Synthesis,characterization and crystal structures of 2-[(E)-2-(4-hydroxy-3,5-dimethylphenyl)-1-diazenyl]benzoic acid and its polymeric and monomeric triorganotin(IV) complexes

Three triorganotin(IV) complexes of composition R₃SnLH (R = Me, Bu and Ph and LH = 2-[(E)-2-(4-hydroxy-3,5-dimethylphenyl)-1-diazenyl]benzoate) have been synthesized and characterized by ¹H, ¹³C, ¹¹⁹Sn NMR, and IR spectroscopic techniques in combination with elemental analysis. The crystal structures of the carboxylate ligand HO₂CC₆H₄{NN(C₆H₂-4-OH-3,5-(CH₃)₂)}-o in its neutral form and three triorganotin(IV) complexes, viz., polymeric (R₃Sn[O₂CC₆H₄{N–N(H)(C₆H₂-4-O-3,5-(CH₃)₂)}-o])_n (R = Me (1) and Bu (2)) and monomeric Ph₃Sn[O₂CC₆H₄{N–N(H)(C₆H₂-4-O-3,5-(CH₃)₂)}-o] (3) complexes are reported. The polymeric complexes 1 and 2 exist as extended chains in which the LH-bridged Sn-atoms adopt a trans-R₃SnO₂ trigonal bipyramidal configuration with R groups in the equatorial positions and the axial sites occupied by an oxygen atom from the carboxylate ligand and the phenoxide O atom of the next carboxylate ligand. The Sn atom in complex 3 has a distorted tetrahedral geometry. In all three complexes, the carboxylate ligand is in the zwitterionic form with the phenolic proton moved to the nearby azo nitrogen atom, in contrast to the free carboxylic acid ligand which is in the azo form.