CRYSTAL-STRUCTURES, VIBRATIONAL AND P-31 NMR-STUDIES OF COMPLEXES OF TERTIARY PHOSPHINE-LIGANDS WITH MERCURY(II) HALIDES

The mercury(II) phosphine complexes (R3P)2HgX2 (R3P - PPh3, PEt3, 1-ph enyldibenzophosphole (DBP), 1-phenyl-3,4-dimethylphosphole (DMPP); X = Cl, Br, I and PBu3; X = Cl) have been prepared and their solution and solid state structures determined by a combination of elemental analy ses, IR, Raman and NMR spectroscopy. The structures of (DBP)2HgBr2 (1) , (PPh3)2Hg2Br4 (2), (DMPP)2Hg2I4 (3) and (Bu3P)2Hg2I4 (4) have been d etermined from three-dimensional X-ray data collected by counter metho ds. Compound 1 crystallizes in space group P1BAR with a = 10.568(6), b = 17.390(6), c = 9.610(3) angstrom, alpha = 106.02(4), beta = 100.62( 4), gamma = 101.41(5)-degrees and Z = 2. Compound 2 crystallizes in sp ace group P2(1)/a with a = 18.619(7), b = 10.938(4), c = 18.762(5) ang strom, beta = 90.36(2)-degrees and Z = 4. Compound 3 crystallizes in s pace group Pbc2(1) with a = 8.516(4), b = 19.404(7), c = 19.545(6) ang strom and Z = 4. Compound 4 crystallizes in space group P2(1)/c with a = 16.450(16), b = 20.609(21), c = 24.263(31) angstrom, beta = 109.38( 8)-degrees and Z = 8. Compound 1 deviates from ideal C2 symmetry havin g slightly different Hg-Br (2.618(2), 2.604(2) angstrom) and Hg-P (2.5 13(3), 2.490(3) angstrom) bond distances. The inequivalence of the pho sphines is manifested as a second order ABX CP/MAS P-31{H-1} NMR spect rum for 1. Compound 2 is a symmetric doubly bromide bridged dimer with essentially equivalent Hg-P (2.40(2), 2.44(2) angstrom) bond distance s but its Cp/MAS P-31{H-1} NMR spectrum displays two AX resonances, sh owing that the phosphines are not magnetically equivalent. Compound 3 is a symmetric, doubly iodide bridged dimer having slightly different Hg-P (2.437(7), 2.470(7) angstrom) bond distances and displays three A X resonances in its CP/MAS P-31{H-1} NMR spectrum. Compound 4 is an un symmetrical doubly iodide bridged dimer [(Bu3P)2HgI2HgI2] having equiv alent Hg-P (2.393(21), 2.391(22) A) bond lengths but its CP/MAS P-31{H -1} NMR spectrum shows two ABX resonances arising from the two differe nt molecules in the unit cell with the phosphines being magnetically i nequivalent in each molecule. Variable temperature P-31 NMR spectrosco py shows that equilibria between monomeric (R3P)2HgX2 and dimeric [R3P HgX2]2 occur in solution and for R3P = DMPP and BU3P the dimers are ve ry easily formed from the monomers.