Substituent Effects on the Spin-Transition Temperature in Complexes with Tris(pyrazolyl) Ligands

TL;DR

This study investigates how different substituents on tris(pyrazolyl) ligands affect the spin-transition temperature in iron(II) complexes, combining experimental spectroscopy and magnetic measurements with density functional theory calculations.

Contribution

It provides new insights into substituent effects on spin-transition temperatures using combined experimental and theoretical approaches.

Findings

Most substituents decrease the transition temperature.

Bromine is an exception, not decreasing the transition temperature.

Theoretical calculations align with experimental trends.

Abstract

Iron (II) complexes with substituted tris(pyrazolyl) ligands, which exhibit a thermally driven transition from a low-spin state at low temperatures to a high-spin state at elevated temperatures, have been studied by M\"ossbauer spectroscopy and magnetic susceptibility measurements. From the observed spectra the molar high-spin fraction and the transition temperature have been extracted. All substituents, except for bromine, lead to a decrease of the transition temperature. Density functional calculations have been carried out to compare the experimentally observed shifts of the transition temperature with those derived from theory.