Syntheses, Structures, and Magnetic Properties of Heterobimetallic Clusters with Tricyanometalate and π-Conjugated Ligands Containing 1,3-Dithiol-2-ylidene

Two new π-conjugated 1,3-dithiol-2-ylidene-containing ligands, 4,5-[1′,4′]dithiino[2′,3′-b]quinoxaline-2-bis(2-pyridyl)methylene-1,3-dithiole (L1) and 4,5-bis(methylthio)-2-bis(2-pyridyl)methylene-1,3-dithiole (L2), have been synthesized and characterized. Using L1, L2, or dimethyl 2-[di(pyridin-2-yl)methylene]-1,3-dithiole-4,5-dicarboxylate (L3) as the auxiliary ligand and [(Tp)Fe(CN)3]− or [(i-BuTp)Fe(CN)3]− [Tp = tris(pyrazolyl)borate; i-BuTp = 2-methylpropyltris(pyrazolyl)borate] as the building block, two rectangular-square Fe2Ni2 clusters [(Tp)Fe(CN)3Ni(L1)2]2·2ClO4·6H2O (1) and [(i-BuTp)Fe(CN)3Ni(L3)2]2·2ClO4·6H2O (2) and two trinuclear clusters [(Tp)2Fe2(CN)6Ni(L2)2]·8H2O (3) and [(Tp)2Fe2(CN)6Co(L3)2]·5H2O (4) have been prepared in parallel and structurally characterized. Complexes 1 and 2 show similar square structures, and weaker intermolecular π−π-stacking interactions through the pyrazolyl groups of the Tp− ligands are observed. 2D sheet structures are formed in complexes 3 and 4 through intermolecular π−π-stacking interactions. In 3, shorter S···S contacts further connect the 2D sheets to 3D supramolecular structures. Magnetic studies show intramolecular ferromagnetic coupling in complexes 1−4. Complexes 1 and 2 show obvious frequency dependencies in the alternating-current magnetic susceptibility data, indicating single-molecule-magnet behavior with effective spin-reversal barriers of 8.7 K for 1 and 13.5 K for 2, respectively.