{[oPONit]MnCl(mu-Cl)}(2) is a di-chloro-bridged Mn(II) binuclear compound in which each Mn(II) is coordinated by (o-nitronyl nitroxide-phenyl)diphenylphosphine oxide acting as a bidentate ligand via the oxygen atoms of the P=O and N-O groups. The spectrum of the low-lying states has been deduced from the magnetic and EPR properties. Antiferromagnetic Mn-radical and ferromagnetic Mn-Mn interactions lead to a S = 4 ground state.