Trends in the structure and bonding of [MCl2{(C4H3S)ECH3}2] (M = Pd, Pt; E = Te, Se)

The complex formation of (C4H3E)E'Me (E = S, O; E' = Te, Se) (1-4) with palladium and platinum has been explored by use of NMR spectroscopy and X-ray diffraction. Whereas the Te-125-NMR spectra of [PdCl2{(C4H3E)TeMe}(2)] [E = S (5), E=O (6)] show the existence of both cis- and trans-isomers in solution the spectroscopic information of [MCl2{(C4H3E)SeMe}(2)] (M=Pd, Pt, E=S, O; 8-10) indicates the presence of only one isomer. The crystal structure determinations have shown that 5 and 6 are isomorphous and crystallize as cis-isomers forming dimers with close chalcogen-halogen contacts. In contrast, 8 and 10 have turned out to be trans-isomers and form skewed stacks that are bound together in a helical arrangement by weak hydrogen bonds. The structural data indicate that back donation may weakly contribute to the palladium-tellurium bonding in 5 and 6. In 8 and 10 the effects of the back bonding are negligible. (C) 1998 Elsevier Science S.A. All rights reserved.