Flexible crystals of perovskite-like coordination polymers with a tunable and switchable organic guest: (CHNH)[KFe(CN)] and (CHNH)[KCo(CN)].

The crystal structure has been determined for (CHNH)[KCo(CN)] at temperatures 100 and 443 K. It crystallizes in the monoclinic space group C2/c (LT) and in the cubic one Fm3[combining macron]m (HT). The dielectric response has been investigated for single crystals of pure K[A'(CN)] and guest-hosts of (CHNH)[KA'(CN)], where A' is a trivalent metal, Co or Fe. Their dielectric properties were measured in the frequency range between 135 Hz and 2 MHz in a wide temperature range between 200 and 460 K. The anisotropy of the electric permittivity for single crystals of (CHNH)[KCo(CN)] was analysed in terms of the crystal structure. The relaxation processes were observed in the case of the pure host KFe(CN) and the guest/host crystal (CHNH)[KFe(CN)]. The activation energies of the dielectric relaxation have been estimated to be equal to 44 and 40 kJ mol for (CHNH)[KFe(CN)] and KFe(CN), respectively. The mechanism of the phase transitions found at 425 K and 421 K for (CHNH)[KFe(CN)] and (CHNH)[KCo(CN)], respectively, has been postulated. From the dielectric losses the value of the electric ac conductivity has been estimated and analyzed in terms of the activation process of the current carriers.