Mössbauer parameters of the two long-lived metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

Diffraction Studies of Photoexcited Crystals: Metastable Nitrosyl-Linkage Isomers of Sodium Nitroprusside

“…The reduction in bending of the equatorial ligands away from N−O can be understood in terms of 1−3 nonbonded interactions, in which the distance from the C( cis -cyano) to the proximal atom of the nitrosyl group remains approximately constant. The high symmetry structure is consistent with the very small Mössbauer asymmetry parameter η that has been reported (η ≤ 0.04) 6 Geometric Differences between MS 1 , MS 2 , and Ground-State Nitroprusside Anions MS 1 this study (50 K)Pressprich et al …”

“…The identification of the metastable states must be based on the available unambiguous experimental evidence, which can be summarized as follows: (1) The generation of both metastable states requires the presence of an {MNO} 6 (M ) Fe, Ru, Os) species and is not dependent on the counterion or the crystalline environment. 18 (2) Mo ¨ssbauer 19 and ESR 16 evidence indicate that both metastable states are diamagnetic. (3) The Mo ¨ssbauer Electric Field Gradient 19 and the lack of splitting of the cyano stretching frequencies in the Raman spectra 22 indicate that both metastable states retain the approximate C 4V symmetry of the ground state.…”

“…(2) Mössbauer 19 and ESR 16 evidence indicate that both metastable states are diamagnetic. (3) The Mössbauer Electric Field Gradient and the lack of splitting of the cyano stretching frequencies in the Raman spectra 22 indicate that both metastable states retain the approximate C 4 v symmetry of the ground state. (4) Infrared and Raman measurements show C−N, N−O, and Fe−N stretching modes and the Fe−N−O bending mode to be downshifted on formation of the metastable states, the shifts for the modes associated with the metal−N−O group being an order of magnitude larger than the small (∼10 cm -1 ) downshifts for the other vibrational frequencies…”

Photo-Induced Linkage Isomerism of Transition Metal Nitrosyl and Dinitrogen Complexes Studied by Photocrystallographic Techniques

“…The ®nding that the metastable states are linkage isomers rather than electronically excited states provides a logical explanation for this apparent paradox, and is in agreement with the observed diamagnetism of the new species. 17,18 DFT calculations con®rm that the new linkage isomers correspond to local minima on the potential energy surface of the diamagnetic ground state. Theoretical geometry optimization leads to quite reasonable agreement with experimental geometries.…”

Density functional study of nitroprusside: Mechanism of the photochemical formation and deactivation of the metastable states

“…In 1990, Güdel 28 pointed out that the lifetime of the metastable states is inconsistent with any one‐electron transfer model and that either a large structural change or a multielectron promotion is required to explain the stability of the species 28. Mössbauer 29 and EPR 30 spectroscopy indicate that both metastable states are diamagnetic. The geometries of the two metastable states of SNP and that of its ground state have been identified experimentally by X‐ray diffraction at 50 K by Carducci et al 23.…”