Crystal structure analysis and extremely long-living light-induced metastable states in RbY[Fe(CN)(5)NO](2) center dot 10 H2O and CsY[Fe(CN)(5) NO](2) center dot 10 H2O

Abstract

Crystal structures of both isostructural compounds were solved from single crystal X-ray diffraction data (space group P2(1)/In; Z = 4; Rb-compound: a = 9.812(1) Angstrom, b = 25.793(3) Angstrom, c = 11.777(2) Angstrom, beta = 104.68(1)degrees, R-gt(F) = 0.0458, wR(ref)(F-2) = 0.0918; Cs-compound: a = 9.9058(8) Angstrom, b = 25.919(2) Angstrom, c = 11.883(1) Angstrom, beta = 105.542(7)degrees, R-gt(F) = 0.0450, wR(ref)(F-2) = 0.0951. The main structural feature is the nitrosylpentacyanoferrate(II)-complex [Fe(CN)(5)NO](2-). The iron atoms are coordinated to five cyanide and one nitrosyl ligand. The coordination polyhedron of the Y3+ cation is a distorted tetragonal antiprism built up from three nitrogen atoms of three complexes and five water molecules. Both rubidium and cesium ions are surrounded by seven cyanide groups of five complexes and one water molecule to form a distorted bicapped trigonal prism. One metastable state (SI) can be excited by irradiation with light in the spectral range of 400-500 nm at temperatures below 180 K. The radiationless thermal decay is detected by Differential Scanning Calorimetry by heating above T = 180 K. Evaluating the exothermal heat flow using the Arrhenius law yields an activation energy of E-A = 0.64(2) eV and a frequency factor of Z = 20(8). 10(12)s(-1) for the rubidium compound and E-A = 0.56(2) eV, Z = 30(8) . 10(10) s(-1) for the cesium compound. The contribution of the cations on the decay temperature of the metastable states is discussed on the basis of the atomic distances and coordinations.