SOLID-STATE CD-113 NMR OF 3 STRUCTURAL ISOMERS OF [S4CD10(SPH)16]4-

Solid-state Cd-113 NMR chemical shift (delta(iso)) and chemical shift anisotropy (delta(ii)) data are reported for crystalline samples of three different compounds containing the [S4Cd10(SPh)16]4- cluster. This cluster is a supertetrahedral fragment of the cubic (sphalerite) CdS lattice and contains two types of CdS4 coordination, Cd(i){(mu3-S)2(mu-SPh)2} and Cd(o){(mu-SPh)3(SPh)}. Although the Cd sites in these compounds are all pseudotetrahedral, there are in these three different samples small distortions and variations in the coordination geometry at the Cd atoms, arising from configurational isomerism at (mu-SPh) and crystal packing variations at the periphery of the clusters. The chemical shift data reflect these geometrical variations. Chemical shift anisotropies (delta33 - delta11) range from 207 to 480 ppm for the pseudotetrahedral CdS4 coordination. Variations in the chemical shift data correlate principally with S-Cd-S angle variation. Isotropic chemical shifts for Cd(o) vary by only 20 ppm, but individual delta(ii) and chemical shift anisotropies (delta33 - delta11) are changed by up to 70 ppm for 5-degrees variations in angles at Cd(o). At Cd(i), angle differences of similar magnitude cause delta(iso) values to vary by 46 ppm, delta(ii) values by 80 ppm, and (delta33-delta11) values by 100 ppm. It is postulated that delta33 for Cd(i) is oriented normal to the S-Cd(i)-S plane and is due to the Cd(i)-S coordination: the delta33(Cd(i)) range of 807 to 887 ppm is 110-190 ppm greater than delta(iso) for CdS, an effect which is attributed to the substantial difference in Cd-S bond lengths, 2.48 angstrom in [S4Cd10(SPh)16]4- and 2.53-2.55 angstrom in CdS. The data and correlations reported will be valuable in the interpretation of Cd-113 NMR chemical shift data for biological and electronic materials based on cadmium sulfide and thiolate clusters. Crystal structure data for (Et3NH)4[S4Cd10(SPh)16] are reported.