Mutual Influence of Spacer Length and Noncoordinating Anions on Thermal and Light-Induced Spin-Crossover Properties of Iron(II)-alpha,omega-Bis(tetrazol-1-yl)-alkane Coordination Polymers

摘要

The influence of noncoordinating anions is analysed in an extension of our systematic investigations into iron(II)spin-crossover coordination polymers.We present here ditetrazole complexes of iron(II)tetrafluoroborate where the two tetra-zole moieties are separated by alkylene spacers.The number of carbon atoms in the spacer(n)was varied between n=5-10,12,and the complexes were compared with their ClO_4~-analogues.Pronounced magnetic and magneto-optical differences were found in the comparison of the two series.A chain-type arrangement in the complexes'crystal structures is proposed with decreased interactions between iron centres as n increases,leading to more gradual spin transitions.When n=5-7 the smaller tetrafluoroborate causes the spin transitions of the respective complexes to occur at higher temperatures than those of the equivalent perchlorate series.Both series exhibit a parity effect,but at n=8 the parity effect reverses for tetrafluoroborate.With increasing n,however,iron-iron interactions seem to fade away and a limiting value of T_(SC)=160 K is approached by both series.