Research paperStructural analysis of diorganotin(IV) complexes derived from thio bis-tridentate Schiff base ligands
Graphical abstract
A multicomponent reactions are used to synthesized diorganotin(IV) derivatives based on bis-tridentate Schiff bases ligands. In solution, the 119Sn NMR spectra in non-coordinating solvent indicated the five-coordination of tin atoms for all twelve complexes. Nonetheless, the structural analysis in solid state for dimethyl tin derivatives (1c, 1d) reveals the geometry change to distorted octahedral owing the presence of Sn···O intermolecular interactions. Polymeric wave 1D polymeric chains were observed as result of these secondary interactions.
Introduction
Schiff bases are a well-known class of versatile ligands obtained by facile condensation reactions involving primary amines and carbonyl compounds [1]. The appropriate choice of initial fragments and substituents can tune the physical, chemical and electronic properties of the Schiff bases [2]. The importance of the Schiff base ligands can be noticed from the publication of over 15,000 related papers described at scifinder, these compounds can be easily combined with either alkaline, main group or transition metals [3]. Generally, Schiff bases are used in neutral or deprotonated forms to give metal complexes with variable stoichiometry and different coordination modes [4].
By the way, tin complexes derived from Schiff bases have been widely studied showing interesting applications in industrial, agriculture or medicinal fields [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. In fact, mainly diorganotin(IV) Schiff base complexes are reported to have excellent biological properties such as antimicrobial [18], [19], [20], [21], [22], antifungal [23], [24], antibacterial [25], [26], antitumor [27], [28], [29], [30], antioxidant [31], anti-insecticidal [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69], [70], antiviral [34], [35], antitubercular [36], antifertility [37], [38], and anti-inflammatory [39], [40].
Previously, we have described the synthesis of diorganotin(IV) complexes derived from Schiff bases including a double set of ONO donor atoms. Monomeric, dimeric or 1D polymeric structures were observed depending on the coordination tin geometry [41]. In this work, the introduction of a sulfur atom connecting two aromatic aldehyde fragments was done, with the aim to analyze structural and conformation changes on this type of complexes. Therefore, we hope to contribute to the investigation dealing with the study of diorganotin(IV) species derived from Schiff base ligands [42], [43], [44]. Twelve diorganotin(IV) complexes derived from 5,5-thio-bis(salicylaldehyde), four different aminophenols and diorganotin(IV) oxides (R = Me, n-Bu, Ph) are described. All compounds were obtained in moderate yields by using multicomponent reactions. Products consist on dinuclear metal complexes in where each metal is bonded to a set of ONO donor atoms together with two carbon atoms from the organic groups.
Section snippets
Materials and methods
The compound 5,5́-thio-bis(salicylaldehyde) was prepared according to the procedure described [45]. All reagents and solvents were obtained from commercial suppliers and used without further purification.
The 1H, 13C and 119Sn NMR spectra were recorded at room temperature using a Varian Gemini 500. TMS (internal, 1H, δ = 0.00 ppm, 13C, δ = 0.00 ppm) and SnMe4 (external, 119Sn, δ = 0.00 ppm) were used as standard references. Two dimensional COSY and HSQC correlation experiments have been carried
Results and discussion
The 5,5′-thio-bis(salicylaldehyde) ligand was prepared as reported with small modifications [45]. The dinuclear tin compounds 1a-1l were prepared by multicomponent reactions using one equivalent of dialdehyde, two equivalents of o-aminophenol p-substituted (X = H, Me, Cl, NO2) and two equivalents of diorganotin(IV) oxide derivative (R = Me, n-Bu, Ph), Scheme 1. Reactions were carried out under reflux for 12 h (1a-1d), 8 h (1e-1h) and 24 h (1i-1l) for methyl, butyl and phenyl derivatives
Conclusions
Twelve new dinuclear tin(IV) Schiff base ligands derivatives have been synthesized and characterized by spectroscopic methods. In solution, the 119Sn NMR chemical shift showed values for 1a-1l at the region of five-coordinate tin atoms for all complexes. Chemical Shift values change depending on the organic substituent attach to the tin atom, as reported previously. Furthermore, the substituent present at the aromatic moiety also affect the chemical shift being the NO2 group whom has more
Acknowledgments
The authors would like to thanks to the CONACYT for financial supports (157743 and 281251) and Beatriz. E. Noriega-Ortega by redaction revision. Authors also acknowledge to CIQ-LANEM for structural analysis.
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