Rietveld refinement of whitlockite-related K(0.8)Ca(9.8)Fe(0.2)(PO(4))(7).

The title compound, K(0.8)Ca(9.8)Fe(0.2)(PO(4))(7) (potassium deca-calcium iron hepta-phosphate), belongs to the whitlockite family. The structure is built up from several types of metal-oxygen polyhedra: two [CaO(8)], one [CaO(7)] and one [(Ca/Fe)O(6)] polyhedron with a mixed Ca/Fe occupancy in a 0.8:0.2 ratio, as well as three tetra-hedral [PO(4)] units. Of the 18 sites in the asymmetric unit, the site with the mixed Ca/Fe occupation, the K site, one P and one O site are on special positions 6a with 3 symmetry, whereas all other sites are on general positions 18b. The linkage of metal-oxygen polyhedra and [PO(4)] tetra-hedra via edges and corners results in formation of a three-dimensional framework with composition [Ca(9.8)Fe(0.2)(PO(4))(7)](0.8-). The remaining K atoms (site-occupation factor = 0.8) are located in large closed cavities and are nine-coordinated by oxygen.

Related literature

For the structure of the mineral whitlockite with idealized composition Ca3(PO4)2 (β-polymorph), see: Calvo & Gopal (1975 ▶); Yashima et al. (2003 ▶). For KCa10(PO4)7, see: Sandström & Boström (2006 ▶). For powder diffraction investigations and Rietveld refinements of other phosphate-based whitlockites, see: Morozov et al. (2000 ▶) for M ICa10(PO4)7 (M I = Li, Na, K); Lazoryak et al. (1996 ▶) for Ca9Fe(PO4)7; Morozov et al. (2002 ▶) for Ca9In(PO4)7; Strunenkova et al. (1997 ▶) for Na1.5Ca9Fe0.5(PO4)7. For the profile function used in the Rietveld refinement, see: Thompson et al. (1987 ▶).

Experimental

Crystal data

K0.8Ca9.8Fe0.2(PO4)7

M = 1100.02

Trigonal,

a = 10.44282 (1) Å

c = 37.29443 (3) Å

V = 3522.17 (1) Å3

Z = 6

Cu Kα radiation, λ = 1.540598 Å

T = 293 K

Flat sheet, 25 × 25 mm

Data collection

Shimadzu LabX XRD-6000 diffractometer

Specimen mounting: glass container

Data collection mode: reflection

Scan method: step

2θmin = 8.92°, 2θmax = 99.92°, increment in 2θ = 0.02°

Refinement

R p = 8.711

R wp = 11.243

R exp = 4.919

R Bragg = 3.849

R(F) = 2.48

4551 data points with 839 reflections

131 parameters

4 restraints

Data collection: PCXRD (Shimadzu, 2006 ▶); cell refinement: DICVOL 2004 (Boultif & Louër, 2004 ▶); data reduction: FULLPROF (Rodriguez-Carvajal, 2006 ▶); program(s) used to solve structure: FULLPROF; program(s) used to refine structure: FULLPROF; molecular graphics: DIAMOND (Brandenburg, 1999 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶) and enCIFer (Allen et al., 2004 ▶).

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810014327/wm2324sup1.cif

Rietveld powder data: contains datablocks I. DOI: 10.1107/S1600536810014327/wm2324Isup2.rtv

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

K0.8Ca9.8Fe0.2(PO4)7	Dx = 3.112 Mg m−3
Mr = 1100.02	Cu Kα radiation, λ = 1.540598 Å
Trigonal, R3c	T = 293 K
Hall symbol: R 3 -2"c	Particle morphology: isometric
a = 10.44282 (1) Å	light pink
c = 37.29443 (3) Å	flat_sheet, 25 × 25 mm
V = 3522.17 (1) Å3	Specimen preparation: Prepared at 293 K and 101.3 kPa
Z = 6

Shimadzu LabX XRD-6000 diffractometer	Data collection mode: reflection
Radiation source: X-ray tube, X-ray	Scan method: step
graphite	2θmin = 8.91°, 2θmax = 99.92°, 2θstep = 0.02°
Specimen mounting: glass container

Rp = 8.711	Profile function: Thompson–Cox–Hastings pseudo-Voigt * Axial divergence asymmetry
Rwp = 11.243	131 parameters
Rexp = 4.919	4 restraints
RBragg = 3.849	4 constraints
R(F) = 2.48	Standard least squares refinement
χ2 = 5.368	(Δ/σ)max = 0.001
4551 data points	Background function: Linear Interpolation between a set background points with refinable heights
Excluded region(s): undef	Preferred orientation correction: Modified March's Function

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ca1	0.3986 (5)	0.1868 (7)	0.0212 (4)	0.0022 (18)*
Ca2	0.3922 (6)	0.1887 (10)	0.1265 (4)	0.0022 (16)*
Ca3	0.1776 (11)	0.3817 (6)	0.0949 (5)	0.003 (2)*
Ca4	0.33333	0.66667	0.0288 (5)	0.002 (2)*	0.80000
Fe4	0.33333	0.66667	0.0288 (5)	0.002 (2)*	0.20000
K1	0.00000	0.00000	0.0447 (5)	0.004 (4)*	0.80000
P1	0.00000	0.00000	0.1293 (5)	0.0031 (11)*
P2	0.1351 (9)	0.3124 (6)	−0.0032 (4)	0.0031 (11)*
P3	0.4897 (11)	0.4749 (11)	0.0609 (5)	0.0031 (11)*
O11	0.00000	0.00000	0.1699 (8)	0.0025 (11)*
O12	0.0071 (19)	0.1449 (14)	0.1115 (7)	0.0025 (11)*
O21	0.0912 (15)	0.2697 (15)	0.0349 (4)	0.0025 (11)*
O22	0.222 (2)	0.233 (2)	−0.0145 (6)	0.0025 (11)*
O23	−0.0066 (16)	0.265 (2)	−0.0248 (5)	0.0025 (11)*
O24	0.229 (3)	0.4728 (17)	−0.0110 (6)	0.0025 (11)*
O31	0.408 (3)	0.567 (3)	0.0709 (7)	0.0025 (11)*
O32	0.5039 (17)	0.4689 (16)	0.0203 (5)	0.0025 (11)*
O33	0.6427 (19)	0.5475 (19)	0.0808 (6)	0.0025 (11)*
O34	0.3720 (19)	0.3100 (19)	0.0752 (7)	0.0025 (11)*

	U11	U22	U33	U12	U13	U23
?	?	?	?	?	?	?

Ca1—O11i	2.519 (10)	Ca4—O31viii	2.229 (35)
Ca1—O21ii	2.702 (13)	Fe4—O24viii	2.299 (30)
Ca1—O22	2.509 (26)	Fe4—O24	2.299 (30)
Ca1—O23ii	2.397 (20)	Fe4—O24vii	2.299 (30)
Ca1—O32	2.579 (17)	Fe4—O31	2.229 (35)
Ca1—O32iii	2.573 (23)	Fe4—O31vii	2.229 (35)
Ca1—O33iii	2.591 (27)	Fe4—O31viii	2.229 (35)
Ca1—O34	2.479 (28)	K1—O12	2.896 (30)
Ca2—O12ii	2.474 (16)	K1—O12ii	2.896 (30)
Ca2—O23iv	2.629 (26)	K1—O12ix	2.896 (30)
Ca2—O24iv	2.444 (19)	K1—O21	2.508 (19)
Ca2—O24v	2.484 (33)	K1—O21ii	2.508 (19)
Ca2—O32v	2.410 (23)	K1—O21ix	2.508 (19)
Ca2—O33iii	2.207 (27)	K1—O22	3.245 (26)
Ca2—O34	2.362 (29)	K1—O22ii	3.245 (26)
Ca3—O12	2.295 (15)	K1—O22ix	3.245 (26)
Ca3—O21	2.477 (22)	P1—O11	1.51 (4)
Ca3—O22vi	2.485 (29)	P1—O12	1.62 (2)
Ca3—O23iv	2.301 (25)	P1—O12ix	1.62 (2)
Ca3—O31	2.383 (25)	P1—O12ii	1.62 (2)
Ca3—O31vii	2.468 (36)	P2—O21	1.49 (2)
Ca3—O33vii	2.781 (25)	P2—O22	1.56 (2)
Ca3—O34	2.597 (27)	P2—O23	1.53 (2)
Ca4—O24viii	2.299 (30)	P2—O24	1.486 (17)
Ca4—O24	2.299 (30)	P3—O31	1.62 (3)
Ca4—O24vii	2.299 (30)	P3—O32	1.53 (3)
Ca4—O31	2.229 (35)	P3—O33	1.57 (3)
Ca4—O31vii	2.229 (35)	P3—O34	1.63 (2)
O24—Fe4—O24vii	82.8 (11)	O22—P2—O23	114.2 (13)
O24—Fe4—O31vii	101.7 (10)	O22—P2—O24	108.3 (15)
O24viii—Fe4—O31	101.6 (10)	O23—P2—O24	104.3 (15)
O31—Fe4—O31viii	75.9 (12)	O31—P3—O32	110.2 (15)
O24vii—Fe4—O31	175.2 (13)	O31—P3—O33	108.4 (15)
O31—Fe4—O31vii	75.9 (14)	O31—P3—O34	102.1 (15)
O24viii—Fe4—O31viii	99.6 (11)	O32—P3—O33	113.1 (14)
O24viii—Fe4—O24vii	82.8 (11)	O32—P3—O34	108.6 (13)
O24viii—Fe4—O31vii	175.2 (12)	O33—P3—O34	113.8 (14)
O24vii—Fe4—O31viii	101.7 (11)	O12ix—P1—O12ii	104.3 (12)
O31viii—Fe4—O31vii	75.9 (13)	O11—P1—O12ii	114.2 (11)
O24vii—Fe4—O31vii	99.6 (13)	O11—P1—O12	114.2 (11)
O24—Fe4—O31	99.6 (9)	O11—P1—O12ix	114.2 (11)
O24—Fe4—O24viii	82.8 (11)	O12—P1—O12ix	104.4 (12)
O24—Fe4—O31viii	175.2 (12)	O12—P1—O12ii	104.4 (13)
O21—P2—O22	105.8 (12)	Fe4—O24—P2	128.4 (15)
O21—P2—O23	107.5 (11)	Fe4—O31—P3	121.8 (16)
O21—P2—O24	117.0 (13)

Table 1

Selected bond lengths (Å)

Ca1—O11i	2.519 (10)
Ca1—O21ii	2.702 (13)
Ca1—O22	2.51 (3)
Ca1—O23ii	2.40 (2)
Ca1—O32	2.579 (17)
Ca1—O32iii	2.57 (2)
Ca1—O33iii	2.59 (3)
Ca1—O34	2.48 (3)
Ca2—O12ii	2.474 (16)
Ca2—O23iv	2.63 (3)
Ca2—O24iv	2.444 (19)
Ca2—O24v	2.48 (3)
Ca2—O32v	2.41 (2)
Ca2—O33iii	2.21 (3)
Ca2—O34	2.36 (3)
Ca3—O12	2.295 (15)
Ca3—O21	2.48 (2)
Ca3—O22vi	2.49 (3)
Ca3—O23iv	2.30 (3)
Ca3—O31	2.38 (3)
Ca3—O31vii	2.47 (4)
Ca3—O33vii	2.78 (3)
Ca3—O34	2.60 (3)
Ca4—O24	2.30 (3)
Ca4—O31	2.23 (4)
Fe4—O24	2.30 (3)
Fe4—O31	2.23 (4)
K1—O12	2.90 (3)
K1—O21	2.508 (19)
K1—O22	3.25 (3)
P1—O11	1.51 (4)
P1—O12	1.62 (2)
P2—O21	1.49 (2)
P2—O22	1.56 (2)
P2—O23	1.53 (2)
P2—O24	1.486 (17)
P3—O31	1.62 (3)
P3—O32	1.53 (3)
P3—O33	1.57 (3)
P3—O34	1.63 (2)

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