A Weak Antiferromagnetic Interaction between Mn²⁺ Centers through a TCNQ Column: Crystal Structures and Magnetic Properties of [Mn^II(tpa)(TCNQ)(CH₃OH)](TCNQ)₂·CH₃CN, [Mn^II(tpa)(μ-O₂CCH₃)]2(TCNQ)₂·2CH₃CN, and [Mn^II(tpa)(NCS)₂]·CH₃CN (tpa = Tris(2-pyridylmethyl)amine)

Reaction of Mn(CH₃COO)₂·4H₂O and Mn(PF₆)₂·4H₂O with tpa and Li(TCNQ) (tpa = tris(2-pyridylmethyl)-amine, TCNQ = tetracyanoquinodimethane) in acetonitrile-methanol solution gave [Mn^II(tpa)(μ-O₂-CCH₃)]₂(TCNQ)₂·2CH₃CN (1) and [Mn^II(tpa)(TCNQ)(CH₃OH)](TCNQ)₂·CH₃CN (2), respectively. Crystal structures and magnetic properties have been studied in comparison with those of [Mn^II(tpa)(NCS)₂]·CH₃CN (3). Complex 1 crystallizes with an inversion center located in the center of the bis(μ-acetato)dimanganese(II) core, and TCNQ units form diamagnetic dimers which stack to form a column structure. The acetates bridge the two Mn(II) centers in a syn-anti mode, with a Mn-Mn separation of 4.145(1) Å, and mediate a weak antiferromagnetic interaction with J = −0. 972(6) cm⁻¹ (where H = −2JS₁·S₂). In 2, four crystallographically independent TCNQ ions, called A, B, C, and D, respectively, were revealed in the unit cell, and anions C and D are located on the crystallographic inversion center. Anions A and B form dimeric units (AA and BB), respectively, and these dimers respectively stack with C and D to form columns (⋯AACAA⋯) and (⋯BBDBB⋯). The [Mn^II(tpa)(CH₃OH)] unit was directly bound by the anion B, and as a result, two manganese atoms were connected through two B anions with a Mn-Mn separation of 15.397(2) Å. The temperature dependence of the magnetic susceptibility of 2 has shown an antiferromagnetic behavior; that is, _χMT values start to gradually decrease from 4.4 emu K mol⁻¹ at 100 K to 1.76 emu K mol⁻¹ at 2 K. In 3, a manganese ion has a six-coordinate geometry, which is similar to that of 2, and the closest Mn-Mn separation is 6.8873(9) Å. Magnetic susceptibility measurement for 3 has revealed the Curie behavior down to 4 K and this leads one to conclude that zero-field splitting for the manganese ion and an antiferromagnetic dipole-dipole interaction between manganese ions with a Mn-Mn separation longer than 6.8873-(9) Å are negligible down to 4 K. By considering the magnetic behavior of 3, the antiferromagnetic behavior of 2 is concluded to be due to the antiferromagnetic interaction between two manganese ions (15.397(2) Å separation) through TCNQ columns (⋯BBCBB⋯), where the anions are antiferromagnetically coupled to be diamangetic, and the exchange coupling constant (J) was estimated to be −0. 197(6) cm⁻¹. Crystal data: [Mn^II(tpa)(μ-O₂-CCH₃)]₂(TCNQ)₂·2CH₃CN (1), monoclinic, space group P2₁/n, a = 18.798(6) Å, b = 19.260(3) Å, c = 8.973(2) Å, β = 99.03(2)°, V = 3208(1) ų, Z = 2, and R = 0.059 (R_w = 0.059) for 4185 data with ∣F_o∣ > 3σ(F_o); [Mn^II(tpa)(TCNQ)(CH₃OH)](TCNQ)₂.CH₃CN(2), triclinic, space group P1̄, a = 9.937(3) Å, b = 31.608(4) Å, c = 8.207(2) Å, α = 96.33(1)°, β = 92.91(2)°, γ = 89.19(2)°, V= 2559(1) ų, Z = 2, and R = 0.045 (R_w = 0.058) for 5074 data with ∣F_o∣ > 6σ(F_o); [Mn^II(tpa)(NCS)₂]·CH₃CN (3), orthorhombic, space group P2₁2₁2₁, with a = 13.271(2) Å, b = 15.717(2) Å, c = 11.800(2) Å, V= 2461.2(5) ų, Z = 4, and R = 0.037 (R_w = 0.042) for 2380 data with ∣F_o∣ > 6σ(F_o).