Structural scope of six new layered to pillar-layered hybrid inorganic–organic networks bearing [BW12O40]5− and lanthanoid-cluster; database study toward ligand role in assemblies

Abstract

The objective of the present work is to explore the ratio of polyoxometalate charge to size together with the effect of the cation in coordination assemblies. In this regard, 12-borotungstic acid as a Keggin-type polyoxometalate which has a high negative charge density and is very rare in hybrid categories is used to synthesize six new hybrid networks, [M₃(H₂O)₁₃(pydc-OH)₂][BW₁₂O₄₀]·xH₂O (H₂pydc-OH = chelidamic acid; 4-hydroxy-2,6-pyridinedicarboxylic acid, M = Sm (1), Nd (2), and x = 17 (1), 19 (2)), [Ce₃(H₂O)₁₁(pydc-OH)₂(μ₂-OH)][HBW₁₂O₄₀]·20H₂O (3), and {K[M(H₂O)₄(pydc)]₄}[BW₁₂O₄₀]·2H₂O (M = Sm (4), Nd (5), Ce (6), H₂pydc = 2,6-pyridinedicarboxylic acid) under hydrothermal conditions and characterized by elemental analysis, FT-IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Single crystal X-ray diffraction analyses show that complexes 1 and 2 feature a 2D hybrid coordination polymer which further expands to a 3D supramolecular network through a dense layer of water chains, while compound 3 exhibits a 3D hybrid inorganic–organic network through μ₂-OH bridges. Compounds 4–6 are isostructural and each consist of tetramer units to construct cationic sheets where the POMs interconnect these sheets to make 3D covalent hybrid frameworks. Furthermore, a CSD survey was carried out on the cation and ligand roles in the structure formation.