Experimental Investigations and Ab Initio Studies of Tellurium(II) Dithiolates, Te(SR)₂

Abstract

The reaction between Te(O(i)Pr)(4) and HSR offers a new and effective route to tellurium dithiolates, Te(SR)(2). Te(S(i)Pr)(2) (1) and Te(S(t)Bu)(2) (2) are stable compounds whereas Te(SPh)(2) (3) slowly decomposes at room temperature to give Te and Ph(2)S(2). IR spectra of 1-3 and ab initio calculations (HF/3-21G(d) and MP2 with double-zeta polarization effective core potential basis set) show nu(as)(Te-S) and nu(s)(Te-S) to be around 340 and 380 cm(-)(1), respectively. UV spectra exhibit similar lambda(max) (346-348 nm) for all three compounds, with the greater extinction coefficient of 3 accounting for its different and more intense color. Analysis of the molecular orbitals of the model compound Te(SCH(3))(2) shows that the phototransition is likely to be of n(p)(Te)-sigma(Te-S) type, thus rationalizing the instability of 3 when irradiated. Single-crystal X-ray diffraction of 1-3 revealed the following basic structural parameters: 1 d(av)(Te-S) 239.4(1) and d(av)(S-C) 183.8(5) pm, angle(STeS) 99.61(4) and angle(av)(TeSC) 105.8(3) degrees, tau(CSTeS) 77.0(2) and 90.3(2) degrees; 2 d(Te-S) 239.1(1) and d(S-C) 186.4(2) pm, angle(STeS) 103.88(2) and angle(TeSC) 107.6(1) degrees, tau(CSTeS) 78.01(8) degrees; 3 d(Te-S) 240.6(2) and d(S-C) 177.4(7) pm, angle(STeS) 100.12(6) angle(TeSC) 103.2(2) degrees, tau(CSTeS) 69.0(3) and tau(CCSTe) 81.6(6) degrees. Geometries of model compounds Te(SH)(2) and Te(SCH(3))(2) optimized at the MP2 level exhibit d(Te-S), angle(STeS), and tau(XSTeS) (X = H, C) values similar to those of 1-3. Natural bond orbital analysis revealed n(p)(S(1))-sigma(Te-S(2)) hyperconjugation as the cause for the CSTeS torsion angles being close to 90 or -90 degrees. Thermochemical calculations on the HF and MP2 level proved Te(SH)(4) to be unstable with respect to Te(SH)(2) and HSSH, thus rationalizing the reduction of Te(IV) to Te(II) when Te(O(i)Pr)(4) or TeO(2) are reacted with thiols. NMR spectra reveal ligand exchange reactions between different tellurium(II) dithiolates and between Te(SR)(2) and HSR'. These types of reaction offer other routes to tellurium(II) dithiolates.