X-ray Diffraction Analysis of Geometry Changes upon Excitation: The Ground-State and Metastable-State Structures of K2[Ru(NO2)4(OH)(NO)]

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Abstract
The structure of the laser-light-induced metastable state MS1 of the [Ru(NO2)4(OH)(NO)]2- anion in K2[Ru(NO2)4(OH)(NO)] was determined by X-ray analysis at 50 K of a crystal with a 16% excited-state population. Results of an independent determination of the ground-state structure were used in the analysis. The most pronounced geometrical change upon excitation was an increase of the Ru−(NO) distance by 0.097(11) Å, significantly larger than the change of the corresponding distance in sodium nitroprusside (Pressprich, M. R.; White, M. A.; Vekhter, Y.; Coppens, P. J. Am. Chem. Soc. 1994, 116, 5233−5238). A decrease in the ∠Ru−(N−O) angle from 174.0(2) to 169(1)° was observed. The diffraction results provide evidence that the photoinduced state MS1 of the transition metal nitrosyl complexes is a linkage isomer in which the NO group is attached to the metal atom through the oxygen, instead of through the nitrogen atom, rather than an electronic excited state as reported previously.