Structure analysis and the existence of light-induced long-lived metastable states in Xn[Fe(CN)5NO] with inorganic and organic cations: X n = Pb, (H3O+CH6N+), (C2N2H7)2 and (C16H36N)2

Abstract

Abstract The crystal structures of four compounds X n[Fe(CN)5NO] with the different inorganic and organic cations X n = Pb, (H3O+CH6N+), (C2N2H7)2 and (C16H36N)2 were determined. (H3O+CH6N+)[Fe(CN)5NO] and (C2N2H7)2[Fe(CN)5NO] crystallize in the non-centrosymmetric space groups Cmc21 and Pca21, respectively. Two metastable states can be excited by irradiation with light in each of these two compounds. Pb[Fe(CN)5NO] and (C16H36N)2[Fe(CN)5NO] crystallize in the centrosymmetric space groups Pnma and P21/n, respectively, but only one metastable state can be obtained at 110 K. In (H3O+CH6N+)[Fe(CN)5NO] and (C2N2H7)2[Fe(CN)5NO] the cations are disordered. The disorder is produced by symmetry related hydrogen bonds. The hydrogen bonds are established for all organic cations, but they are weak in (C16H36N)2[Fe(CN)5NO]. The donor-acceptor relation is fulfilled between the hydrogen atoms of the cations and the nitrogen atoms of the cyanide ligands. The light-induced metastable states, created by irradiation with light in the spectral range Δλ = 410–500 nm at 110 K, were investigated by Differential Scanning Calorimetry. The isothermal measurements show that the decay of the metastable states is purely exponential. From the dynamical measurements of heat flow versus temperature the activations energies and frequency factors of the metastable states are obtained.