Rapid cooling experiments and use of an anionic nuclear probe to sense the spin transition of the 1D coordination polymers [Fe(NH(2)trz)(3)]SnF6 center dot nH(2)O(NH(2)trz=4-amino-1,2,4-triazole)

[Fe(NH(2)trZ)(3)]SnF6 center dot nH(2)O (NH(2)trz = 4-amino-1,2,4-triazole; n = 1 (1), n = 0.5 (2)) are new 1D spin-crossover coordination polymers. Compound 2 exhibits an incomplete spin transition centred at around 210 K with a thermal hysteresis loop approximately 16 K wide. The spin transition of 2 was detected by the Mossbauer resonance of the Sn-119 atom in the SnF6 (2-) anion primarily on the basis of the evolution of its local distortion. Rapid-cooling Fe-57 Mossbauer and superconducting quantum interference device experiments allow dramatic widening of the hysteresis width of 2 from 16 K up to 82 K and also shift the spin-transition curve into the room temperature region. This unusual behaviour of quenched samples on warming is attributed to activation of the molecular motion of the anions from a frozen distorted form towards a regular form at temperatures well above approximately 210 K. Potential applications of this new family of materials are discussed.