Photophysical studies of XRe(CO)4L (X = Cl, I; L = CO, pip, PPh) complexes. Examples of ligand field luminescence from organometallic complexes in fluid solution

Abstract

A series of cis-XRe(CO)/sub 4/L (X = Cl, I; L = NC/sub 5/H/sub 11/ (pip), PPh/sub 3/) complexes have been prepared via photochemical and thermal reactions of the parent XRe(CO)/sub 5/ species. Electronic absorption spectra have been recorded for these complexes in solution at 293 K and in EPA glasses at 80 K. The lowest lying absorption system is assigned definitively to ligand field (LF) /sup 1/A/sub 1/(e/sup 4/b/sub 2//sup 2/) ..-->.. /sup 1,3/(e/sup 3/b/sub 2//sup 2/a/sub 1//sup 1/) transitions; the band energies depend on L and are ordered CO > P donor > N donor, in accordance with the LF strength. Luminescence spectra, lifetimes, quantum yields, and excitation spectra from the cis-XRe(CO)/sub 4/L (L = pip, PPh/sub 3/) derivatives in both 293 K solution and EPA glasses at 80 K are consistent with emission from the lowest energy /sup 3/LF state. In contrast, the parent XRe(CO)/sub 5/ molecules were not found to emit under identical experimental conditions. The photochemistry of these cis-XRe(CO)/sub 4/L complexes has also been investigated. Irradiations at 313 or 366 nm of cis-XRe(CO)/sub 4/L in solution at 293 K that contains an excess concentration of entering ligand give rise to ligand-substitution processes involving replacement of bothmore » CO and PPh/sub 3/ ligands. Irradiation at 313 nm of cis-IRe(CO)/sub 4/(PPh/sub 3/) in solution at 293 K without added scavenging ligands leads to formation of carbonyl-bridged (Re(CO)/sub 4/(PPh/sub 3/))/sub 2/ dimer and I/sub 2/ products. These photochemical processes are correlated with the model of lowest lying electronically excited states.« less