Crystal Structures and Spin Crossover in the Polymeric Material [Fe(Htrz)2(trz)](BF4) Including Coherent-Domain Size Reduction Effects

The high-spin and low-spin crystal structures of [Fe(Htrz)(2)(trz)](BF4) (Htrz = 1H-1,2,4-triazole, trz(-) = deprotonated triazolato ligand) were determined and refined on the basis of X-ray diffraction data obtained from a high-quality crystalline powder. Noteworthy differences to the previously reported structural hypothesis are obtained, which includes a revision of the space group to orthorhombic Pnma. Notably, the distinction between the positions of the Htrz and the trz(-) ligand along the chains reveals their respective roles in the formation of direct interchain interactions. The latter are also mediated by the anions. In addition, the pair-distribution-function (PDF) method was applied to investigate the potential modification of the crystal structure by a reduction of the coherent-domain size from 50 nm to 10 nm. First, the PDF investigation confirms the validity of the crystal structures presented here. Furthermore, in a first approach, it reveals that the crystal structure description remains suitable for the whole range of coherent-domain sizes investigated.