Synthesis and characterisation of dinuclear Co(II), Ni(II) and Cu(II) unsaturated helical complexes from a novel dipyridyl-bispyrazole ligand

Abstract

Reported here is the synthesis of a novel bis-bidentate ligand 4,4′-methylenebis(1-(2-pyridyl)-3,5-dimethylpyrazole), L, along with the synthesis and structural characterisation of three unsaturated dinuclear helical complexes that it forms with Co(II), 1, Ni(II), 2, and Cu(II), 3. The structure of 1, [LCoCl(H2O)]2[CoCl4]·2MeCN, is comprised of two Co(II) ions with octahedral geometry around which two ligand molecules wrap to generate a compact unsaturated double helicate, with coordination about each Co(II) completed by a water molecule and chloride ion. Packing of the complex is such that helicate species align head-to-tail, with the metal bound water molecule and chloride ligand on adjacent helicates hydrogen-bonding to each other in a reciprocal fashion to form a 1D polymer. Complex 2, [LNiCl]2·xH2O, possesses a similar molecular structure to that found in 1, however in this instance the coordination about each octahedral Ni(II) ion is comprised from two ligand molecules and two chloride ions to yield a charge neutral unsaturated double helical species. Packing of adjacent helical species in 2 creates large void spaces throughout the crystal lattice within which disordered solvent molecules reside. The structure of 3, [LCu2Cl4], is a single stranded dinuclear helical species whereby one ligand molecule wraps about two highly distorted square planar Cu(II) centres, with two chloride ions completing the coordination sphere to yield a neutral species.