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X-ray crystallography has traditionally been limited to the study of the ground-state structure of molecules and solids. Recent technical advances are removing this limitation as demonstrated here by a time-resolved stroboscopic study of the photo-induced 50 micros lifetime excited triplet state of the Pt(2)(pop)(4)(4-)ion pop = pyrophosphate, (H(2)P(2)O(5))(2-), performed at helium temperatures with synchrotron radiation. The shortening of the Pt-Pt bond by 0.28(9)A upon excitation is compatible with the proposed mechanism involving promotion of a Pt-Pt antibonding dsigma* electron to a weakly bonding p orbital. The contraction is accompanied by a 3 degree molecular rotation. The time-resolved diffraction technique described here is applicable to reversible light-driven processes in the crystalline solid state.
Kim et al. (Thu,) studied this question.