Electron and spin density distributions and magnetic anisotropy in mixed-valent diruthenium(v) tetracarboxylates assessed via crystallographic and theoretical analyses

Abstract

The electron and spin density distributions of a tetracarboxylato mixed-valent diruthenium(II,III) complex, (NBu₄)[Ru^V₂Br₂(O₂CC₃H₇)₄], were determined using high-resolution X-ray diffraction and polarized neutron diffraction (PND) on single crystals. Experimental and theoretical spin density distributions show that the spin density is predominantly localized on the ruthenium atoms, with partial delocalization onto bromide and carboxylate ligands. Charge-density analysis supports these findings, showing charge accumulation on the metal centres and typical donor–acceptor ligand–metal interactions. The experimental topological analysis of the Ru⋯Ru bond confirms an open-shell metal–metal interaction. Local magnetic anisotropy was explored through angle-resolved magnetic susceptibility measurements and PND. Magnetic data reveal significant magnetic anisotropy, with an easy axis along the crystallographic c axis and a hard magnetization axis along the crystallographic b axis. Local magnetic susceptibility tensors derived from PND highlight pronounced planar magnetic anisotropy oriented along the equatorial Ru–O plane. The experimentally determined anisotropy parameters are in excellent agreement with ab initio calculations.