Camphor Sulfonimine Compounds: Bottom-Up Design of MOFs from Organic Frameworks Based on X-rays and DFT-D3

Abstract

DFT-D3 calculations based on structural X-ray diffraction data obtained for 3-oxo-camphorsulfonyl imine (1), camphorsulfonyl chloride (2) and seven camphor sulfonimines (O₂SNC₁₀H₁₃NR, L¹−L⁷), from which L² (R=4-OHC₆H₄), L⁴ (R=4-ClC₆H₄) and L⁶ (R=3,5-(CH₃)₂C₆H₃) are synthesized and characterized in this work, provide information into the intra- and inter-molecular interactions with concomitant elucidation of the supramolecular arrangement of the compounds. The DFT-D3 calculations performed in small clusters of two or three molecular units reproduce the interactions observed via X-ray analyses, showing that, as a general trend, the structural arrangement of the molecules is driven by electronic rather than by packing parameters. In all compounds, the self-assembly of 3D structures involves the sulfonyl imine group (-NSO₂) either to establish hydrogen bonds through oxygen atoms or non-classic oxygen–aliphatic hydrogen or non-bonding interactions (NBIs), which also involve sulfonyl oxygen atoms. Interestingly, the camphor sulfonimine compounds (L², L³), having protic groups (R=C₆H₄X:X=OH, L² or X=NH₂, L³) at the aromatic imine substituents (=NR), present an extra π-π stacking, which is absent in the other compounds’ aromatic derivatives. The X-ray analysis shows that all the reported camphor sulfonimine compounds display the E configuration with respect to the imine substituent (R). The study of the redox behavior of the compounds by cyclic voltammetry enables insight into the solution properties of the compounds and the rationalization of the molecular interactions that stand in the solid and solution states. Camphor sulfonimine compounds (L) display appropriate binding atoms to coordinate transition metals. The results herein show that monodentate coordination through the nitrogen atom of the sulfonimine five-membered ring to the {Ag(NO₃)} metal center is favored. When this imine nitrogen atom is not itself involved in the organic framework, DFT-D3 calculations show that the complexation does not affect the non-covalent interactions that are reproduced in the MOF structure.

1. Introduction

The molecular structure of coordination compounds is formed by organic and inorganic moieties that combine to form new metal–ligand interactions. The formation of the new compounds can involve a major change in the pre-existing structural arrangement of the ligand or the metal precursors, or be shaped through binding of one of them into the pre-organized structures of the other without a major reorganization.

In the case of complexes based on neutral ligands, covalent dative bonds are established involving the ligand heteroatom’s lone pair (e.g., N, O, S) without change to the metal oxidation state or modification of the ligand composition. This is the case with camphor sulfonimines (RNC₁₀H₁₃NSO₂), which typically bind the metal through the nitrogen lone pair (=NSO₂), forming dative bonds that, in some cases, are reinforced by Van der Waals interactions (non-bonding interactions, NBIs) involving the imine nitrogen atom (=NR) [1,2,3].

Pre-existing intermolecular NBIs in the organic or inorganic scaffolds can be maintained or be broken within the formation of the coordination compound. If the NBIs remain, the coordination compound eventually acquires a polymeric character. NBIs play a significant role in the structural, reactivity and selectivity of the coordination compounds [4,5] and are referred to as being the primary transport mechanism by which thermal conductivity is increased in cross-linked polymers [6].

In some cases, a structure/reactivity relationship can be established in complexes [7,8], allowing the prediction of properties based on the structure; e.g., biological and/or catalytic properties of camphor sulfonimine coordination compounds [3,9]. Unfortunately, the structural analysis of coordination compounds based on X-ray diffraction is sometimes impossible due to a lack of suitable crystals. However, if X-ray data on the organic moieties exist, it is possible to predict through computational calculations the structure of the derived coordination compounds. DFT-D3, by providing an approach to the treatment of London dispersion interactions, has been applied to systems depicting NCI. The methodology was extensively review by Goerigk, in particular for NCI energies and geometry optimizations [10].

2. Results and Discussion

Two new coordination compounds [Ag(NO₃)L₂] (C1: L⁶ and C2: L⁷) were synthesized (see Section 4) from the reaction of AgNO₃ with camphor sulfonimines, 3,5-Me₂C₆H₃C₁₀H₁₃SO₂ (L⁶) and C₆H₅C₁₀H₁₃SO₂ (L⁷), which enlarges the pool of [Ag(NO₃)L_n] (n = 1, 2) camphor sulfonimine complexes with potential biological applications as anticancer or antimicrobial agents [3,11]. Unfortunately, the structure of these two camphor sulfonimine Ag(I) complexes, as with that of many others, could not be confirmed by X-ray diffraction analysis since no suitable crystals could be obtained. Therefore, calculations based on X-ray data obtained for the ligands can help to gain insight into the structural arrangement of the complexes. In one case, data obtained from X-rays showed that [Ag(NO₃)L₂] (R=NMe₂) arranges as a calix (Scheme 1) [3].

2.1. Synthesis of Camphor Sulfonimines

The camphor sulfonimine compounds (RNC₁₀H₁₃NSO₂: L¹, R=OH; L², R=4-OHC₆H₄; L³, R=4-NH₂C₆H₄; L⁴, R=4-ClC₆H₄; L⁵, R=4-CH₃C₆H₄; L⁶, R=3,5-(CH₃)₂C₆H₃; L⁷, R=C₆H₅) were obtained by condensation (Scheme 2, right) of the convenient primary amine (H₂NR) with (1S)-3-oxo-camphorsulfonyl imine (1). Precursor 1 was obtained from camphor sulfonic acid through a sequential process that involves the formation of compound 2 (Scheme 2, left) and ends on the oxidative annulation of a third ring to the bicyclic camphor precursor.

With respect to the camphorimine species under study (L¹−L⁷), four are new (L¹, L², L⁴ and L⁶) and were characterized by conventional analytical and spectroscopic techniques (FTIR, ¹H NMR, ¹³C NMR and 2D NMR). The remaining compounds were just recrystallized to obtain single crystals. The structural arrangement of all compounds was then studied by X-ray diffraction analysis. Based on the X-ray data, the intra- and inter-molecular NBIs were predicted via DFT-D3. Therefore, the supramolecular arrangement of compounds 1 and 2 and camphor sulfonimines L¹−L⁷ was elucidated.

2.2. Structural Arrangement Predicted via DFT-D3

Compounds 1 and 2

The X-ray data obtained for compound 1 indicate that a 3D helicoidal packing exists around the 3₁ crystallographic axes due to non-conventional oxygen∙∙∙hydrogen (aliphatic) NBIs (Figure 1a). DFT-D3 calculations, performed on a subset dimer of 1, confirm the observed NBIs and predict them to be even stronger than those experimentally observed via X-ray analysis, as illustrated by shorter distances (Figure 2b).

For 2, calculations were based on the X-ray data reported by others [12]. The X-ray shows a zig-zag 1D structural arrangement due to chloride–oxygen intermolecular NBIs established by the pendant sulphonyl chloride (SO₂Cl) groups in adjacent molecules (Figure 3). This type of cooperative intermolecular S-Cl∙∙∙O interaction was previously discussed [13] on the basis of the S-Cl∙∙∙O and S-O∙∙∙Cl angles (θ) and classified (Figure 3, insert) as type I (θ₁ = θ₂) or type II (θ₁ = 180°, θ₂ = 90°) [14].

As with 1, DFT-D3 calculations for 2 were carried out on a subset dimer of the structural arrangement found by X-ray diffraction analysis. Once more, the output data show good agreement between experimental and calculated values (

Table 1. Intermolecular interactions in 2 (distances pm; angles deg).

Parameter	X-ray	DFT-D3
Cl∙∙∙O	300	311
S-Cl∙∙∙O	169.4	176.4	NBIs quasi-Type II
S-O∙∙∙Cl	131.5	128.2

), in agreement with the electrostatic directionality of the interactions.

2.3. Camphor Sulfonimines (L¹−L⁷)

X-ray data collected for the sulfonimine compounds L¹ to L⁷ show different packing motives according to the imine substituent (R). In L¹ (R=OH), the asymmetric unit is formed by two structurally different molecules, as shown in Figure 4 (center), since chirality prevents the existence of an inversion center.

The X-ray data show that at the “dimeric” asymmetric unit, the NBIs are type I (θ₁ = θ₂, i.e., S-O∙∙∙H=C-H∙∙∙O = 108°), while the NBIs established between neighboring asymmetric units (involving the sulfonimine oxygen atom and the hydrogen hydroxyl atom) are of type II (θ₁ ≠ θ₂, i.e., S-O∙∙∙H=109° and O-H∙∙∙O=171°). The DFT-D3 calculations corroborate the type II nature of this NBI (Figure 5, left), but concerning the asymmetric unit, DFT-D3 calculations predict a type II NBI (Figure 5, right), in contrast to those experimentally observed by X-ray diffraction. Such results indicate that NBI type I experimental observations are due to packing constraints rather than to electrostatic effects.

Figure 4 and Figure 5 show that the asymmetric unit remains unchanged both experimentally and in DFT-D3 calculations, with the two nitrogen atoms not involved in NBIs and, thus, available for complexation with the metal center AgNO₃. The introduction of the metal center in the calculations (Figure 6) confirms that an MOF can form through coordination of the cyclic imine nitrogen atom in the metal, keeping the 1D chain of the organic framework (OF).

Camphor sulfonimine compounds with aromatic substituents (R, Scheme 2) at the imine group (L² to L⁷) display self-assembly behaviors quite different from L¹ (R=OH).

A 1D assembly, which exists in L⁴ (R=4-ClC₆H₄), L⁵ (R=4-CH₃C₆H₄), L⁶ (3,5-(CH₃)₂C₆H₄) and L⁷ (R=C₆H₅), is formed by non-conventional NBIs established between the nitrogen atom of the -SO₂N- group and one of the hydrogen atoms of the methylene (CH₂) group of the five-membered sulfonimine ring of a neighboring molecule. As a representative example, X-ray diffraction data are displayed for L⁷ (Figure 7, left). The results from the DFT-D3 calculations agree well with the experimentally obtained X-ray data (Figure 7, right). As with 1, the predicted NBI distances are shorter than those experimentally measured, pointing to stronger electronic interactions.

In the aromatic substituted camphor sulfonimines (L⁴ to L⁷), the cyclic nitrogen imine atom of the 1D organic framework is involved in NBIs, which means that complexation would break down the self-assembly trends observed in the OF. So, MOFs are expected to have different frameworks from those observed in ligands L⁴ to L⁷.

For the camphor sulfonimines bearing a protic substituent (R=OH in L² or R=NH₂ in L³) at the -NR imine group (Scheme 2), the characteristics of the NBIs differ from those observed in L⁴−L⁷. In L² and L³, the NBIs are of the stacking π-π type, established between aromatic carbon atoms of two distinct asymmetric units occupying the ortho positions relative to the heterogeneous (N or O) atoms, as depicted for L² (Figure 8, left). In L² and L³, NBIs involving the sulfonyl imine group (not observed for L⁴−L⁷) are established by a symmetry-related chain of molecules (Figure 8, left). These additional interactions were included in the DFT-D3 calculations (Figure 8, right) to obtain consistency between X-ray and calculated structures. Here again, as with L¹, the two nitrogen imine atoms are free to complex the AgNO₃ metal center to form an MOF mimicking the self-assembly characteristics of the corresponding OF.

2.4. Redox Properties

Packing and electronic parameters have distinct effects on the properties of molecules. While electronic characteristics persist no matter the physical state (solid or solution), packing essentially drives solid-state properties.

The above results show that the structural arrangement in camphor sulfonimines (L²−L⁷) and in compounds 1 and 2 is essentially directed by electronic parameters. In contrast, packing plays an important role in the supramolecular arrangement of L¹ by imposing a type I NBI geometry (see above).

In order to obtain insights as to whether a correlation exists between structural parameters and redox potentials, and to try to ascertain whether NBI interactions remain in a solution, the electrochemical behavior of the L¹−L⁷ compounds was studied by cyclic voltammetry.

In acetonitrile, compounds L¹−L⁷ display one irreversible anodic wave and one (L¹, L², L⁵, L⁶, L⁷) or two (L³, L⁴) cathodic waves (Figure 9). In the case of two cathodic waves, the higher potential wave (I) typically displays a higher intensity than the lower potential one (wave II). The reversibility of wave I decreases upon scanning at the potential of wave II, as shown (Figure 9, left). The loss of reversibility and emergence of anodic wave X is consistent with chemical reactivity being induced by electron transfer.

The anodic and cathodic potentials measured for L¹−L⁷ are displayed in

Table 2. Cyclic voltammetry data ^a for camphor sulfonimine compounds L¹−L⁷.

R			${}^{\mathrm{I}}\mathit{E}_{1/2}^{\mathit{red}}$	${}^{\mathrm{II}}\mathit{E}_p^{\mathit{red}}$	${\mathit{E}}_{\mathit{p}}^{\mathit{o}\mathit{x}}$	σpb
				Volt
	OH	L1	−1.03	—	—	0.12
	4-OHC6H4	L2	−1.35	—	1.25	−0.37
	4-NH2C6H4	L3	−1.24	−1.69	0.87	−0.66
	4-ClC6H4	L4	−1.08	−1.61	—	0.23
	4-CH3C6H4	L5	−1.25	—	1.80	−0.17
	3,5-(CH3)2C6H3	L6	−1.15	—	1.80	0.017
	C6H5	L7	−1.16	—	—	0

^a Values in Volt ± 10 mV versus SCE using ferrocene as internal reference. ^b Hammett parameter.

.

The potential trend observed for wave I (Table 2) suggests that reduction involves the imine >C=N-R group. In fact, an excellent correlation exists (Figure 10, left) between the redox potential and the Hammett sigma parameter (σ_p) [15] which accounts for the electronic characteristics of the R group driving the cathodic process. Compounds L¹ (R=OH) and L³ (4-NH₂C₆H₄) are aside from the linear correlation (R² = 0.987) established by the other compounds, showing that other than electronic parameters operate.

With respect to L¹, such behavior was somehow expected due to the non-aromatic character of the R group (unlike the R groups at L²−L⁷) and the distinct type of NBI (see DFT-D3 discussion, above) compared to the other compounds.

With respect to the relationship between ${}^{\mathrm{I}}E_{1/2}^{\mathit{red}}$ and the LUMO (Figure 10, right), the energy calculations for L¹ show that there is a decrease of 0.11 eV in the absolute value of the energy in the H-bonded dimer. Such an energy shift may account for the non-fitting of the potential (Figure 10, right), pointing to L¹ keeping some dimer characteristics in the electrolyte solution.

L³ is the other compound that does not fit either the ${}^{\mathrm{I}}E_{1/2}^{\mathit{red}}$ versus σ_p (Figure 10, left) or the ${}^{\mathrm{I}}E_{1/2}^{\mathit{red}}$ versus LUMO (Figure 10, right) correlations. The two compounds (L¹, R=OH and L³, R=C₆H₄NH₂) have in common the protic character of the R imine substituent, which induces formation of H-bonded dimers (see above).

With respect to the anodic behavior, only L², L³, L⁵ and L⁶ show oxidation processes. L² and L³ display the lowest oxidation potentials, in agreement with the electron releasing characteristics of the aromatic R groups, as corroborated through linear correlation with Hammett σ_p parameters (Figure 11, left). A good correlation with the HOMO was found (Figure 11, right).

The calculated HOMO and LUMO contours for compound L⁷ show that the HOMO is mostly localized at the aromatic ring (all carbons), while the LUMO is localized at the camphor skeleton, with an important contribution from the two-, four- and six-ring carbon atoms (Figure 12).

The electrochemical behavior of [Ag(NO₃)L₂] (C1, C2) complexes studied by cyclic voltammetry shows that a cathodic process exists at a potential ($E_p^{red}$ = −1.18 V, C1 and $E_p^{red}$ = −1.17 V, C2) similar to that measured for organic precursors L⁶ and L⁷, respectively (Table 2). Such patterns indicate that the electronic properties of the sulfonimine ligands remain essentially identical in the complexes. As expected, the cyclic voltammograms of C1 and C2 display a cathodic wave attributed to the Ag(I)→Ag(0) reduction at a potential ($E_p^{red}$ = 0.16 V) that does not differ much from that reported for related complexes [3].

The redox behavior of 1 was also studied by cyclic voltammetry, showing a quasi-reversible cathodic wave ($E_{1/2}^{red}$ = −0.92 V; ipc/ipa = 1, E_pa − E_pc = 133 mV) but no anodic process. According to the cathodic potential value, the reduction of 1 is easier than for any of the sulfonimine compounds (L¹−L⁷, Table 1). Therefore, sulfonimines are more electron rich than 1 and, consequently, better ligands for metal sites. In fact, no Ag(I) complex based on 1 could be experimentally obtained, in contrast with several complexes derived from sulfonimine ligands; for example, the new [Ag(NO₃)L₂] (C1 and C2) now reported (see Section 4).

3. Conclusions

DFT-D3 calculations based on X-ray data obtained for a series of camphor sulfonimine compounds corroborate that NBIs are responsible for their organic framework. For ²L−⁷L, the NBIs are essentially electrostatic, in contrast with ¹L, where packing plays a relevant role in the solid-state arrangement observed via X-ray analysis.

The characteristics of the sulfonimine substituent (R) drives the NBIs established and directs the ability of the L compounds to bind the Ag(I) metal center forming MOFs, such as those detected for [Ag(NO₃)(O₂SNC₁₀H₁₃NNMe₂)₂], whose X-ray structure was formerly reported.

It was found that complexation of the metal center always occurs in a monodentate fashion through the imine nitrogen atom in the sulphonyl five-membered ring. It was predicted via DFT-D3 calculations that NBI interactions not involving this atom remain after complexation transfer to the MOF. The conjugation of the X-ray structures of the organic ligands with DFT-D3 calculations proved to be a powerful tool to predict the self-assembly trends of the corresponding MOF structures of the complexes.

The correlation between the redox potentials of ¹L−⁷L (studied by cyclic voltammetry), the Hammett σ-parameter and calculated HOMO and LUMO energies are in excellent agreement with different types of NBIs being established by ¹L and ²L compared to the other camphor sulfonimine compounds.

The results presented in this work are expected to enable the bottom-up design of new MOFs by probing, in silica, the incorporation of metal fragments in the OF of existing ligands.

4. Experimental Section

The camphor sulfonimines L¹, L³, L⁵ and L⁷ were synthesized according to published procedures [16]. The complexes were synthesized under nitrogen using Schlenk and vacuum techniques. The FTIR spectra were obtained from KBr pellets using a JASCO FT/IR 4100 spectrometer. The NMR spectra (¹H, ¹³C, DEPT, HSQC, and HMBC) were obtained from CDCl₃, CD₃CN or DMSO solutions using Bruker Avance II+ (300 or 400 MHz) spectrometers. The NMR chemical shifts are referred to TMS (δ = 0 ppm).

The redox properties were studied by cyclic voltammetry using a three-compartment cell equipped with Pt wire electrodes (work and secondary) and interfaced with VoltaLab PST050 equipment. The cyclic voltammograms were obtained from NBu₄BF₄/CH₃CN (0.10 M) solutions used as electrolyte. The potentials were measured in Volts (±10 mV) versus SCE at 200 mV/s using [Fe(η⁵-C₅H₅)₂]^0/+ ($E_{1/2}^{ox}$ = 0.382 V; CH₃CN) as an internal reference. The window of potential was established by scanning a fresh solution of the electrolyte to the limits.

4.1. Synthesis

4.1.1. Camphor Sulfonimines

(E)-7-(hydroxyimino)-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-ethanobenzo[c] isothiazole 2,2-dioxide (L¹)-Compound 1 (682 mg; 3 mmol) was dissolved in ethanol (10 mL) acidified with acetic acid (0.4 mL) and the mixture was stirred for ca. 15 min before the hydroxylamine (99 mg, 3 mmol) was added. The reaction was stopped after 24 h of stirring with the addition of 5 mL of water. The organic phase was then extracted with dichloromethane (3 × 5 mL) and dried over MgSO₄ for a couple of hours. After filtration, the solvent was allowed to evaporate slowly in the exhaust hood. Yield 71%. Elem. Anal. (%) for C₁₀H₁₄N₂O₃S: Found: C, 49.8; N, 11.3; H, 6.0; S, 13.7. Calc.: C, 49.6; N, 11.6; H, 5.8; S, 13.2. FTIR (KBr, cm⁻¹): 3367, 1668, 1633, 1327, 1158. ¹H NMR (DMSO, δ_ppm): 12.8 (s, 1H); 3.59, 3.36 (2d, J = 14.0 Hz, 2H); 3.25 (d, J = 4.2 Hz, 1H); 2.22–2.01 (m, 2H); 1.63–1.40 (m, 2H); 1.01 (s, 3H); 0.78 (s, 3H). ¹³C NMR (DMSO, δ_ppm): 184.7, 155.3, 64.2, 49.0, 47.9, 47.1, 28.8, 23.6, 19.5, 18.1.

(E)-7-((4-hydroxyphenyl)imino)-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methanobenzo[c]isothiazole 2,2-dioxide (L²)-3-oxo-camphorsulfonimide (1, 682 mg; 3 mmol) was dissolved in ethanol (10 mL) acidified with CH₃COOH (0.4 mL). The mixture was stirred for 15 min before adding 4-aminophenol (329 mg; 3 mmol). A light brown compound was formed upon overnight stirring at 50 °C that was filtered off the solution and dried. Yield 81%. Elem. Anal. (%) for C₁₆H₁₈N₂O₃S·H₂O: Found: C, 56.9; N, 8.0; H, 6.2; S, 11.1. Calc.: C, 57.1; N, 8.3; H, 6.0; S, 9.5. FTIR (KBr, cm⁻¹): 3567, 1653, 1633, 1330, 1160. ¹HNMR (CD₃CN, δ_ppm): 7.35 (s, 1H, OH), 7.00 (d, J = 7.8 Hz, 2H), 6.88 (d, J = 7.8 Hz, 2H), 3.48, 3.25 (2d, J = 13.9 Hz, 2H), 3.10 (d, J = 2.6 Hz, 1H), 2.34–2.23 (m, 2H), 1.89–1.75 (m, 2H), 1.06 (s, 3H), 0.84 (s, 3H). ¹³C NMR (CD₃CN, δ_ppm): 187.9, 166.0, 157.3, 141.9, 124.9, 116.7, 64.1, 52.6, 50.5, 47.8, 29.4, 24.4, 19.9, 18.3.

(E)-7-((4-chlorophenyl)imino)-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methanobenzo[c]isothiazole 2,2-dioxide (L⁴)-Compound 1 (682 mg; 3 mmol) was dissolved in acidified (acetic acid, 0.4 mL) ethanol (10 mL) and stirred for ca. 15 min. Upon addition of 4-chloroaniline (384 mg, 3 mmol) the reaction was stirred overnight at 40 °C. A yellow precipitate formed that was filtered off solution and dried. Yield 76%. Elem. Anal. (%) for C₁₆H₁₇ClN₂O₂S·¹/₅H₂O: Found: C, 56.5; N, 8.1; H, 5.3; S, 10.1. Calc.: C, 56.5; N, 8.2; H, 5.2; S, 9.4. FTIR (KBr, cm⁻¹): 1664, 1636, 1340, 1161. ¹H NMR (CDCl₃, δ_ppm): 7.39 (d, J = 8.6 Hz, 2H); 6.93 (d, J = 8.6 Hz, 2H); 3.42, 3.21 (2d, J = 13.4 Hz, 2H); 2.99 (d, J = 8.6 Hz, 1H); 2.29–2.21 (m, 2H); 2.10–2.00 (m, 1H); 1.82–1.74 (m, 1H); 1.11 (s, 3H); 0.95 (s, 3H). ¹³C NMR (CDCl₃, δ_ppm): 185.0, 167.5, 147.2, 132.1, 129.4, 122.0, 62.7, 51.4, 50.0, 46.8, 28.4, 24.1, 20.0, 18.4.

(E)-7-((3,5-dimethylphenyl)imino)-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methanobenzo[c]isothiazole 2,2-dioxide (L⁶)-Compound 1 (454 mg; 2 mmol) was dissolved in ethanol (7 mL) acidified with acetic acid (0.2 mL) and the mixture stirred for ca. 15 min. Then, 3,5-dimethylaniline (0.25 mL, 2 mmol) was added and the reaction stirred for 24 h at RT. A brown precipitate formed that was filtered off the solution and dried. Yield 86%. Elem. Anal. (%) for C₁₈H₂₂N₂O₂S: Found: C, 65.3; N, 8.4; H, 6.7; S, 9.5. Calc.: C, 65.4; N, 8.5; H, 6.7; S, 9.7. FTIR (KBr, cm⁻¹): 1665, 1636, 1339, 1161. ¹H NMR (CDCl₃, δ_ppm): 6.87 (s, 1H); 6.56 (s, 2H); 3.39, 3.18 (2d, J = 13.4 Hz, 1H); 3.01 (d, J = 4.0 Hz, 1H); 2.34 (s, 6H); 2.24–2.19 (m, 2H); 2.05–1.98 (m, 1H); 1.82–1.75 (m, 1H); 1.09 (s, 3H); 0.94 (s. 3H). ¹³C NMR (CDCl₃, δ_ppm): 185.4, 166.5, 149.1, 139.1, 128.1, 118.2, 113.6, 62.9, 51.5, 50.1, 46.8, 28.6, 24.3, 21.5, 21.4, 20.1, 18.5.

4.1.2. Complexes (See Supplementary Material for FTIR and 1H and 13C NMR Spectra)

[Ag(NO₃){(3,5-Me₂C₆H₃)NC₁₀H₁₃NSO₂}₂] (C1)–AgNO₃ (42.5 mg; 0.25 mmol) was added to a solution of L⁶ (165 mg; 0.50 mmol) in CH₃CN (5 mL) and the mixture was stirred for 2 h. A light suspension formed that was filtered to separate silver residues. The filtered solution was evaporated and dried under vacuum to afford C_B as a dark yellow compound. Yield 72%. Elemental analysis for AgC₃₆H₄₄N₅O₇S₂·¹/₅HNO₃ Exp.: C, 51.2; N, 8.4; H, 5.5; S, 8.8. Calc.: C, 51.3; N, 8.6; H, 5.3; S, 7.6. FTIR (KBr, cm⁻¹): 1666, 1644, 1384, 1338, 1161. ¹H NMR (400 MHz, CD₃CN, δ_ppm): 6.91 (s, 1H); 6.59 (s, 2H); 3.51, 3.28 (2d, J = 14 Hz, 2H); 2.96 (d, J = 4.8 Hz, 1H); 2.31 (s, 6H); 2.24–2.30 (m, 1H); 1.71–1.88 (m, 3H); 1.05 (s, 3H); 0.87 (s, 3H). ¹³C NMR (400 MHz, CD₃CN, δ_ppm): 186.5, 167.7, 149.2, 139.2, 127.6, 117.8, 63.2, 51.4, 49.7, 46.5, 28.0, 23.6, 20.3, 19.1, 17.1.

[Ag(NO₃)(C₆H₅NC₁₀H₁₃NSO₂)₂] (C2)-Silver nitrate (42.5 mg; 0.25 mmol) was added to a solution of L⁷ (151 mg; 0.50 mmol) in CH₃CN (3 mL) and the mixture was stirred for 2 h.

The suspension was then filtered to remove silver residues. Upon solvent evaporation and drying under vacuum, the compound was obtained as a yellow powder. Yield 62%. Elemental analysis for AgC₃₂H₃₆N₅O₇S₂·H₂O Exp.: C, 48.6; N, 9.0; H, 4.7; S, 7.6. Calc.: C, 48.5; N, 8.8; H, 4.8; S, 8.1. FTIR (KBr, cm⁻¹): 1664, 1635, 1384, 1346, 1165. ¹H NMR (400 MHz, DMSO, δ_ppm): 7.46 (t, J = 15.7 Hz, 2H); 7.25 (t, J = 7.4 Hz, 1H); 7.00 (d, J = 8.4 Hz, 2H); 3.74, 3.52 (2d, J = 14 Hz, 2H); 2.88 (d, J = 4.8 Hz, 1H); 2.34–2.25 (m, 1H); 2.19–2.10 (m, 1H); 1.80–1.70 (m, 2H); 1.01 (s, 3H); 0.84 (s, 3H). ¹³C NMR (400 MHz, DMSO, δ_ppm): 186.0, 167.8, 148.8, 129.3, 126.0, 120.1, 63.0, 51.0, 49.3, 46.3, 27.7, 23.4, 19.2, 17.5.

4.2. Computational Methods

All theoretical calculations were of the DFT type, carried out using GAMESS-US version R3 [17], using the implemented version of the B3LYP functional and a 6-31G** basis set for organic molecules and SBKJC basis set/ECP in metal complexes. DFT-D3 [18], with standard parametrization of GAMESS-US, was used in all computational work. Optimized geometries were confirmed to be minima by checking for absence of imaginary frequencies in the Hessian.

4.3. X-ray Diffraction Analysis

X-ray diffraction analysis (Bruker, Karlsruhe, Germany) was performed on mono crystals of 1,3 and L1 to L7. Data were collected on a Bruker AXS-KAPPA APEX II area detector apparatus using graphite-monochromatized Mo Kα (λ = 0.71073 Å) radiation and were corrected for Lorentz’s polarization and for empirical absorption. The structure was solved via direct methods using SHELX97 [19] and refined via full matrix least squares against F² using SHELX97, all included in the suite of WinGX v1.70.01 programs for Windows [20]. Non-hydrogen atoms were refined anisotropically and H atoms were inserted in idealized positions and allowed to refine riding on the parent carbon atom. Crystal data and refinement parameters are summarized in

Table 3. Crystallographic data for 1 and L¹ to L⁴, L⁶, L⁷.

	1.	L1	L4	L6	L7
Emp. formula	C10H13NO3S	C20H28N4O6S2	C16H17ClN2O2S	C18H22N2O2S	C16H18N2O2S
Formula weight	227.27	484.58	336.83	330.43	302.38
Crystal system	Tetragonal	Monoclinic	Orthorhombic	Orthorhombic	Orthorhombic
Space group	P43212	P21	P212121	P212121	P212121
Unit cell dim.
a/Å	7.6255(5)	6.9975(4)	8.8877(6)	9.121(2)	9.375(1)
b/Å	7.6255(5)	13.9378(9)	12.0522(7)	11.174(2)	11.724(1)
c/Å	36.400(2)	11.3550(7)	14.9100(6)	35.256(6)	14.130(2)
β/deg	90	95.520(3)	90	90	90
Volume (Å−3)	2116.6(2)	1102.3(1)	1597.1(2)	3593(1)	1553.1(3)
Z, Dcal (g/cm3)	8, 1.426	2, 1.460	4, 1.401	8, 1.222	4, 1.293
Abs. coeff. (mm−1)	0.292	0.288	0.378	0.191	0.214
F(000)	960	512	704	1408	640
Crystal size (mm)	0.3 × 0.3 × 0.3	0.3 × 0.3 × 0.3	0.2 × 0.1 × 0.1	0.4 × 0.3 × 0.2	0.2 × 0.2 × 0.3
θ range (deg)	2.2 to 29.9	2.3 to 32.7	2.2 to 26.4	1.9 to 32.0	2.3 to 32.2
Refl. Collect./uni.	12,072/3022	16,791/7667	7174/3253	220,676/12,299	12,152/5275
	[R(int) = 0.0486]	[R(int) = 0.0347]	[R(int) = 0.0349]	[R(int) = 0.5558]	[R(int) = 0.0361]
	3022/0/138	7667/1/301	3253/0/199	12,299/0/423	5275/0/192
Data/restr./par.	R1 = 0.0342,	R1 = 0.0334,	R1 = 0.0409,	R1 = 0.0756,	R1 = 0.0438,
Final R (obs.)	wR2 = 0.0896	wR2 = 0.0865	wR2 = 0.1026	wR2 = 0.155	wR2 = 0.1055

. Illustrations of the molecular structures were made with Chemcraft [21] or Mercury [22].

CCDC 2252538 to 2252543 and CCDC 2252556 contain the supplementary crystallographic data for this paper, which can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (accessed on 1 September 2023) (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; fax: +44 1223 336033; or [email protected]).