SOLID-STATE HG-199 MAS NMR-STUDIES OF MERCURY(II) THIOCYANATE COMPLEXES AND RELATED-COMPOUNDS - CRYSTAL-STRUCTURE OF HG(SECN)(2)

The solid-state Hg-199 MAS NMR spectra of [Hg(SCN)(2)], [Hg(SeCN)(2)], M[Hg(SCN)(3)], M-2[Hg(SCN)(4)] (M = K, Cs). and K-2[Hg-3(NCO)(8)] hav e been measured, and the (monoclinic) crystal structure of [Hg(SeCN)(2 )] has been determined to assist in the interpretation of the NMR data . The asymmetric unit of Hg(SeCN)2 contains one molecule at an inversi on center which shows linear Se-Hg-Se bonding (Hg-Se = 2.4738(10) Angs trom, Se-Hg-Se = 180 degrees. Hg-Se-C = 97.5(3)degrees). Secondary Hg- Se and Hg-N contacts are 3.4246(9) and 2.835(12) Angstrom, respectivel y; this arrangement differs from that in Hg(SCN)(2) where there are no secondary Hg-S contacts. A redetermination of the monoclinic crystal structure of K[Hg(SCN)(3)] is also reported, revealing substantial dif ferences from the earlier work. Spinning sideband analysis has been us ed to determine the Hg-199 shielding anisotropy and asymmetry paramete rs Delta sigma and eta from the solid-state Hg-199 MAS NMR spectra. Th e effects of changes in the mercury coordination number and of distort ion of the coordination environment on the shielding parameters are in terpreted in terms of changes in the local paramagnetic contribution. The same method is employed to assess the effects of secondary bonding on shielding, and it is shown that the substantial differences betwee n the values for Hg(SCN) and Hg(SeCN)(2) can be attributed to these ef fects. The v(HgS) modes have been assigned in the IR and Raman spectra of the thiocyanate complexes, and the correlation between the wavenum bers and splittings of these bands and the Hg-199 shielding parameters is discussed.