Vibrational spectroscopy and solid-state MAS NMR studies of mercury(II) acetate complexes [Hg(X)OAc]: Crystal structure of [Hg(CN)OAc

Abstract

The syntheses of [Hg(X)OAc] (OAc=acetate; X=CN, Cl, Br, I, SCN) are reported, and the crystal structure of the cyano complex has been determined. The asymmetric unit contains two [Hg(CN)OAc] molecules which show almost linear C–Hg–O bonding (Hg–C=2.019(13), 2.016(11) Å; Hg–O=2.067(9), 2.058(8) Å; C–Hg–O=176.0(4), 172.3(5)°), with only one of the two acetate oxygen atoms bound directly to the mercury atom. Secondary Hg⋯O and Hg⋯N contacts in the range 2.6–2.8 Å are about 0.2 Å shorter than the secondary Hg⋯O contacts in the corresponding X=Ph complex. The ν(HgX) and ν(HgO) modes have been assigned in the IR and Raman spectra of [Hg(X)OAc] (X=CN, Cl, Br, I, SCN); these spectra show that the complexes have structures with essentially linear O–Hg–X bonding, similar to that of the cyanide. Solid-state 199Hg MAS NMR spectra have been recorded for HgX 2 (X=CN, Cl) and [Hg(X)OAc] (X=Me, Ph, CN, Cl, SCN), and spinning sideband analysis has been used to determine the 199Hg shielding anisotropy and asymmetry parameters Δ σ and η. A semi-empirical method for the calculation of the local paramagnetic contribution to the shielding is given, and a linear relationship between Δ σ and the isotropic shielding σ iso which is predicted by this model for linear HgXY species is found to be obeyed reasonably well by the experimental data for HgX 2 and [Hg(X)OAc]. The same method is used to analyse the effects of secondary bonding on the 199Hg shielding parameters. The 13C MAS NMR spectrum of [Hg(SCN)OAc] shows 2J( 199 Hg 13 C) and 3J( 199 Hg 13 C) coupling to the acetate carbon atoms, with magnitudes similar to those found previously for Hg(OAc) 2. The CN carbon signals in Hg(CN) 2 and [Hg(CN)OAc] are split into 2:1 doublets due to residual dipolar coupling to the quadrupolar 14N nucleus.