Rietveld refinement of Sr(5)(AsO(4))(3)Cl from high-resolution synchrotron data.

The apatite-type compound, penta-strontium tris-[arsenate(V)] chloride, Sr(5)(AsO(4))(3)Cl, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite [Pb(5)(AsO(4))(3)Cl] with SrCO(3) as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A(5)(YO(4))(3)X (A = divalent cation, Y = penta-valent cation, and X = F, Cl or Br) in the space group P6(3)/m. The structure consists of isolated tetra-hedral AsO(4) (3-) anions (the As atom and two O atoms have m symmetry), separated by two crystallographically independent Sr(2+) cations that are located on mirror planes and threefold rotation axes, respectively. One Sr atom is coordinated by nine O atoms and the other by six. The chloride anions (site symmetry ) are at the 2a sites and are located in the channels of the structure.

Related literature

For crystal chemistry of apatites, see: Mercier et al. (2005 ▶); White & ZhiLi (2003 ▶); Wu et al. (2003 ▶). For powder diffraction data on Sr As-apatite, see: Kreidler & Hummel (1970 ▶). Atomic coordinates as starting parameters for the Rietveld (Rietveld, 1969 ▶) refinement of the present phases were taken from Bell et al. (2008 ▶); Dai et al. (1991 ▶); de Villiers et al. (1971 ▶). For related Sr—Cl-apatites, see: Đordević et al. (2008 ▶); Sudarsanan & Young, (1974 ▶, 1980 ▶); Beck et al. (2006 ▶); Noetzold et al. (1995 ▶); Noetzold & Wulff (1996 ▶, 1997 ▶, 1998 ▶); Swafford & Holt (2002 ▶); Wardojo & Hwu (1996 ▶). For synthetic work, see: Baker (1966 ▶); Essington (1988 ▶); Harrison et al. (2002 ▶).

Experimental

Crystal data

Sr5(AsO4)3Cl

M = 890.31

Hexagonal,

a = 10.1969 (1) Å

c = 7.28108 (9) Å

V = 655.63 (2) Å3

Z = 2

Synchrotron radiation

λ = 0.998043 Å

T = 298 K

Specimen shape: cylinder

40 × 0.7 × 0.7 mm

Specimen prepared at 100 kPa

Specimen prepared at 1258 K

Particle morphology: powder, white

Data collection

In-house design diffractometer

Specimen mounting: capillary

Specimen mounted in transmission mode

Scan method: step

Absorption correction: fixed at 0

2θmin = 2, 2θmax = 60°

Increment in 2θ = 0.01°

Refinement

R p = 0.052

R wp = 0.066

R exp = 0.047

R B = 0.090

S = 2.00

Excluded region(s): 2-6° 2θ

Profile function: Pseudo Voigt

225 reflections

16 parameters

Preferred orientation correction: none

Data collection: local software; cell refinement: CELREF (Laugier & Bochu, 2003 ▶) and GSAS (Larson & Von Dreele (2004 ▶); data reduction: local software; method used to solve structure: coordinates taken from a related compound; program(s) used to refine structure: GSAS and EXPGUI (Toby, 2001 ▶); molecular graphics: VESTA (Momma & Izumi, 2008 ▶); software used to prepare material for publication: publCIF (Westrip, 2009 ▶).

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809005054/br2096sup1.cif

Rietveld powder data: contains datablocks I. DOI: 10.1107/S1600536809005054/br2096Isup2.rtv

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

Sr5(AsO4)3Cl	Dx = 4.510 (1) Mg m−3
Mr = 890.31	Synchrotron radiation, λ = 0.998043 Å
Hexagonal, P63/m	T = 298 K
a = 10.1969 (1) Å	Particle morphology: powder
c = 7.28108 (9) Å	white
V = 655.63 (2) Å3	cylinder, 40 × 0.7 mm
Z = 2	Specimen preparation: Prepared at 1258 K and 100 kPa

In-house design diffractometer	Data collection mode: transmission
Radiation source: Synchrotron	Scan method: step
Si(111) channel-cut crystal	2θmin = 6°, 2θmax = 60°, 2θstep = 0.01°
Specimen mounting: capillary

Rp = 0.052	Profile function: Pseudo Voigt
Rwp = 0.066	16 parameters
Rexp = 0.047	0 restraints
RBragg = 0.090	4 constraints
R(F2) = 0.33148	(Δ/σ)max = 0.001
χ2 = 3.992	Background function: Cosine Fourier Series
5801 data points	Preferred orientation correction: None
Excluded region(s): 2-6° 2θ

Experimental. Absorption correction fixed at zero, all attempts to refine this term in GSAS were unsuccessful so this term was fixed at zero. CELREF was used for initial lattice parameter determinations before Rietveld refinement. Lattice parameters from GSAS refinement are quoted in the paper.

	x	y	z	Uiso*/Ueq
Sr1	0.33333	0.66667	0.008 (1)	0.0246 (9)
Sr2	0.2496 (5)	0.9936 (6)	0.25	0.0246 (9)
As1	0.4057 (5)	0.3718 (5)	0.25	0.029 (2)
O1	0.337 (3)	0.496 (2)	0.25	0.015 (4)
O2	0.598 (2)	0.464 (2)	0.25	0.015 (4)
O3	0.354 (2)	0.284 (2)	0.063 (2)	0.015 (4)
Cl1	0.0000	0.0000	0.0000	0.031 (5)

Sr1—O1i	2.49 (2)	Sr2—O3vi	2.44 (1)
Sr1—O1ii	2.49 (2)	Sr2—O3vii	2.94 (1)
Sr1—O1	2.49 (2)	Sr2—O3viii	2.94 (1)
Sr1—O2iii	2.59 (2)	Sr2—O1ii	3.02 (2)
Sr1—O2iv	2.59 (2)	Sr2—Cl1viii	3.156 (3)
Sr1—O2v	2.59 (2)	Sr2—Cl1ix	3.156 (3)
Sr1—O3iv	3.01 (1)	As1—O3	1.57 (1)
Sr1—O3iii	3.01 (1)	As1—O3x	1.57 (1)
Sr1—O3v	3.01 (1)	As1—O1	1.72 (2)
Sr2—O2i	2.53 (2)	As1—O2	1.70 (2)
Sr2—O3iv	2.44 (1)
O3—As1—O3x	121 (1)	O3—As1—O2	106.3 (6)
O3—As1—O1	105.8 (7)	O3x—As1—O2	106.3 (6)
O3x—As1—O1	105.8 (7)	O1—As1—O2	112 (1)

Sr1—O1	2.49 (2)
Sr1—O2i	2.59 (2)
Sr1—O3i	3.01 (1)
Sr2—O2ii	2.53 (2)
Sr2—O3iii	2.44 (1)
Sr2—O3iv	2.94 (1)
Sr2—O1v	3.02 (2)
Sr2—Cl1iv	3.156 (3)
As1—O3	1.57 (1)
As1—O1	1.72 (2)
As1—O2	1.70 (2)

O3—As1—O3vi	121 (1)
O3—As1—O1	105.8 (7)
O3—As1—O2	106.3 (6)
O1—As1—O2	112 (1)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .