Synthesis, characterization and anti-diabetic assay of diorganotin() azo-carboxylates: crystal structure and topological studies of azo-dicarboxylic acid ligand and its cyclic tetranuclear dimethyltin() complex

Diorganotin( iv ) complexes with ( E )-5-((2-carboxyphenyl)diazenyl)-2-hydroxy benzoic acid [H 3 L] were synthesized by reacting the sodium salt of the azo-dicarboxylic acid ligand [Na 2 HL] with an appropriate diorganotin( iv ) dichloride [R = 1 (Me), 2 (Bu) and 3 (Ph)] in anhydrous methanol. The complexes were characterized using elemental analysis, UV, IR, NMR and mass spectrometry. 119 Sn NMR study of complexes 1 and 2 indicates the presence of exo -and endo -cyclic tin atoms in the complexes and both the tin atoms are suggested to have 5-coordinate geometry in solution; in complex 3 , a single 119 Sn-resonance was observed in the range specified for a 4-coordinate structure. The molecular structure of H 3 L and its dimethyltin( iv ) complex {[Me 2 SnHLSnMe 2 ]O} 2 ( 1 ) were determined using X-ray crystallography. The structure of 1 reveals that the compound is a centro -symmetric cyclic tetranuclear tin complex which contains a Sn 2 O 4 core. In the structure, the central Sn 2 O 2 ring is connected to two exo -cyclic tin atoms by two μ 3 -oxo oxygen atoms. Each exo - and endo -cyclic tin atom exhibited a five coordinate distorted trigonal bipyramidal geometry and suggested that the five coordinate structure of the complex in the solid state is also retained in solution. Topological studies of the azo-dicarboxylic acid ligand [H 3 L] and its cyclic tetranuclear dimethyltin( iv ) complex were also carried out. The H-bonding network in H 3 L has been topologically classified as 2-periodic three-dimensional KIa . For the molecular packing in 1 , a multilevel topological description is provided. Finally, the complexes have been screened for α-glucosidase enzyme inhibition assay as an indicator for their anti-diabetic properties and the results of the tests showed that they had better anti-diabetic activity than the standard drug acarbose. Two novel cyclic tetranuclear and a cyclic dimeric diorganotin( iv ) azo-dicarboxylates have been reported. The complexes exhibited effective anti-diabetic activity.