SYNTHESIS AND CHARACTERIZATION OF LEAD(II)-SEMICARBAZONE COMPLEXES - CRYSTAL-STRUCTURES OF DINITRATO DI-2-PYRIDYLKETONE SEMICARBAZONE LEAD(II) AND DICHLORO CYCLOHEXANE-1,2-DIONE BIS(SEMICARBAZONE) DIMETHYLFORMAMIDE LEAD(II)

Two new heptacoordinated semicarbazone lead complexes [Pb(Hdips)(NO3)( 2)] (1) and [Pb(H(2)chds)Cl-2(dmf)] (2) (Hdips = di-2-pyridylketone se micarbazone; H(2)chds = cyclohexane-1,2-dione bis(semicarbazone)) were synthesized and characterized by conventional methods and X-ray cryst al analysis. Compound 1 is triclinic, a = 7.856(1), b = 8.148(1), c = 13.788(1) Angstrom, alpha = 74.39(1), beta = 82.77(1), gamma = 77.21(1 )degrees, space group P ($) over bar 1, Z = 2, R = 0.0241. Three sites of the heptacoordinated metal are occupied by the hydrazone ligand: P b-O(1) 2.548(4), Pb-N(3) 2.547(4), Pb-N(5) 2.598(4) Angstrom; the two asymmetric nitrate groups complete the coordination with Pb-O(2) 2.651 (5), Pb-O(3) 2.801(5) Angstrom and Pb-O(5) 2.676(6), Pb-O(7) 2.755(4) Angstrom. The coordination polyhedron shows a space characterized by l arge angles which is suggestive of lone pair stereochemical activity. Compound 2 is monoclinic: a = 12.926(4), b = 12.376(4), c = 12.023(3) Angstrom, beta = 109.70(6)degrees, space group C2/c, Z = 4, R = 0.0319 . The molecule is symmetrically related by a twofold axis passing thro ugh Pb and the midpoints of the C(2)-C(2') and C(4)-C(4') bonds, the l igand is planarly four-coordinated with Pb-O 2.577(6), Pb-N(3) 2.585(6 ) Angstrom and lies on the equatorial plane of a distorted pentagonal bipyramid, the two chlorines are at the apical sites (Pb-CI 2.870(3) A ngstrom), the oxygen of a dmf statistically distributed molecule affor ds the seventh site with Pb-O(f) 2.805(17) Angstrom.