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.