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 [MnIIMIIIMnII] heterotrinuclear complexes (MIII = 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 χMTversusT 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.