Structural characterization of catena-[bis(μ-4-nitrobenzoato)-diaqua-calcium 4,4'-bipyridine] and catena-[bis(μ-4-nitrobenzoato)-diaqua-calcium 1H-1,2,4-triazole]

Abstract

An attempted incorporation of N-donor ligand in the coordination sphere of Ca in the molecular solid [Ca(H₂O)₄(4-nba)₂] (4-nba=4-nitrobenzoate) resulted in the formation of the one-dimensional (1D) coordination polymers catena-[bis(μ-4-nitrobenzoato)-diaqua-calcium 4,4'-bipyridine] 1 and catena-[bis(μ-4-nitrobenzoato)-diaqua-calcium 1H-1,2,4-triazole] 2 with the N-heterocycle functioning as a solvate. The syntheses, crystal structures and properties of [Ca(H₂O)₂(4-nba)₂]·L (L=4,4′-bipyridine 1; L=1H-1,2,4-triazole 2) are reported. The central Ca(II) in 1 and 2 exhibits eight-coordination and the aqua ligands are terminal, while 4-nitrobenzoate functions as a μ₂-bridging ligand. The μ₂-η²:η¹ tridentate binding mode of the 4-nba ligand results in the formation of an infinite chain of edge-sharing {CaO₈} polyhedra flanked by the 4-nitrobenzoates. The solvate 4,4′-bipyridine in 1 (or 1,2,4-triazole in 2) links adjacent polymeric chains with the aid of O-H∙∙∙N hydrogen bonding interactions. A comparative study of {CaO_x} polyhedral linking in structurally characterized calcium coordination polymers based on 4-nitrobenzoate is described.