TCNE Dimer Dianion Coordination Complexes, [Mn(TPA)(TCNE)]<sub>2</sub>[μ<sub>2</sub>-(TCNE)<sub>2</sub>] and [Mn(TPA)(μ<sub>4</sub>-C<sub>4</sub>(CN)<sub>8</sub>)<sub>0.5</sub>]·ClO<sub>4</sub>, TPA = tris(2-Pyridylmethyl)amine: Synthesis, Structure and Magnetic Properties
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The structures and magnetic properties of two products that result from the reactions of [Mn(TPA)(CH3CN)2](ClO4)2, TPA = tris(2-pyridylmethyl)amine and potassium tetracyanoethylenide, KTCNE, are reported. [Mn(TPA)(TCNE)]2[μ2-(TCNE)2] (1) and [Mn(TPA)(μ4-C4(CN)8)0.5]·ClO4 (2) are obtained by using two different ratios of the initial reactants. Each was intended to possess two or more cis-TCNE radical anions (TCNE•/-) as ligands. 1 is a dinuclear species that crystallizes in the triclinic system in the space group P1̄, with a = 10.4432(17), b = 12.2726(16), and c = 13.708(2) Å; α = 88.505(12), β = 75.560(14), and γ = 87.077(12)°; V = 1698.9(4) Å3; and Z = 1 and features two metal centers each with three nearly orthogonal TCNE•/- ligands. However, the three TCNE•/- ligands are all dimerized via the formation of four-center, two-electron bonds: two bridge the two Mn(II) centers, and a third TCNE•/- ligand forms an intermolecular bond to another equivalent TCNE•/-. 2 crystallizes in the tetragonal system in the space group P42212, with a = 17.170(3), b = 17.170(3), and c = 17.1837(6) Å; V = 5065.9(13) Å3; and Z = 8. It consists of a ribbon-like coordination polymer containing the previously observed but still relatively rare octacyanobutyl dianion. The [C4(CN)8]2- anion is derived from the dimerization of two TCNE radical anions via the formation of a new σ bond, and each anion bridges four Mn(II) centers. Both 1 and 2 display magnetic behavior consistent with only weak antiferromagnetic coupling between the high-spin d5 Mn(II) in which the TCNE•/- are rendered diamagnetic through dimerization.
