Putting a New Spin on Supramolecular Metallacycles: Co3Triangle and Co4Square Bearing Tetrazine-Based Radicals as Bridges

The synthesis of two new radical-bridged compounds [Co3(bptz)3(dbm)3]·2toluene (1) and [Co4(bptz)4(dbm)4]·4MeCN (2) (bptz = 3,6-bis(pyridyl)-1,2,4,5-tetrazine; dbm = 1,3-diphenyl-1,3-propanedionate) is reported. The presence of the ligand-centered radical has been confirmed by X-ray crystallography and SQUID magnetometry. These complexes are the first metallacycles bearing nitrogen heterocyclic radicals as bridges. Magnetic studies reveal strong antiferromagnetic metal···radical coupling with coupling constants of J= −67.5 and −66.8 cm–1for 1and 2, respectively. DFT calculations further support the strong antiferromagnetic coupling between CoIIions and bptz radicals and confirm S= 3 and S= 4 spin ground states for 1and 2, respectively.