Structural studies of diorganotin(IV) sulfonates: The synthesis of [(n-C4H9)2Sn{OSO2C6H3(CH3)2-2,5}2] and [(n-C4H9)2Sn{OSO2R)2 · 2(hexamethylphosphoric triamide)] [R = CH3, 4-C6H4CH3, 2,5-C6H3(CH3)2, 2,4,6-C6H2(CH3)3] and crystal structures of [(n-C4H9)2S

The syntheses of [(n-C4H9)2Sn{OSO2C6H3(CH3)2-2,5}2] (1) and [(n-C4H9)2Sn{OSO2R)2 · 2HMPA] [R = CH3 (3),4-C6H4CH3 (4), 2,5-C6H3(CH3)2 (5), 2,4,6-C6H2(CH3)3 (6)] have been carried out to study their structures and to delineate the coordination behavior of the weakly coordinating sulfonate anions. Compound 1 hydrolyzes slowly to [(n-C4H9)2Sn(μ-OH)(OSO2C6H3(CH3)2-2,5)]2 (2) when kept in CH2Cl2 for a few days. The crystal structure shows that 2 has a dimeric structure in which tin atoms are bridged by two hydroxy groups and each tin atom is further bonded to two n-Bu groups and a mono-coordinated sulfonate anion thus generating a trigonal bipyramidal geometry at tin atom. However, the coordination geometry at tin can be visualized as a severely distorted octahedron, if a relatively weak Sn–O bond of 2.690 Å between Sn and an O atom of the neighboring sulfonate anion is also considered. Compounds 3–6 are obtained by the consecutive reaction of (n-C4H9)2SnO with the appropriate sulphonic acid and hexamethylphosphoric triamide (HMPA). X-ray crystal structures of 4, 5 and 6 show octahedral geometry around tin atom in the two compounds in which the sulfonate ligands are covalently bonded in a monodentate mode. Compounds 3–6 are nonionic in polar solvents. The Sn–O (sulfonate) bond distances 2.354(2), 2; 2.233(2), 4; 2.237(5), 5 and 2.227(3) Å, 6 suggest some degree of ionic character in the metal-anion bonds. These compounds have also been characterized by multinuclear (1H, 13C and 119Sn) NMR studies.

Graphical abstractReaction of (n-C4H9)2SnO with 2,5-dimethylbenzenesulphonic acid yields [(n-C4H9)2Sn{OSO2C6H3(CH3)2-2,5}2] which on crystallization yields a dimeric compound [(n-C4H9)2Sn(μ-OH)(OSO2C6H3(CH3)2-2,5)]2 containing bridging hydroxyl groups between Sn atoms and covalently bonded sulfonate anions.Figure optionsDownload full-size imageDownload as PowerPoint slide