A heteroleptic diradical Cr(iii) complex with extended spin delocalization and large intramolecular magnetic exchange.

Successive chemical reductions of the heteroleptic complex [(tpy)CrIII(tphz)]3+ (tpy = terpyridine; tphz = tetrapyridophenazine) give rise to the mono- and di-radical redox isomers, [(tpy)CrIII(tphz˙-)]2+ and [(tpy˙-)CrIII(tphz˙-)]+, respectively. As designed, the optimized overlap of the involved magnetic orbitals leads to extremely strong magnetic interactions between the S = 3/2 metal ion and S = 1/2 radical spins, affording well isolated ST = 1 and ST = 1/2 ground states at room temperature.