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Acta Cryst. (2012). E68, i9-i10    [ doi:10.1107/S1600536811054286 ]

Lotharmeyerite, Ca(Zn,Mn)2(AsO4)2(H2O,OH)2

Y. W. Yang, S. H. Evans, R. T. Downs and H. Yang

Abstract top

Lotharmeyerite, calcium bis­(zinc/manganese) bis­(arsenate) bis­(hydroxide/hydrate), Ca(Zn,Mn3+)2(AsO4)2(H2O,OH)2, is a member of the natrochalcite group of minerals, which are characterized by the general formula AM2(XO4)2(H2O,OH)2, where A may be occupied by Pb2+, Ca2+, Na+, and Bi3+, M by Fe3+, Mn3+, Cu2+, Zn2+, Co2+, Ni2+, Al3+, and Mg2+, and X by PV, AsV, VV, and SVI. The minerals in the group display either monoclinic or triclinic symmetry, depending on the ordering of chemical components in the M site. Based on single-crystal X-ray diffraction data of a sample from the type locality, Mapimi, Durango, Mexico, this study presents the first structure determination of lotharmeyerite. Lotharmeyerite is isostructural with natrochalcite and tsumcorite. The structure is composed of rutile-type chains of edge-shared MO6 octa­hedra (site symmetry \overline1) extending along [010], which are inter­connected by XO4 tetra­hedra (site symmetry 2) and hydrogen bonds to form [M2(XO4)2(OH,H2O)2] sheets parallel to (001). These sheets are linked by the larger A cations (site symmetry 2/m), as well as by hydrogen bonds. Bond-valence sums for the M cation, calculated with the parameters for Mn3+ and Mn2+ are 2.72 and 2.94 v.u., respectively, consistent with the occupation of the M site by Mn3+. Two distinct hydrogen bonds are present, one with O...O = 2.610 (4) Å and the other O...O = 2.595 (3) Å. One of the H-atom positions is disordered over two sites with 50% occupancy, in agreement with observations for other natrochalcite-type minerals, such as natrochalcite and tsumcorite.

Comment top

The natrochalcite group of minerals is characterized by the general formula AM2(XO4)2(H2O,OH)2, where currently it is observed that A = Pb, Ca, Na, and Bi, M = Fe3+, Mn3+, Cu2+, Zn2+, Co2+, Ni2+, Al3+, and Mg2+, and X = P5+, As5+, V5+, and S6+ (Krause et al., 1998, 2001; Brugger et al., 2000; 2002). The majority of minerals in this group crystallize in monoclinic C2/m symmetry and a few in triclinic P1 symmetry. In particular, monoclinic natrochalcite-group minerals with A = Ca and X = As can be further assigned to the lotharmeyerite subgroup, which includes six members: lotharmeyerite (M = Zn) (Dunn, 1983; Kampf et al., 1984; Brugger et al., 2002), ferrilotharmeyerite (M = Fe3+) (Ansell et al., 1992; Krause et al., 1998), cobaltlotharmeyerite (M = Co) (Krause et al., 1999), nickellotharmeyerite (M = Ni) (Krause et al., 2001), manganlotharmeyerite (M = Mn3+) (Brugger et al., 2002), and cabalzarite (M = Mg) (Brugger et al., 2000).

Lotharmeyerite from the Ojuela mine, Mapimi, Mexico was first described by Dunn (1983) with the chemical formula CaZnMn3+(AsO4)2(OH).2H2O. This formula, however, was revised to CaZnMn3+(AsO3OH)2(OH)3 by Kampf et al. (1984) on the basis of the infrared spectroscopic data measured on the specimen from the type locality. Unfortunately, due to the very small crystals in drusy growths, which gave somewhat diffuse and split spots on precession films, Kampf et al. (1984) only obtained the unit-cell parameters for this mineral: a = 9.066 (4), b = 6.276 (2), c = 7.408 (2) Å, β = 116.16 (3)°, V = 378.3 (4) Å3. From the structure refinement of ferrilotharmeyerite, the Fe3+ analogue of lotharmeyerite, Krause et al. (1998) proposed a new chemical formula for lotharmeyerite as Ca(Mn3+,Zn)2(AsO4)2(OH,H2O)2. Yet, by defining lotharmeyerite and manganlotharmeyerite to represent the Zn- and Mn-dominant endmembers of the lotharmeyerite subgroup, Brugger et al. (2002) made another revision of the chemical formula of lotharmeyerite to Ca(Zn,Mn3+)2(AsO4)2(H2O,OH)2 based on a new chemical analysis from a lotharmeyerite crystal from the type locality. Thus far, the crystal structures of all minerals, except lotharmeyerite, in the lotharmeyerite subgroup have been determined. This study reports the first structure refinement of lotharmeyerite from the type locality by means of single-crystal X-ray diffraction data.

Lotharmeyerite is isotypic with other monoclinic natrochalcite-group minerals (e.g., Tillmanns & Gebert, 1973; Chevrier et al., 1993; Krause et al., 1998, 1999, 2001; Brugger et al., 2000; 2002). Its structure is composed of rutile-type chains of edge-shared MO6 octahedra extending along [010], which are interconnected by XO4 tetrahedra and hydrogen bonds to form [M2(XO4)2(OH,H2O)2] sheets parallel to (001) (Fig. 1). These sheets are linked together by the larger A cations, as well as hydrogen bonds. Bond-valence sums for the M cation, calculated with the parameters for Mn3+ and Mn2+ (Brese & O'Keeffe, 1991), are 2.72 and 2.94 v.u., respectively, consistent with the occupation of the M site by Mn3+ (Brugger et al. 2002).

The presence of protonated AsO3OH groups was postulated for lotharmeyerite by Kampf et al. (1984) from the infrared spectral measurement and by analogy also for ferrilotharmeyerite by Ansell et al. (1992). According to Ferraris & Ivaldi (1984), a protonated AsO3OH tetrahedron is generally distorted with the As—OH bond distance noticeably longer than the other three As—O bond distances. This appears to be the case for all monoclinic arsenate minerals in the natrochalcite-group, such as ferrilotharmeyerite, tsumcorite, mounanaite, gartrellite (Krause et al., 1998), cobaltlotharmeyerite (Krause et al. 1999), nickellotharmeyerite (Krause et al., 2001), and manganlotharmeyerite (Brugger et al., 2002). In all these minerals, the As—O2 bond distance is the longest within the AsO4 group. However, from the crystal-chemical considerations, Krause et al. (1998) ruled out the likelihood for O2 being protonated, due to its coordination by one A, two M, and one X cations, which gives rise to a nearly ideal bond-valence sum (2.0 v.u.) for O2. Moreover, Krause et al. (1998) argued that a protonated AsO3OH tetrahedron, in general, exhibits a decrease in the OH—As—O angles and an increase in the O—As—O angles, but they were unable to verify such a variation for the natrochalcite-group minerals. Our refinement on lotharmeyerite lends further support to the conclusion by Krause et al. (1998) that there is no evidence for the presence of the HAsO4 group in this structure. Specifically, the As—O bond lengths in lotharmeyerite vary from 1.671 (2) to 1.698 (2) Å, with an average of 1.688 Å. No outstanding long As—O bond is observed. Considering the experimental uncertainties, the difference between the longest As—O2 and next longest As—O3 bond distances is essentially insignificant [1.698 (2) Å versus. 1.692 (1) Å]. Furthermore, the O2—As—O3 and O2—As—O4 angles are 111.60 (6) and 101.87 (11)°, respectively, which are compared to the O3—As—O3 and O3—As—O4 angles of 108.93 (10) and 111.37 (7)°, respectively. The calculated bond-valence sum for O2 in lotharmeyerite is 1.94 v.u.

Two distinct hydrogen bonds are present in lotharmeyerite, one between symmetry related O1 atoms [(x, y, z) and (1-z, y, 1-z)] and the other between O1 and O4 [at (x, y, z) and (0.5-x, 0.5+y, -z) respectively]. However, our refined H1 position is not half way between the two O1 atoms, indicating a non-centric, i.e. split position of the H1 atom. Similar results have been observed in other natrochalcite-type minerals, such as natrochalcite NaCu2(SO4)2(OH).H2O (Chevrier et al., 1993), cabalzerite CaMg2(AsO4)2.2H2O (Brugger et al. 2000), and synthetic Co- and Ni-analogs of natrochalcite (Krickl & Wildner, 2007). Such a hydrogen bonding scheme has also been discussed in detail by Tillmanns & Gebert (1973), Krause et al. (1998, 1999, 2001), and Brugger et al. (2002).

Related literature top

For lotharmeyerite, see: Dunn (1983); Kampf et al. (1984); Brugger et al. (2002). For related minerals in the natrochalcite group, see: Tillmanns & Gebert (1973); Chevrier et al. (1993); Ansell et al. (1992); Krause et al. (1998, 1999, 2001); Brugger et al. (2000, 2002). Parameters for bond-valence calculations were taken from Brese & O'Keeffe (1991). For additional information on related minerals, see: Ferraris & Ivaldi (1984); Krickl & Wildner (2007).

Experimental top

The lotharmeyerite crystal used in this study is from the type locality Mapimi, Durango, Mexico and is in the collection of the RRUFF project (deposition No. R060682; The experimental chemical composition, Ca0.99(Zn1.01Mn3+0.85)(As1.03O4)2(H2O,OH)2, was determined with a CAMECA SX100 electron microprobe at the conditions of 15 kV, 10 nA, and a beam size of 5 µm (http//

Refinement top

A further empirical absorption correction for the X-ray intensity data was made using the program XABS2 (Parkin et al., 1995), which significantly flattened the residual difference map features from 1.425 and -0.847 eÅ-3 to 0.808 and -0.767 eÅ-3 and lowered R1 to 1.88% from 2.24%. Two H atoms were located near O1 from difference Fourier syntheses and their positions refined freely with a fixed isotropic displacement (Uiso = 0.04). The occupancy of the H1 site was fixed to 50% because of its splitting. During the structure refinements, for simplicity, we assumed the full occupations of the three non-hydrogen cation sites A, M, and X by Ca, (Zn + Mn), and As, respectively, with the Zn/Mn ratio refined. The resultant structural formula is Ca1.00(Zn1.02Mn3+0.98)(As1.00O4)2[(OH)]. The amount of OH is given for the charge balance. The highest residual peak in the difference Fourier maps was located at (0.3600, 0, 0.2766), 0.82 Å from O2, and the deepest hole at (0.4798, 0, 0.6433), 1.10 Å from As1.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. Crystal structure of lotharmeyerite. The large green and small blue spheres represent Ca and H atoms, respectively. The yellow octahedra and red tetrahedra represent MO4(H2O,OH)2 and AsO4 groups.
calcium bis(zinc/manganese) bis(arsenate) bis(hydroxide/hydrate) top
Crystal data top
Ca(Zn·Mn)2(AsO4)2(H2O·OH)2F(000) = 448
Mr = 474.14Dx = 4.186 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yCell parameters from 1568 reflections
a = 9.0727 (6) Åθ = 4.0–29.5°
b = 6.2530 (4) ŵ = 14.38 mm1
c = 7.4150 (5) ÅT = 293 K
β = 116.739 (4)°Cube, brown
V = 375.68 (4) Å30.06 × 0.05 × 0.05 mm
Z = 2
Data collection top
Bruker APEXII CCD area-detector
739 independent reflections
Radiation source: fine-focus sealed tube659 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.022
ϕ and ω scanθmax = 32.6°, θmin = 3.1°
Absorption correction: multi-scan
[SADABS (Sheldrick, 2005) and XABS2 (Parkin et al., 1995)]
h = 1313
Tmin = 0.477, Tmax = 0.532k = 89
2512 measured reflectionsl = 118
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.019All H-atom parameters refined
wR(F2) = 0.045 w = 1/[σ2(Fo2) + (0.030P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.91(Δ/σ)max < 0.001
739 reflectionsΔρmax = 0.81 e Å3
49 parametersΔρmin = 0.77 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0
Crystal data top
Ca(Zn·Mn)2(AsO4)2(H2O·OH)2V = 375.68 (4) Å3
Mr = 474.14Z = 2
Monoclinic, C2/mMo Kα radiation
a = 9.0727 (6) ŵ = 14.38 mm1
b = 6.2530 (4) ÅT = 293 K
c = 7.4150 (5) Å0.06 × 0.05 × 0.05 mm
β = 116.739 (4)°
Data collection top
Bruker APEXII CCD area-detector
739 independent reflections
Absorption correction: multi-scan
[SADABS (Sheldrick, 2005) and XABS2 (Parkin et al., 1995)]
659 reflections with I > 2σ(I)
Tmin = 0.477, Tmax = 0.532Rint = 0.022
2512 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0190 restraints
wR(F2) = 0.045All H-atom parameters refined
S = 0.91Δρmax = 0.81 e Å3
739 reflectionsΔρmin = 0.77 e Å3
49 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ca10.00000.00000.00000.01360 (16)
Zn10.25000.25000.50000.00936 (11)0.512 (8)
Mn10.25000.25000.50000.00936 (11)0.488 (8)
As10.41579 (3)0.00000.20474 (4)0.00864 (9)
O10.3390 (3)0.50000.4132 (3)0.0140 (4)
O20.3182 (3)0.00000.3536 (3)0.0153 (4)
O30.03469 (18)0.2798 (2)0.2437 (2)0.0127 (3)
O40.2569 (3)0.00000.0265 (3)0.0199 (5)
H10.440 (9)0.50000.464 (16)0.040*0.50
H20.298 (6)0.50000.313 (7)0.040*
Atomic displacement parameters (Å2) top
Ca10.0185 (4)0.0120 (3)0.0108 (4)0.0000.0070 (3)0.000
Zn10.00931 (18)0.00899 (16)0.0080 (2)0.00002 (10)0.00232 (14)0.00002 (11)
Mn10.00931 (18)0.00899 (16)0.0080 (2)0.00002 (10)0.00232 (14)0.00002 (11)
As10.00787 (14)0.00860 (12)0.00895 (16)0.0000.00336 (11)0.000
O10.0098 (10)0.0201 (10)0.0092 (11)0.0000.0017 (8)0.000
O20.0192 (11)0.0116 (8)0.0220 (12)0.0000.0155 (10)0.000
O30.0122 (7)0.0110 (6)0.0146 (8)0.0023 (5)0.0057 (6)0.0005 (5)
O40.0150 (11)0.0294 (12)0.0111 (11)0.0000.0020 (9)0.000
Geometric parameters (Å, º) top
Ca1—O4i2.426 (2)Zn1—O11.9940 (14)
Ca1—O42.426 (2)Zn1—O3iv2.0303 (15)
Ca1—O32.4318 (14)Zn1—O32.0303 (15)
Ca1—O3i2.4318 (14)Zn1—O2iv2.1468 (14)
Ca1—O3ii2.4318 (14)Zn1—O22.1468 (14)
Ca1—O3iii2.4318 (14)As1—O41.671 (2)
Ca1—O22.898 (2)As1—O3v1.6918 (13)
Ca1—O2i2.898 (2)As1—O3vi1.6918 (13)
Zn1—O1iv1.9940 (14)As1—O21.698 (2)
O4i—Ca1—O4180.00 (10)O3ii—Ca1—O2i114.55 (4)
O4i—Ca1—O375.38 (5)O3iii—Ca1—O2i65.45 (4)
O4—Ca1—O3104.62 (5)O2—Ca1—O2i180.00 (9)
O4i—Ca1—O3i104.62 (5)O1iv—Zn1—O1180.0
O4—Ca1—O3i75.38 (5)O1iv—Zn1—O3iv89.12 (7)
O3—Ca1—O3i180.00 (7)O1—Zn1—O3iv90.88 (7)
O4i—Ca1—O3ii75.38 (5)O1iv—Zn1—O390.88 (7)
O4—Ca1—O3ii104.62 (5)O1—Zn1—O389.12 (7)
O3—Ca1—O3ii92.03 (7)O3iv—Zn1—O3180.0
O3i—Ca1—O3ii87.97 (7)O1iv—Zn1—O2iv99.04 (6)
O4i—Ca1—O3iii104.62 (5)O1—Zn1—O2iv80.96 (6)
O4—Ca1—O3iii75.38 (5)O3iv—Zn1—O2iv88.18 (7)
O3—Ca1—O3iii87.97 (7)O3—Zn1—O2iv91.82 (7)
O3i—Ca1—O3iii92.03 (7)O1iv—Zn1—O280.96 (6)
O3ii—Ca1—O3iii180.00 (12)O1—Zn1—O299.04 (6)
O4i—Ca1—O2121.94 (7)O3iv—Zn1—O291.82 (7)
O4—Ca1—O258.06 (7)O3—Zn1—O288.18 (7)
O3—Ca1—O265.45 (4)O2iv—Zn1—O2180.0
O3i—Ca1—O2114.55 (4)O4—As1—O3v111.37 (7)
O3ii—Ca1—O265.45 (4)O4—As1—O3vi111.37 (7)
O3iii—Ca1—O2114.55 (4)O3v—As1—O3vi108.93 (10)
O4i—Ca1—O2i58.06 (7)O4—As1—O2101.87 (11)
O4—Ca1—O2i121.94 (7)O3v—As1—O2111.60 (6)
O3—Ca1—O2i114.55 (4)O3vi—As1—O2111.60 (6)
O3i—Ca1—O2i65.45 (4)
Symmetry codes: (i) x, y, z; (ii) x, y, z; (iii) x, y, z; (iv) x+1/2, y+1/2, z+1; (v) x+1/2, y+1/2, z; (vi) x+1/2, y1/2, z.
Hydrogen-bond geometry (Å, º) top
O1—H1···O1vii0.82 (7)1.79 (8)2.610 (4)177 (11)
O1—H2···O4viii0.66 (5)1.95 (5)2.595 (3)163 (6)
Symmetry codes: (vii) x+1, y+1, z+1; (viii) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaCa(Zn·Mn)2(AsO4)2(H2O·OH)2
Crystal system, space groupMonoclinic, C2/m
Temperature (K)293
a, b, c (Å)9.0727 (6), 6.2530 (4), 7.4150 (5)
β (°) 116.739 (4)
V3)375.68 (4)
Radiation typeMo Kα
µ (mm1)14.38
Crystal size (mm)0.06 × 0.05 × 0.05
Data collection
DiffractometerBruker APEXII CCD area-detector
Absorption correctionMulti-scan
[SADABS (Sheldrick, 2005) and XABS2 (Parkin et al., 1995)]
Tmin, Tmax0.477, 0.532
No. of measured, independent and
observed [I > 2σ(I)] reflections
2512, 739, 659
(sin θ/λ)max1)0.757
R[F2 > 2σ(F2)], wR(F2), S 0.019, 0.045, 0.91
No. of reflections739
No. of parameters49
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.81, 0.77

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), XtalDraw (Downs & Hall-Wallace, 2003), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top
O1—H1···O1i0.82 (7)1.79 (8)2.610 (4)177 (11)
O1—H2···O4ii0.66 (5)1.95 (5)2.595 (3)163 (6)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1/2, y+1/2, z.
Acknowledgements top

The authors gratefully acknowledge support of this study by the Arizona Science Foundation.