Part I: Synthesis and structural characterization of some transition metal complexes derived from Schiff base ligands Part II: Crystallographic studies of pharmacologically active compounds.

摘要

New mono, di- and tri-nuclear transition metal complexes have been synthesized from Schiff bases derived from salicylaldehyde. The Schiff bases are of the type H2L and the complexes of the type ML where M is Ni(II), Mn(II), Co(II), Co(III) and Cu(II). The L are Schiff bases derived from the reaction of both unsubstituted and methoxy substituted salicylaldehyde with different amines. We characterize the Schiff bases using proton NMR, IR and UV-vis spectroscopy. The metal complexes were characterized using UV-vis, IR, cyclic voltammetry, Xray crystallography and by room temperature magnetic susceptibility. The electronic spectra of the ligands showed strong absorption bands in the UV region due to pi-pi* transitions. The metal complexes showed strong bands in both UV and visible regions (due to d-d transitions) of the electromagnetic spectrum. Most of the complexes showed characteristic bands between 390 and 430 nm region. These bands are due to the ligand to metal charge transfer transitions. The charge transfer bands that occurred in the UV region are due to transitions between sigma and sigma* and due to donor accepter transitions between 4 pig* and sigma u*. Magnetic susceptibility studies at room temperature indicated that the Mn(II) complexes had mueff in the range of 4.5-5.3 BM while those of Ni(II) complexes were in the range of 0.39-3.01 BM. Those of Cu(II) complexes were in the range of 1.53 to 3.58 BM. The X-ray structures of Mn(II), Co(II) and Cu(II) showed coordination number of 6 while one of the Cu(II) complexes showed coordination number of 5. The Ni(II) Schiff base complexes showed coordination number of 4. Cyclic voltammetry analysis of these complexes in dry acetonitrile revealed that complex 8 Ni2+ was quasi reversibly reduced to Ni+ between -1552 V and -1814 V (vs Ag/AgCl). Complexes 9 and 10 Ni2+ were quasi reversibly reduced to Ni + with redox potentials of -1430 V and -1735 V, and -1571 V and - 1814 V respectively.;In part two of this project, we studied the X-ray crystal structures of the pharmacologically active compounds obtained from the School of Pharmacy of Howard University. These compounds were N-Benzenesulfonamide enaminones that are potential anticonvulsant agents. These compounds were; 4-chloro-N-(5,5-dimethyl-3-oxo-cyclohex-1-enyl)-benzenesulfonamide (a), N-(5,5-Dimethyl-3-oxo-cyclohex-1-enyl)-4-isopropylbenzenesulfonamide (b), 4-bromo-N-(5-methyl-3-oxo-cyclohex-1-enyl)-benzenesulfonamide (c), 4-Chloro-N-(5-methyl-3-oxo-cyclohex-1-enyl)-benzenesulfonamide (d) 5,5-Dimethyl-3-(5-methyl-isoxazol-3-ylamino)-cyclohex-2-enone (e), 4-Methyl-N-(3-oxo-cyclohex-1-enyl)-benzenesulfonamide (f), 4-isopropyl-N-(5-methyl-3-oxo-cyclohex-1-enyl)-benzenesulfonamide (g), 3-hydroxy-5,5-dimethyl-cyclohex-2-enone (h). The complexes a, b, c, d, f, g and h crystallize in monoclinic crystal system, while complex e crystallizes in a triclinic system. The space group for compounds a, b, c, d, and f is P21/c while that of compound e is P-1 and that of compound g is P21/n. Other structural characteristics of these compounds are reported in the later sections of this dissertation.