Structures, semi-empirical calculations and thermolyses of some five- and six-membered chelate organotin mercaptide complexes

Characterization of Ph2Sn(Cl)(MBT) (1) (HMBT=2-mercaptobenzothiazole) has been carried out by IR, Mössbauer, 1H, 13C and 119Sn spectroscopies and by X-ray crystallography for 1 together with that of Ph2Sn(SCH2CH2S) (2). Compound 1, unexpectedly obtained from the reaction between Ph2SnCl2 and KMBT in a 1:2 mole ratio, has a trigonal-bipyramidal geometry, due to intramolecular SnN interactions, both in the solid state and in solution; the axial sites are occupied by N and Cl, N(24)SnCl(4)=155.27(17)°, the chelate bite angle, N(24)SNS(15), is 64.65(17)°. Compound 2 is essentially monomeric in the solid state and has a distorted tetrahedral structure; the bond angles at tin vary from 92.50(16)° [S(2)SnS(5)] to 116.4(6)° [C(6)SnC(12)]. The shortest intermolecular Sn⋯S contact in 2 is 3.885 Å, just within the sum of the van der Waals’ radii for Sn and S (4.0 Å). PM3 semi-empirical calculations for 2 indicated that the geometry at the tin center can be accounted for by a high degree of p-character in the tin bonding orbitals to sulfur; PM3 semi-empirical calculations on Ph2Sn(SCH2CH2CH2S) (3) indicated the geometry at tin to be less distorted from tetrahedral, with a SSnS angle of 99°; the calculations further indicated that the only stable conformation of the six-membered ring in 3 is the chair form.