SEVERAL COORDINATION MODES OF THE PENTADENTATE LIGAND 2,6-DIACETYLPYRIDINEBIS(THIOSEMICARBAZONE)

The reaction between Zn(II) salts and the pentadentate ligand 2,6-diacetylpyridinebis(thiosemicarbazone) (H-2daptsc) produces various compounds, depending upon the H+ ion concentration and the nature of the solvent from which the complex crystallizes. In the presence of nitric acid, the compound [Zn(H2daptsc)(H2O)2](NO3)2 (1) is obtained. The mononuclear complex in 1 possesses a pentagonal bipyramidal geometry with an almost planar, fully protonated, H-2daptsc ligand and two axially bonded water ligands. Compound 2, [Zn2(daptsc)2].2DMF, was prepared and crystallized from dimethylformamide. The dinuclear complex in 2 contains two fully deprotonated ligands which are coordinated to two Zn(II) ions with a distorted octahedral geometry. Compound 3, [Zn2(daptSC)2].MeOH.H2O, was prepared and crystallized from methanol. The dinuclear unit in 3 is a structural isomer of complex 2. The complex is asymmetric in which one zinc atom is six-coordinate and the other one is four-coordinate. Compound 1 is monoclinic, space group Cc with a=21.930(3), b=12.940(2), c=7.345(1) angstrom, beta=104.22(3)-degrees, V=2020(1) angstrom3 and Z=4. Compound 2 is monoclinic, space group C2/c with a=18.189(2), b=15.716(2), c=14.653(2) angstrom, beta=115.86(2)-degrees, V=3769(1) angstrom3 and Z=4. Compound 3 is triclinic, space group P1BAR with a=10.666(2), b=16.282(2), c=10.458(2) angstrom, alpha=90.79(2), beta=117.94(2), gamma=80.70(2)-degrees, V=1579(1) angstrom3 and Z=2.