SYNTHESIS AND CHARACTERIZATION OF COPPER(II) COMPLEXES OF NEW TRIPODAL POLYIMIDAZOLE LIGANDS

Several copper(II) complexes containing new tripodal polyimidazole lig ands have been synthesized and characterized by X-ray crystallography, UV-vis and EPR spectroscopies, and cyclic voltammetry. The tripodal p olyimidazole ligands have been prepared in good yields and characteriz ed by IH and 13C NMR and mass spectrometry. X-ray crystallographic par ameters for the copper(II) compounds are as follows: compound 8, C15H2 1N7PClF6Cu, 543.34 g/mol, monoclinic space group (P2(1)/c), a = 16.585 (3) angstrom, b = 12.570(3) angstrom, c = 10.540(3) angstrom, beta = 1 05.34(2)degrees, V = 2118.8 angstrom3, Z = 4, 3042 independent reflect ions with I > 3sigmaAbsolute value of I to a maximum 2theta scan of 50 -degrees, R = 0.040, R(w) = 0.039; compound 9, C15H21N7PClF6Cu, 543.34 g/mol, orthorhombic space group (Pbca), a = 16.487(5) angstrom, b = 1 6.246(5) angstrom, c = 16.555(5) angstrom, V = 4434.1 angstrom3, Z = 8 , 2240 independent reflections with I > 3sigmaAbsolute value of I to a maximum 2theta scan of 50-degrees, R = 0.075, and R(w) = 0.057. Both compounds have distorted trigonal bipyramidal structures. Three imidaz ole nitrogen atoms of each tripod occupy equatorial positions of the t rigonal bipyramid, while the amine nitrogen atom and chlorine atom occ upy apical sites. In both complexes the imidazole pendants are twisted from the chelate planes with torsion angles ranging from 6.7 to 22-de grees. The Cu-N(amine) bond length in compound 8 is 0.023 angstrom lon ger than the Cu-N(amine) bond length in compound 9. The EPR spectral d ata for both compounds are consistent with the retention of the solid- state structure in frozen DMF/MeOH (1:1) solution. The UV-vis spectrum of compound 8 is red-shifted relative to compound 9, indicating that the corresponding tripod ligand in 8 is a weaker field ligand. Both co mpounds display quasireversible one-electron redox behavior in acetoni trile. The E1/2 values for compound 8 and 9 are -0.193 and -0.225 V vs Ag/AgCl, respectively. The redox potentials of 8 and 9 are shifed cat hodically compared to a related copper(II) complex, [Cu(TMIMA)Cl]+ (TM IMA = tris((1-methylimidazol-2-yl)methyl)amine), which contain only 2- substituted 1-methylimidazole pendants.