No abstract

Visible light excitation of [Cu(I)(dmp)(2)](BArF), where dmp is 2,9-dimethyl-1,10-phenanthroline and BArF is tetrakis(3,5-bis(trifluoromethylphenyl))borate, in toluene produces a photoluminescent, metal-to-ligand charge-transfer (MLCT) excited state with a lifetime of 98 +/- 5 ns. Probing this state within 14 ns after photoexcitation with pulsed X-rays establishes that a Cu(II) center, borne in a Cu(I) geometry, binds an additional ligand to form a five-coordinate complex with increased bond lengths and a coordination geometry of distorted trigonal bipyramid. The average Cu-N bond length increases in the excited state by 0.07 A. The transiently formed five-coordinate MLCT state is photoluminescent under the condition studied, indicating that the absorptive and emissive states have distinct geometries. The data represent the first X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.

The observation and fast time-scale kinetic determination of a primary dioxygen-copper interaction have been studied. The ability to photorelease carbon monoxide from [Cu(I)(tmpa)(CO)](+) in mixtures of CO and O(2) in tetrahydrofuran (THF) between 188 and 218 K results in the observable formation of a copper-superoxide species, [Cu(II)(tmpa)(O(2)(-))](+) lambda(max) = 425 nm. Via this "flash-and-trap" technique, temperature-dependent kinetic studies on the forward reaction between dioxygen and [Cu(I)(tmpa)(thf)](+) afford activation parameters DeltaH = 7.62 kJ/mol and DeltaS = -45.1 J/mol K. The corresponding reverse reaction proceeds with DeltaH = 58.0 kJ/mol and DeltaS = 105 J/mol K. Overall thermodynamic parameters are DeltaH degrees = -48.5 kJ/mol and DeltaS degrees = -140 J/mol K. The temperature-dependent data allowed us to determine the room-temperature second-order rate constant, k(O2) = 1.3 x 10(9) M(-1) s(-1). Comparisons to copper and heme proteins and synthetic complexes are discussed.

The Friedländer condensation was employed to synthesize two series of 3,3'-polymethylene bridged ligands, L, based on 2-(2'-pyridyl)-benzo[h]quinoline and 2,2'-bibenzo[h]quinoline (BHQ) along with the fully aromatic naphtho[1,2-b]-1,10-phenanthroline. Complexes [Cu(L)(2)](+) were prepared as their perchlorate or hexafluorophosphate salts. The solution state structures were analyzed by NMR and shielding effects reflected significant interligand pi-stacking interaction in the complexes. Solid-state structures of the complexes where L = 3,3'-tetramethylene-2,2'-bibenzo[h]quinoline or naphtho[1,2-b]-1,10-phenanthroline were determined by X-ray analysis. The tetramethylene bridged complex showed a highly distorted coordination geometry with the BHQ rings of opposing ligands pi-stacked at a interplanar distance of about 3.37 A. Complexes of the BHQ series showed a pronounced MLCT absorption maximum which shifted bathochromically from 496 to 610 nm as the 3,3'-bridge decreased from 4 to 2 carbons. The BHQ complexes luminesced strongly in CH(2)Cl(2) solution and the tetramethylene-bridged system showed the longest yet recorded excited-state lifetime for a copper MLCT excited state, tau = 5.3 micros and Phi = 0.10.