Flexible crystals of perovskite-like coordination polymers with a tunable and switchable organic guest: (CH3NH3)2[KFe(CN)6] and (CH3NH3)2[KCo(CN)6]Electronic supplementary information (ESI) available: Crystal structure and thermal properties. CCDC 1508843 and 1508844. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt03915d

The crystal structure has been determined for (CH 3 NH 3 ) 2 [KCo(CN) 6 ] at temperatures 100 and 443 K. It crystallizes in the monoclinic space group C 2/ c (LT) and in the cubic one Fm 3&cmb.macr; m (HT). The dielectric response has been investigated for single crystals of pure K 3 [A′(CN) 6 ] and guest-hosts of (CH 3 NH 3 ) 2 [KA′(CN) 6 ], 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 (CH 3 NH 3 ) 2 [KCo(CN) 6 ] was analysed in terms of the crystal structure. The relaxation processes were observed in the case of the pure host K 3 Fe(CN) 6 and the guest/host crystal (CH 3 NH 3 ) 2 [KFe(CN) 6 ]. The activation energies of the dielectric relaxation have been estimated to be equal to 44 and 40 kJ mol −1 for (CH 3 NH 3 ) 2 [KFe(CN) 6 ] and K 3 Fe(CN) 6 , respectively. The mechanism of the phase transitions found at 425 K and 421 K for (CH 3 NH 3 ) 2 [KFe(CN) 6 ] and (CH 3 NH 3 ) 2 [KCo(CN) 6 ], 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. The crystal structure has been determined for (CH 3 NH 3 ) 2 [KCo(CN) 6 ] at temperatures 100 and 443 K.