Tuning the framework formation of copper coordination compounds by using neutral bi and tetradentate flexible pyrazole-based ligands

Abstract

Two new coordination compounds, [Cu(μ-bbd)(NCS)2]n (1) and [Cu2Cl4(μ-tdmpp)(H2O)2] (2), were prepared at room temperature by the reaction of CuX2 (X=Cl, SCN) salts with the flexible linker ligands 1,4-bis(3,5-dimethypyrazol-1-yl)butane (bbd) and 1,1,3,3-tetrakis(3,5-dimethypyrazol-1-yl)propane (tdmpp). The complexes were characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction. In the polymeric structure of 1, the copper(II) ion lies on a center of symmetry within a square-planar trans-CuN4 coordination geometry. The NCS groups are terminally N-bonded to the metal center and the μ-bbd ligand, with a gauche-anti-gauche conformation, acts as a centrosymmetric bridging bidentate ligand, linking the Cu(II) centers into a one-dimensional zigzag chain structure. In contrast to 1, complex 2 has a dinuclear structure in which each of the copper(II) ions is five-coordinated in a distorted CuN2Cl2O square-based pyramidal coordination geometry. The neighboring discrete [Cu2Cl4(μ-tdmpp).(H2O)2] molecules are connected by intermolecular O–H⋯Cl hydrogen bonds to form an infinite chain of neutral molecules. The adjacent 1D chains of complex 2 are further extended into a non-covalent 3D network structure by C–H⋯O intermolecular hydrogen bonds. The polymeric structure of [Cu(CH3CN)(μ3-SCN)]n (3) was obtained as an unexpected product in an attempt to synthesize the [Cu(μ-bpp)(SCN)2]n polymer in acetonitrile solution.