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Article

The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad

by
Matthias Weil
Institute for Chemical Technologies and Analytics, Division of Structural Chemistry, TU Wien, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
Crystals 2017, 7(11), 340; https://doi.org/10.3390/cryst7110340
Submission received: 11 October 2017 / Revised: 30 October 2017 / Accepted: 3 November 2017 / Published: 6 November 2017
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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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.

Graphical Abstract

1. Introduction

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. In compounds of these elements with ionic or predominantly ionic character, zinc exclusively exhibits oxidation state +II, cadmium with very few exceptions has an oxidation state of +II (Cd2(AlCl4)2 being one of them with an oxidation state of +I [1,2]), whereas a multitude of mercuric (oxidation state +II), mercurous (oxidation state +I) and mixed-valent mercury compounds are known. The crystal-chemical features of all three elements are remarkably different. The most frequently observed coordination numbers for zinc in its compounds are 4, 5, and 6 with (distorted) tetrahedral, trigonal-bipyramidal, and octahedral coordination environments, respectively. The larger cadmium cation has a coordination number of four only in combination with larger anions (like in CdS), and in the majority of cases exhibits coordination numbers of six, or higher. For most of the latter cases, the coordination spheres are considerably distorted and difficult to derive from simple polyhedra. In many aspects, including structural characteristics, zinc and cadmium compounds resemble their alkaline earth congeners magnesium and calcium, respectively, which likewise have a closed shell electronic configuration. Mercury, on the other hand, is unique amongst all metals (cf. the low melting point) and has a peculiar crystal chemistry, showing a preference for linear coordination by more electronegative elements (coordination number of two). To a certain extent, these features can be related to relativistic effects that are pronounced for this element [3,4]. While a number of review articles devoted to the crystal chemistry of mercury have been published over the years [5,6,7,8,9,10,11], to the best of the author’s knowledge, apart from chapters in a compendium on coordination chemistry [11,12], special reviews on the crystal chemisty of zinc or cadmium did not appear thus far.
During previous crystal growth experiments it was successfully shown that mixed-metal compounds of the zinc triad can be prepared under hydrothermal conditions in form of their sulfate or selenate salts, viz. CdXO4(HgO)2 (X = S, Se) [13], (MXO4)2(HgO)2(H2O) (X = S, Se; M = Cd, Zn), CdSeO4(Hg(OH)2), and (ZnSeIVO3)(ZnSeVIO4)HgI2(OH)2 [14]. In the present study it was intended to replace the sulfate (SO42−) or selenate (SeO42−) anions with chromate anions (CrO42−) to search for new mixed-metal compounds of the zinc triad. Chromates, in particular, appeared to be promising candidates for formation of new compounds because they show pH-dependent chromate ⇌ dichromate equilibria and are able to stabilize different oxidation states for mercury. Mercurous chromates(VI) are scarce and known only for dimorphic Hg2CrO4 [15] and Hg6Cr2O9 [16], whereas mercuric chromates are more frequent with structure determinations reported for dimorphic HgCrO4 [17,18], for Hg3O2CrO4 [19], HgCr2O7 [20], HgCrO4(H2O)0.5 [21], and HgCrO4(H2O) [18]. In addition to these mercurous and mercuric chromates(VI), the mixed-valent Hg(I/II) compounds (HgI2)2O(CrO4)(HgIIO) (mineral name wattersite [22]) and Hg6Cr2O10 (=2Hg2CrO4·2HgO) [16] are also known. The two lead(II) mercury(II) chromates(VI) Pb2HgCrO6 [23] and Pb2(Hg3O4)(CrO4) [24] served as a proof of concept that additional metal ions can be incorporated into mercury oxochromates(VI). Crystallographic data for zinc and cadmium chromates, on the other hand, are restricted to CrVO4-type ZnCrO4 [25], Zn2(OH)2CrO4 [26], and to dimorphic CdCrO4 (low-temperature form, Cmcm; high-temperature form, C2/m) and Cd2CrO5 [27], respectively.

2. Results and Discussion

Three mixed-metal oxochromates(VI) were obtained under the given hydrothermal conditions, viz. Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4). Although the educt ratio Hg:Cd(Zn):Cr was 2:1:1, the ratio in the solid reaction products was different with a much higher mercury content, namely 7:1:2 for Cd(HgI2)2(HgII)3O4(CrO4)2, 4:1:1 for Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4), and 5:0:1 for wattersite crystals. The formation of mixed-valent mercury(I,II) compounds, i.e., wattersite in both batches and Cd(HgI2)2(HgII)3O4(CrO4)2 in the cadmium-containing batch, indicates that complex redox equilibria between different mercury species (Hg(0) ⇌ Hg(I) ⇌ Hg(II)) must have been present under the chosen hydrothermal reaction conditions. Such redox equilibria are easily influenced by the presence of additional redox partners, here, for example Cr(VI) ⇌ Cr(III), and other interacting parameters like temperature, pressure, pH, concentration of the reactants, etc. Such a complex interplay between different adjustable parameters not only makes a prediction of solid products difficult, but can also lead to multi-phase formation and the presence of element species with different oxidation states in one batch. This kind of behaviour is not only exemplified by the three title compounds but also for other mixed-valent mercury oxocompounds that were obtained under similar hydrothermal conditions [16,28,29,30].
The strong preference for linear coordination of mercuric and mercurous cations is confirmed in the crystal structures of the three title compounds where O–Hg–O and/or Hg–Hg–O units with Hg–O bond lengths less than 2.2 Å are present. Representative bond lengths of the three title compounds are listed in Table 1.
The mixed-valent Cd(HgI2)2(HgII)3O4(CrO4)2 phase crystallizes with one formula unit in space group P 1 ¯ . It comprises four unique mercury cations, two of which (Hg2, Hg3) belong to a Hg22+ dumbbell, and two of which (Hg1, Hg4) to Hg2+ cations. Hg1 is bound to two O atoms (O4, O5) at a distance of 2.002(8) and 2.016(8) Å with a nearly linear O4–Hg1–O5 angle of 175.2(3)°. Hg4, located on an inversion centre, shows two short distances of 2.037(8) Å to O5, and due to the symmetry restriction a linear O5–Hg4–O5(−x + 1, −y + 1, −z) angle. The Hg22+ dumbbell exhibits a Hg2–Hg3 distance of 2.5301(6) Å, which is slightly above the arithmetic mean of 2.518(25) Å calculated for more than one hundred different Hg22+ dumbbells that are present in crystal structures of various inorganic oxocompounds [30]. The two O atoms tightly bonded to the Hg2–Hg3 dumbbell have distances of Hg2–O6 = 2.192(8) Å and Hg3–O4 = 2.098(8) Å but only one of them has an arrangement approaching linearity with respect to the dumbbell (O6–Hg2–Hg3 = 165.6(2)°) while the other is virtually vertical to the dumbbell (O4–Hg2–Hg3 = 94.91(17)°). Under consideration of one longer Hg3–O5 bond of 2.528(8) Å, the mercuric and mercurous cations and the three oxygen sites O4–O6 are fused into strings with the composition {(HgI2)2(HgII)3O6}2− that are aligned into sheets extending parallel to (01 1 ¯ ) (Figure 1).
The Cd2+ cation (located on an inversion centre) and the Cr(VI) atom are situated between the sheets. They are bound to six and four oxygen sites in form of slightly distorted polyhedra with octahedral and tetrahedral configurations, respectively. The [CdO6] octahedron is flanked by two [CrO4] tetrahedra sharing two corner O atoms (O2 and its symmetry-related counterpart). The range of Cd–O bond lengths in the [CdO6] octahedron is narrow (2.252(7)–2.322(11) Å), with a mean of 2.29 Å; the corresponding values for the [CrO4] tetrahedron are 1.611(11)–1.677(8) and 1.65 Å, in good agreement with typical values for oxochromates(VI) comprising isolated [CrO4]2− anions (1.646(25) Å) [31]. By sharing some of the oxygen sites of the resulting {CdO4(CrO4)2} groups with the {(HgI2)2(HgII)3O6} network and also by additional Hg–O interactions > 2.2 Å, the three-dimensional framework structure of Cd(HgI2)2(HgII)3O4(CrO4)2 is established (Figure 2).
The second cadmium-containing phase, Cd(HgII)4O4(CrO4), and the zinc-containing phase, Zn(HgII)4O4(CrO4), have the same formula type but are not isotypic. The cadmium compound shows orthorhombic symmetry (space group Pbca, eight formula units) whereas the symmetry of the zinc compound is triclinic (space group P 1 ¯ , two formula units). Nevertheless, the general set-up of the two structures is very similar. Both structures contain two types of Hg–O chains defined by short Hg–O distances between 2.01 and 2.05 Å and more or less linear O–Hg–O angles (164–177°). The Hg–O–Hg angles in all these chains are around 120°, thus defining a zigzag arrangement. In the Cd(HgII)4O4(CrO4) structure one of the chains, [Hg4–O4–Hg1–O3]1∞, runs parallel [010], the other, [Hg3–O2–Hg2–O1]1∞, runs parallel [100] (Figure 3a). In the Zn(HgII)4O4(CrO4) structure the directions of propagation of the Hg–O chains are [100] for [Hg2–O1–Hg4–O2]1∞ and [110] for [Hg3–O4–Hg1–O3]1∞ (Figure 3b).
The Cd2+ and Zn2+ cations, respectively, are located between the Hg–O chains and have the function as bridging groups between adjacent Hg–O chains. Under consideration of other oxygen atoms (O5, O6) that are not part of the Hg–O chains, both metal sites have a distorted octahedral coordination environment. The Cd–O bond lengths are in a greater range than those of the [CdO6] octahedron in the structure of Cd(HgI2)2(HgII)3O4(CrO4)2, 2.237(6)–2.421(6) Å, but have the same mean value of 2.29 Å. The Zn–O bond lengths in Zn(HgII)4O4(CrO4) are expectedly shorter (2.045(8)–2.325(7) Å; mean 2.12 Å). In both M(HgII)4O4(CrO4) structures (M = Cd, Zn) two [MO6] octahedra are fused via edge-sharing into a [M2O10] double octahedron. These double octahedra are aligned in layers parallel (001) and have the same orientation in each layer in the structure of Zn(HgII)4O4(CrO4) (Figure 4), whereas their orientations alternate in the structure of Cd(HgII)4O4(CrO4) due to the presence of the a glide plane (Figure 5).
The Cr(VI) atoms sit above and below the [M2O10] double octahedra and link them through two bridging vertex O atoms into “MCrO4” (M = Cd (Zn)) slabs extending parallel [100]. The structural characteristics of the tetrahedral [CrO4] groups in the two structures follow the general trend [31] and in direct comparison show subtle differences. A somewhat greater distortion for the cadmium-containing structure (1.620(7)–1.658(7) Å, 108.8(4)–111.0(4)°) is observed compared to the zinc-containing structure (1.634(7)–1.657(6) Å, 108.5(4)–110.9(4)°).
The presence of two distinct structural subunits in each of the Cd(HgI2)2(HgII)3O4(CrO4)2 and M(HgII)4O4(CrO4) structures, viz., a mercury-oxygen network and cadmium/zinc cations bound directly to [CrO4]2− anions, allows to reformulate them as [{(HgI2)2(HgII)3O4}2+{Cd(CrO4)2}2−] and MCrO4·4HgO (M = Cd, Zn), respectively. The alternative formulae also emphasize the “basic” character (in an acid/base sense) of these compounds which is associated with the presence of oxygen atoms that are exclusively bonded to metal cations, here, those of mercury, cadmium (zinc), or mixtures thereof. Since these oxygen atoms do not belong to a chromate anion they are defined as “basic”. In the vast majority of cases, such “basic” oxygen atoms are surrounded by four metal cations in the form of distorted tetrahedra. Krivovichev and co-workers have resumed the use of such oxygen-centred [OM4] tetrahedra for a rational structure description and classification of mineral and synthetic lead(II) oxo-compounds [32]. A general review of anion-centred [OM4] tetrahedra in the structures of inorganic compounds with different metals M has been published some time ago, including [OHg4] tetrahedra [33]. However, mixed [OM4] tetrahedra with M = Hg and Cd or Zn are unknown so far.
In the structure of Cd(HgI2)2(HgII)3O4(CrO4)2, the “basic” oxygen atoms are represented by O4 and O5, both being bound to three mercury cations and one cadmium cation. The two types of [OHg3Cd] tetrahedra are considerably distorted, with O–M distances between 2.002(8) and 2.692(9) Å and M–O–M angles ranging from 98.6(3) to 123.5(4)°. Based on the alternative description by using oxygen-centred polyhedra, the [OHg3Cd] tetrahedra are linked through common edges (Cd---Hg2) and corners (Cd, Hg1, Hg4) into sheets with a width of two tetrahedra parallel (001). Adjacent sheets are connected along [001] through the Hg–Hg bond of the Hg2–Hg3 dumbbell. The remaining [CrO4] tetrahedra are situated in the voids of this arrangement and connected to the “basic” metal-oxygen network through additional Cd–O and Hg–O bonds (Figure 6).
The “basic” O atoms in the crystal structures of Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4) are atoms O1–O4. In the cadmium-containing structure, O1 is surrounded distorted tetrahedrally by two Hg2+ and two Cd2+ cations (bond lengths range 2.045(7)–2.421(6) Å, bond angles range 96.3(2)–118.6(3)°), O2 from one Cd2+ and three Hg2+ cations (2.062(6)–2.667(6) Å; 88.8(2)–117.8(3)°) and O4 from four Hg2+ cations (2.014(7)–2.838(8) Å; 93.1(3)–122.2(3)°). With two Hg2+ and one Cd2+ cation, O3 has only three bonding partners (2.026(6)–2.237(6) Å; 107.9(3)–119.6(3)°) that form a distorted trigonal-pyramidal polyhedron. The different types of [OM4] tetrahedra (M = Hg, Cd] and the [OHg2Cd] trigonal pyramid are linked by sharing vertices and edges into a three-dimensional framework. Like in the structure of Cd(HgI2)2(HgII)3O4(CrO4)2, the tetrahedral [CrO4] groups in the Cd(HgII)4O4(CrO4) structure are located in the voids of this arrangement and are connected with the framework through additional M–O bonds (Figure 7).
The above discussed similarities between the Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4) crystal structures are also valid by using oxygen-centred polyhedra as an alternative description. The general structural set-up of Zn(HgII)4O4(CrO4) is likewise accomplished by edge- and vertex-sharing of oxygen-centred polyhedra with [CrO4] tetrahedra in the free space and completion of the cohesion through additional M–O bonds (Figure 8). However, one of the oxygen-centered polyhedra is distinctly different. While O1 and O2 are again surrounded tetrahedrally by Hg2+ and Zn2+ cations (2.009(6)–2.805(8) Å, 87.0(2)–123.8(3)°; 2.027(6)–2.325(7) Å, 98.8(3)–116.7(3)°), and O3 in the form of a trigonal pyramid by two Hg2+ and one Zn2+ cations (2.015(6)–2.045(8) Å, 112.5(3)–123.2(4)°), O4 has increased the number of Hg cations to which it is bound from four to five. The resulting coordination polyhedron is that of a distorted trigonal bipyramid, with the τ5 index [34] being 0.90 [35]. The O4–Hgequatorial bond lengths and corresponding angles range between 2.024(6) and 2.728(7) Å and 117.8(3)–121.6(3)°, respectively; the O4–Hgaxial bond lengths are 2.819(7) and 2.933(7) Å with an angle Hg1–O4–Hg3 of 175.5(2)°.
Bond valence sums (BVS) [36], using the bond valence parameters of Brese and O’Keeffe [37], were calculated for the three structures. The results are reasonably close to the expected values (in valence sums) of 1 for mercurous Hg, 2 for mercuric Hg, 2 for Cd and Zn, 6 for Cr and 2 for O (Table 2). The global instability index GII was used as a measure of the extent to which the valence sum rule is violated [36]. The resultant GII values of 0.14 v.u. for Cd(HgI2)2(HgII)3O4(CrO4)2, 0.14 v.u. for Cd(HgII)4O4(CrO4) and 0.11 v.u. for Zn(HgII)4O4(CrO4) indicate stable structures with some lattice-induced strain [38].

3. Materials and Methods

3.1. Preparation

For the hydrothermal experiments, Teflon containers with an inner volume of 5 mL were used. The metal oxides HgO, CrO3 and ZnO (CdO), all purchased from Merck (Darmstadt, Germany), were used without further purification. 1 mmol HgO, 0.5 mmol CrO3, and 0.5 mmol ZnO (CdO) were mixed, placed in a Teflon container and poured with 3 mL water. The container was sealed with a Teflon lid, placed in a steel autoclave, heated at 215 °C for one week and cooled within 12 h to room temperature. In both cases (cadmium- and zinc-containing batches) the final supernatant solution was colourless (pH ≈ 8), and the different crystal colours and forms indicated multi-phase formation. The solid reaction products were filtered off with a glass frit, washed with water, ethanol, and acetone and air-dried. In both the cadmium- and the zinc-containing batch, dark-red crystals of wattersite [22] were identified as the main product. In the cadmium-containing batch the two title compounds, Cd(HgI2)2(HgII)3O4(CrO4)2 and Cd(HgII)4O4(CrO4), were obtained as dark-red rods and orange plates, respectively, in an estimated ratio of 1:2. In the zinc-containing batch, orange plates of Zn(HgII)4O4(CrO4) could be isolated as a minor product.

3.2. Single Crystal X-ray Diffraction

Prior to the diffraction measurements, crystals were separated from wattersite crystals and checked for optical quality under a polarizing microscope. Selected crystals were fixed with superglue on the tip of thin silica glass fibres. Intensity data were measured at room temperature with Mo-Kα radiation, using either a SMART CCD three-circle diffractometer (Bruker, Madison, WI, USA) or a CAD-4 four-circle diffractometer with kappa geometry (Nonius, Delft, The Netherlands). After data reduction, a numerical absorption correction was performed for each data set with the aid of the HABITUS program by optimizing the crystal shape [39]. The crystal structures were solved by Direct Methods [40] and were refined using SHELXL-97 [41].
Numerical details of the data collections and structure refinements are gathered in Table 3, selected bond lengths are given in Table 1. Structure graphics were produced with ATOMS [42]. Further details of the crystal structure investigations may be obtained from the Fachinformationszentrum (Karlsruhe, Eggenstein-Leopoldshafen, Germany, Fax: +49-7247-808-666; E-Mail: crysdata@fiz-karlsruhe.de, https://www.fiz-karlsruhe.de/) on quoting the depository numbers listed at the end of Table 3.

4. Conclusions

During the present study it was shown that SO42− or SeO42− anions could be replaced with isovalent and isoconfigurational CrO42− anions to prepare new mixed-metal oxocompounds of the zinc triad. The hydrothermally-grown crystals of Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4), and Zn(HgII)4O4(CrO4) each were obtained as minor reaction products in phase mixtures besides the mixed-valent mercury(I/II) compound (Hg2)2O(CrO4)(HgO) as the major product. All three compounds adopt unique structure types, with characteristic crystal-chemical features of the respective metal cations, namely a linear (or nearly) linear coordination of the Hg22+ and Hg2+ cations, a distorted octahedral coordination of the Cd2+ and Zn2+ cations, and a tetrahedral coordination of Cr in the oxochromate(VI) anions.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 07 00340 g001 550
Figure 1. The Hg–O network in the structure of Cd(HgI2)2(HgII)3O4(CrO4)2 in a projection along [ 1 ¯ 30 ] . Displacement ellipsoids are drawn at the 74% probability level. Short Hg–O bonds < 2.2 Å are given as solid lines, and longer Hg–O bonds as open lines.
Figure 1. The Hg–O network in the structure of Cd(HgI2)2(HgII)3O4(CrO4)2 in a projection along [ 1 ¯ 30 ] . Displacement ellipsoids are drawn at the 74% probability level. Short Hg–O bonds < 2.2 Å are given as solid lines, and longer Hg–O bonds as open lines.
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Crystals 07 00340 g002 550
Figure 2. Crystal structure of Cd(HgI2)2(HgII)3O4(CrO4)2 emphasizing the layered arrangement of the Hg–O network and the [CdO6] (green) and CrO4 (red) polyhedra. Displacement ellipsoids are as in Figure 1.
Figure 2. Crystal structure of Cd(HgI2)2(HgII)3O4(CrO4)2 emphasizing the layered arrangement of the Hg–O network and the [CdO6] (green) and CrO4 (red) polyhedra. Displacement ellipsoids are as in Figure 1.
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Crystals 07 00340 g003 550
Figure 3. The two different Hg–O chains in the structures of (a) Cd(HgII)4O4(CrO4) and (b) Zn(HgII)4O4(CrO4). Displacement ellipsoids are drawn at the 90% probability level.
Figure 3. The two different Hg–O chains in the structures of (a) Cd(HgII)4O4(CrO4) and (b) Zn(HgII)4O4(CrO4). Displacement ellipsoids are drawn at the 90% probability level.
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Crystals 07 00340 g004 550
Figure 4. The crystal structure of Zn(HgII)4O4(CrO4). [CrO4] tetrahedra are red, [ZnO6] octahedra are green. Displacement ellipsoids are as in Figure 3.
Figure 4. The crystal structure of Zn(HgII)4O4(CrO4). [CrO4] tetrahedra are red, [ZnO6] octahedra are green. Displacement ellipsoids are as in Figure 3.
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Crystals 07 00340 g005 550
Figure 5. The crystal structure of Cd(HgII)4O4(CrO4). [CrO4] tetrahedra are red, and [CdO6] octahedra are green. Displacement ellipsoids are as in Figure 3.
Figure 5. The crystal structure of Cd(HgII)4O4(CrO4). [CrO4] tetrahedra are red, and [CdO6] octahedra are green. Displacement ellipsoids are as in Figure 3.
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Crystals 07 00340 g006 550
Figure 6. Crystal structure of Cd(HgI2)2(HgII)3O4(CrO4)2 using oxygen-centred [OHg3Cd] tetrahedra (yellow) for visualisation. Displacement ellipsoids are as in Figure 1.
Figure 6. Crystal structure of Cd(HgI2)2(HgII)3O4(CrO4)2 using oxygen-centred [OHg3Cd] tetrahedra (yellow) for visualisation. Displacement ellipsoids are as in Figure 1.
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Crystals 07 00340 g007 550
Figure 7. Crystal structure of Cd(HgII)4O4(CrO4) using oxygen-centred tetrahedra for visualisation. [OHg2Cd2] and [OHg3Cd] tetrahedra are yellow, [OHg2Cd] trigonal pyramids are orange and [OHg4] tetrahedra are turquoise. Displacement ellipsoids are as in Figure 3.
Figure 7. Crystal structure of Cd(HgII)4O4(CrO4) using oxygen-centred tetrahedra for visualisation. [OHg2Cd2] and [OHg3Cd] tetrahedra are yellow, [OHg2Cd] trigonal pyramids are orange and [OHg4] tetrahedra are turquoise. Displacement ellipsoids are as in Figure 3.
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Crystals 07 00340 g008 550
Figure 8. Crystal structure of Zn(HgII)4O4(CrO4) using oxygen-centred tetrahedra for visualisation. [OHg2Cd2] and [OHg3Cd] tetrahedra are yellow, [OHg2Cd] trigonal pyramids are orange and [OHg5] trigonal bipyramids are turquoise. Displacement ellipsoids are as in Figure 3.
Figure 8. Crystal structure of Zn(HgII)4O4(CrO4) using oxygen-centred tetrahedra for visualisation. [OHg2Cd2] and [OHg3Cd] tetrahedra are yellow, [OHg2Cd] trigonal pyramids are orange and [OHg5] trigonal bipyramids are turquoise. Displacement ellipsoids are as in Figure 3.
Crystals 07 00340 g008
Table
Table 1. Selected bond lengths (Å) and angles (°).
Table 1. Selected bond lengths (Å) and angles (°).
Cd(HgI2)2(HgII)3O4(CrO4)2Zn(HgII)4O4(CrO4)
Hg1O42.002(8) Hg1O32.030(7)
Hg1O52.016(8) Hg1O42.045(6)
Hg1O32.732(11) Hg1O82.703(7)
Hg1O22.734(13) Hg1O12.805(8)
Hg2O62.192(8) Hg1O42.819(7)
Hg2O52.528(8) Hg1O72.840(7)
Hg2Hg32.5301(6) Hg2O12.043(6)
Hg2O42.692(9) Hg2O22.069(6)
Hg3O42.098(8) Hg2O42.728(7)
Hg3O12.734(10) Hg2O52.776(7)
Hg3O12.803(11) Hg2O52.896(7)
Hg4O52.037(8)2xHg2O82.903(7)
Hg4O62.600(9)2xHg3O32.015(6)
CdO52.252(7)2xHg3O42.024(6)
CdO42.293(9)2xHg3O72.610(7)
CdO22.322(11)2xHg3O82.838(8)
CrO11.611(11) Hg3O42.932(7)
CrO31.615(10) Hg4O12.009(6)
CrO21.665(12) Hg4O22.027(6)
CrO61.697(8) Hg4O62.625(7)
Hg4O82.731(8)
O4Hg1O5175.2(3)Hg4O72.746(7)
O5Hg4O5180.0ZnO32.045(8)
O6Hg2Hg3165.6(2)ZnO12.055(6)
Hg3Hg2O494.91(17)ZnO22.075(6)
ZnO52.097(6)
Cd(HgII)4O4(CrO4)ZnO62.146(6)
Hg1O42.016(7) ZnO22.325(7)
Hg1O32.049(6) CrO81.634(7)
Hg1O72.638(7) CrO71.643(7)
Hg1O22.667(6) CrO61.652(7)
Hg1O72.790(7) CrO51.657(6)
Hg2O22.012(6)
Hg2O12.045(7) O3Hg1O4172.8(3)
Hg2O52.584(7) O1Hg2O2163.3(3)
Hg2O72.740(7) O3Hg3O4176.6(3)
Hg2O82.882(8) O1Hg4O2175.7(3)
Hg3O12.057(6) Hg4O1Hg2115.1(3)
Hg3O22.062(6) Hg4O2Hg2116.0(3)
Hg3O42.577(6) Hg3O3Hg1123.2(4)
Hg3O82.725(7) Hg3O4Hg1120.2(3)
Hg3O62.752(7)
Hg3O42.838(8)
Hg4O42.014(7)
Hg4O32.026(6)
Hg4O82.700(7)
Hg4O42.838(8)
CdO32.237(6)
CdO52.251(7)
CdO22.273(6)
CdO62.283(7)
CdO12.299(6)
CdO12.421(6)
CrO81.620(7)
CrO71.627(7)
CrO61.633(7)
CrO51.658(7)
O4Hg1O3173.6(3)
O2Hg2O1174.0(3)
O1Hg3O2166.4(2)
O4Hg4O3176.6(3)
Hg2O1Hg3118.6(3)
Hg2O2Hg3117.0(3)
Hg4O3Hg1109.3(3)
Hg4O4Hg1122.2(3)
Table
Table 2. Results of bond valence calculations/valence units (1).
Table 2. Results of bond valence calculations/valence units (1).
Cd(HgI2)2(HgII)3O4(CrO4)2
Hg1 2.07, Hg2 1.03, Hg3 1.04, Hg4 2.05, Cd1 2.13, Cr1 5.99, O1 1.82 [2 Hg, 1 Cr], O2 1.87 [1 Hg, 1 Cd, 1 Cr], O3 1.75 [1 Hg, 1 Cr], O4 1.94 [3 Hg, 1 Cd], O5 2.29 [3 Hg, 1 Cd], O6 1.91 [1 Cr, 2 Hg].
Cd(HgII)4O4(CrO4)
Hg1 2.13, Hg2 2.21, Hg3 2.13, Hg4 2.18, Cd1 2.12, Cr1 6.16, O1 2.21 [2 Hg, 2 Cd], O2 2.20 [3 Hg, Cd], O3 2.08 [2 Hg, Cd], O4 2.07 [4 Hg], O5 2.12 [Cr, Cd, 2 Hg], O6 2.02 [Cr, Cd, Hg], O7 1.97 [Cr, 3 Hg], O8 1.96 [Cr, 3 Hg].
Zn(HgII)4O4(CrO4)
Hg1 2.12, Hg2 2.00, Hg3 2.11, Hg4 2.19, Zn1 1.99, Cr1 5.96, O1 2.20 [3 Hg, Zn], O2 2.18 [2 Hg, 2 Zn], O3 2.15 [2 Hg, Zn], O4 1.98 [5 Hg], O5 1.99 [Cr, Zn, 2 Hg], O6 1.94 [Cr, Zn, Hg], O7 1.98 [Cr, 4 Hg], O8 1.98 [Cr, 4 Hg].
(1) For oxygen atoms the type and number of atoms they are bound to are indicated in brackets.
Table
Table 3. Details of data collections and structure refinements.
Table 3. Details of data collections and structure refinements.
CompoundCd(HgI2)2(HgII)3O4(CrO4)2Cd(HgII)4O4(CrO4)Zn(HgII)4O4(CrO4)
DiffractometerSiemens SMARTNonius CAD4Siemens SMART
Formula weight1812.531094.761047.73
Crystal dimensions/mm30.08 × 0.10 × 0.250.04 × 0.04 × 0.230.01 × 0.05 × 0.10
Crystal descriptionred, irregular fragmentorange, plateyellow, plate
Space groupP 1 ¯ PbcaP 1 ¯
Formula units Z182
a/Å6.1852(5)6.9848(10)6.873(3)
b/Å7.3160(6)12.8019(15)6.928(3)
c/Å8.5038(7)19.227(3)10.413(4)
α/°85.5840(10)9089.725(7)
β/°87.2820(10)9070.903(7)
γ/°72.0160(10)9061.694(7)
V/Å3364.80(5)1719.3(4)405.7(3)
μ/mm−176.24174.83279.606
X-ray density/g·cm−38.2508.4598.576
Range θmin–θmax/°2.40–30.473.18–29.993.40–30.58
Rangeh−8 → 7−9 → 9−9 → 9
k−10 → 9−17 → 17−9 → 9
l−12 → 12−27 → 27−14 → 12
Measured reflections424518,4394655
Independent reflections217724862408
Obs. reflections [I > 2σ(I)]215317721996
Ri0.04500.08980.0431
Absorption correction?HABITUS?
Trans. coeff. Tmin/Tmax0.004/0.0550.1393/0.21850.0222/0.5407
Ext. coef. (SHELXL97)0.0057(2)0.000177(9)0.00054(7)
Number of parameters104128128
Δemax; Δemax/e−·Å−32.10; −1.781.94, −1.942.50; −2.24
R[F2 > 2σ(F2)]0.03360.02440.0284
wR2(F2 all)0.07270.04460.0570
Goof1.3041.0210.925
CSD number433,656433,657433,658

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Weil, M. The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad. Crystals 2017, 7, 340. https://doi.org/10.3390/cryst7110340

AMA Style

Weil M. The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad. Crystals. 2017; 7(11):340. https://doi.org/10.3390/cryst7110340

Chicago/Turabian Style

Weil, Matthias. 2017. "The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad" Crystals 7, no. 11: 340. https://doi.org/10.3390/cryst7110340

APA Style

Weil, M. (2017). The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad. Crystals, 7(11), 340. https://doi.org/10.3390/cryst7110340

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