X-RAY DIFFRACTION ANALYSIS OF GEOMETRY CHANGES ON EXCITATION: THE GROUND STATE AND EXCITED STATE STRUCTURES OF K₂[Ru(NO₂)₄(NO)(OH)]. Dmitry V. Fomitchev and Philip Coppens, Department of Chemistry, State University of New York at Buffalo, Buffalo, NY 14260-3000, USA

In the potassium nitroso-hydroxytetranitro ruthenate, K₂[Ru(NO₂)₄(NO)(OH)], two light-induced long-lived metastable excited states can be populated by irradiation at low temperature with 458 nm radiation from an Ar₊ laser [1]. In continuation of our diffraction studies of excited state complexes [2], we have collected data sets at 50K before and after exposure to the exciting radiation. In the excited state experiment, the second metastable state was eliminated by maintaining the crystal at 160K for 5 min. The imaging plate data collection technique and seed-skewness integration method were used [3]. 1571 and 2057 reflections were obtained for the least squares refinement of the ground and excited state structures respectively. Final agreement factors are R=0.024, Rw=0.029 and R=0.025, Rw=0.030, for the two data sets. The population of the metastable excited state was estimated as 16%, based on a differential scanning calorimetry experiment.

The statistically significant geometrical distortions of the metastable state are an elongation of the Ru-N(nitrosyl) bond by 0.079(15) Å from 1.769(3) Å to 1.848(15) Å and a decrease in the angle Ru-N-O by 4.0(1.0)[[ring]] from 174.0(2)[[ring]] to 170.(1)[[ring]]. This is similar to our previous results on the first metastable electronic state of [Fe(CN)₅(NO)]₂- [2], though the angular change is larger in the Ru-compound. The elongation of N-O bond, expected from the shift of the stretching frequency of (NO) from 1886 cm-1 to 1722 cm-1 [1], was not observed in either study.

(1) Th. Woike and S. Haussühl, Solid State Comm. 86, 333 (1993).

(2) M. R. Pressprich, M. A. White, Y. Vekhter, P. Coppens, J. Am. Chem. Soc. 116, 5233 (1994).

(3) R. Bolotovsky, M. A. White, A. Darovsky, P. Coppens, J. Appl. Cryst. 28, 86 (1995).

Support of this work by NSF (CHE9317770) and the Donors of the Petroleum Research Fund, administered by the American Chemical Society (PRF28664-AC3), is gratefully acknowledged.