Hydrated and dehydrated Ca-coordination polymers based on benzene-dicarboxylates: mechanochemical synthesis, structure refinement, and spectroscopic characterization

Abstract

A series of Ca-based coordination polymers were prepared mechanochemically by milling Ca(OH)₂ with phthalic acid (H₂oBDC), isophthalic acid (H₂mBDC), and terephthalic acid (H₂pBDC). The hydrated compounds [Ca(oBDC)(H₂O)] (1), [Ca(mBDC)(H₂O)_3.4] (2), and [Ca(pBDC)(H₂O)₃] (3) were prepared for the first time via mechanochemical routes. The refined structures were validated by extended X-ray absorption data. The new dehydrated compound [Ca(oBDC)] (1-H₂O), obtained after the thermal post-treatment of 1 in a reversible phase transition process, was determined ab initio based on the powder X-ray diffraction (PXRD) data. The materials were thoroughly characterized using elemental analysis, thermal analysis, and spectroscopic methods: magic-angle spinning NMR and attenuated total reflection-infrared spectroscopy. The specific surface areas and sorption properties of the hydrated and dehydrated samples were determined using the isotherms of gas sorption and dynamic vapor sorption measurements.