Synthesis, structure and magnetic properties of a geminal μ2-tetracyanoethylene radical anion bridged coordination polymer

A tetracyanoethylene (TCNE) bridged coordination polymer, [Mn(cyclen)(μ2-TCNE)] · TCNE (1), (cyclen = 1,4,7,10-tetraazacyclododecane, TCNE = tetracyanoethylene), has been synthesized by combining [MnII(cyclen)]2+ and the potassium salt of TCNE radical anion, K[TCNE]. The compound crystallizes in two polymorphs. Both structures feature formal TCNE radical anion ligands in an unusual geminal (or 1,1−) bridging geometry between two high spin Mn(II) centers. The NTCNE–Mn–NTCNE bond angles of two bridging TCNE/− ligands are 88.07(9)° 1a and 85.44(14)° 1b, respectively. Each bridging TCNE/− is π stacked with an uncoordinated TCNE/− to form what can be construed as a diamagnetic dianion, TCNE 2 2 - , containing a 4-center 2-electron (4c/2e−) bond. The results of variable-temperature magnetic susceptibility measurements indicate behavior consistent with weak antiferromagnetic coupling between two Mn(II) centers with no significant contribution of spin from the organic radicals.