Synthesis and structural characterization of a barium coordination polymer based on a μ₂-monoatomic bridging 4-nitrobenzoate

The synthesis, spectral characterization, crystal structure and properties of [Ba(H2O)2(NMF)2(4-nba)2], 1 (NMF = N-methylformamide; 4-nba = 4-nitrobenzoate), are reported. 1H and 13C NMR spectral data reveal the presence of NMF in 1. A strong band at 1660 cm−1 in the infrared spectrum indicates the binding of amide oxygen to Ba(II) which is confirmed by the single crystal structure. The unique Ba(II) in 1 situated on a mirror plane exhibits nine coordination and is bonded to two symmetry related monodentate terminal NMF ligands via the amide oxygen, and a terminal aqua ligand. The μ2-monoatomic bridging binding mode of each of a crystallographically independent 4-nba ligand and a unique water ligand link the Ba(II) cations into an infinite chain extending along a, leading to the formation of a 1D coordination polymer with Ba···Ba separations of 4.2522(3) Å. In the chain, the {BaO9} polyhedra are linked in a face sharing fashion. Thermal decomposition of 1 results in the formation of BaCO3 residue. A comparative study of the structural chemistry of several barium coordination polymers is described.本文报道了配合物[Ba(H₂O)₂(NMF)₂(4-nba)₂]（编号为1，其中NMF为N-甲基甲酰胺（N-methylformamide），4-nba为4-硝基苯甲酸根（4-nitrobenzoate））的合成、光谱表征、晶体结构及其性能。¹H与¹³C核磁共振（NMR）光谱数据证实了配合物1中存在NMF配体。红外光谱中于1660 cm⁻¹处出现的强吸收峰表明酰胺氧与Ba(II)发生配位，该结论经单晶结构分析得以验证。配合物1中唯一的Ba(II)离子位于对称面上，配位数为9，通过酰胺氧与两个对称相关的单齿端基NMF配体以及一个端基配位水分子配位。每个晶体学独立的4-nba配体与一个独特的水分子均采用μ₂-单原子桥联配位模式，将Ba(II)阳离子连接成沿a轴延伸的无限链状结构，形成Ba···Ba间距为4.2522(3) Å的一维配位聚合物。在该链中，{BaO₉}多面体以面共享方式相互连接。配合物1的热分解产物为碳酸钡残渣。本文还对多种钡基配位聚合物的结构化学进行了比较研究。