Tin(IV) complexes with salen type Schiff base: synthesis, spectroscopic characterization, crystal structure, antibacterial screening and cytotoxicity

A series of six tin(IV) complexes [SnCl₂(L) (I), Me₂Sn(L) (II), Bu₂Sn(L) (III), Ph₂Sn(L) (IV), Oct₂Sn(L) (V), BuSnCl(L) (VI)] derived from N,N'-bis(2-hydroxy-1-naphthylidene)-1,2-diaminobenzene [LH₂] have been synthesized. The obtained compounds were characterized by elemental analysis, mass spectrometry, FT-IR and NMR (¹H, ¹³C) spectroscopy. The crystal structures of compounds (IV) and (VI) have also been determined by single crystal X-ray analysis (CIF files CCDC nos. 856596 (IV) and 856595 (VI)). The study revealed that the complexes exist as discrete monomeric species and the tin atom is hexa-coordinated in a distorted octahedral geometry. The two phenyl groups in compound (IV) are at trans-positions. Similarly, in complex (VI) the butyl and chloro groups also adopt trans-orientation. The in vitro antibacterial screening and cytotoxicity investigations revealed that the biological activities significantly depend upon the alkyl or others groups present on tin atom. Most of the tin(IV) complexes are active against Escherichia coli and highest activity is shown by complex (IV) against Bacillus subtilis. Furthermore, complex (IV) has also demonstrated the highest cytotoxicity against brine shrimp with LD₅₀ value 0.858 μg/mL.