Synthesis, structural characterization and solvent effect of copper(II) complexes with a variational multidentate Salen-type ligand with bisoxime groups

Four new solvent-induced Cu(II) complexes with the chemical formulae [{Cu(HL)(CH3OH)}2Cu] · CH3OH (1), [{(Cu(HL))2(CH3CH2OH)2}Cu] (2), [{CuL(H2O)}2Cu2] · 2CH3CH2CH2OH (3) and [{(Cu(HL))2(CH3CH2CH2CH2OH)2}Cu] (4), where H4L = 6,6′-dihydroxy-2,2′-[ethylenediyldioxybis(nitrilomethylidyne)]diphenol, have been synthesized and characterized by elemental analyses, 1H NMR, FT-IR, UV–Vis spectra, TG-DTA, molar conductances and X-ray crystallography. Complexes 1, 2 and 4 have an elongated square-pyramidal geometry with an unusually long bond from the penta-coordinated Cu(II) centres to the oxygen atoms of the apically coordinated solvent (methanol, ethanol or n-butanol) molecules for the terminal Cu(II) ions, and a square planar geometry distorted tetrahedrally for the central Cu(II) ion. In complex 3, the terminal Cu(II) ions have trigonal bipyramidal coordination geometries constituted by equatorial O2N donor sites, with one oxygen atom from one of the coordinated water molecules and one nitrogen atom from a completely deprotonated L4− ligand unit in the axial positions, and the central Cu(II) ions are in slightly tetrahedrally distorted square planar geometries constituted by four phenoxo oxygen donors from two completely deprotonated L4− ligand units, and these form a tetrametal Cu–O–Cu–O–Cu–O–Cu–O eight-membered ring. These four complexes exhibit strong hydrogen bonding interactions in the solid state. Moreover, co-crystallizing n-propanol molecules link two other adjacent complex molecules into a self-assembled infinite 2D supramolecular structure via the intermolecular hydrogen bonds in complex 3.

Graphical abstractFour new solvent-induced Cu(II) complexes have been synthesized and structurally characterized. Because of the introduction of different solvent molecules, these complexes present two kinds of stoichiometric ratio and different structural features with a different performance of the ligand. Complex 3 forms a tetrametal Cu–O–Cu–O–Cu–O–Cu–O eight-membered ring.Figure optionsDownload full-size imageDownload as PowerPoint slide