Spectroscopic studies of photochemically important transition metal excited states. 2. The /sup 1/T/sub 1g/, /sup 3/T/sub 1g/, and /sup 5/T/sub 2g/ excited states of hexaamminecobalt(III)

Low-temperature, high-resolution, polarized single crystal absorption studies of the /sup 1/T/sub 1g/ ..-->.. /sup 1/A/sub 1g/, /sup 3/T/sub 1g/ ..-->.. /sup 1/A/sub 1g/ electronic transitions in hexaamminecobalt(III) are reported. Analysis of the structure in the electronic origin regions of these transitions combined with Franck-Condon analysis of the absorption band shapes demonstrates that the photochemically active /sup 3/T/sub 1g/ state (and /sup 1/T/sub 1g/ state)undergoes a large e/sub g/ Jahn-Teller effect. This produces a D/sub 4h/ excited state geometry with an expansion of approx. 0.12 A in the Co-NH/sub 3/ bond length along two axes and a contraction of approx. 0.02 A along the third axis. In addition, an analysis of the multiplet splitting pattern of the /sup 3/T/sub 1g/ pure electronic origins allows an approximate determination of the energetic position of the /sup 5/T/sub 2g/ state which interacts with the triplet through spin-orbit coupling. An experimentally derived potential surface diagram of the above states is presented which indicates an efficient radiationless deactivation pathway for the /sup 3/T/sub 1g/ state. The photochemical implications of these results and their relation to other photochemically active d/sup 3/ and d/sup 6/ complexes are also discussed.