Hypercoordinated Organosilicon(IV) and Organotin(IV) Complexes: Syntheses, Spectral Studies, and Antimicrobial Activity In Vitro

This paper deals with the syntheses and structural features of some new diorganosilicon(IV) and diorganotin(IV) complexes having general formulae (CH3)2MCl(L1), (CH3)2MCl(L2), (CH3)2M(L1)2, and (CH3)2M(L2)2 with new Schiff bases (M = Si and Sn). The Schiff bases HL1 and HL2 have been derived from the condensation of 3-bromobenzaldehyde with 4-amino-3-ethyl-5-mercapto-1,2,4-triazole and 4-amino-5-mercapto-3-propyl-1,2,4-triazole, respectively. The compounds have been characterized by the elemental analyses, molar conductance, and spectral (UV, IR, 1H, 13C, 29Si, and 119Sn NMR) studies. The resulting complexes have been proposed to have trigonal bipyramidal and octahedral geometries. In vitro antimicrobial activities of the compounds have been carried out. 1. Introduction The chemistry of complexes with hypercoordinated silicon and tin atoms is interesting from many points of view such as reactivity, biological activity, and structural features as reported in several reviews [1–3]. The Schiff bases bearing additional donor groups represent the most important class of heteropolydentate ligands capable of forming mono-, bi-, and polynuclear complexes with different metal ions. Enhanced reactivities of silicon complexes due to increased coordination number as well as modified electronic properties as a result of modified ligand sphere and coordination geometries have been reported [4, 5]. Singh et al. recently reported the activity of Schiff base complexes with silicon against pathogenic fungi and bacteria [6, 7]. The insecticidal and nematicidal activities were also reported for some hypercoordinated silicon complexes [8]. Organosilicon compounds of N- and S-containing ligands are well known for their anticarcinogenic, tuberculostatic, antimicrobial, and acaricidal activities [9, 10]. Similarly organotin(IV) compounds have been receiving increasing attention in the area of inorganic and metal organic chemistry due to the important industrial [11] (pesticides, antifouling paints, and fire retardants), pharmacological [12, 13] (antifungal, antibacterial, and antitumor drugs), and environmental applications. Organotin(IV) complexes are extensively studied due to their coordination geometries as well as structural diversity (Monomeric, dimeric, hexameric, and oligomeric) [14]. So by keeping in mind the various applications of the organosilicon(IV) and organotin(IV) complexes and further continuation of our work [15, 16], we report here the syntheses, characterization, and biological activity of some new silicon and tin complexes of the Schiff bases derived from