Synthesis, characterization and Nuclear Magnetic Resonance study of the stoichiometry and stability of several zwitterionic mercury(II) complexes in dimethylsulfoxide

The reaction of the non-symmetric phosphonium salts [PPh2CH2PPh2CH2C(O)R]Br2 (R = 4′-biphenyl (L1); OCH2Ph (L2); 4-methylphenyl (L3); 2-naphtyl (L4); 3-nitrophenyl (L5) and [PPh2CH2PPh2CH2C(O)R]Cl2 (R = 2,4-dichlorophenyl (L6)), with mercury(II) halides in 1:1 (for chloride and bromide) and 1:2 (for iodide) mole ratio in methanol under mild conditions afford the monomeric P-coordinated complexes, [HgCl2(Br)(Ph2PCH2PPh2CH2C(O)R)] (R = 4′-biphenyl (1), OCH2Ph (2), 4-methylphenyl (3), 2-naphtyl (4), 3-nitrophenyl (5)) and [HgCl3(Ph2PCH2PPh2CH2C(O)C6H4Cl2)] (6), [HgBr3(Ph2PCH2PPh2CH2C(O)R)] (R = 4′-biphenyl (7), OCH2Ph (8), 4-methylphenyl (9), 2-naphtyl (10), 3-nitrophenyl (11) and [HgBr2(Cl)(Ph2PCH2PPh2CH2C(O)C6H4Cl2)] (12)), [HgBr2(I)(Ph2PCH2PPh2CH2C(O)R)] (R = 4′-biphenyl (13), OCH2Ph (14), 4-methylphenyl (15), 2-naphtyl (16), 3-nitrophenyl (17)) and [HgCl2(I)(Ph2PCH2PPh2CH2C(O)C6H4Cl2)] (18). These complexes were fully characterized by elemental analysis and IR, 1H, 13C and 31P{1H} NMR spectra. In addition, 31P{1H} NMR spectroscopy was used to investigate the stoichiometry and stability of all complexes in pure dimethylsulfoxide solvent. The formation constants of the resulting 1:1 complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. It was found that, in pure dimethylsulfoxide, the stabilities of the resulting 1:1 complexes vary in the order L3 > L4 > L1 > L5 > L6 > L2 and HgCl2 > HgBr2 > HgI2.