Exchange interactions at the supramolecular level -: Synthesis, crystal structure, magnetic properties, and EPR spectra of [Mn(MAC)(TCNQ)2] (MAC = pentaaza macrocyclic ligand; TCNQ•- = radical anion of 7,7,8,8-tetracyano-p-quinodimethane)

The reaction between [Mn(MAC)(H2O)(2)]Cl-2.4H(2)O and LiTCNQ (MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) affords a complex with the formula [Mn(MAC)(TCNQ)(2)] (1), whose crystal structure has been determined. Its structure consists of neutral mononuclear entities. The manganese(II) ion is heptacoordinated, with a pentagonal bipyramidal geometry. The apical positions are occupied by the TCNQ.(-) radicals, while the macrocyclic ligand is coordinated at the equatorial positions. The seven Mn-N distances range from 2.273(3) to 2.301(6) Angstrom The strong intermolecular pi-pi stacking interactions between the TCNQ radicals (3.2 Angstrom) leads to weave-like infinite chains, which propagate along the crystallographic c axis. The cryomagnetic investigation of 1 revealed a weak intermolecular antiferromagnetic coupling of the Mn2+ ions (J = -0.18 cm(-1)), which is mediated by the diamagnetic (TCNQ)(2)(2-) pairs resulting from the stacking interactions in the crystal. The intermolecular exchange interaction between the Mn2+ ions was further confirmed by variable temperature EPR spectroscopic measurements [\J\ 0.15(5) cm(-1)], which have been carried out in both the X and Q bands. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.