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

Abstract

Crystal structures of both isostructural com-pounds were solved from single crystal X-ray diffraction data (space group P2₁/n; Z = 4; Rb-compound: a = 9.812(1) Å, b = 25.793(3) Å, c = 11.777(2) Å, β = 104.68(1)°, R_gt(F) = 0.0458, wR_ref(F²) = 0.0918; Cs-compound: a = 9.9058(8) Å, b = 25.919(2) Å, c = 11.883(1) Å,β = 105.542(7)o, R_gt(F) = 0.0450,wR_ref(F²) = 0.0951. The main structural feature is the nitrosylpentacyanoferrate(II)-complex [Fe(CN)₅NO]^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)·10¹²s^–1 for the rubidium compound and E_A = 0.56(2) eV, Z = 30(8)·10¹⁰s^–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.