Solvatomagnetism-induced Faraday effect in a cobalt hexacyanochromate-based magnet

Area of Science:

• Coordination Chemistry
• Magnetochemistry
• Spectroscopy

Background:

• Solvent-induced changes in coordination complexes can significantly alter their physical properties.
• Understanding these solvent effects is crucial for designing functional materials.
• Cobalt(II) and Chromium(III) cyanide complexes are known for their interesting magnetic and optical properties.

Purpose of the Study:

• To investigate the reversible changes in color, magnetic properties, and Faraday spectra of a Co(II)(1.5)[Cr(III)(CN)(6)].7.5H2O compound upon solvent exchange.
• To correlate these observed property changes with alterations in the coordination geometry of the Co(II) ion.
• To explore the phenomenon of solvatomagnetism and solvatochromism in this coordination compound.

Main Methods:

• Synthesis of Co(II)(1.5)[Cr(III)(CN)(6)].7.5H2O in water.
• Solvent exchange by immersing the compound in ethanol (EtOH).
• Characterization using colorimetry, magnetic susceptibility measurements, and Faraday ellipticity (FE) spectroscopy.
• Computational simulation of Faraday spectra including ligand field splitting and spin-orbital coupling.

Main Results:

• Reversible color change from peach to deep blue upon solvent exchange, indicating a change from six-coordinate pseudo-octahedral (OhCo(II)) to four-coordinate pseudo-tetrahedral (TdCo(II)) geometry.
• Significant changes in magnetic properties, including a decrease in critical temperature, saturation magnetization, and coercive field.
• Drastic changes in Faraday spectra, with new bands appearing and existing peaks shifting, assigned to specific electronic transitions in OhCo(II) and TdCo(II) ions.
• Successful reproduction of Faraday spectra via simulation, validating the proposed structural and magnetic coupling changes.

Conclusions:

• Solvent exchange induces reversible solvatochromism and solvatomagnetism in the cobalt-chromium cyanide complex.
• The observed property changes are directly linked to the solvent-dependent alteration of the Co(II) coordination geometry.
• The study demonstrates a clear relationship between coordination geometry, magnetic coupling, and optical properties in this functional material.