Abstract
Structural changes of chloride and bromide complexes, [Ni(Et2en)2(H2O)2]Cl2 (designated as 1a) and [Ni(Et2en)2]Br2 (2a), have been investigated by using simultaneous measurements of powder X-ray diffraction (XRD) and differential scanning calorimetry data under the temperature and humidity controls. The hydrate form of chloride complex 1a was transformed into an anhydrate form (1b) by heating at a temperature of 361 K. Then the 1b was reversibly returned to the original 1a by humidification at 25% relative humidity (RH) and temperature of 300 K. On the other hand, the anhydrate form of the bromide complex 2a was first transformed into a hydrate form (2b) at 30% RH and 300 K. On heating, the 2b turned to a new anhydrate form (2c) at 344 K, and then it returned to the original form 2a on further heating. In the present experiments, a series of reactions of 2a proceeded via 2c, which was newly found with the benefit of differential scanning calorimetry (DSC) measurements performed in parallel to the XRD measurements. Crystal structures of new crystalline forms of 1b, 2b, and 2c were determined from the powder XRD data.
Highlights
The physical and chemical properties of crystalline materials are largely dependent on their crystal structures as well as their chemical compositions
With increasing relative humidity (RH) from 5 to 70%, an exothermic reaction was observed at 30% RH
Observations of X-ray diffraction (XRD) patterns indicated that the new crystalline form 2c underwent a structural phase transition during heating, while the chart indicated that the structural change was not so drastic
Summary
The physical and chemical properties of crystalline materials are largely dependent on their crystal structures as well as their chemical compositions. In investigating structural changes with varying environmental factors, the determination of a crystal structure is, in general, an easy task when a single crystal, suitable for a diffraction experiment, is available, whereas it becomes a difficult task when the original crystal is, for example, fragmented into pieces accompanied with the volume expansion during the phase transition. In such a case, crystal structure determination from powder diffraction data becomes indispensable. Crystal structures of 1b, 2b, and 2c have been determined from powder XRD data collected with laboratory diffractometer systems
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