Photochemistry metal solutions

These IR kinetic experiments (75) were the first examples of vibrationally excited metal carbonyls to be observed. More detailed studies on the behavior of hot carbonyls should provide an intriguing insight into the photophysics of these molecules. We now look at metal carbonyl photochemistry in solution. 

In both equations 23 and 24, addition of CO to the product solution causes the system to back-react to reform the starting materials. Once again, the main point to be made is that the solution photochemistry of the polymers is analogous to the solution photochemistry of the discrete metal-metal bonded dimers. 

In the early days of colloid chemistry, it has occasionally been observed that metal solutions degrade when exposed to light. The ongoing photochemistry, however, has rarely been investigated. The question is, whether hot electrons that are produced in a metal by the absorption of photons are able to initiate chemical reactions before they recombine with the holes Photo-electron emission from compact electrodes has been studied in photo-electrochemistry. The quantum yield of this process is of the order of lO" electrons per absorbed photon. It increases with the negative potential of the electrode. However, electron emission into the solvent from nano-sized particles might be facilitated since 1) the rate of thermalization of hot electrons is decreased due to the lower density of states, and 2) only a short distance has to be traversed by a hot electron in order to reach the surface. 

Weitz and co-workers extended gas phase TRIR investigations to the study of coordinatively unsaturated metal carbonyl species. Metal carbonyls are ideally suited for TRIR studies owing to their very strong IR chromophores. Indeed, initial TRIR work in solution, beginning in the early 1980s, focused on the photochemistry of metal carbonyls for just this reason. Since that time, instrumental advances have significantly broadened the scope of TRIR methods and as a result the excited state structure and photoreactivity of organometallic complexes in solution have been well studied from the microsecond to picosecond time scale. ... 

To date, most of the photochemical data available for transition metal complexes comes from condensed phase studies (1). Recently, the primary photochemistry of a few model transition metal carbonyl complexes has been investigated in gas phase (5.). Studies to date indicate that there are many differences between the reactivity of organometallic species in gas phase (5.6) as conq>ared with matrix (7-10) or solution (11-17) environments. In most cases studied, photoexcitation of isolated transition metal... 

It has been our goal for some time to run photochemical energy storage reactions without relay molecules or separate catalysts. We have concentrated on the photochemistry of polynuclear metal complexes in homogeneous solutions, because we believe it should be possible to facilitate multielectron transfer processes at the available coordination sites of such cluster species. 

Selective Photochemistry. It is well known that for many substituted metal carbonyl compounds in solution, photochemical loss of either CO or the substituent L can be promoted depending... 

Pressure-Tuning Photochemistry of Metal Complexes in Solution (Eldik... 

The chemistry of these systems is identical to that already described for 02 and H2 production in homogeneous systems except that MV+ or [Ru(bipy)3]3+ generated during the photochemistry of the bulk solution then regenerate MV2+ or [Ru(bipy)3]2+ by donation or acceptance of an electron at the electrode. Photopotentials of —1.0 V and currents of —1 mA can be generated for long periods in this way. Similar photoelectrical cells using metal phthalocyanine or porphyrin sensitizers have also been developed.359-362... 

There are several classes of Re(II) complexes that exhibit luminescence in both solution and in the solid state, the cyclopentadienyl systems Cp2Re and Cp 2Re [23] and the singular case of the homoleptic diphosphine, Re(dmpe)3 2+ (Cp is pentamethylcyclopentadienyl) [24]. Emission has been shown to be LMCT in nature (Re - P sigma bond to dn Re(II)). These complexes are also rare examples in transition metal photochemistry of doublet-double emission, i.e., a fluorescence. 

The photochemistry in solution of the polymers with metal-metal bonds in their backbones is qualitatively similar to the reactions of the discrete metal-metal... 

---