Magnetic Coupling in a Tris-hydroxo-Bridged Chromium Dimer Occurs through Ligand Mediated Superexchange in Conjunction with Through-Space Coupling

Quantum chemistry can explain and predict many properties of molecules and materials. However, there are some systems, among which are magnetic systems, that remain a challenge for all electronic structure methods. The tris-hydroxo-bridged chromium dimer, known as Kremer's dimer, contains two antiferromagnetically coupled chromium(III) metal ions and provides a classic example of a magnetic molecular system that poses a challenge for computational quantum chemistry. In this study we show that combining multiconfiguration pair-density functional theory with large-active-space density matrix renormalization group wave functions can predict the correct spin-state ordering, energy spacing, and magnetic coupling constant. We also use the unpaired electron density to analyze the superexchange contribution. This methodology offers promise for revolutionary rational design of molecular magnets.