Zharchikhite, AlF(OH)₂: a novel structure type related to α-PbO₂

The crystal structure of zharchikhite, AlF(OH)₂, from the Zharchikhinskoe deposit (Buryatia, Russia) is solved here using single-crystal X-ray diffraction. The mineral is monoclinic, space group P2₁/c, a = 5.1788 (4), b = 7.8386 (4), c = 5.1624 (4) Å, β = 116.276 (10)°, V = 187.91 (3) ų and Z = 4. Zharchikhite demonstrates a novel structure type roughly related to the α-PbO₂ structure type and different from other compounds of the Al–F–OH system. The crystal structure of zharchikhite is based on the octahedral pseudoframework built from zigzag chains of edge-sharing AlF₂(OH)₄ octahedra; adjacent chains are linked via F vertices and the pseudoframework contains wide channels.

Computing details

(I)

Crystal data

AlFH2O2	F(000) = 160
Mr = 80.00	Dx = 2.828 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 5.1788 (4) Å	Cell parameters from 1113 reflections
b = 7.8386 (4) Å	θ = 4.4–30.6°
c = 5.1624 (4) Å	µ = 0.74 mm^−1
β = 116.276 (10)°	T = 293 K
V = 187.91 (3) Å^3	Irregular, colorless
Z = 4	0.26 × 0.26 × 0.14 mm

Data collection

Xcalibur, Sapphire3 diffractometer	463 independent reflections
Radiation source: fine-focus sealed X-ray tube	445 reflections with I > 2σ(I)
Detector resolution: 16.0630 pixels mm^-1	Rint = 0.016
ω scans	θmax = 28.3°, θmin = 4.4°
Absorption correction: multi-scan	h = −6→6
Tmin = 0.762, Tmax = 1.000	k = −9→10
1342 measured reflections	l = −5→6

Refinement

Refinement on F^2	2 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.025	All H-atom parameters refined
wR(F^2) = 0.063	w = 1/[σ^2(Fo^2) + (0.0363P)^2 + 0.0333P] where P = (Fo^2 + 2Fc^2)/3
S = 1.19	(Δ/σ)max = 0.001
463 reflections	Δρmax = 0.37 e Å^−3
45 parameters	Δρmin = −0.60 e Å^−3

Special details

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Al	0.74234 (6)	0.08386 (4)	0.98407 (7)	0.00435 (18)
O1	0.34054 (18)	0.06447 (10)	0.77768 (18)	0.0064 (2)
H1	0.275 (3)	0.054 (2)	0.598 (2)	0.023 (4)*
O2	0.85510 (19)	−0.09266 (10)	0.80783 (19)	0.0062 (2)
H2	0.781 (3)	−0.1920 (14)	0.782 (4)	0.023 (4)*
F	0.72572 (14)	0.26973 (9)	0.19524 (15)	0.0084 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Al	0.0041 (3)	0.0048 (2)	0.0043 (3)	0.00009 (10)	0.00200 (18)	−0.00002 (11)
O1	0.0058 (4)	0.0086 (4)	0.0040 (4)	−0.0006 (3)	0.0015 (3)	0.0007 (3)
O2	0.0052 (4)	0.0057 (4)	0.0072 (4)	−0.0010 (3)	0.0022 (4)	−0.0013 (3)
F	0.0097 (4)	0.0080 (4)	0.0082 (4)	−0.0001 (2)	0.0046 (3)	−0.0031 (2)

Geometric parameters (Å, º)

Al—F^i	1.8443 (7)	Al—O2	1.8852 (9)
Al—F^ii	1.8531 (7)	Al—Al^iii	2.9020 (6)
Al—O1^iii	1.8752 (9)	Al—Al^iv	2.9136 (6)
Al—O2^iv	1.8767 (9)	O1—H1	0.838 (9)
Al—O1	1.8776 (9)	O2—H2	0.852 (9)
F^i—Al—F^ii	89.352 (16)	O2^iv—Al—Al^iii	138.91 (3)
F^i—Al—O1^iii	91.03 (3)	O1—Al—Al^iii	39.32 (3)
F^ii—Al—O1^iii	165.73 (4)	O2—Al—Al^iii	98.94 (3)
F^i—Al—O2^iv	87.90 (3)	F^i—Al—Al^iv	127.18 (3)
F^ii—Al—O2^iv	94.70 (4)	F^ii—Al—Al^iv	92.29 (2)
O1^iii—Al—O2^iv	99.56 (4)	O1^iii—Al—Al^iv	98.81 (3)
F^i—Al—O1	93.98 (4)	O2^iv—Al—Al^iv	39.34 (3)
F^ii—Al—O1	87.05 (4)	O1—Al—Al^iv	138.83 (3)
O1^iii—Al—O1	78.70 (4)	O2—Al—Al^iv	39.13 (3)
O2^iv—Al—O1	177.45 (4)	Al^iii—Al—Al^iv	125.87 (2)
F^i—Al—O2	166.07 (4)	Al^iii—O1—Al	101.30 (4)
F^ii—Al—O2	88.86 (4)	Al^iii—O1—H1	124.8 (12)
O1^iii—Al—O2	94.08 (4)	Al—O1—H1	115.9 (10)
O2^iv—Al—O2	78.48 (4)	Al^iv—O2—Al	101.52 (4)
O1—Al—O2	99.73 (4)	Al^iv—O2—H2	115.5 (11)
F^i—Al—Al^iii	93.24 (2)	Al—O2—H2	122.1 (10)
F^ii—Al—Al^iii	126.36 (3)	Al^v—F—Al^vi	165.26 (5)
O1^iii—Al—Al^iii	39.38 (3)

Symmetry codes: (i) x, y, z+1; (ii) x, −y+1/2, z+1/2; (iii) −x+1, −y, −z+2; (iv) −x+2, −y, −z+2; (v) x, y, z−1; (vi) x, −y+1/2, z−1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^vii	0.84 (1)	1.92 (1)	2.7386 (14)	165 (2)
O2—H2···O1^viii	0.85 (1)	1.99 (1)	2.8370 (12)	172 (1)

Symmetry codes: (vii) −x+1, −y, −z+1; (viii) −x+1, y−1/2, −z+3/2.