inorganic chemistry

V. Conclusion

Even the most stable and least reactive molecules such as H 2 O,
CO 2 , and N 2 can be photocleaved by intramolecular electron
transfer between suitable redoxactive metal centers and these
molecules or simple derivatives such as carbonate instead of car-
bon dioxide. The photoactivation is achieved by CT excitation
which corresponds to a shift of electron density. The formation
of stable products is determined by the availability of appropri-
ate oxidation states at the metal centers. While these photo-
reactions are very interesting in their own right, applications
are conceivable in particular for solar energy utilization. Espe-
cially, organometallic approaches to water splitting have been
anticipated to be rather promising in the future( 76 ).

VI. Abbreviations

CT transitions are classified according to the redox sites at the
metals and ligands(2,77). Their energy depends roughly on the
reducing and oxidizing strength of the donor and acceptor,
respectively. Accordingly, the labels Mox,Mred,Lox, and Lredare
used to stress the possibility of a low-energy transition:

Mox–Lred Ligand-to-metal LMCT
Mred–Lox Metal-to-ligand MLCT
Mred–L–Mox Metal-to-metal MMCT
Mred–Mox Metal-to-metal MMCT
Lred–M–Lox Ligand-to-ligand LLCT
M–L (L¼Aox–Dred) Intraligand ILCT

ACKNOWLEDGMENT

We are grateful for financial support from the DFG (Grant VO
211/18-1).

REFERENCES

1. Lewis, N. S.; Nocera, D. G.Proc. Natl. Acad. Sci. USA 2006, 103 ,
   15729 – 15735.

PHOTOCHEMICAL ACTIVATION AND SPLITTING OF H 2 O 367