Mononuclear, Tetra-, Penta- 3d Molecular Clusters Based on the Variability of SS-1,2-Bis(1H-benzimidazole-2-yl)-1,2-ethanediol Ligand Arising from Hydroponic and Hydrothermal Conditions: Structure, Crystal Growth, and Magnetic Properties

Abstract

Four compounds Co(SS-H2bzimed-H)2·CH3OH·2H2O (1), Zn4(SS-H2bzimed-H)4(NO3)4·5H2O (2), Co5(Hbzimed-H)6Cl4·2.5H2O (3), Ni5(Hbzimed-H)6Cl4·4H2O (4) (SS-H2bzimed = SS-1,2-bis(1H-benzimidazole-2-yl)-1,2-ethanediol; Hbzimed = 1,2-bis(1H-benzimidazol-2-yl)-1,2-ethenol) have been synthesized by methods of alternative hydroponic and hydrothermal reactions, and their crystal structures were determined. Room temperature reaction of SS-H2bzimed with Co(NO3)2·6H2O yielded compound 1 which crystallizes in the chiral orthorhombic space group C2221, where SS-H2bzimed ligands act as facially tridentate ligands through both bis-benzimidazole nitrogen atoms and one deprotonated hydroxyl group. By using Zn(NO3)2·6H2O instead of Co(NO3)2·6H2O, under refluxed stirring at 80 °C, compound 2 was obtained similarly to 1 which crystallizes in the chiral monoclinic space group C2, showing a Zn4[μ3-O]4 cubic core constructed by four monodeprotonated, μ3-κN,O:κO,O′:κN′,O′-SS-H2bzimed ligands. Under 140 °C at hydrothermal conditions, the SS-H2bzimed ligand unexpectedly changes to Hbzimed by an in situ intramolecular dehydration coupling reaction, and the neonatal ligands bridge metal systems into two kinds of rare single crystal microtubes constructed by a trigonal bipyramid M5[μ-O]6 (M = CoII: 3, NiII: 4) core where each apical Oh metal atom is linked to equatorial Td metal atoms through six μ2-κN,O:κN′,O-Hbzimed-H ligands. Magnetic studies show that 3 exhibits spin-canting behavior below 10 K, whereas 4 shows only simple antiferromagnetic coupling. Such magnetic behavior of 3 mainly arises from Oh−Td mixed geometries of pentameric Co(II) ions, which can result in relatively noncompensated moments, according to different efficient spins of Co(II) at very low temperature and the Dzyaloshinski−Moriya interaction. A discussion of the coordination properties of H2bzimed ligands upon different geometries of the central ions, and a probable mechanism for in situ reaction of ligand and the formation of single crystal microtubes is provided.