Interpretation of the electronic spectra of low-spin d6 M(CO)5X complexes. Primary excited state decay paths in Re(CO)5X complexes

Abstract

The electronic spectra of Re(CO)sX (X = Cl, Br, I), [M(CO)5NH2CH3]Cl (M = Mn, Re), and [(C2Hs)4N] [M(CO)sBr] (M = Cr, W) have been measured. The emission spectra and photochemistry of the Re(CO)sX complexes have also been investigated. The new electronic spectral studies along with data in the literature allow definitive assignment of the lowest absorptions as ligand field (LF) 1Ai (e4b22) -*• 1 -3E(e3b22ai1) for a large class of low-spin d6 M(CO)sX complexes. Emission from Re(CO)sX occurs from the 3E(e3b22ai') state and is strongly dependent on temperature in the range 20-100 K. Quantitative emission measurements have been made for the pure solids. Photochemistry of Re(CO)sX at 298 K involves substitution of CO with a quantum yield of up to 0.76 depending on X and the excitation wavelength. The observed chemistry and variable quantum yields accord well with the electronic nature of the lowest excited states.

The structure of rhenium pentacarbonyl chloride, Re(CO)5Cl

“…The pentacarbonyl halides, M(CO)sX, with M = Mn, Tc and Re and X = C1, Br, I, have long been of interest for the study of bonding in metal carbonyls and their spectra have been extensively investigated (Wozniak & Sheline, 1972;Ceasar, Milazzo, Cihonski & Levenson, 1974;Hall, 1975;Wrighton, Morse, Gray & Ottesen, 1976;Behrens, 1978). In view of this it is surprising that their structures have not been studied much.…”

Catalytic Hydrosilylation of Carbonyls via Re(CO)5Cl Photolysis

“…The quantum yields for Re(CO) 5 Cl dissociation at 313 and 366 nm have been determined to be 0.44 and 0.06, respectively. 19 The light source used in our work is broad band, ranging from 300 to 800 nm. Since Re(CO) 5 Cl absorbs in the 300−350 nm region, the quantum yield would also be expected to be similar to the range quoted.…”

“…The value of 0.25 represents an "average" quantum yield of Re(CO) 5 Cl dissociation from 300 to 400 nm. 19 The x value is proportional to this quantum yield of 0.25. Under the described experimental conditions above, y = 0.12 ± 0.05 mmol and x = 0.004 ± 0.002 mmol, and hence the quantum yield for catalysis is 7.5 ± 4.8.…”

“…18 It was previously reported 19 that the air-and moisture-stable Re(CO) 5 Cl dissociates a CO ligand readily upon photolysis (quantum yield of 0.06 to 0.44 from 366 nm to 313 nm). In light of efforts to utilize energy from light rather than from fossil fuel sources, much work would have to be carried out to further explore light-driven catalytic processes.…”

The Effects of the Substitution on the lmidazole Ligand on the Photochemical Properties of fac[Mn(CO)3(phen)(lmidazole)](SO3CF3) Complexes¶

“…For various [MnX(L‐L)(CO) 3 ] + type complexes, the lowest energy transitions were assigned to the Mn → (α‐diimine) π* orbital transitions (8–17). However, some π*‐character contribution of Mn → CO transition may be expected as well (22,23). In addition, the intensity of the LF transitions for these complexes are expected to be large because of the high degree of covalence in these compounds, i.e.…”