The Canadian Mineralogist; June 2007; v. 45; no. 3;
p. 445-449; DOI: 10.2113/gscanmin.45.3.445
© 2007 Mineralogical Association of Canada
THE CRYSTAL STRUCTURE OF LENINGRADITE, PbCu3(VO4)2Cl2
Oleg I. Siidra1,
Sergey V. Krivovichev1,
,
Thomas Armbruster2,
Stanislav K. Filatov3 and
Igor V. Pekov4
1 Department of Crystallography, St. Petersburg State University, University Emb. 7/9, St. Petersburg, 199034, Russia
2 Laboratorium für chemische und mineralogische Kristallographie, Universität Bern, Freiestrasse 3, CH–3102 Bern, Switzerland
3 Department of Crystallography, St. Petersburg State University, University Emb. 7/9, St. Petersburg, 199034, Russia
4 Department of Mineralogy, Moscow State University, Vorob’evy Gory, GSP-2, Moscow,119992, Russia
E-mail address: skrivovi{at}mail.ru
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ABSTRACT
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The crystal structure of leningradite, PbCu3(VO4)2Cl2, a mineral from the fumaroles of the Great fissure Tolbachik eruption, located in the Kamchatka Peninsula, Russia, has been solved by direct methods from single-crystal X-ray-diffraction data and refined to R1 = 0.047 for 1235 unique reflections with |Fo| 
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F. The mineral is orthorhombic, space group Ibam, a 9.005(7), b 11.046(9), c 9.349(7) Å, V 929.9(13) Å3, Z = 4. The structure contains one symmetrically unique Pb position coordinated by four O and four Cl atoms. The V5+ cation is tetrahedrally coordinated by four O atoms. There are two symmetrically independent Cu sites in distorted octahedral [4O + 2Cl] coordination. The structure can be described in terms of fundamental chains consisting of corner-sharing CuO4 squares and VO4 tetrahedra. The chains are parallel to the c axis and are linked into a three-dimensional framework with elliptical channels occupied by the Pb2+ cations and Cl– anions.
Keywords: leningradite, lead copper vanadate chloride, crystal structure, Kamchatka Peninsula, Russia.
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INTRODUCTION
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Leningradite, PbCu3(VO4)2Cl2, is a rare lead–copper vanadate chloride first described by Vergasova et al. (1990) from fumaroles of the Great fissure Tolbachik eruption (GFTE) in the Kamchatka Peninsula, Russia (Fedotov 1984). Crystals of the mineral less than 0.3 mm across occur in fumarole incrustations. Leningradite was found in close association with anglesite, hematite, P-bearing lammerite, Cu3[(As,P)O4]2 (Filatov et al. 1984), and tolbachite, CuCl2 (Vergasova & Filatov 1983). The mineral was named in honor of the city of Leningrad, where many studies of Tolbachik minerals have been undertaken since 1978. Though the city name was changed back to Saint Petersburg, the mineral name remains intact.
Our aim in this paper is to report results of the first determination of the structure of leningradite.
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EXPERIMENTAL
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The crystal of leningradite selected for data collection was mounted on a Bruker three-circle CCD-based X-ray diffractometer operated at 50 kV and 40 mA. More than a hemisphere of three-dimensional data was collected using monochromatic MoK
X-radiation, with frame widths of 0.3° in 
, and with a 40 s count for each frame. The unit-cell parameters (Table 1) were refined using least-squares techniques. The unit-cell parameters determined are in good agreement with those reported previously (Vergasova et al. 1990). The intensity data were integrated and corrected for Lorentz, polarization, and background effects using the Bruker program SAINT. A semi-empirical absorption-correction was made using 686 intense reflections. The crystal was modeled as an (100) plate, and reflections with plate-glancing angle of less than 3° were discarded from the dataset, which lowered the Razimuthal from 11.9 to 3.5%.
The Bruker SHELXTL Version 5 system of programs was used for determination and refinement of the crystal structure. The structure was solved by direct methods and refined to an R1 value of 0.025, calculated for the 538 unique observed (|Fo| 4F) reflections. Final coordinates and displacement parameters of the atoms are given in Table 2, selected interatomic distances are in Table 3. Table 4 provides a bond-valence analysis calculated using bond-valence parameters taken from Krivovichev & Brown (2001) for the Pb2+–O bonds and from Brese & O’Keeffe (1991) for other bonds. Note the low bond-valence sum for the Cl site (0.55 valence units), which is typical of anhydrous Cl-containing minerals of fumarolic origin. Calculated and observed structure-factors are available from the Depository of Unpublished Data on the MAC website [document Leningradite CM45_445].
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RESULTS
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Cation coordination
The structure of leningradite contains one symmetrically unique Pb position, located on a twofold axis. The Pb atom is coordinated by four O atoms and four Cl– anions (Fig. 1). The coordination of the Pb2+ cation is rather symmetrical, which is not typical for Pb oxide chlorides (Krivovichev & Burns 2001, 2002, Pasero & Vacchiano 2000, Keller et al. 2001).
The Cu(1) and Cu(2) sites are coordinated by four O2– anions at the vertices of planar squares and two apical Cl– anions, so that elongate [CuO4Cl2] octahedra are formed (Fig. 1). Similar coordinations are typical for the mixed-ligand Cu2+ coordination polyhedra and have been observed, for example, at the Cu(1) site in allochalcoselite (Krivovichev et al. 2006), the Cu(2) site in georgbokiite (Krivovichev et al. 1999) and the Cu(5) site in chloromenite (Krivovichev et al. 1998). The octahedral [CuO4Cl2] coordinations are distorted owing to the Jahn–Teller effect (Jahn & Teller 1937, Burns & Hawthorne 1995a, b).
There is one symmetrically independent V5+ cation in the structure, which is coordinated by four O atoms. The configuration and geometry of the VO4 tetrahedron are characteristic of the structures of vanadates.
Description of the structure
The structure of leningradite is shown in Figure 2a. It can be described in terms of fundamental chains consisting of Cu2+O4 squares and V5+O4 tetrahedra. The chains are parallel to the c axis and are of two types. The first chain, C', is formed by the Cu(1)O4 squares and VO4 tetrahedra, whereas the second, C'', consists of the Cu(2)O4 squares and VO4 tetrahedra. The chains are arranged in such a way that a three-dimensional copper vanadate framework is formed (Fig. 2b). The framework has large elliptical channels occupied by the Pb2+ cations and Cl– anions.
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FIG. 2. The crystal structure of leningradite projected along the c axis. The three-dimensional metal oxide framework consisting of CuO4 squares and VO4 tetrahedra is highlighted; sections of the C' and C'' chains are shown (a). C' (b) and C'' (c) chains of CuO4 squares and VO4 tetrahedra are projected along the c and b axes, respectively.
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DISCUSSION
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The structure of leningradite provides another example of a fumarolic mineral based upon a three-dimensional metal oxide framework (copper vanadate in leningradite) with channels occupied by metal chloride species (PbCl2 in leningradite). In a similar way, the structure of allochalcoselite, Cu+Cu2+5PbO2(SeO3)2Cl5, consists of porous metal oxide layers with large cavities occupied by the [Cu+Cl2] – anions (Krivovichev et al. 2006). This "host–guest" character of some of fumarolic minerals may be the result of their formation from volcanic gases. The metal oxide species tend to organize in such a structure that allows inclusion of metal chloride species into a basic oxide matrix. It is noteworthy that in leningradite, interactions of Pb2+ and Cl– ions are much stronger than the Cu2+–Cl– interactions, which are rather weak in comparison to the Cu2+–O2– bonds.
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AKNOWLEDGEMENTS
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We are grateful to Paul Keller, an anonymous referee, and Robert F. Martin for useful comments on the manuscript. Thanks are due to the Alexander von Humboldt Stiftung and the Swiss Science Foundation (grant on Crystal Chemistry of Minerals to T.A.). The Russian group thanks the Ministry of Science and Education (grant #RNP 2.1.1.3077) and the Federal Agency on Education (SPbSU innovational project "Innovational educational environment in the classic University") for financial support.
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REFERENCES
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Received March 10, 2006
,revised manuscript accepted October 15, 2006.
Copyright © 2008 by Mineralogical Association of Canada
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Abstract
Introduction
