Four-coordinate and pseudo five-coordinate Hg(II) complexes of a new bidentate phosphorus ylide: X-ray crystal structure and spectral characterization

The reaction of Ph2PCH2PPh2 (dppm) with BrCH2C(O)C6H4NO2 in chloroform produces the new phosphonium salt [Ph2PCH2PPh2CH2C(O)C6H4NO2]Br (1). Further, by reacting the phosphonium salt with appropriate base the bidentate phosphorus ylide, Ph2PCH2PPh2double bond; length as m-dashC(H)C(O)C6H4NO2 (2) was obtained. The reaction of ligand 2 with mercury(II) halides in dry methanol led to the formation of the P, C-coordinated mononuclear complexes [HgX2(Ph2PCH2PPh2C(H)C(O)C6H4NO2)] [X = Cl (3), Br (4), I (5)]. Characterization of the obtained compounds was performed by elemental analysis, IR, 1H, 31P, and 13C NMR. The X-ray crystal structure of 5 as well as the complex derived from crystallization of 4 in DMSO, [HgBr2(Ph2PCH2PPh2C(H)C(O)C6H4NO2)(DMSO)] (6), is reported. In both complexes 5 and 6 the title ylide is coordinated through the ylidic carbon and the phosphine atom. However, in compound 6 the Hg–C bond length is considerably weakened due to coordination of DMSO molecule to the metal ion and locating of ylidic carbon atom in the axial position of the resulting trigonal bipyramidal complex. Theoretical studies on ligand and all complexes at DFT (B3LYP) level of theory are also reported. The results show that the addition of DMSO molecule to the compound 4 and formation of compound 6 is energetically favored.