Synthesis and size-dependent spin crossover of coordination polymer [Fe(Htrz)2(trz)](BF4)

Abstract

The synthesis of quality single crystals is central to materials chemistry for optical, magnetic, and electronic device applications. The present work reports on the synthesis of single crystals of iron-triazole coordination polymer [Fe(Htrz)₂(trz)](BF₄) where (Htrz) = 1H-1,2,4-triazole. Crystals of size as long as 80 μm can be achived by controlling the temperature, precursor concentration, and solvent type. It is found that its thermal spin crossover depends largely on the crystal size. Fine crystals are ideal for depositing a thin film that exhibits redox activity. The largest crystals allow reliable electrical conductance measurements that reveal two different activation energies at the low spin state and the high spin state, which are one order of magnitude smaller than the electronic gaps calculated based on density functional theory. The synthetic route sought in the present study can be applied to other coordination polymers and related materials and provides the basis for their applications.