Abstract
The three mixed-metal oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4), and Zn(HgII)4O4(CrO4) were grown under hydrothermal conditions. Their crystal structures were determined from single-crystal X-ray diffraction data. The crystal-chemical features of the respective metal cations are characterised, with a linear coordination for mercury atoms in oxidation states +I and +II, octahedral coordination spheres for the divalent zinc and cadmium cations and a tetrahedral configuration of the oxochromate(VI) anions. In the crystal structures the formation of two subunits is apparent, viz. a mercury-oxygen network and a network of cadmium (zinc) cations that are directly bound to the oxochromate(VI) anions. An alternative description of the crystal structures based on oxygen-centred polyhedra is also given.
Highlights
The three elements of the zinc triad have a closed-shell nd10 (n + 1)s2 electronic configuration with n = 3, 4, and 5 for zinc, cadmium, and mercury, respectively
Cr(III), and other interacting parameters like temperature, pressure, pH, concentration of the reactants, etc. Such a complex interplay between different adjustable parameters makes a prediction of solid products difficult, but can lead to multi-phase formation and the presence of element species with different oxidation states in one batch. This kind of behaviour is exemplified by the three title compounds and for other mixed-valent mercury oxocompounds that were obtained under similar hydrothermal conditions [16,28,29,30]
The alternative formulae emphasize the “basic” characterof oxygen atoms that are of exclusively bonded to metaliscations, here,with those mercury,ofcadmium, these compounds which associated theofpresence oxygen atoms or mixtures thereof. Since these oxygen atoms do not belong to a chromate anion they are defined that are exclusively bonded to metal cations, here, those of mercury, cadmium, or mixtures as “basic”
Summary
The three elements of the zinc triad have a closed-shell nd (n + 1)s2 electronic configuration with n = 3, 4, and 5 for zinc, cadmium, and mercury, respectively. HgCrO4 [17,18], for Hg3 O2 CrO4 [19], HgCr2 O7 [20], HgCrO4 (H2 O)0.5 [21], and HgCrO4 (H2 O) [18] In addition to these mercurous and mercuric chromates(VI), the mixed-valent Hg(I/II) compounds (HgI 2 ) O(CrO4 )(HgII O) (mineral name wattersite [22]) and Hg6 Cr2 O10 (=2Hg2 CrO4 ·2HgO) [16] are known. (low-temperature form, Cmcm; high-temperature form, C2/m) and Cd2 CrO5 [27], respectively
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