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6,6′-((Ethane-1,2-diylbis(azanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenolate)zirconium(IV) Dichlorido
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Evgenia Smirnova
Ruslan Baichurin
Nikolai Viktorov
Dar’ya Spiridonova
Alexander Timonov
1,* and
Mikhail Karushev
Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Ioffe Institute), 194021 St. Petersburg, Russia
Herzen State Pedagogical University of Russia, 191186 St. Petersburg, Russia
Saint Petersburg State Institute of Technology (Technical University), 190013 St. Petersburg, Russia
Research Park, St Petersburg State University, 199034 St. Petersburg, Russia
Independent Researcher, Aktau 130000, Kazakhstan
Authors to whom correspondence should be addressed.
Molbank 2022, 2022(4), M1512;
Submission received: 28 October 2022 / Revised: 22 November 2022 / Accepted: 25 November 2022 / Published: 2 December 2022
(This article belongs to the Section Structure Determination)


The title compound, which is potentially interesting as a building block for electrochemically active metallopolymers, was synthesized and characterized by single-crystal X-ray diffraction, IR and NMR spectroscopies.

1. Introduction

Nickel complexes with tetradentate N2O2 Schiff bases are used as monomers to prepare polymeric functional materials for advanced electrochemical energy storage devices, electrocatalytic systems, sensors, and electrochromic devices [1,2,3,4,5,6]. The properties of these materials depend on the presence of electron-donating or electron-withdrawing substituents in the Schiff base [7,8,9,10] and on the structure of the metal complex [7,8,11]. The 1,2-phenylenediimine bridging unit of the Salphen-type Schiff base complexes is a prospective structural site for modulating properties that are insufficiently explored in the literature.
Introducing vicinal hydroxyl groups in para positions to imine units of 1,2-phenylenediimine provide additional metal binding sites in Salphen-type complexes [12]. Crown-etherification of these sites further tunes the coordination ability of complexes [13,14]. Etherification of the hydroxyls has been reported with the intent of solubility enhancement for supramolecular [15] and polymeric [16] systems and for control of the supramolecular assembly of tris(salphen)-type trinickel(II) metallocryptands encapsulated a guanidinium ion [17] or alkali metal cations [18]. Oxidative chemistry of protected (unpolymerizable) nickel complex with a doubly methoxylated bridging unit of the Salphen complex has also been reported [19].
The structure of the simplest dimetoxylated Salphen nickel complex has not been reported so far. Thus, we perform a synthesis and investigations of structural and spectral properties of the novel complex N,N′-(4,5-dimethoxy-1,2-phenylene)bis(salicylideneaiminato)nickel(II) ([Ni(Salphen(CH3O)2)]) bearing two strongly donating methoxy substituents in the bridging phenylenediimine unit as a first step in exploring the influence of such monomer structural modification on metallopolymers electrochemistry.

2. Results and Discussion

2.1. X-ray Structural Analysis

The crystal structures of the [Ni(Salphen(CH3O)2)] was determined by the X-ray structural analysis. Samples of the complex suitable for studying were isolated by crystallization from a saturated acetonitrile solution (Avantor Performance Materials).
According to the X-ray diffraction data, the compound under study crystallizes in two forms (a and b) that differ in the way of the complex molecule solvation by acetonitrile (Figure 1) (Table 1).
Figure 1 and Figure 2 represent the molecular structures of the complex structures a and b. The Ni atom in the complex is bound to two phenolate oxygen atoms and two nitrogen atoms located at the vertices of a distorted square. The distortion degree can be characterized with the values of the torsion angles Ni1O1C1C2 [3.1(2)°] (structure a), [12.5(5)°] (b) and Ni1N2C14C12 [0.6(2)°] (a), [5.5(5)°] (b). The values of the torsion angles show that the distortion of structure (b) (Figure 2b) is higher than structure (a) (Figure 2a).
At the same time, the bond angles characterizing nickel bonds with donor atoms are approximately the same for both structures: O1Ni1N2 [179.47(5)°] (a) and [179.17(12)°] (b), N1Ni1O2 [178.57(5)°] (a) and [179.03(11)°] (b).
The different nature of the solvation of structures (a) and (b), as well as a higher degree of distortion of the structure (b), lead to the following differences in crystal lattices: monoclinic (a) and trigonal (b), and a much larger unit cell volume of (b) (see Table 1).
In general, the [Ni(Salphen(CH3O)2)] complex, as well as most nickel complexes of the salen- and salphen types, has a distorted square-planar geometry, which suggests the possibility of obtaining on its basis functional polymeric materials for electrochemical devices.

2.2. Infrared Spectroscopic and Nuclear Magnetic Resonance Studies

IR spectra (Figure S1) were registered on Shimadzu IRPrestige-21 spectrometers with samples in KBr pellets. The main experimental IR bands and their assignment are shown in Table 2. 1H, 13C-{1H} NMR spectra (Figures S2 and S3), 1H–13C HMQC (Figure S4), 1H–13C HMBC (Figure S5), 1H-1H dqf-COSY (Figure S6) as well as 1H-1H NOESY (mixing time from 0.5 to 2 s) (Figure S7) experiments were acquired on a Jeol ECX400A spectrometer (400 MHz for 1H nuclei and 100 MHz for 13C nuclei) in DMSO-d6. The residual signals of the solvent (DMSO-d6: 2.50 ppm for 1H nuclei and 39.6 ppm for 13C nuclei) were used as internal standard.
1H NMR: 3.83 (3H, OCH3), 6.61 (1H, ddd, H4, 3J 7.9, 6.8, 4J 0.9 Hz), 6.82 (1H, br.d, H6, 3J 8.5 Hz), 7.23 (1H, ddd, H5, 3J 8.5, 6.8, 4J 1.7 Hz), 7.52 (1H, dd, H3, 3J 7.9, 4J 1.7 Hz), 7.59 (1H, s, H2′), 8.64 (1H, s, CH=N) (Atom labeling shown on Figure 3).
13C{1H} NMR: 56.73 (OCH3), 99.05 (C2′), 115.58 (C4), 120.57 (C6), 120.91 (C2), 134.29 (C3), 135.10 (C5), 136.12 (C1′), 149.75 (C3′), 155.20 (C=N), 164.95 (C1).
Assignment of signals of protons and carbon atoms in 1H and 13C NMR spectra was carried out using homo- (1H-1H COSY, 1H-1H NOESY) and heteronuclear (1H-13C HMQC, 1H-13C HMBC) experiments. Notably, the presence of cross peaks in the 1H-1H COSY spectrum due to long-range spin–spin interactions through 5 bonds (CH3/H2′, H2′/CH=N, CH=N/H6), as well as typical for ortho-substituted benzene ring J-coupling constant through 4 bonds (H3/H5, H4/H6). The key cross peaks used for interpretation in the 1H-13C HMBC spectrum are 3.83 (OCH3)/149.75 (C3′); 7.59 (H2′)/136.12 (C1′); 8.64 (CH=N)/120.91 (C2); 7.52 (H3)/155.20 (C=N); 7.23 (H5)/164.95 (C1) (Figure 3).
Analysis of the 1H-1H NOESY spectrum (mixing time variation) indicates the planar structure of the complex. Thus, the cross-peaks H2′/CH=N, CH=N/H3, due to the nuclear Overhauser effect, indicate the spatial proximity of the azomethine proton simultaneously with two protons of different aromatic rings, which is possible with the coplanar organization of the (E)-azomethine block.

3. Materials and Methods

All chemicals used in the synthesis were of “reagent-grade” purity and were purchased from local suppliers.
4,5-Dimethoxy-1,2-phenylenediamine was obtained in two steps, as reported in [21]. 1,2-Dimethoxybenzene was converted into 4,5-dimethoxy-1,2-dinitrobenzene (86% yield) by the reaction with concentrated nitric acid (65%) followed by the reduction with hydrazine monohydrate and Pd/C catalyst yielding 4,5-dimethoxy-1,2-phenylenediamine (55% yield).
The ligand was prepared by the standard method of refluxing an ethanolic solution containing salicylaldehyde (Aldrich) and a 4,5-dimethoxy-1,2-phenylenediamine in stoichiometric amounts (95% yield). Nickel(II) complex [Ni(Salphen(CH3O)2)] was prepared by refluxing ethanolic solutions of nickel(II) acetate (Aldrich) with the Schiff base ligand, as described in [22]. Obtained complexes were recrystallized from acetonitrile and dried at 60 °C for several hours (70% yield).
X-ray diffraction analysis was performed at 100 K on a XtaLAB Synergy-S diffractometer (Rigaku, Japan) equipped with a HyPix-6000HE CCD detector (Rigaku, Tokio, Japan), CuKα radiation (λ 1.54184 Å). The structure was solved using the ShelXT-2013 software package [23] and refined using the ShelXL-2013 package [24] included in the OLEX2 interface [25]. The crystallographic parameters have been deposited in the Cambridge X-Ray Database (CCDC 2189692-2189693).

Supplementary Materials

Figure S1: IR spectrum of N,N′-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in KBr; Figure S2: 1H NMR spectrum of N,N′-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6; Figure S3: 1H{13C} NMR spectrum of N,N′-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6; Figure S4: 1H-13C HMQC spectrum of N,N′-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6; Figure S5: 1H-13C HMBC spectrum of N,N’-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6; Figure S6: 1H-1H dqf-COSY spectrum of N,N’-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6; Figure S7: 1H-1H NOESY spectrum of N,N′-4,5-dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II) in DMSO-d6. CCDC 2189692-2189693 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033; E-mail: [email protected]).

Author Contributions

Conceptualization, M.K. A.T. and E.S.; synthesis, N.V. and E.S; methodology, M.K.; investigation, R.B. and D.S.; writing—original draft preparation, E.S., A.T. and R.B.; writing—review and editing, M.K. All authors have read and agreed to the published version of the manuscript.


This research received no external funding.

Data Availability Statement

Not applicable.


We would like to thank the Center for Collective Use «Physico-chemical methods for the study of nitro compounds, coordination compounds, biologically active substances, and nanostructured materials» of the Interdisciplinary Resource Center for Collective Use «Modern physico-chemical methods of formation and research of materials for the needs of industry, science, and education» of the Herzen State Pedagogical University of Russia for NMR and IR spectral studies and the Research Centre for X-ray Diffraction Studies of the Research park of St. Petersburg State University for the structural studies.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds are available from the authors upon request.


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Figure 1. Molecular view of [Ni(Salphen(CH3O)2)]·CH3CN in representation of atoms with thermal ellipsoids (p = 50%), structures (a,b).
Figure 1. Molecular view of [Ni(Salphen(CH3O)2)]·CH3CN in representation of atoms with thermal ellipsoids (p = 50%), structures (a,b).
Molbank 2022 m1512 g001
Figure 2. Comparison of the distortion of structures (a,b) with thermal ellipsoids at a 50% probability.
Figure 2. Comparison of the distortion of structures (a,b) with thermal ellipsoids at a 50% probability.
Molbank 2022 m1512 g002
Figure 3. Key correlations in 1H-13C HMBC (blue arrows) and 1H-1H NOESY (double-edged red arrows) spectra.
Figure 3. Key correlations in 1H-13C HMBC (blue arrows) and 1H-1H NOESY (double-edged red arrows) spectra.
Molbank 2022 m1512 g003
Table 1. Crystallographic data, experimental parameters, and refinement of the [NiSalphen(CH3O)2)]·CH3CN complex structure.
Table 1. Crystallographic data, experimental parameters, and refinement of the [NiSalphen(CH3O)2)]·CH3CN complex structure.
Empirical formulaC24H21NiN3O4C24H21NiN3O4
Crystal systemmonoclinictrigonal
Space groupP21/nR3c
ρ calc/g/cm31.5391.515
Crystal size/mm0.1 × 0.08 × 0.050.16 × 0.04 × 0.02
Radiation/λ/ÅCuKα1.54184)CuKα (1.54184)
2Θ range for data collection/°8.142–138.2124.564 to 139.994
Index ranges−9 ≤ h ≤ 9, −10 ≤ k ≤ 15,
−24 ≤ l ≤ 24
−46 ≤ h ≤ 32, −47 ≤ k ≤ 41,
−8 ≤ l ≤ 8
Reflections collected1151718976
Independent reflections3812 [Rint = 0.0261,
Rsigma = 0.0245]
3872 [Rint = 0.0453,
Rsigma = 0.0347]
GOOF by F21.0741.039
R factors [I > = 2σ (I)]R1 = 0.0278, wR2 = 0.0721R1 = 0.0310, wR2 = 0.0773
R factors [all reflections]R1 = 0.0304, wR2 = 0.0737R1 = 0.0325, wR2 = 0.0783
Largest diff. peak/hole, e Å−30.23/−0.290.29/−0.28
Table 2. IR band assignment according to [20].
Table 2. IR band assignment according to [20].
IR band, cm−1Assignment
ligand core molecule
1585–1608C = N str in azomethine and C –C str in phenolic ring
1518C–C str in phenolic ring
1450–1465C–O, C=N and C–C str in phenolic and six-membered chelate ring
1367C = N in six-membered chelate ring and C –C str in phenolic ring
1333C –O and C –C str in phenolic ring
1244C –C str in phenolic and six-membered chelate ring
1109–1189C –N str in five-membered chelate ring
729–753ring vib and C –H out-of-plane def in phenolic ring
metal chelate
594asym O –Ni –O str
459asym N –Ni –N str
substituents in phenolate moieties
2831sym and asym C –H str in –O–CH3
1090–1100sym C–O–C str in phenyl–O–CH3
diimine backbone
3042–3012sym and asym C–H str in o –phenylene
1146C–H in-plane def in o –phenylene
753ring vib and C –H out-of-plane def in o -phenylene
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Smirnova, E.; Baichurin, R.; Viktorov, N.; Spiridonova, D.; Timonov, A.; Karushev, M. N,N′-4,5-Dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II). Molbank 2022, 2022, M1512.

AMA Style

Smirnova E, Baichurin R, Viktorov N, Spiridonova D, Timonov A, Karushev M. N,N′-4,5-Dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II). Molbank. 2022; 2022(4):M1512.

Chicago/Turabian Style

Smirnova, Evgenia, Ruslan Baichurin, Nikolai Viktorov, Dar’ya Spiridonova, Alexander Timonov, and Mikhail Karushev. 2022. "N,N′-4,5-Dimethoxy-1,2-phenylenebis(salicylideneiminato)nickel(II)" Molbank 2022, no. 4: M1512.

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