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.

Graphical abstractTriorganotin(IV) complexes of composition R3SnLH (R = Me (1), Bu (2) and Ph (3) and LH = 2-[(E)-2-(4-hydroxy-3,5-dimethylphenyl)-1-diazenyl]benzoate) have been synthesized and characterized by NMR and IR spectroscopic techniques. The crystal structures reveal that neutral azo ligand coordinate to Sn atom in zwitterionic form in the polymeric (1 and 2) and monomeric (3) complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New triorganotin(IV) complexes of composition R3SnLH have been synthesized. ► The complexes were identified by NMR and IR spectroscopic techniques. ► Neutral azo ligands coordinate in their zwitterionic form in the complexes. ► The coordination pattern at the Sn centre has been established by X-ray diffraction.