Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

Abstract

The solid state reaction of [Ca(H2O)4(eta1-4-nba)(eta2-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L2) at 100 degrees C results in the formation of a Ca(II) coordination polymer [Ca(H2O)(L2)(4-nba)2]n 2. Compound 2 was characterized by elemental analysis, spectral and thermal methods, and its structure determined. The coordination polymer 2 crystallizes in the centrosymmetric monoclinic space group P2(1)/n with all atoms situated in general positions and its structure consists of a central Ca(II), a monodentate 2-methylimidazole, a bridging water ligand (mu2-H2O), a bidentate bridging (mu2-eta1:eta1) 4-nba ligand and a monoatomic bridging (mu2-eta2) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L2) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO6N} polyhedron. Due to the bridging nature of the aqua and 4-nba ligands [(2-methylimidazole)calcium(II)] units in 2 are linked into a one-dimensional coordination polymer consisting of three chains, all of which propagate along b-axis. In the triple chain coordination polymer a Ca...Ca separation of 3.8432(3) angstrom is observed between neighbouring Ca(II) ions. The oxygen atoms of the carboxylate and nitro functionalities of the 4-nba ligand and the coordinated water are involved in O-H...O, N-H...O and C-H...O interactions. A comparative study of nine alkaline-earth 4-nitrobenzoate compounds is described.