Magnetization and EPR of a series of Cr3+ squarate dimers

A series of Cr(III) dimers were synthesized from a parent compound [Cr2(μ-oxo)2(μ1,2-C4O4)2(H2O)4]·2H2O (I) by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. The parent compound exhibits a broad maximum around 34 K characteristic of a dimer with antiferromagnetic coupling that fit the Van Vleck susceptibility model well. It was found that the maxima could be tuned from 34 to 80 K by ligand substitution of the waters. Each compound possesses a characteristic color spanning the range of teal to pink. The g-value of each compound was found to be ∼1.98 using spectral simulation. The DMSO derivative is water soluble and has a high LC50 for PC3 cancer cells, suggesting its use as a magnetic resonance imaging agent. X-ray crystal structure of the DMSO derivative [Cr2(μ-oxo)2(μ1,2-C4O4)2(C2H6SO)4]·2H2O (II) revealed that the DMSO ligands are equatorial, and the squarate groups bridge the two chromiums. This is in contrast to the previously proposed structure of the parent compound where the water ligands were axial and the equatorial squarate groups did not bridge the chromiums. These compounds are interesting because of their ease of synthesis, and their wide range of magnetic behavior. The compounds are good probes into antiferromagnetic dimer exchange by controlling the ligand field surrounding the superexchange pathway present in the molecule.

A series of Cr3+ squarate dimers were synthesized from a parent compound [Cr2(μ-oxo)2[μ1,2-squarate]2(H2O)4] · 2H2O by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. These compounds are interesting because of their ease of synthesis and their wide range of magnetic behavior.Figure optionsDownload as PowerPoint slide