Phase Transitions and Crystal Structures of Ni(II) Complexes Determined with X-ray Powder Diffraction Data

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.

Manipulation of the Thermochromic Transition Temperature in a Classic Metal–Organic Complex by Selective Anion Doping

“…As mentioned previously, the reported [Ni­( dieten ) 2 ]­(Br) 2 has a structure and hydrogen bonding network similar to [Ni­( dieten ) 2 ]­(BF 4 ) 2 (Figure ) but displays no significant temperature-dependent thermochromism . Doping Br – in place of tetrafluoroborate at low percentages (5, 10, and 25% at synthesis) should result in a perturbation of the hydrogen bonding network without changing the overall crystal structure of the material.…”

“…As mentioned previously, the reported [Ni(dieten) 2 ](Br) 2 has a structure and hydrogen bonding network similar to [Ni(dieten) 2 ](BF 4 ) 2 (Figure 1) but displays no significant temperature-dependent thermochromism. 40 S13). Elemental analysis of the bulk product of each of the doped syntheses determined that the actual doped percentage is consistent with the intended target.…”

An Open Inquiry Lab Experiment Preparing Bis(N,N-diethylethylenediamine) Nickel(II) Complexes

“…The hydrated and nonhydrated forms have very different colors, and the hydrated and nonhydrated bromide complexes also have different magnetic susceptibilities. Recent studies by Kanaka and Sasaki , using X-ray powder diffraction coupled with differential scanning calorimetry show that the hydration changes are reversible even at the crystal level.…”

“…While this series of Et 2 en complexes was originally reported by Goodgame and Venanzi in 1963, these complexes have received continued interest since they exhibit color changes based on hydration/dehydration transitions or thermochromism depending on the selected anion. − A thermochromic experiment using [Cu­(Et 2 en) 2 ]­(BF 4 ) 2 and [Cu­(Et 2 en) 2 ]­(NO 3 ) 2 has been published in this Journal …”

Crystal Structure Characterization by Powder Diffraction

“…The [1] under the temperature and humidity controls. The authors studied the transition phenomena accompanied by dehydration and hydration and their reverse processes by simultaneous measurements of powder X-ray diffraction (XRD) and differential scanning calorimetry data.…”