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(H 2O) 4(η 1-4-nba)(η 2-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L 2) at 100 °C results in the formation of a Ca(II) coordination polymer [Ca(H 2O)(L 2)(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 (μ 2-H 2O), a bidentate bridging (μ 2-η 1:η 1) 4-nba ligand and a monoatomic bridging (μ 2-η 2) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L 2) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO 6N} 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) Å 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.