DFT-BS examination of exchange coupling in chromium(III) dimers containing the μ1,2-squarato bridge

A series of Cr(III) dimers previously reported has had certain structural parameters refined and/or revised using theoretical techniques. These compounds were modeled with isotropic J-couplings that vary between −11.1 and −25.8 K. Each dimer contains a bis(μ-hydroxo) bridge. The existence or absence of a bis(μ1,2-squarato) bridge was determined using the density functional theory-broken symmetry approach. The bis(μ1,2-squarato) bridge was determined to be countercomplementary to the bis(μ-hydroxo) bridge. The hydroxo bridges contribute ferromagnetically to the exchange coupling. The results show that triple-ζ basis sets with polarization in conjunction with the B3LYP hybrid DFT method are highly accurate in predicting exchange coupling in these weakly antiferromagnetically coupled Cr(III) systems. The use of the RIJCOSX approximation was also shown to greatly speed up the calculations with a minimal loss in accuracy. Fine structure parameters were also generated using density functional methods, and these parameters matched well with the experimental ones. These results can be used to help verify predicted structures that cannot be crystallized, and they can also aid in designing new compounds tailored to exhibit specific magnetic properties.