interaction
(Element of Symmetry)		H⋅⋅⋅Cg, ÅH–Perp, Åγ, degC–X⋅⋅⋅Cg, degC⋅⋅⋅Cg, Å
1
C9–H9…Cg2(C2–C7)
(3/2 − x, −1/2 + y, 1/2 − z)		2.762.6814.11423.585(4)
C22–H22…Cg2(C2–C7)
(3/2 − x, 1/2 + y, 1/2 − z)		2.842.7316.31423.661(4)
3
C4–H4…Cg5(C13–C18)2.872.6821.31413.641(6)
C11–H11…Cg6(C25–C30)2.942.7322.01393.697(6)
C16–H16…Cg6(C25–C30)
(−1/2 − x, y, 1/2 − z)		2.692.669.61543.552(8)
C2S–H2SB…Cg5 (C13–C18)
(x, 1/2 − y, 1/2 + z)		2.802.7510.71313.502(14)
C4–H4…Cg5(C13–C18)2.872.6821.31413.641(6)
Table 5. The CV data for compounds 1–4 (CH3CN, GC, 0.15 M nBu4ClO4, C = 2 × 10−3 M, Ar, vs. Ag/AgCl/KCl (sat.)).
Table 5. The CV data for compounds 1–4 (CH3CN, GC, 0.15 M nBu4ClO4, C = 2 × 10−3 M, Ar, vs. Ag/AgCl/KCl (sat.)).
CompoundEred11/2, VIa/IcEred21/2, VIa/IcEred31/2, VIa/IcEoxp, V
1–0.420.60–1.600.71––0.74
2–0.470.75–1.650.71––0.73
3–0.530.78–1.450.70−1.950.900.74
4 *–0.540.86–1.65––––
* data from ref. [56].
Table 6. Crystallographic data, details of data collection, and characteristics of data refinement for 1–4.
Table 6. Crystallographic data, details of data collection, and characteristics of data refinement for 1–4.
ParameterValue
1234
Molecular
formula		C20H24I2N2ZnC26H36I2N2ZnC38H43I2N3ZnC26H34Cl2N2Zn
Mw, g mol−1611.58695.74860.92510.82
T, K150(2)100(2)296(2)150(2)
Crystal systemMonoclinicMonoclinicOrthorhombicMonoclinic
Space groupC2/cC2/cPbcaC2/c
a, Å22.0117(10)20.515(4)19.6052(7)20.9923(11)
b, Å7.0135(3)7.0920(13)19.3380(8)6.7220(4)
c, Å16.2294(8)20.165(4)19.8200(7)19.7409(12)
β, deg117.8317(16)107.500(7)90106.909(2)
V, Å32215.65(18)2798.1(9)7514.3(5)2665.2(3)
Z4484
ρcalcd, g cm−31.8331.6521.5221.273
μ, mm−13.9003.0992.3251.137
Tmin, Tmax0.5943, 0.74670.2532, 0.38130.5125, 0.74610.5823, 0.7460
θ range, deg3.19–33.962.08–26.002.32–28.283.28–26.00
F(000)1176136834241072
Index range−34 ≤ h ≤ −31
−9 ≤ k ≤ 10
−24 ≤ l ≤ 24		−25 ≤ h ≤ 25
−8 ≤ k ≤ 8
−24 ≤ l ≤ 24		−26 ≤ h ≤ 26
−25 ≤ k ≤ 25
−26 ≤ l ≤ 26		25 ≤ h ≤ 24
0 ≤ k ≤ 8
0 ≤ l ≤ 24
Number of reflections collected12,055797877,5272697
Number of unique reflections3964272393172697
Rint0.03200.03860.08260.0465
Number of reflections with
I > 2σ(I)		3070250766312490
GooF1.1321.1701.1421.151
R factor on F2 > 2σ(F2)0.04140.06240.07710.0397
R factor (all data)0.11120.16620.14430.1224
Δρmax/Δρmin, e/Å31.307/−1.3392.245/−1.9780.990/−0.7400.633/−0.346
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Yambulatov, D.S.; Gogoleva, N.V.; Smolyaninov, I.V.; Bushuev, V.A.; Tychinina, A.A.; Samulionis, A.S.; Voronina, J.K.; Skabitsky, I.V.; Shapovalov, S.S.; Nikolaevskii, S.A.; et al. Zinc(II) Iodide Complexes with Redox-Active α-Diimine Ligands: Synthesis, Structure, Spectroscopic and Electrochemical Properties. Crystals 2025, 15, 967. https://doi.org/10.3390/cryst15110967

AMA Style

Yambulatov DS, Gogoleva NV, Smolyaninov IV, Bushuev VA, Tychinina AA, Samulionis AS, Voronina JK, Skabitsky IV, Shapovalov SS, Nikolaevskii SA, et al. Zinc(II) Iodide Complexes with Redox-Active α-Diimine Ligands: Synthesis, Structure, Spectroscopic and Electrochemical Properties. Crystals. 2025; 15(11):967. https://doi.org/10.3390/cryst15110967

Chicago/Turabian Style

Yambulatov, Dmitriy S., Natalia V. Gogoleva, Ivan V. Smolyaninov, Vladimir A. Bushuev, Anna A. Tychinina, Alexandra S. Samulionis, Julia K. Voronina, Ivan V. Skabitsky, Sergey S. Shapovalov, Stanislav A. Nikolaevskii, and et al. 2025. "Zinc(II) Iodide Complexes with Redox-Active α-Diimine Ligands: Synthesis, Structure, Spectroscopic and Electrochemical Properties" Crystals 15, no. 11: 967. https://doi.org/10.3390/cryst15110967

APA Style

Yambulatov, D. S., Gogoleva, N. V., Smolyaninov, I. V., Bushuev, V. A., Tychinina, A. A., Samulionis, A. S., Voronina, J. K., Skabitsky, I. V., Shapovalov, S. S., Nikolaevskii, S. A., & Kiskin, M. A. (2025). Zinc(II) Iodide Complexes with Redox-Active α-Diimine Ligands: Synthesis, Structure, Spectroscopic and Electrochemical Properties. Crystals, 15(11), 967. https://doi.org/10.3390/cryst15110967

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