X-ray Study of M ^II(ClO₄)₂.6H₂O (M ^II = Zn, Ni): Twinning, Disorder and Phase Transitions

Abstract

X-ray studies of zinc and nickel perchlorate hexahydrate, Zn(ClO4)2.6H2O and Ni(ClO4)2.6H2O, respectively, at different temperatures have been carried out to correlate the structural changes with phase transitions in the compounds. The crystals are pseudohexagonal (P63 mc), exhibiting a three-component orthorhombic twinning (Pmn21). At high temperatures a slight deviation of the b/a ratio of the three twinned orthorhombic cells from 31/2 results in a three-component splitting of each spot in the X-ray photograph, which on cooling to room temperature coalesce into single ones, thus restoring the original b/a ratio. The diffuse streaks disappear in the high-temperature photographs due to a decrease in the probability of error in repetition along the b axes of the three orthorhombic cells with temperature. A successful refinement of the heat-treated ordered Zn(ClO4)2.6H2O crystal verifies the continuous perchlorate–water arrangement and three-component twinning of the orthorhombic cell. Low-temperature X-ray photographs indicate no structural change.

Hydrogen dynamics in [Me(H2O)6](ClO4)2 with Me=Mg, Mn, Fe, Ni, and Zn investigated with quasielastic neutron scattering

“…1͒. [7][8][9][10] The H 2 O molecules lie in planes perpendicular to the c-axis of the crystal. 11 Their oxygen atoms form nearly perfect octahedra around the central metal ions.…”

Temperature dependence of the EPR spectrum of Co2+ ion in crystals Zn(BF4)2 × 6H2O

“…Zinc fluoroborate as well as perchlorate has a pseudohexagonal structure (P6 3 mc), that exhibits three-component orthorhombic twinning (Pmn2 1 ) [2]. A schematic image of the structure (a = 7.62, b = 13.2, c = 5.30, and z = 2) is presented in [1,2]. The bivalent metal impurity ion is surrounded by six H 2 O molecules forming an octahedron slightly distorted along the c-axis.…”

“…The crystals were not hygroscopic under standard atmospheric conditions. Zinc fluoroborate as well as perchlorate has a pseudohexagonal structure (P6 3 mc), that exhibits three-component orthorhombic twinning (Pmn2 1 ) [2]. A schematic image of the structure (a = 7.62, b = 13.2, c = 5.30, and z = 2) is presented in [1,2].…”

“…Firstly, these crystals undergo a series of phase transitions induced by weak orientation interaction forces [1]. Secondly, their structure contains bivalent impurity ions arranged in the form of chains with weak bonds between them [2]; this could be responsible for some unusual properties of these compounds. Thirdly, these crystals are readily compressible and can serve as model objects in investigations at high pressure.…”

The EPR Zero-Field Splitting D and its Pressure and Temperature Dependence for Trigonal Mn2+ Centers in [Zn(H2O)6](BF4)2:Mn2+ Crystal

“…n ions have attracted great interest because: (i) there are several phase transitions induced by weak orientation interaction forces in these crystals [1,2]; (ii) these crystals have unusual properties caused by bivalent impurity ions arranged in the form of chains weakly linked to each other [3]; (iii) they are very compressible and can serve as model objects in studies at high pressure [4,5]. So, many EPR spectra for bivalent 3d n ions (e. g., Mn 2+ , Ni 2+ and Co 2+ ) in these crystals have been measured [4 -8].…”