Structural and spectroscopic studies on mercury(II) tribenzylphosphine complexes

The tribenzylphosphine (PBz(3)) complexes of mercury(II), [Hg(PBz(3))(2)](BF4)(2), [Hg(PBz(3))(2)(NO3)(2)] and [HgX(NO3)(PBz(3))] (X = Cl, Br, I and SCN), have been synthesised and their structures determined by single-crystal X-ray crystallography. [Hg(PBz(3))(2)](BF4)(2) contains [Hg(PBz(3))(2)](2+) cations with linear P-Hg-P coordination, the first example of a truly two-coordinate [Hg(PR3)(2)](2+) complex. The mercury coordination in [Hg(PBz(3))(2)(NO3)(2)] can be described as distorted tetrahedral, with a significant deviation of the P-Hg-P angle from linearity as a result of coordination of the nitrate groups. Nitrate coordination is also observed in [HgX(NO3)(PBz(3))] (X = Cl, Br, I), resulting in significantly non-linear P-Hg-X coordination. The thiocyanate complex is a centrosymmetric thiocyanate-bridged dimer with distorted trigonal-pyramidal mercury coordination to the P atom of PBz(3), to the S and N atoms of two bridging thiocyanate groups, and to the O atom of one nitrate group. For all the nitrato complexes, secondary mercury-nitrate interactions (Hg-O 2.7-3.1 angstrom) effectively raise the coordination number of the Hg(II) centres to six. High-resolution P-31 solid-state NMR spectra of the six tribenzylphosphine mercury(II)-complexes, obtained by combining magic-angle spinning, proton dipolar decoupling and proton-phosphorus cross-polarization (CP-MAS), have been recorded. The spectra of [Hg(PBz(3))(2)](BF4)(2) and [HgX(NO3)(PBz(3))] (X = Cl, Br, I and SCN) exhibit a single line, due to species that contain non-magnetic isotopes of mercury, and satellite lines, due to (1)J(P-31-Hg-199) coupling. The asymmetric unit of [Hg(PBz(3))(2)(NO3)(2)] contains two molecules with four phosphorus environments, resulting in two AB spectra with (2)J(P-31-P-31) coupling, due to species that contain non-magnetic isotopes of mercury, and satellite lines consisting of two ABX spectra, due to (1)J(P-31-Hg-199) coupling. These spectra have been analysed to yield all of the chemical shifts and coupling constants involved. A remarkable increase in (1)J(P-31-Hg-199) is observed from [Hg(PBz(3))(2)](BF4)(2) to [Hg(PBz(3))(2)(NO3)(2)] as a consequence of the incorporation of the nitrate group into the Hg coordination sphere in the latter case. Several of the spectra also exhibit broader satellites due to the presence of scalar spin-spin coupling between P-31 and the quadrupolar Hg-201 nucleus. Slow-spinning methods have been used to analyze the spinning-sideband intensities of the NMR spectra, in order to obtain the P-31 shielding anisotropy and asymmetry parameters Delta sigma and eta. The Hg-199 and P-31 NMR shielding tensors of PMe3 models of the above six compounds have been calculated using relativistic density functional theory. The P-31 results are in good agreement with experiment and assist in the assignment of some of the signals.