Putting a New Spin on Supramolecular Metallacycles: Co 3 Triangle and Co 4 Square Bearing Tetrazine-Based Radicals as Bridges.

The synthesis of two new radical-bridged compounds [Co ₃ (bptz) ₃ (dbm) ₃ ]·2toluene (1) and [Co ₄ (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 Co ^II ions and bptz radicals and confirm S = 3 and S = 4 spin ground states for 1 and 2, respectively.