Solid-State Dinuclear-to-Trinuclear Conversion in an Oxalato-Bridged Chromium(III)−Cobalt(II) Complex as a New Route toward Single-Molecule Magnets

A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)−cobalt(II) complex of formula [CrL(ox)2CoL′(H2O)2][CrL(ox)2]·4H2O (1) has been self-assembled in solution using different aromatic α,α′-diimines as blocking ligands, such as 2,2′-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L′ = Me2phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 CrIII anions and the S = 3 CrIIICoII cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)−cobalt(II) complex of formula {[CrL(ox)2]2CoL′} (2). Complex 2 possesses a moderately anisotropic S = 9/2 CrIII2CoII ground state, and it exhibits slow magnetic relaxation behavior at very low temperatures (TB < 2.0 K).