Putting a New Spin on Supramolecular Metallacycles: Co3 Triangle and Co4 Square 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–1 for 1 and 2, respectively. DFT calculations further support the strong antiferromagnetic coupling between CoII ions and bptz radicals and confirm S = 3 and S = 4 spin ground states for 1 and 2, respectively.