Variation of the Cooperativity in Diluted Hofmann-Based Spin-Crossover Coordination Solids {Fe1–x M x (pz)[Pd(CN)4]}

This work is devoted to the investigation of the influence of dopants on the cooperativity of 3D Hofmann-based spin-crossover solids {Fe1–x M x (pz)­[Pd­(CN)4]}, as reflected in the abruptness, position, shape, and completeness of the thermal spin transition and on the width of accompanying hysteresis loop. We present systematic experimental studies, including FTIR, powder X-ray diffraction, energy-dispersive X-ray analysis, and magnetic susceptibility measurements for pure and diluted compounds using Zn, Ni, Mn, and Co as dopants. The shift of the thermal transition temperature toward lower temperatures is, in most cases, correlated with the dopant sizes and the effective dilution. By using a 3D mechanoelastic model considering the different sizes of dopants and the change in intermolecular interactions induced by them, we have satisfactorily reproduced the observed macroscopic experimental behavior. In addition, the microscopic scale images obtained during the HS-LS thermal transition show how the presence of the dopants prevents the spreading of the clusters, reducing the cooperativity in the system.