Disorder of the Water Molecules and Sulfate Anion in the Crystal Structure of Fe-substituted Synthetic Chalcanthite Crystals (Cu1–xFex)SO4·5H2O (x = 0.1 and 0.20)

The isomorphism and isodimorphism of the d metal sulfates are of particular importance for the crystal chemistry of minerals, materials science, solid solutions physics and processing of the ores. The thermodynamic theory of solid-solution aqueoussolution interactions and available the effects of ionic substitutions on the thermodynamic properties of binary sulfate solid solutions were discussed before in detail.1 Chalcanthite is paramagnetic compound, and doping another paramagnetic atom, Fe2+, to it allow to modify it’s magnetic susceptibility.2 Crystals of chalcanthite have an optical band pass with a transmission band of 0.280 – 0.570 nm with a maximal transmission of 75%; they can be successfully used as an optical bandpass in higher resolution spectral devices.3 Some Fe-containing chalcanthite crystals were studied by the single crystal X-ray diffraction method and the distribution of the Cu and Fe atoms over the crystallographic sites are determined by using of the results of analytical chemistry or according to the degree of the distortion of the coordination polyhedrons around sites.4,5 Site occupations of the Cu and Fe atoms are not possible because of the similar scattering-factors of these elements. To except the problems of non-distinguishability of Cu and Fe during an X-ray diffraction study, we have synthesized the solid solutions of chalcanthite with a priory known chemical compositions, (Cu0.90Fe0.10)SO4·5H2O (I) and (Cu0.80Fe0.20) SO4·5H2O (II), and have studied (Fig. 1). The influence of substituting Cu for Fe ion on the structural disorders of the subunits in the crystal of chalcanthite was not performed. For this reason, this work is aimed at an X-ray diffraction study of the crystal structure of these compounds. Single crystals of (I) and (II) were synthesized by stirring 0.01 M sulfuric acid solution of CuSO4·5H2O and FeSO4·7H2O in molar of ratios of 9:1 and 8:2 at a temperature of ∼45°C, respectively. The X-ray diffraction data were collected on a Xcalibur, Ruby diffractometer using graphite-monochromated Cu-Kα radiation. Crystal and experimental data details are given in the Table 1. The values of the |E2 – 1| statistical parameters show that both crystals are centrosymmetric, and because it’s crystal structures were solved in the space group P1 and refined by a full-matrix least-squares method.6 The hydrogen atoms were found from difference maps, though not refined. Disorder manifests itself as a splitting of the O atoms sites and trigonal planar configuration of the O atoms of aqua ligands. The perceptible residual electron density remain around the M2 site on the distance 0.52 Å. Both crystal structures are composed of the square-planar [Cu(H2O)4] located at the M1(0,0,0) site and [(Cu,Fe)(H2O)4] at the M2(0,1/2,–1/2) site. The SO4 tetrahedra acts as a μ2-bridging ligand between these cations, which lead to a chain structure (Figs. 2 and 3). The water of crystallization takes place in the hydrogen bonds. Selected Cu–O bond lengths are presented in Table 2. Refinements of the crystal structures (I) and (II) showed that the M1 site is occupied fully by the Cu, and the M2 site is shared by Cu and Fe with relatively site occupations of 0.80 and 0.20 for (I) and 0.60 and 0.40 for (II), respectively. The M1O6 and M2O6 octahedrons are distorted because the Cu2+ ion in the electronic configuration d 9 exhibits the Jahn–Teller effect. In the both structures, as well as in the crystal structure of chalcanthite, the apical M1–Oap bonds are shorter than the apical M2–Oap 2021 © The Japan Society for Analytical Chemistry