Experimental investigations and ab initio studies of tellurium(II) dithiolates, Te(SR)(2)

The reaction between Te((OPr)-Pr-i)(4) and HSR offers a new and effective r oute to tellurium dithiolates, Te(SR)(2). Te((SPr)-Pr-i)(2) (1) and Te((SBu )-Bu-t)(2) (2) are stable compounds whereas Te(SPh)(2) (3) slowly decompose s at room temperature to give Te and Ph2S2. 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 v(as)(Te-S) and v(s)(Te-S) to be around 340 and 380 cm(-1), respectively. UV spectra exhibit similar lambda(max) (346-3 48 nm) for all three compounds, with the greater extinction coefficient of 3 accounting for its different and more intense color. Analysis of the mole cular orbitals of the model compound Te(SCH3)(2) shows that the phototransi tion 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 r evealed the following basic structural parameters: 1 d(av)(Te-S) 239.4(1) a nd 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(S TeS) 100.12(6) angle(TeSC) 103.2(2)degrees, tau(CSTeS) 69.0(3) and tau(CCST e) 81.6(6)degrees. Geometries of model compounds Te(SH)(2) and Te(SCH3)(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 revea led n(p)(S-1)-sigma*(Te-S-2) hyperconjugation as the cause for the CSTeS to rsion 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((OPr)-Pr-i)(4) or TeO2 are reacted with thiols. NMR spectra reveal ligan d exchange reactions between different tellurium(II) dithiolates and betwee n Te(SR)(2) and HSR'. These types of reaction offer other routes to telluri um(II) dithiolates.