Investigation on Thermally Induced Spin Crossover in Fe (Phen) Molecules

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Hayder Fahim, Hashim Jabbar, Adil A. Al-Fregi

Abstract

This study focuses on investigating the impact of an external stimuli of temperature on spin crossover in coordination complexes composed of 〖(Fe(phen)〗_2  〖(NCS)〗_2, where (phen) stands for 1,10-phenanthroline). Based on the structure of the coordinating ligand sphere, these complexes are capable of thermally induced spin transitions or (SCO: spin crossover) from a low-spin (LS) to a high-spin (HS) state. We have shown that this unique effect lowers the equilibrium temperature and increases the HS fraction at lower temperatures. Due to both short- and long-range molecular interactions, the crossover proceeds as a function of temperature, resulting in a first-order phase transition. The complex 〖(Fe(phen)〗_2  〖(NCS)〗_2 contains Fe(II) surrounded by six nitrogen atoms. Our aim is to explore the thermodynamics of spin crossover systems to simulate bistable behaviors and multistep conversions observed in first-order spin transitions. These transitions are driven by the cooperative interactions of SCO molecules within the crystal structure, leading to the observed bistability. 

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