Water-induced phase transformation of a Cu-II coordination framework with pyridine-2,5-dicarboxylate and di-2-pyridyl ketone: synchrotron radiation analysis

作者：Llano Tome Francisco; Bazan Begona; Karmele Urtiaga M; Barandika Gotzone; Fidalgo Marijuan Arkaitz; Fernandez de Luis Roberto; Arriortua Maria I

来源：CrystEngComm, 2015, 17(33): 6346-6354.

DOI：10.1039/c5ce01033k

Phase transformations in solid coordination frameworks (SCFs) are of interest for several applications, and this work reports a crystal-to-crystal transformation found for hydrogen-bonded Cu-II-based solid coordination frameworks (SCFs). Thus, the combination of PDC and (py)(2)C(OH)(2) ligands, where PDC is pyridine-2,5- dicarboxylate and (py)(2)C(OH)(2) is the derivative gem-diol of di-2-pyridyl ketone ((py)(2)CO), produces [Cu(PDC)((py)(2)C(OH)(2))(H2O)] (1). Compound 1 transforms into [Cu(PDC)((py)(2)C(OH)(2))] (2) by thermally-induced dehydration. Characterization of both compounds has been carried out by means of IR spectroscopy, single crystal and powdered sample X-ray diffraction (XRD) through conventional and synchrotron radiation, thermogravimetry (TG), X-ray thermodiffractometry (TDX), and scanning electron microscopy (SEM). Since the molecules of water in 1 are coordinated to the metal ions, their removal induces local distortions on the coordination sphere (square pyramidal for 1 and square planar for 2), which extend through the whole framework, affecting the hydrogen bond system and the packing. In fact, the wavy nature of the planes in 1 becomes sharper in 2, producing an oscillation of the framework, i.e., from open (1) to close (2) waves. The crystal-to-crystal transformation is reversible (1 -> 2) and hysteresis has been observed associated with it. Quantum-mechanical calculations based on density functional theory (DFT) show that the 1 -> 2 structural rearrangement involves a high amount of energy, which means that the role of the coordinated molecule of water exceeds the mere formation of hydrogen bonds.

• 出版日期2015