Conformation versus coordination: synthesis and structural investigations of tellurium(II) dithiolates derived from beta-donor-substituted thiols.

Abstract

New methods of preparing tellurium(II) dithiolates, Te(SR)(2), are presented. Te(SCH(2)CH(2)OAc)(2), 1, was made from Te(SCH(2)CH(2)OH)(2) by acetylation of the hydroxyl groups. Te(SCH(2)CH(2)SAc)(2), 2, [Te(SCH(2)CH(2)NH(3))(2)]Cl(2), 3, and Te(SC(6)H(4)(o-NH(2)))(2), 4, were synthesized by ligand exchange reactions of Te(S(t)Bu)(2) with 2 equiv of HSCH(2)CH(2)SAc, [HSCH(2)CH(2)NH(3)]Cl, and HSC(6)H(4)(o-NH(2)), respectively. Of all compounds, 4 exhibits the strongest thermal sensitivity toward decomposition and the largest low-field shift of the (125)Te NMR signal, two features that are attributed to weak Te.N interactions. The structural parameters of the CSTeSC unit exhibit very similar values for all four compounds, while the torsion angles of the side chains differ between the molecules, a feature rationalized by ab initio studies. In the solid state, different kinds of intermolecular aggregation and contacts to the Te atoms are present. 1 and 2 crystallize in the same space group (orthorhombic, Pbcn) and exhibit C(2) symmetric molecules, with two intermolecular Te.S contacts, leading to a trapezoidal coordination mode of the Te atoms. SCCE and C(S)CEC (with E = O, S) torsion angles represent the major differences between 1 and 2, which are attributed to their unlike intermolecular hydrogen bridges. In the solid state structure of 3, [Te(SCH(2)CH(2)NH(3))(2)](2+) cations and Cl(-) anions form a three-dimensional network via N-H...Cl and C-H...Cl hydrogen bonds (triclinic, P(-)1). Two neighboring [Te(SCH(2)CH(2)NH(3))(2)](2+) cations are linked via two Te...S contacts, and each Te atom forms one additional Te...Cl contact, resulting in a slightly distorted trapezoidal coordination mode. In the solid state structure of 4, adjacent molecules form Te...Te and Te...N contacts as well as hydrogen bridges. Two chemically different Te atoms are present, both of which are tetracoordinate with distorted sawhorse configurations. The absence of intramolecular Te...O, Te...S, or Te...N contacts in 1, 2, and 4, respectively, is attributed to the conformational rigidity of the CSTeS unit, where conformation ruling coordination is the case.