Different behavior of PDA as a preorganized ligand versus PCA ligand in constructing two inorganic-organic hybrid materials based on Keggin-type polyoxometalate

Two lanthanoid-based inorganic-organic hybrids, [Nd-4(PDA)(4)(H2O)(9)(SiW12O40)]center dot 5H(2)O (1), (PDA = deprotonated preorganized 1,10-phenanthroline-2,9-dicarboxylic acid) and [Gd(PCA)(3)(H2O)(2)](2) [HSiW12O40](2)center dot 10H(2)O (2), (PCA = pyridine-4-carboxylic acid) have been hydrothermally synthesized utilizing the [SiW12O40](4-) Keggin-type polyoxometalate as a building block. These two compounds were characterized by elemental analysis, infrared spectroscopy and single crystal X-ray crystallography. Structural characterizations by single crystal X-ray diffraction reveals that hybrid 1 is one of the rarely reported inorganic-organic hybrid POMs with PDA ligand based on CSD search (CSD version 5.38/May 2017) while hybrid 2 with PCA ligand is a coordination compound. At the supramolecular level, hybrid 1 presents 3-D pillar-layered framework with the [SiW12O40](4-) anions located on the voids of the 2-D Nd-PDA bilayer. Hybrid 2 consists of discrete Gd-PCA dimer and Keggin anions interacted via hydrogen bond interactions.