Spin-transition behaviour in chains of Fe-II bridged by 4-substituted 1,2,4-triazoles carrying alkyl tails

A family of polymeric 1-dimensional chains of iron(ii) species showing the spin-crossover phenomenon has been synthesized using 4-n-alkyl-1,2,4-triazo les as bridging ligands. The influence of the length of the alkyl tails on the triazole ligands on characteristic features of the spin transition was studied, showing degrading of steepness with increasing length. A set of fo ur counter ions has been used to access a wider range of transition tempera tures. Large hysteresis loops are detected with small tails, mainly for the methyl and ethyl substituted products. In most cases longer tails weaken c o-operativity and hysteresis gradually decreases to zero. However it is sho wn that with certain anions hysteresis remains, even with very long tails o n the triazoles. Weakening of the co-operativity mainly arises from a dimin ution of the length of the polymeric chains with increasing alkyl tails on the triazole. This effect is anion dependent. A strong interaction along th e polymeric chains is confirmed.