Copper(I) Complexes of N-(2-{[(2E)-2-(4-Nitrobenzylidenyl)Hydrazinyl]Carbonyl}Phenyl)Benzamide and Triphenylphosphine: Synthesis, Characterization and Luminescence Properties.

Copper(I) complexes of the formula [Cu(L)(PPh3)2]X (1-4) (X = Cl(1), ClO4(2), BF4(3) and PF6(4)) [where L = N-(2-{[(2E)-2-(4-nitrobenzylidenyl)hydrazinyl]carbonyl}phenyl)benzamide; PPh3 = triphenylphosphine] have been prepared by the condensation of N-[2-(hydrazinocarbonyl)phenyl]benzamide with 4-nitrobenzaldehyde followed by the reaction with CuCl, [Cu(MeCN)4]ClO4, [Cu(MeCN)4]BF4 and [Cu(MeCN)4]PF6 in presence of triphenylphosphine as a coligand. Complexes 1-4 were then characterized by elemental analyses, FTIR, UV-visible and 1H NMR spectroscopy. Mononuclear copper(I) complexes 1-4 were formed with L in its keto form by involvement of azomethine nitrogen and the carbonyl oxygen along with two PPh3 groups. A single crystal X-ray diffraction study of the representative complex [(Cu(L)(PPh3)2]CIO4 (2) reveals a distorted tetrahedral geometry around Cu(I). Crystal data of (2): space group = C2/c, a = 42.8596 (9) Å, b = 14.6207 (3) Å, c = 36.4643 (7) Å, V = 20,653.7 (7) Å3, Z = 16. Complexes 1-4 exhibit quasireversible redox behaviour corresponding to a Cu(I)/Cu(II) couple. All complexes show blue-green emission as a result of fluorescence from an intra-ligand charge transition (ILCT), ligand to ligand charge transfer transition (LLCT) or mixture of both. Significant increase in size of the counter anion shows marked effect on quantum efficiency and lifetime of the complexes in solution.