Trinuclear magnetic clusters based on cyanide metal complexes: synthesis, crystal structures, and magnetic properties of four new [MnII2MIII] complexes (M = Cr, Fe, Co)

Abstract

Four new cyano-bridged [Mn^IIM^IIIMn^II] heterotrinuclear complexes (M^III = Cr, Fe, Co) have been synthesized and crystallographically characterized: {[(H₂O)L¹Mn–NC–Cr(CN)₄–CN–MnL¹(H₂O)]}₃[Cr(CN)₆]·10H₂O 1, [(H₂O)L²Mn–NC–M(CN)₄–CN–MnL²(NCS)]·2H₂O 2, [(H₂O)L²Mn–NC–Fe(CN)₄–CN–MnL²(H₂O)](NCS)·1.5H₂O 3, and [(H₂O)L²Mn–NC–Co(CN)₄–CN–MnL²(H₂O)](NCS)·1.5H₂O 4 (L¹ = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L² = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene). The crystal structure of 1 consists of independent [MnCrMn] monocations whose charges are counterbalanced by [Cr(CN)₆]³⁻ anions. The crystal structure of 2 consists of neutral heterotrinuclear [MnCrMn] species, with the isothiocyanato ion coordinated to one of the manganese atoms. Compounds 3 and 4 are isomorphous. Their crystal structure consists of centrosymmetric [MnMMn] entities, uncoordinated NCS⁻ ions, and solvent molecules. The magnetic properties of the four complexes have been investigated. Compounds 1 and 2 are new examples of systems with an irregular spin state structure, exhibiting the characteristic minimum on the the χ_MTversusT curves. The exchange interaction between the chromium(III) and the manganese(II) ions is antiferromagnetic (1: J = −9.8 cm⁻¹; 2: J = −6.52 cm⁻¹). For compound 3, the exchange interaction between manganese(II) and iron(III) was found to be ferromagnetic.