Photoexcited Structure of a Diplatinum Complex

The second group developed a new detector which can collect a whole intensity data of a crystal within a second. They succeeded that a whole intensity data of a standard sample were collected within 2 s and the structure was successfully analyzed, using the new gas detector developed, MSGC, and a rotating anode X-ray generator [58]. A crystal of the Pn complex was mounted on the diffractometer with 

The differences in the unit-cell dimensions between the light-on and light-off stages were measured for the five crystals [64]. The temperatures were fixed at 173 K for the Bu, Pn and Bzdmp crystals and at 103 K for the Bzte and Bztbu crystals. The space group, number of molecules in a unit cell, crystal density, unit-cell volume change, 14i, and the ratio of 14i /Kff, for the five crystals are shown in Table 7.1. The ratios of the volume changes, A 14i- are more than 

6 % for the Bu, Pn, and Bzte complexes, whereas those of the Bztbu and Bzdmp complexes were less than 0.2. 

The structures of each crystal at light-off and light-on stages showed no significant differences in the alkylammonium cations. On the other hand, the bond 

It is noticeable that the shortenings of the Pt-Pt and Pt-P distances, A(Pt-Pt) and A(Pt-P), of the Pn and Bzte crystals are 0.0081(3) and 0.005(1)A, and 0.0127(5) and 0.008(1) A, respectively, which are the largest two among the five crystals. The ratios of A(Pt-Pt) / A(Pt-P) are 1.62 and 1.59 for the Pn and Bzte crystals, respectively, which are very close to each other. This suggests that the excited diplatinum complex anion may have the same structure in the two crystals, and the concentrations of the excited molecules may be different between the two crystals. On the other hand, the excited structures in the Bu, Bztbu and Bzdmp crystals may be different due to the different crystal environment. The change at the excited state is schematically drawn in Fig. 7.26. Not only the Pt-Pt distance but also Pt-P distance is shortened at the excited state of the diplatinum complex anion, which is in good agreement with the experimental results observed from the combination of the EXAFS method with rapid-flow laser spectroscopy [54]. 

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