High-Spin Ribbons and Antiferromagnetic Ordering of a MnII-Biradical-MnII Complex

A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis­(1,2,3,5-dithiadiazolyl)­pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn­(hfac)2-biradical-Mn­(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of ST = 4 resulting from antiferromagnetic coupling between the Sbirad = 1 biradical bridging ligand and two SMn = 5/2 MnII ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.