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The metastable state which is produced by irradiation with the green-blue region of light was studied by IR and other spectroscopic techniques for solid states of newly synthesized nitrosyl-ruthenium complexes; cis-[Ru(Hox)-. Continued irradiation at 77 K results in development of a photostationary state in the same way as for sodium nitroprusside. The population of the metastable state molecule in the photostationary state of each sample depends on the irradiation wavelength and reaches a maximum at 441.6 nm which is the shortest wavelength in the present study. A broad absorption band with an absorbance maximum at ≈600 nm is observed for the metastable state of a trans-[Ru(Hox)(en) 2 NO]Cl 2 single crystal. The short wavelength tail of the band is considered to be involved in the photostationary equilibrium under blue light radiation. The metastable state molecules decay to the ground state at temperatures considerably higher than the two metastable molecules (MS 1 and MS 2 ) of sodium nitroprusside. The decay temperature of trans-[Ru(Hox)(en) 2 NO]Cl 2 , which is defined as the temperature at which the rate constants of the thermal decay becomes 10 Ϫ3 s Ϫ1 , is 277 K, which is the highest value reached among the metastable states of nitrosyl complexes reported so far. In the Raman spectra of trans-[Ru(Hox)(en) 2 NO]Cl 2 , the Ru-(NO) stretching vibrations are observed at 604 cm Ϫ1 and 476 cm Ϫ1 for the ground and metastable state molecules, respectively. ExperimentalThe starting material [Ru(ox)(en) 2 ][Ru(ox) 2 (en)] was prepared according to the procedure of Broomhead and Kane-Maguire. 17 A mixture of cis-[Ru(Hox)(en) 2 NO]Cl 2 ؒEtOH (abbreviated to 1a, hereafter), cis-K[Ru(ox) 2 (en)NO]ؒ3H 2 O (2), cis-[Ru(Hox)(ox)(en)NO] (3), and cis-K[Ru(ox) 2 (en)NO] (4) was obtained from [Ru(ox)(en) 2 ][Ru(ox) 2 (en)] treated with NO gas in an acidic solution, and the complexes were separated and purified by ion exchange column chromatography (SP-Sephadex C-25 and QAE-Sephadex A-25).

Blue-laser irradiation of a single crystal of the chloride salt of a cationic complex, trans-[Ru(en) 2 (H 2 O)(NO)] 3ϩ (en = ethylenediamine), yielded MS 1 (a metastable state of end-on type) which is remarkably stable (decay temperature T d = 267 K) compared with MS 1 of sodium nitroprusside Na 2 [Fe(CN) 5 (NO)] (SNP). No MS 2 state (side-on type) was observed by X-ray diffraction and IR spectroscopy. Even with a low population of 8% of the metastable species, the structure was clearly determined by X-ray analysis. For the first time, we observed an elongation of the N-O bond by X-ray diffraction, corresponding to a frequency downshift of the ν(NO) stretching vibration. The remarkably long lifetime of the metastable state of trans-[Ru(en) 2 (H 2 O)(NO)] 3ϩ compared with that of SNP is explained by a stereochemical analysis using reaction cavity diagrams.

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K6[Co2(CN)10(N2O2)]·2H2O (orange salt) was prepared by reaction of [Co(NO)(NH3)5]Cl2 with an aqueous solution of potassium cyanide. K6[Co2(CN)10(N2O2)]·4H2O (yellow salt) was obtained by adding an aqueous solution of the orange salt to methanol. On the basis of IR and Raman spectra for their 14NO- and 15NO-salts, and of IR spectra for their gaseous decomposition products, the orange salt is considered to be a linkage isomer of the yellow salt with respect to the trans-hyponitrito bridge. It is presumed that the orange salt is potassium μ-(trans-hyponitrito-N,N′-bis{pentacyanocobaltate(III)}, the yellow salt being potassium μ-(trans-hyponitrito-O,O′)-bis{pentacyanocobaltate(III)}.