Crystal chemistry of natural and synthetic lead oxyhalides. Part I. Crystal structure of Pb<Subscript>13</Subscript>O<Subscript>10</Subscript>Cl<Subscript>6</Subscript>

Crystals of lead oxychloride Pb₁₃O₁₀Cl₆ have been synthesized on the basis of high-temperature solid-state reactions. The Pb₁₃O₁₀Cl₆ structure was studied using X-ray single-crystal diffraction analysis. The compound is monoclinic, and the space group is C2/c; the unit-cell dimensions are a = 16.1699(14), b = 7.0086(6), c = 23.578(2) Å, β = 97.75°, and V = 2647.6(4) ų. The structure has been solved by direct methods and refined to R ₁ = 0.0505 for 2671 observed unique reflections. The structure is a 3D framework consisting of OPb₄ tetrahedrons. Chlorine atoms are located in the framework channels. The structure contains seven symmetrically independent Pb atoms, which are coordinated by 2 to 4 O^2? and 2 to 4 Cl^? anions. The synthesized compound is compared with other natural and synthetic lead oxyhalides.     

Crystal chemistry of selenates with mineral-like structures: VII. The structure of (H<Subscript>3</Subscript>O)[(UO<Subscript>2</Subscript>)(SeO<Subscript>4</Subscript>)(SeO<Subscript>2</Subscript>OH)] and some structural features of selenite-selenates

The crystal structure of a new compound, (H₃O)[(UO₂)(SeO₄)(SeO₂OH)] (monoclinic, P2₁/n, a = 8.6682(19), b = 10.6545(16), c = 9.846(2) Å, β = 97.881(17)°, V = 900.7(3) ų), was solved by direct methods and refined to R ₁ = 0.050. The structure contains two symmetrically different Se atoms. The Se1 site is coordinated by three O atoms as is characteristic of Se⁴⁺ cations. The Se2 site is coordinated by four O atoms and forms selenate anion SeO ₄ ^2? . The structure is based on selenite-selenate sheets [(UO₂)(SeO₄)(SeO₂OH)]^? linked by the interlayer H₃O^? ions. The sheets are parallel to (101). The structure is compared to that of schmiederite, Pb₂Cu₂(SeO₃)(SeO₄)(OH)₄.     

Crystal chemistry of selenates with mineral-like structures. III. Heteropolyhedral chains in the crystal structure of [Mg(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(SeO<Subscript>4</Subscript>)]<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)

The crystal structure of a new compound [Mg(H₂O)₄(SeO₄)]₂(H₂O) (monoclinic, P2 ₁/a, a = 7.2549(12), b = 20.059(5), c = 10.3934(17) Å, β = 101.989(13), V = 1479.5(5) ų) has been solved by direct methods and refined to R ₁ = 0.059 for 2577 observed reflections with |F _hkl | ≥ 4σ|F _hkl |. The structure consists of [Mg(H₂O)₄(SeO₄)]⁰ chains formed by alternating corner-sharing Mg octahedrons and (SeO₄)^2? tetrahedrons. O atoms of Mg octahedrons that are shared with selenate tetrahedrons are in a trans orientation. The heteropoly-hedral octahedral-tetrahedral chains are parallel to the c axis and undulate within the (010) plane. The adjacent chains are linked by hydrogen bonds involving H₂O molecules not bound with M²⁺ cations.     

Plumboselite, Pb3O2(SeO3), a new oxidation-zone mineral from Tsumeb, Namibia

Plumboselite, ideally Pb₃O₂(SeO₃), is a new selenite (IMA2010?C028) from the Tsumeb mine, Namibia. It occurs as fibres on clausthalite and is also associated with smithsonite, mimetite and vaterite. Plumboselite occurs in subparallel to divergent clusters of thin, flattened, colourless fibres up to 0.3?mm in length, but not exceeding 5???m in width and 2???m in thickness. The fibres are elongated parallel to [001] and flattened on {010}, with {010} the only form observed. The crystals have a dull to adamantine lustre and a white streak. The tenacity is brittle and the Mohs hardness is estimated to be between 2 and 3. Plumboselite crystals are optically biaxial with parallel extinction and are length fast in all orientations. The Gladstone-Dale relationship predicts n _av?=?2.115. The high indices of refraction and small crystal size prevented the determination of other optical properties. The calculated density is 7.814?g/cm³. The empirical formula (based on 5 O atoms) is Pb_2.92Ca_0.01Se_1.03O₅. Plumboselite is orthorhombic, space group Cmc2₁, a?=?10.5384(11), b?=?10.7452(13), c?=?5.7577(7) ?, V?=?651.98(12) ?³ and Z?=?4. The five strongest lines in the powder X-ray diffraction pattern are [d _obs in ?/(I)/hkl]: 3.155/(100)/221; 1.956/(26)/042,402; 2.886/(22)/311,002; 1.713/(21)/223; 2.691/(17)/040. The crystal structure was solved from single-crystal X-ray diffraction data and refined to R ₁?=?0.0371 on the basis of 200 unique reflections with F _o?>?4??F. The structure is based on double [O₂Pb₃] chains of edge-sharing oxo-centered [OPb₄] tetrahedra along c, between which are sited SeO₃ triangles. The two independent Pb²⁺ atoms and the Se⁴⁺ atom have sterochemically active lone electron pairs.     

Refinement of the crystal structure of fornacite using the rietveld method

The crystal structure of fornacite Pb₂(Cu,Fe)[CrO₄(As,P)O₄OH] from the Berezovskii deposit (Central Urals, Russia) was refined by X-ray powder diffraction data using the Rietveld method. Fornacite is monoclinic, space group P2₁/c, the unit cell dimensions are a = 8.09015(12), b = 5.90913(9), c = 17.4839(2) Å, β = 109.99(2), V = 785.5(3) ų, and Z = 4. The structure was refined in the isotropic approximation of the atomic displacement parameters up to R _p = 0.0516, R _wp = 0.0692, R _B = 0.0229, and R _F = 0.0200. The fornacite structure is similar to that of minerals of the brackebuschite-group and consists of heteropolyhedral chains, built by the columns of edge-sharing Cu²⁺O₆ octahedra connected with isolated Cr⁶⁺O₄ and As⁵⁺O₄ tetrahedra. The chains are linked by ninefold Pb²⁺ polyhedra.     

Crystal chemistry of selenates with mineral-like structures: VIII. Butlerite chains in the structure of K(UO<Subscript>2</Subscript>)(SeO<Subscript>4</Subscript>)(OH)(H<Subscript>2</Subscript>O)

A new potassium uranyl selenate compound K(UO₂)(SeO₄)(OH)(H₂O) has been synthesized for the first time using the technique of evaporation from water solution. Its crystal structure has been solved by direct methods (monoclinic, P2₁/c,a = 8.0413(9) Å, b = 8.0362(9) Å, c = 11.6032(14) Å, β = 106.925(2)°, V = 717.34(14) ų) and refined to R ₁ = 0.0319 (wR ₂ = 0.0824) for 1285 reflections with |F ₀| > 4σ _F . The structure consists of [(UO₂(SeO₄)(OH)(H₂O)]^? chains extending along axis b. In the chains, the uranyl pentagonal bipyramids are linked via bridged hydroxyl anions and tetrahedral oxoanions [SeO₄]^2?. Potassium ions are situated between these chains. No chains of that type have been observed in uranyl compounds earlier, but they had been detected in the structures of butlerite, parabutlerite, uklonskovite, fibroferrite, and a number of synthetic compounds.     

Solubility and equilibrium constants of lead in carbonate solutions (25°C,I = 0.3 mol dm−3)

The solubilities of PbCO₃(s), 2PbCO₂·Pb(OH)₂(s), and of 3PbCO₃ 2Pb(OH)₂(s) have been studied at 25°C ± 0.1°C in solutions of the constant ionic strength I = 0.3 mol/dm³, consisting primarily of sodium perchlorate. A few experiments with hydrocerussite were performed in solutions of 0.1 M KNO₃. The concentrations of lead and hydrogen ions have been determined in solution in contact with the solid phase. From experimental data the following values for equilibrium constants are obtained: log [Pb²⁺]·pCO₂·[H⁺]^?2 = 5.20log [Pb²⁺]·pCO^0.67₂·[H⁺]^?2 = 6.80log [Pb₂₊]³·[CO^2?₃]²·[OH^?]² = ?44.08 (and ?44.8 forI = 0.1 M)log [PbCO⁰₃]·[Pb²⁺]^?1·[CO^2?₃]^?1 = 5.40log [Pb(CO₃)^2?₂]·[Pb₂₊]^?1·[CO^2?₃]^?2 = 8.86 The data indicate that hydrocerussite is the most stable solid phase in natural waters. Comparison with the literature and needs for further research are also presented.     

Crystal chemistry of selenates with mineral-like structures. VI. Hydrogen bonds in the crystal structure of [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2]

The crystal structure of a new compound, [(H₅O₂)(H₃O)(H₂O)][(UO₂)(SeO₄)₂] (monoclinic, P2₁/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) Å, β = 103.880(13)°, V = 1182.4(3) ų), has been solved by direct methods and refined to R ₁ = 0.036. The structure is based on [(UO₂)(SeO₄)₂]^2? sheet complexes formed by corner-shared UO₇ pentagonal bipyramids and SeO₄ tetrahedrons. The sheets are parallel to the ( $ \bar 1 The crystal structure of a new compound, [(H₅O₂)(H₃O)(H₂O)][(UO₂)(SeO₄)₂] (monoclinic, P2₁/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) ?, β = 103.880(13)°, V = 1182.4(3) ?³), has been solved by direct methods and refined to R ₁ = 0.036. The structure is based on [(UO₂)(SeO₄)₂]²⁻ sheet complexes formed by corner-shared UO₇ pentagonal bipyramids and SeO₄ tetrahedrons. The sheets are parallel to the (01) plane. Oxonium ions and water molecules forming [(H₃O)·(H₂O)·(H₅O₂)]²⁺ complexes are interlayer. Among minerals, the existence of (H₅O₂)⁺ has been unambiguously confirmed only in rhomboclase, (H₅O₂)⁺[Fe₂(SO₄)₂(H₂O)₂]. Original Russian Text ? S.V. Krivovichev, 2008, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2008, No. 2, pp. 123–130.     

The crystal structure of alumoklyuchevskite,K<Subscript>3</Subscript>Cu<Subscript>3</Subscript>AlO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript>

The crystal structure of the unstable mineral alumoklyuchevskite K₃Cu₃AlO₂(SO₄)₄ [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R ₁ = 0.131 for 2450 unique reflections with F ≥ 4σF _hkl. The structure is based on oxocentered tetrahedrons (OAlCu ₃ ⁷⁺ ) linked into chains via edges. Each chain is surrounded by SO₄ tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K₃Cu₃Fe³⁺O₂(SO₄)₄; and piypite, K₂Cu₂O(SO₄)₂.     

Ivsite,Na<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>, a new mineral from volcanic exhalations of fumaroles of the Fissure Tolbachik Eruption of the 50th Anniversary of the Institute of Volcanology and Seismology,Far East Branch,Russian Academy of Sciences

Fine-granular (<0.1 mm) flattened colorless transparent crystals of ivsite form white aggregates. The empirical formula (Na_2.793Cu_0.056)_2.849HS_2.016O₈ is close to the ideal Na₃H(SO₄)₂. The structure was refined up to R = 0.040. Ivsite has a monoclinic symmetry, P2₁/c, a = 8.655(1) Å, b = 9.652(1) Å, c = 9.147(1) Å, β = 108.76(1)°, V = 723.61(1) ų, Z = 4. Na atoms occur at six- and seven-fold sites (NaO₆ and NaO₇); S atoms, in isolated SO₄ tetrahedrons; these polyhedrons form a three-dimensional framework. The diagnostic lines of powder diffraction patterns (d[Å]–I–hkl) are 4.010–53–12-1, 3.949–87–012, 3.768–100–210, 3.610–21–20-2, 3.022–22–031, 2.891–42–22-2, 2.764–49–31-1, and 2.732–70–13-1.     

Crystal chemistry of selenates with mineral-like structures. IV. Crystal structure of Zn(SeO<Subscript>4</Subscript>)(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>, a new compound with a mixed framework of the variscite type

The crystal structure of a new compound Zn(SeO₄)(H₂O)₂ (orthorhombic, Pbca, a = 9.0411(13), b = 10.246(2), c = 10.3318(15) Å, V = 957.1(3) ų) has been solved by direct methods and refined to R ₁ = 0.033 on the basis of 1076 observed reflections with |F _hkl | ≥ 4σ|F _hkl |. The structure contains one independent Zn²⁺ cation coordinated by two water molecules and four oxygen atoms of selenate group. The only independent (SeO₄)^2? tetrahedral oxoanion is tetradentate, sharing its corners with four adjacent [Zn²⁺O₂(H₂O₄)]²⁺ octahedrons. The structure can be described as consisting of heteropolyhedral sheets parallel to the (001) plane and linked together into a three-dimensional network. The compound belongs to the variscite structure type and is the first structurally characterized selenate of this group.     

High-pressure perovskites on the join CaTiO3-FeTiO3

An exploratory high-pressure study of the join CaTiO₃-FeTiO₃ has uncovered two intermediate perovskites with the compositions CaFe₃Ti₄O₁₂ and CaFeTi₂O₆. These perovskites have ordering of Ca²⁺ and Fe²⁺ on the A sites. Both of these perovskites are unusual in that the A sites containing Fe²⁺ are either square planar or tetrahedral, due to the particular tilt geometries of the octahedral frameworks. For CaFe₃Ti₄O₁₂, the structure has been refined from a powder using the Rietveld technique. This compound is a cubic double perovskite (SG Im $\bar 3$ , a = 7.4672 Å), isostructural with NaMn₇O₁₂. Fe²⁺ is in a square-planar A site (similar to Mn³⁺ in NaMn₇O₁₂) with Fe-O = 2.042(3) Å, with distant second neighbors in a rectangle at Fe-O = 2.780(6) Å. Calcium is in a distorted icosahedron with Ca-O =2.635(5) Å. CaFeTi₂O₆ crystallizes in a unique tetragonal double perovskite structure (SG P4₂/nmc, a = 7.5157(2), c = 7.5548(2)), with A-site iron in square-planar (Fe-O = 2.097(2) Å) and tetrahedral (Fe-O = 2.084(2) Å) coordination, again with distant second neighbor oxygens near 2.8 Å. Rietveld refinement was also performed for the previously known perovskite-related form of FeTiO₃ recovered from high pressure (lithium niobate type). This compound is trigonal R3c, with a = 5.1233(1) and c = 13.7602(2). The ordered perovskites appear to be stable at 1215 GPa and CaFe₃Ti₄O₁₂ is found as low as 5 GPa. Thus these perovskites may be important to upper mantle mineralogy, particularly in kimberlites. These compounds are the first known quenchable perovskites with large amounts of A-site ferrous iron, and add greatly to the known occurrences of ferrous iron in perovskites.     

Ultraviolet spectroscopic evidence for polynuclear lead (II) complexes in synthetic Red Sea brines

The Pb complexes in a synthetic brine solution with a composition comparable to that of the Atlantis II Deep 56°C Brine have been identified by UV absorption spectroscopy. The important species at ambient temperatures are PbCl^2?₄ and Pb(OH)BrCl₂^2?. At 56°C the former complex partially dissociates to form lower chloro complexes while the latter undergoes halide exchange reactions forming Pb(OH)Br₂Cl^2?. Evidence has also been found for the following polymeric lead hydroxo complexes: Pb₄(OH)₄Cl₄, Pb₆(OH)₃Cl₁₂ and Pb₃(OH)₁₂Cl₄. The predominant polynuclear complex in the brine, Pb₄(OH)₄Cl₄, tends to dissociate at 56°C to form lower polymeric species. The formulation of the limiting binary chloro complex as PbCl₄^2? rather than PbCl₆^4? is supported by the reflectance spectrum of Cs₄PbCl₆.     

The Crystal Structure of Lisiguangite

The crystal structure of lisiguangite,CuPtBiS3,from Yanshan mountains,Chengde Prefecture,Hebei Province,China has been determined by single crystal X-ray diffraction.It belongs to orthorhombic space group P2_12_12_1 with a = 7.7372(15) A,b = 12.844(3) A,c = 4.9062(10) A,V =487.57(17) A~3,Z = 4.The final full-matric least-square refinement on F2 converged with Rl = 0.0495 and wR2 = 0.0992 for 704 observed reflections[I≥2σ(I)].Lisiguangite is the isomorph of known CuNiSbS_3 and CuNiBiS_3· Pt~(2+) and Bi~(3+) have the distorted octahedral coordination enviroments composed of two metal and four S and Cu~(+2) has a distorted tetrahedral coordination environment with four S atoms.Each S atom is surrounded by four metals to give a tetrahedral environment.The crystal structure is a complex 3 dimensional network.     

A quantum chemical investigation of the oxidation and dissolution mechanisms of Galena

The oxidation and dissolution mechanisms of galena (PbS) remain uncertain with a wide variety of possible mechanisms having been proposed in the literature. In this study, the thermodynamic viability of some possible mechanisms has been tested using semi-empirical quantum chemical calculations applied to a perfect (001) galena surface.The adsorption of O₂ and H₂O has been examined in both the gaseous and aqueous environments. In agreement with previous ab initio quantum chemical calculations, the surface induced dissociation of H₂O in either environment was found to be energetically unfavourable. However, the dissociative adsorption of O₂ was found to be possible and resulted in two O atoms bonded to diagonally adjacent S atoms with the O atoms oriented along the diagonal.The adsorption of H⁺ and possible subsequent dissolution mechanisms have been examined in the aqueous environment. An anaerobic mechanism leading to the dissolution of hydroxylated Pb²⁺ was identified. The mechanism involves the protonation of 3 surface S atoms surrounding a central surface Pb atom followed by substitution of this Pb by a further H⁺. The activation energy of this mechanism was estimated to be ≈100 kJ mol⁻¹. Pb²⁺ dissolution could only occur with vacancy stabilisation by a H⁺. The analogous mechanisms for systems comprising H⁺ adsorbed on either 2 or 4 of the S atoms surrounding a central surface Pb were not found to be energetically viable. Subsequent dissolution of one of the protonated S atoms to form H₂S_(g) was not found to be possible thus indicating the likely formation of a Pb-deficient S-rich surface under acidic anaerobic conditions.Acidic aerobic dissolution has also been examined. Congruent dissolution to form H₂SO₄ and Pb²⁺•6H₂O is energetically viable. The dissolution of one of the protonated S atoms neighbouring the Pb²⁺ vacancy, resulting from the anaerobic dissolution, to form H₂SO₄, is also possible.     

High pressure single-crystal synthesis, structure and compressibility of the garnet Mn2+ 3Mn3+ 2[SiO4]3

Single crystals of the garnet Mn²⁺ ₃Mn³⁺ ₂[SiO₄]₃ and coesite were synthesised from MnO₂-SiO₂ oxide mixtures at 1000°C and 9 GPa in a multianvil press. The crystal structure of the garnet [space group Ia3¯d, a=11.801(2) Å] was refined at room temperature and 100 K from single-crystal X-ray data to R1=2.36% and R1=2.71%, respectively. In contrast to tetragonal Ca₃Mn³⁺ ₂[GeO₄]₃ (space group I4₁/a), the high-pressure garnet is cubic and does not display an ordered Jahn-Teller distortion of octahedral Mn³⁺. A disordered Jahn-Teller distortion either dynamic or static is evidenced by unusual high anisotropic displacement parameters. The room temperature structure is characterised by following bond lengths: Si-O=1.636(4) Å (tetrahedron), Mn³⁺-O=1.995 (4) Å (octahedron), Mn²⁺-O=2.280(5) and 2.409(4) Å (dodecahedron). The cubic structure was preserved upon cooling to 100 K [a=11.788(2) Å] and upon compressing up to 11.8 GPa in a diamond-anvil cell. Pressure variation of the unit cell parameter expressed by a third-order Birch-Murnaghan equation of state led to a bulk modulus K ₀=151.6(8) GPa and its pressure derivatives K′=6.38(19). The peak positions of the Raman spectrum recorded for Mn²⁺ ₃Mn³⁺ ₂[SiO₄]₃ were assigned based on a calderite Mn²⁺ ₃Fe³⁺ ₂[SiO₄]₃ model extrapolated from andradite and grossular literature data.     

Crystal chemistry of selenates with mineral-like structures: V. Crystal structures of (H3O)2[(UO2)(SeO4)2(H2O)](H2O)2 and (H3O)2[(UO2)(SeO4)2(H2O)](H2O), new compounds with rhomboclase and goldichite topology

The crystal structures of two new compounds (H₃O)₂[(UO₂)(SeO₄)₂(H₂O)](H₂O)₂ (1, orthorhombic, Pnma, a = 14.0328(18), b = 11.6412(13), c = 8.2146(13) Å, V = 134.9(3) ų) and (H₃O)₂[(UO₂)(SeO₄)₂(H₂O)](H₂O) (2, monoclinic, P2₁/c, a = 7.8670(12), b = 7.5357(7), c = 21.386(3) Å, β = 101.484(12)°, V = 1242.5(3) ų) have been solved by direct methods and refined to R ₁ = 0.076 and 0.080, respectively. The structures of both compounds contain sheet complexes [(UO₂)(SeO₄)₂]^2? formed by cornershared [(UO₂)O₄(H₂O)] bipyramids and SeO₄ tetrahedrons. The sheets are parallel to the (100) plane in structure 1 and to (?102) in structure 2. The [(UO₂)(SeO₄)₂(H₂O)]^2? layers are linked by hydrogen bonds via interlayer groups H₂O and H₃O⁺. The sheet topologies in structures 1 and 2 are different and correspond to the topologies of octahedral and tetrahedral complexes in rhomboclase (H₂O₂)⁺[Fe(SO₄)₂(H₂O)₂] and goldichite K[Fe(SO₄)₂(H₂O)₂](H₂O)₂, respectively.     

Crystal data for some sodium rare earth silicates

Single crystal synthesis, X-ray powder diffraction data, and electron microprobe data are given for some Na rare earth silicates of the types NaMSiO₄, Na₃MSi₂O₇, Na₃MSi₃O₉, and Na₅MSi₄O₁₂. NaYSiO₄ is orthorhombic with SG Pbn2₁, a=5.132, b=11.156, anc c=6.405 Å. NaGdSiO₄ is tetragonal with SG I4 or I \(\bar 4\) with a=11.743 and c=5.444 Å. A second form of NaGdSiO₄ is orthorhombic with SG P2₁ nb or Pmmb, a=9.179, b=27.29, and c=5.472 Å. Na₃YSi₂O₇ is hexagonal with a=9.416 and c=13.776 Å. Na₃YSi₃O₉ is orthorhombic with a=15.215, b=15.126, and c=15.036 Å. Na ion conductivities of Na₃YSi₂O₇ and Na₃YSi₃O₉ at 300° C of 5×10^?6 (Θ-cm)^?1 and 6×10^?6 (Θ-cm)^?1, respectively, are substantially less than that for Na₆YSi₄O₁₂, 1×10^?1 (Θ-cm)^?1.     

The crystal structure of arsentsumebite, Pb2Cu[(As, S)O4]2(OH)

Summary The crystal structure of arsentsumebite, ideally, Pb₂Cu[(As, S)O₄]₂(OH), monoclinic, space group P2₁/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?³, Z = 2, d_calc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb₂ Me(XO₄)₂(Z) where Me = Cu²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Fe³⁺; X = S, Cr, V, As, P; Z = OH, H₂O. Members of this group include tsumebite, Pb₂Cu(SO₄)(PO₄)(OH), vauquelinite, Pb₂Cu(CrO₄)(PO₄)(OH), brackebuschite, Pb₂ (Mn, Fe)(VO₄)₂(OH), arsenbracke buschite, Pb₂(Fe, Zn)(AsO₄)₂(OH, H₂O), fornacite, Pb₂Cu(AsO₄)(CrO₄)(OH), and feinglosite, Pb₂(Zn, Fe)[(As, S)O₄]₂(H₂O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO₆ octahedra and M–T represents corner sharing between octahedra and XO₄ tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)₂(AsO₄)₂ (OH, H₂O)₂ and tsumcorite-group minerals Me(1)Me(2)₂(XO₄)₂(OH, H₂O)₂. Received June 24, 2000; revised version accepted February 8, 2001     

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds

The crystal structure of ilinskite, NaCu₅O₂(SeO₃)₂Cl₃, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R ₁?=?0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a?=?17.769(7), b?=?6.448(3), c?=?10.522(4) Å, V?=?1205.6(8) ų, Z?=?4. The The CuO_mCl_n coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu₄ and O2Cu₄ tetrahedra share common Cu atoms to form [O₂Cu₅]⁶⁺ sheets. The SeO₃ groups and Cl atoms are adjacent to the [O₂Cu₅]⁶⁺ sheets to form complex layers parallel to (100). The Na⁺ cations are located in between the layers. A review of mixed-ligand CuO_mCl_n coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations.