SE-77 SOLID-STATE NMR-STUDIES OF [M(SE4)2]2- ANIONS (M=ZN, CD, HG)

Se-77 solid-state NMR spectra have been recorded with cross-polarizati on and magic-angle spinning on [M(Se4)2]2-complexes with [Me4N]+ (M = Zn, Cd, Hg) and [Et4N]+ (M = Cd, Hg). The large chemical shift anisotr opies (of the order of 1000 ppm) mean that fast spinning speeds (9-11 kHz) are needed in order to reveal the number of crystallographic sele nium sites present within the solid. The spectra enable the principal components of the Se-77 shielding tensor to be calculated from the spi nning sideband intensities. Differences between the Se-77 isotropic ch emical shifts observed for the [Et4N]+ complexes and for the [Me4N]+ c omplexes reflect small structural changes in the [M(Se4)2]2- geometry with cation. J-coupling to Hg-199 and Cd-11/113 are also observed. The solid-state NMR results are compared with similar work in solution. A single-crystal X-ray structure determination of [Me4N]2-[Hg(Se4)2].0. 5DMF is reported (monoclinic crystal system, space group C2/c). The Hg atom is tetrahedrally coordinated by two chelating tetraselenide liga nds with both HgSe4 rings adopting the envelope conformation. The FT R aman spectrum of [Me4N]2[Cd(Se4)2] is also reported.