Effect of Ligand Modulation on Metal-to-Metal Electron Transfer in a Series of [Fe2Co2] Molecular Square Complexes

A series of three new cyanide-bridged [FeCo] molecular square complexes, namely, {[Fe(Tp*)(CN)(3)](2)[Co-(L)(2)](2)}(BF4)(2)center dot 2DMF (L = bik (1), bik* (2), and vbik (3); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bik = bis(1-methyl-1H-imidazol-2-yl)ketone, bik* = bis(1-ethyl-1H-imidazol-2-yl)ketone, and vbik = bis(1-vinyl-1H-imidazol-2-yl)ketone; DMF = dimethylformamide) were synthesized and characterized by single-crystal X-ray diffraction analyses and by magnetic, electrochemical, and spectroscopic measurements. Magnetic studies reveal that all three complexes exhibit temperature-induced metal-to-metal electron transfer (MMET) from a high-spin Co(II) center to a low-spin Fe(III) center, transforming a high-temperature paramagnetic {Fe-LS(III)-CN-Co-LS(II)} ground state into a low-temperature diamagnetic {Fe il Ls -CN-Co-LS(III)} state with a decrease in the temperature from 300 to 100 K. Complexes 1 and 3 show the interconversion of the paramagnetic {Fe-LS(III)-CN-Co-HS(II)} ground state into a diamagnetic {Fe-LS(II)-CN-Co-LS(III)} state in a single-step transition with T 112 values of 180 and 186 K, respectively, while a two-step MMET with T-1/2 value of 214 and 178 K was observed for complex 2.

Automated summary

This study presents three new cyanide-bridged [FeCo] molecular square complexes, characterized by various methods including single-crystal X-ray diffraction analyses, magnetic, electrochemical, and spectroscopic measurements. The magnetic studies reveal temperature-induced metal-to-metal electron transfer in these complexes, leading to a change in the magnetic states with temperature.