Redetermination of durangite, NaAl(AsO(4))F.

The crystal structure of durangite, ideally NaAl(AsO(4))F (chemical name sodium aluminium arsenate fluoride), has been determined previously [Kokkoros (1938). Z. Kristallogr.99, 38-49] using Weissenberg film data without reporting displacement parameters of atoms or a reliability factor. This study reports the redetermination of the structure of durangite using single-crystal X-ray diffraction data from a natural sample with composition (Na(0.95)Li(0.05))(Al(0.91)Fe(3+) (0.07)Mn(3+) (0.02))(AsO(4))(F(0.73)(OH)(0.27)) from the type locality, the Barranca mine, Coneto de Comonfort, Durango, Mexico. Durangite is isostructural with minerals of the titanite group in the space group C2/c. Its structure is characterized by kinked chains of corner-sharing AlO(4)F(2) octa-hedra parallel to the c axis. These chains are cross-linked by isolated AsO(4) tetra-hedra, forming a three-dimensional framework. The Na(+) cation (site symmetry 2) occupies the inter-stitial sites and is coordinated by one F(-) and six O(2-) anions. The AlO(4)F(2) octa-hedron has symmetry -1; it is flattened, with the Al-F bond length [1.8457 (4) Å] shorter than the Al-O bond lengths [1.8913 (8) and 1.9002 (9) Å]. Examination of the Raman spectra for arsenate minerals in the titanite group reveals that the position of the band originating from the As-O symmetric stretching vibrations shifts to lower wavenumbers from durangite, maxwellite [ideally NaFe(AsO(4))F], to tilasite [CaMg(AsO(4))F].

Related literature

For previous work on durangite, see: Brush (1869 ▶); Des Cloizeaux (1875 ▶); Kokkoros (1938 ▶); Machatschki (1941 ▶); Sumin de Portilla (1974 ▶); Foord et al. (1985 ▶). For minerals isostructural with or similar to durangite, see: Hawthorne (1990 ▶); Groat et al. (1990 ▶); Hawthorne et al. (1991 ▶); Oberti et al. (1991 ▶); Bermanec (1994 ▶); Cooper & Hawthorne (1995 ▶); Troitzsch et al. (1999 ▶); Sebastian et al. (2002 ▶). For Raman spectroscopic measurements on arsenate minerals and compounds, see: Yang et al. (2011a ▶,b ▶); Frost & Xi (2012 ▶); Frost et al. (2012 ▶). For the definition of polyhedral distortion, see: Robinson et al. (1971 ▶).

Experimental

Crystal data

(Na0.95Li0.05)(Al0.91Fe0.09)(AsO4)(F0.73OH0.27)

M = 208.88

Monoclinic,

a = 6.5789 (5) Å

b = 8.5071 (6) Å

c = 7.0212 (5) Å

β = 115.447 (4)°

V = 354.83 (4) Å3

Z = 4

Mo Kα radiation

μ = 10.18 mm−1

T = 293 K

0.10 × 0.10 × 0.09 mm

Data collection

Bruker APEXII CCD diffractometer

Absorption correction: multi-scan (SADABS; Sheldrick, 2005 ▶) T min = 0.429, T max = 0.461

2509 measured reflections

645 independent reflections

641 reflections with I > 2σ(I)

R int = 0.019

Refinement

R[F 2 > 2σ(F 2)] = 0.013

wR(F 2) = 0.033

S = 1.10

645 reflections

44 parameters

3 restraints

H-atom parameters not refined

Δρmax = 0.65 e Å−3

Δρmin = −0.47 e Å−3

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: SAINT (Bruker, 2004 ▶); data reduction: SAINT; 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 ▶).

Click here for additional data file.

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S160053681204384X/wm2690sup1.cif

Click here for additional data file.

Structure factors: contains datablock(s) I. DOI: 10.1107/S160053681204384X/wm2690Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

(Na0.95Li0.05)(Al0.91Fe0.09)(AsO4)(F0.73OH0.27)	F(000) = 395
Mr = 208.88	Dx = 3.915 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2164 reflections
a = 6.5789 (5) Å	θ = 4.2–32.7°
b = 8.5071 (6) Å	µ = 10.18 mm−1
c = 7.0212 (5) Å	T = 293 K
β = 115.447 (4)°	Cuboid, red
V = 354.83 (4) Å3	0.10 × 0.10 × 0.09 mm
Z = 4

Bruker APEXII CCD diffractometer	645 independent reflections
Radiation source: fine-focus sealed tube	641 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
φ and ω scan	θmax = 32.6°, θmin = 4.2°
Absorption correction: multi-scan (SADABS; Sheldrick, 2005)	h = −9→9
Tmin = 0.429, Tmax = 0.461	k = −12→12
2509 measured reflections	l = −10→10

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	H-atom parameters not refined
R[F2 > 2σ(F2)] = 0.013	w = 1/[σ2(Fo2) + (0.0158P)2 + 0.3997P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.033	(Δ/σ)max < 0.001
S = 1.10	Δρmax = 0.65 e Å−3
645 reflections	Δρmin = −0.47 e Å−3
44 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
3 restraints	Extinction coefficient: 0.0311 (12)
Primary atom site location: structure-invariant direct methods

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.

	x	y	z	Uiso*/Ueq	Occ. (<1)
Na	0.5000	0.17173 (9)	0.2500	0.01324 (16)	0.9500 (1)
Li	0.5000	0.17173 (9)	0.2500	0.01324 (16)	0.0500 (1)
Al	0.0000	0.0000	0.0000	0.00554 (10)	0.9100 (1)
Fe	0.0000	0.0000	0.0000	0.00554 (10)	0.0900 (1)
As	0.0000	0.314545 (18)	0.2500	0.00504 (7)
O1	0.19850 (14)	0.43542 (11)	0.41553 (14)	0.00955 (16)
O2	0.10283 (15)	0.20307 (10)	0.11309 (15)	0.00838 (15)
F	0.0000	0.06705 (13)	−0.2500	0.00719 (18)	0.7300 (1)
OH	0.0000	0.06705 (13)	−0.2500	0.00719 (18)	0.2700 (1)

	U11	U22	U33	U12	U13	U23
Na	0.0098 (3)	0.0063 (3)	0.0208 (4)	0.000	0.0039 (3)	0.000
Li	0.0098 (3)	0.0063 (3)	0.0208 (4)	0.000	0.0039 (3)	0.000
Al	0.00567 (19)	0.0052 (2)	0.00565 (19)	0.00045 (13)	0.00233 (15)	0.00008 (14)
Fe	0.00567 (19)	0.0052 (2)	0.00565 (19)	0.00045 (13)	0.00233 (15)	0.00008 (14)
As	0.00470 (9)	0.00455 (9)	0.00563 (9)	0.000	0.00199 (6)	0.000
O1	0.0072 (3)	0.0093 (4)	0.0103 (4)	−0.0026 (3)	0.0020 (3)	−0.0032 (3)
O2	0.0097 (3)	0.0071 (3)	0.0103 (4)	−0.0003 (3)	0.0061 (3)	−0.0020 (3)
F	0.0096 (4)	0.0067 (4)	0.0056 (4)	0.000	0.0036 (3)	0.000
OH	0.0096 (4)	0.0067 (4)	0.0056 (4)	0.000	0.0036 (3)	0.000

Na—Fi	2.2222 (14)	Al—O1vii	1.8913 (8)
Na—O2ii	2.3799 (9)	Al—O1iii	1.8913 (8)
Na—O2	2.3799 (9)	Al—O2vi	1.9002 (9)
Na—O1iii	2.4069 (11)	Al—O2	1.9002 (9)
Na—O1iv	2.4069 (11)	As—O1	1.6761 (8)
Na—O2v	2.5708 (10)	As—O1viii	1.6761 (8)
Na—O2i	2.5708 (10)	As—O2viii	1.6852 (9)
Al—Fvi	1.8457 (4)	As—O2	1.6852 (9)
Al—F	1.8457 (4)
Fvi—Al—F	180.00 (6)	F—Al—O2	88.34 (4)
Fvi—Al—O1vii	87.68 (3)	O1vii—Al—O2	90.23 (4)
F—Al—O1vii	92.32 (3)	O1iii—Al—O2	89.77 (4)
Fvi—Al—O1iii	92.32 (3)	O2vi—Al—O2	180.00 (7)
F—Al—O1iii	87.68 (3)	O1—As—O1viii	104.31 (6)
O1vii—Al—O1iii	180.00 (8)	O1—As—O2viii	109.50 (5)
Fvi—Al—O2vi	88.34 (4)	O1viii—As—O2viii	110.89 (4)
F—Al—O2vi	91.66 (4)	O1—As—O2	110.89 (4)
O1vii—Al—O2vi	89.77 (4)	O1viii—As—O2	109.50 (4)
O1iii—Al—O2vi	90.23 (4)	O2viii—As—O2	111.51 (6)
Fvi—Al—O2	91.66 (4)