Crystal structures vibrational 31p NMR studies of complexes of tertiary phosphine ligands with mercury(II) halides

Abstract

The mercury(II) phosphine complexes (R 3P) 2HgX 2 (R 3P = PPh 3, PEt 3, 1-phenyldibenzophosphole (DBP), 1-phenyl-3, 4-dimethylphosphole (DMPP); X = Cl, Br, I and PBu 3; X = Cl) have been prepared and their solution and solid state structures determined by a combination of elemental analyses, IR, Raman NMR spectroscopy. The structures of (DBP) 2HgBr 2 ( 1), (PPh 3) 2Hg 2Br 4 ( 2), (DMPP) 2Hg 2I 4 ( 3) and (Bu 3P) 2Hg 2I 4 ( 4) have been determined from three-dimensional X-ray data collected by counter methods. Compound 1 crystallizes in space group P 1 with a = 10.568(6), b = 17.390(6), c = 9.610(3) Å, α = 106.02(4), β = 100.62(4), γ = 101.41(5)° and Z = 2. Compound 2 crystallizes in space group P2 1/ a with a = 18.619(7), b = 10.938(4), c = 18.762(5) Å, β = 90.36(2)° and Z = 4. Compound 3 crystallizes in space group Pbc2 1 with a = 8.516(4), b = 19.404(7), c = 19.545(6) Å 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) Å, β = 109.38(8)° and Z = 8. Compound 1 deviates from ideal C 2 symmetry having slightly different HgBr (2.618(2), 2.604(2) Å) and HgP (2.513(3), 2.490(3) Å bond distances. The inequivalence of the phosphines is manifested as a second order ABX CP/MAS 31P{ 1H} NMR spectrum for 1. Compound 2 is a symmetric doubly bromide bridged dimer with essentially equivalent HgP (2.40(2), 2.44(2) Å) bond distances but its CP/MAS 31P{ 1H} NMR spectrum displays two AX resonances, showing 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) Å) bond distances displays three AX resonances in its CP/MAS 31P{ 1H} NMR spectrum. Compound 4 is an unsymmetrical doubly iodide bridged dimer [(Bu 3P) 2HgI 2HgI 2] having equivalent HgP (2.393(21), 2.391(22) Å bond lengths but its CP/MAS 31P{ 1H} NMR spectrum shows two ABX resonances arising from the two different molecules in the unit cell with the phosphines being magnetically inequivalent in each molecule. Variable temperature 31P NMR spectroscopy shows that equilibria between monomeric (R 3P) 2HgX 2 and dimeric [R 3PHgX 2] 2 occur in solution for R 3P = DMPP and Bu 3P the dimers are very easily formed from the monomers.