Derivatographic Studies on Transition Metal Complexes. X. Thermal Octahedral-to-Square Planar Transformation of Ni(NN-deen)2X2·nH2O in Solid Phase

Abstract

Thermal reactions of the complexes [Ni(H2O)2(NN-deen)2]X2·nH2O (NN-deen is N,N-diethylethylene-diamine and X is Cl or Br) were investigated. It was found by derivatography and spectral and magnetic measurements that the bromide undergoes transformation from octahedral to square planar structure by “deaquation” upon heating, whereas the chloride turned to the dichloro complex by thermal “deaquation-anation” losing the coordinated water and drawing chloride ion into the coordination sphere with retention of octahedral structure around the central metal. No such transformation could be found in the corresponding iodide and nitrate, since only diamagnetic complexes, [Ni(NN-deen)2]X2 (X is I or NO3), and no paramagentic complexes were obtained.

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

“…Figure 8 shows the refined crystal structures of 2a, 2b and 2c. The crystal structure of 2a is known to belong to the space group of C2/c in the monoclinic system [2]. The new forms of 2b and 2c have been elucidated to belong to the same space group of P2 1 /n in the monoclinic system.…”

“…The 1a with water molecules exhibits light-blue color. It is transformed into a dehydrated form, [Ni(Et 2 en) 2 Cl 2 ], designated as 1b, on heating [2]. On the other hand, the 2a undergoes a hydration transition to [Ni(Et 2 en) 2 (H 2 O) 2 ]Br 2 (2b) by humidification, and water molecules are supposed to be coordinated to Ni(II) [2].…”

“…It is transformed into a dehydrated form, [Ni(Et 2 en) 2 Cl 2 ], designated as 1b, on heating [2]. On the other hand, the 2a undergoes a hydration transition to [Ni(Et 2 en) 2 (H 2 O) 2 ]Br 2 (2b) by humidification, and water molecules are supposed to be coordinated to Ni(II) [2]. The crystal structures of 1a and 2a have been reported [8,9], while their structures after the dehydration (1b) and hydration (2b) have not yet been reported.…”

“…Ni(II) complexes, with the N,N-diethylethylenediamine (Et 2 en) ligand, are known to exhibit color changes accompanied by hydration/dehydration transitions and thermochromism depending on selected anions, and their physical properties, as well as crystal structures, have been studied by many researchers [1][2][3][4][5][6][7]. The crystal structures of Ni(II) complexes have been elucidated when single crystals capable of X-ray diffraction studies were available, while many of them still remain as unknown structures because they can be obtained just as powders.…”

Photochromism in Ruddlesden–Popper copper-based perovskites: a light-induced change of coordination number at the surface

“…A similar process has been reported as a thermal effect in a hydrated nickel bromide compound. 49 It is also important to underline that the transition from octahedral to square-planar CuCl 4 2À could explain the disorder in the…”