Synthesis and structural characterization of bis(μ₂-aqua)tetrakis(aqua)dilithium(I) bis(4-nitrobenzoate)

Abstract

Reaction of alkali metal carbonates M₂CO₃ (M = Li or Na) with 4-nitrobenzoic acid (4-nbaH) results in the formation of [(H₂O)₄Li₂(μ-H₂O)₂](4-nba)₂ (4-nba = 4-nitrobenzoate) (<b style="">1</b>) and [Na(4-nba)(H₂O)₃] (<b style="">2</b>). Compounds (<b style="">1</b>) and (<b style="">2</b>) have been characterized by analytical, spectral and thermal data. The structure of (<b style="">1</b>) consists of bis(μ₂-aqua)tetrakis(aqua)dilithium(I) dication situated on an inversion centre and a free 4-nba anion. In compound (<b style="">2</b>), one of the two independent 4-nba functions as a μ₂-bridging bidentate ligand, bridging the two unique Na(I) ions via the oxygen atoms of the nitro functionality. Hydrogen bonding of coordinated water ligands in a dinuclear lithium cation with coordinated water molecules in an adjacent unit leads to the formation of a supramolecular chain of [(H₂O)₄Li₂(μ-H₂O)₂]²⁺ cations. The cationic chain is further H-bonded to 4-nba anions resulting in alternating layers of [(H₂O)₄Li₂(μ-H₂O)₂]²⁺ cations and 4-nba anions. Compounds (<b style="">1</b>) and (<b style="">2</b>) exhibit enhanced fluorescence emission. A study of the known <i style="">s</i>-block metal compounds containing 4-nba and coordinated water ligands reveals that the coordination number of the central metal varies from four in Li to nine in Ba.