inorganic compounds
10(PO4)7 from X-ray powder data
of AgCaaDepartment of Inorganic Chemistry, Taras Shevchenko National University, 64/13 Volodymyrska str., 01601 Kyiv, Ukraine
*Correspondence e-mail: Strutynska_N@bigmir.net
Polycrystalline silver(I) decacalcium heptakis(orthophosphate), AgCa10(PO4)7, was obtained by solid-state reaction. It is isotopic with members of the series MCa10(PO4)7 (M = Li, Na, K and Cs), and is closely related to the structure of β-Ca3(PO4)2. The of the title compound is built up from a framework of [CaO9] and two [CaO8] polyhedra, one [CaO6] octahedron (site symmetry 3.) and three PO4 tetrahedra (one with 3.). The Ag+ cation is likewise located on a threefold rotation axis and resides in the cavities of the rigid [Ca10(PO4)7]− framework. It is surrounded by three O atoms in an almost regular triangular environment.
Related literature
For the structure of the mineral whitlockite, see: Calvo & Gopal (1975); Yashima et al. (2003). For powder diffraction studies and Rietveld refinements of phosphate-based whitlockite-related compounds, see: Lazoryak et al. (1996); Morozov et al. (2000, 2002); Zatovsky et al. (2007, 2010, 2011). For physical properties of these materials, see: Dou et al. (2011); Enhai et al. (2011); Lazoryak et al. (2004); Teterskii et al. (2005); Zhang et al. (2011). For the of isotypic KCa10(PO4)7, see: Sandström & Boström (2006). For bond-valence calculations, see: Brown (2002).
Experimental
Crystal data
|
Data collection: PCXRD (Shimadzu, 2006); cell DICVOL (Boultif & Louër, 2004); data reduction: FULLPROF (Rodriguez-Carvajal, 2006); program(s) used to solve structure: FULLPROF (Rodriguez-Carvajal, 2006); program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2006); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: PLATON (Spek, 2009) and enCIFer (Allen et al., 2004).
Supporting information
https://doi.org/10.1107/S1600536813007848/wm2726sup1.cif
contains datablocks global, I. DOI:Rietveld powder data: contains datablock I. DOI: https://doi.org/10.1107/S1600536813007848/wm2726Isup2.rtv
The title compound has been prepared by solid state reactions from a mixture of Ag3PO4, CaCO3 and CaHPO4 in the stoichiometric molar ratio Ag:Ca:P = 1:10:7. The starting components were finely ground in an agate mortar and then placed in a porcelain crucible. The thermal treatment has been carried out in two steps. The first one included preheating to 873 K to decompose the carbonate and calcium hydrogen phosphate. After that, the mixture was annealed at 1173 K for 20 h. The final product was a white powder.
Structure
was performed using KCa10(PO4)7 (Sandström & Boström, 2006) as a starting model. For profile Pearson VII function was used. For the oxygen atoms of each orthophosphate group the isotropic temperature factors were restrained as equal. The result of the final is given in Fig. 5.In recent years phosphates which are isotypic with β-Ca3(PO4)2 (whitlockite; Calvo & Gopal, 1975; Yashima et al., 2003) or whitlockite-related structures have attracted a growing interest due to their ferroelectric (Lazoryak et al., 2004), non-linear optical (Teterskii et al., 2005) or luminescent (Dou et al., 2011; Enhai et al., 2011; Zhang et al., 2011) properties. The structure of β-Ca3(PO4)2 contains three phosphorus (P1—P3) and five metal (M1—M5) sites, that are amenable to different types of substitutions, thus yielding a large number of closely related compounds. The Ca sites in the M1 and M2 positions (6a) are prone to substitution by univalent metals under formation of MCa10(PO4)7 compounds (M = Li, Na, K, Cs; Morozov et al., 2000; Sandström & Boström, 2006; Zatovsky et al., 2011), or by trivalent metals under formation of Ca9M(PO4)7 (M = Cr, Fe, In; Lazoryak et al., 1996; Morozov et al., 2002; Zatovsky et al., 2007), or combinations of univalent and trivalent metals (Zatovsky et al., 2010; Zatovsky et al., 2011). The new title compound AgCa10(PO4)7, (I), is likewise isotopic to the family of MCa10(PO4)7 (M = Li, Na, K, Cs) phosphates.
In the
of (I) four types of Ca sites (three in general positions 18b and one in special position 6a), three P sites (two in 18b one in 6a), ten O atoms (nine in 18b and one in 6a) and one Ag in 6a are present (Fig. 1).The anionic framework [Ca10(PO4)7]- of (I) is formed by interconnection of four types of [CaOx] and [PO4] tetrahedra (Fig. 2). The silver cations reside in cavities and compensate the charge of the rigid framework.
The Ca—O distances in the three types of [CaOx] polyhedra (one [CaO9] (Ca4) and two [CaO8] (Ca2, Ca3)) are in the range 2.28 (4)–2.97 (4) Å which is close to that in the series of MCa10(PO4)7 structures (M = K, Cs; Sandström & Boström, 2006; Zatovsky et al., 2011). The polyhedron [CaO6] (Ca1) is more irregular with Ca—O distances spread over the range 2.17 (4) to 2.40 (4) Å. In the case of MCa10(PO4)7 (M = K, Cs), the corresponding distances are 2.23–2.31 Å. The nearest oxygen environment of the Ag site corresponds to an almost regular triangular arrangement. The position of the Ag site is slightly shifted by 0.30 (3) Å from the plane of the O3 triangle (Fig. 3). On both sides from the central triangular plane two further groups of Ag—O contacts can be observed. Three O2 atoms, which belong to a single orthophosphate tetrahedron, coordinate the Ag atom from one side of the plane and three O9 atoms, which belong to three different orthophosphate tetrahera, complete the other part of the [AgO9] coordination sphere. Such kind of arrangement of O atoms can be described as a distorted three-capped triangular antiprism (Fig. 3). The lengths of Ag—O contacts are 2.476 (19), 3.15 (4) and 3.35 (4) Å. In comparison with MCa10(PO4)7 (M = Na, Cs) the corresponding M—O distances are: d(Na—O) = 2.452, 2.981, 3.362 (Morozov et al., 2000) and d(Cs—O) = 2.803, 3.200, 3.252 Å (Zatovsky et al., 2011) and the coordination numbers of the alkaline metal are six for Na and nine for Cs (Fig. 4(b,c)). For the Ag atom, the Ag—O2 distance (3.15 (4) Å) significantly exceeds that of Ag—O10 (2.471 (15) Å) thus indicating that the
should rather be described as [3 + 6] (Fig. 4a). Bond valence calculations (Brown, 2002) of the Ag+ cation resulted in 0.60 valence units considering the three close O atoms, and 0.67 v.u. considering also the six remote O atoms, thus indicating a rather low contribution to the overall bonding of the latter O atoms.For the structure of the mineral whitlockite, see: Calvo & Gopal (1975); Yashima et al. (2003). For powder diffraction studies and Rietveld refinements of phosphate-based whitlockite-related compounds, see: Lazoryak et al. (1996); Morozov et al. (2000, 2002); Zatovsky et al. (2007, 2010, 2011). For physical properties of these materials, see: Dou et al. (2011); Enhai et al. (2011); Lazoryak et al. (2004); Teterskii et al. (2005); Zhang et al. (2011). For the
of isotypic KCa10(PO4)7, see: Sandström & Boström (2006). For bond-valence calculations, see: Brown (2002).Data collection: PCXRD (Shimadzu, 2006); cell
Dicvol (Boultif & Louër, 2004); data reduction: FULLPROF (Rodriguez-Carvajal, 2006); program(s) used to solve structure: FULLPROF (Rodriguez-Carvajal, 2006); program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2006); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: PLATON (Spek, 2009) and enCIFer (Allen et al., 2004).AgCa10(PO4)7 | Dx = 3.319 Mg m−3 |
Mr = 1173.46 | Cu Kα radiation, λ = 1.540560 Å |
Trigonal, R3c | T = 293 K |
Hall symbol: R 3 -2"c | Particle morphology: isometric |
a = 10.43723 (5) Å | white |
c = 37.3379 (7) Å | flat sheet, 25 × 25 mm |
V = 3522.50 (7) 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 monochromator | 2θmin = 9.045°, 2θmax = 100.045°, 2θstep = 0.020° |
Specimen mounting: glass container |
Rp = 0.094 | 150 parameters |
Rwp = 0.125 | 3 restraints |
Rexp = 0.042 | 3 constraints |
RBragg = 0.051 | Standard least squares refinement |
R(F) = 0.038 | (Δ/σ)max = 0.001 |
4551 data points | Background function: Linear Interpolation between a set background points with refinable heights |
Profile function: Pearson VII | Preferred orientation correction: March-Dollase Numeric Multiaxial Function |
AgCa10(PO4)7 | V = 3522.50 (7) Å3 |
Mr = 1173.46 | Z = 6 |
Trigonal, R3c | Cu Kα radiation, λ = 1.540560 Å |
a = 10.43723 (5) Å | T = 293 K |
c = 37.3379 (7) Å | flat sheet, 25 × 25 mm |
Shimadzu LabX XRD-6000 diffractometer | Scan method: step |
Specimen mounting: glass container | 2θmin = 9.045°, 2θmax = 100.045°, 2θstep = 0.020° |
Data collection mode: reflection |
Rp = 0.094 | R(F) = 0.038 |
Rwp = 0.125 | 4551 data points |
Rexp = 0.042 | 150 parameters |
RBragg = 0.051 | 3 restraints |
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 e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles |
x | y | z | Uiso*/Ueq | ||
Ag1 | 0.00000 | 0.00000 | 0.1780 (8) | 0.042 (2)* | |
Ca1 | 0.33333 | 0.66667 | 0.1632 (9) | 0.002 (2)* | |
Ca2 | 0.4650 (10) | 0.5260 (11) | 0.0955 (8) | 0.0044 (14)* | |
Ca3 | 0.2864 (7) | 0.1558 (12) | 0.0625 (8) | 0.004 (2)* | |
Ca4 | 0.3992 (5) | 0.1876 (9) | 0.1565 (8) | 0.0044 (14)* | |
P1 | 0.66667 | 0.33333 | 0.0976 (8) | 0.002 (4)* | |
P2 | 0.1577 (14) | 0.3495 (13) | 0.0288 (8) | 0.009 (3)* | |
P3 | 0.1366 (11) | 0.3111 (7) | 0.1306 (8) | 0.003 (3)* | |
O1 | 0.66667 | 0.33333 | 0.1387 (11) | 0.006 (11)* | |
O2 | 0.5229 (16) | 0.325 (2) | 0.0860 (9) | 0.006 (6)* | |
O3 | 0.082 (3) | 0.1873 (15) | 0.0421 (9) | 0.005 (3)* | |
O4 | 0.051 (2) | 0.394 (3) | 0.0420 (10) | 0.005 (3)* | |
O5 | 0.173 (2) | 0.3689 (18) | −0.0111 (9) | 0.005 (3)* | |
O6 | 0.316 (2) | 0.440 (2) | 0.0462 (10) | 0.005 (3)* | |
O7 | −0.0093 (19) | 0.267 (3) | 0.1100 (9) | 0.006 (4)* | |
O8 | 0.241 (3) | 0.4824 (13) | 0.1261 (9) | 0.006 (4)* | |
O9 | 0.221 (2) | 0.243 (3) | 0.1161 (10) | 0.006 (4)* | |
O10 | 0.0887 (18) | 0.267 (2) | 0.1700 (10) | 0.006 (4)* |
Ag1—O10 | 2.476 (19) | Ca3—O4ii | 2.62 (4) |
Ag1—O10i | 2.476 (19) | Ca3—O6 | 2.89 (3) |
Ag1—O10ii | 2.476 (19) | Ca4—O7ii | 2.40 (4) |
Ca1—O8 | 2.17 (4) | Ca4—O6ix | 2.45 (4) |
Ca1—O8iii | 2.17 (4) | Ca4—O4vi | 2.46 (4) |
Ca1—O8iv | 2.17 (4) | Ca4—O1 | 2.510 (14) |
Ca1—O3v | 2.40 (4) | Ca4—O5ix | 2.55 (3) |
Ca1—O3vi | 2.40 (4) | Ca4—O5vi | 2.59 (2) |
Ca1—O3vii | 2.40 (4) | Ca4—O9 | 2.67 (4) |
Ca2—O6 | 2.28 (4) | Ca4—O10ii | 2.692 (18) |
Ca2—O5vi | 2.41 (4) | Ca4—O2 | 2.97 (4) |
Ca2—O8 | 2.43 (4) | P1—O1 | 1.54 (5) |
Ca2—O4iii | 2.45 (4) | P1—O2 | 1.52 (2) |
Ca2—O2 | 2.48 (3) | P1—O2x | 1.52 (2) |
Ca2—O8iii | 2.48 (3) | P1—O2xi | 1.52 (2) |
Ca2—O7iii | 2.57 (2) | P2—O3 | 1.55 (2) |
Ca2—O9 | 2.88 (3) | P2—O4 | 1.49 (3) |
Ca3—O7ii | 2.31 (4) | P2—O5 | 1.50 (4) |
Ca3—O3ii | 2.37 (2) | P2—O6 | 1.58 (3) |
Ca3—O2 | 2.37 (2) | P3—O7 | 1.56 (3) |
Ca3—O9 | 2.43 (4) | P3—O8 | 1.570 (15) |
Ca3—O3 | 2.44 (4) | P3—O9 | 1.48 (3) |
Ca3—O10viii | 2.46 (4) | P3—O10 | 1.55 (5) |
O10—Ag1—O10i | 118.5 (9) | O1—P1—O2x | 106.6 (17) |
O10—Ag1—O10ii | 118.6 (7) | O2x—P1—O2xi | 112.3 (18) |
O10i—Ag1—O10ii | 118.6 (8) | O2—P1—O2x | 112.2 (16) |
O7—P3—O8 | 107.7 (19) | O2—P1—O2xi | 112.2 (17) |
O7—P3—O9 | 114 (2) | O3—P2—O4 | 101 (2) |
O7—P3—O10 | 105.0 (17) | O4—P2—O5 | 109 (2) |
O8—P3—O9 | 105.5 (18) | O3—P2—O5 | 115.3 (19) |
O8—P3—O10 | 112 (2) | O3—P2—O6 | 109 (2) |
O9—P3—O10 | 112.7 (19) | O4—P2—O6 | 114 (2) |
O1—P1—O2xi | 106.5 (16) | O5—P2—O6 | 108.6 (19) |
O1—P1—O2 | 106.5 (16) | Ag1—O10—P3 | 109.4 (15) |
Symmetry codes: (i) −y, x−y, z; (ii) −x+y, −x, z; (iii) −y+1, x−y+1, z; (iv) −x+y, −x+1, z; (v) −y+1/3, −x+2/3, z+1/6; (vi) x+1/3, x−y+2/3, z+1/6; (vii) −x+y+1/3, y+2/3, z+1/6; (viii) −y+2/3, −x+1/3, z−1/6; (ix) −x+y+1/3, y−1/3, z+1/6; (x) −y+1, x−y, z; (xi) −x+y+1, −x+1, z. |
Experimental details
Crystal data | |
Chemical formula | AgCa10(PO4)7 |
Mr | 1173.46 |
Crystal system, space group | Trigonal, R3c |
Temperature (K) | 293 |
a, c (Å) | 10.43723 (5), 37.3379 (7) |
V (Å3) | 3522.50 (7) |
Z | 6 |
Radiation type | Cu Kα, λ = 1.540560 Å |
Specimen shape, size (mm) | Flat sheet, 25 × 25 |
Data collection | |
Diffractometer | Shimadzu LabX XRD-6000 |
Specimen mounting | Glass container |
Data collection mode | Reflection |
Scan method | Step |
2θ values (°) | 2θmin = 9.045 2θmax = 100.045 2θstep = 0.020 |
Refinement | |
R factors and goodness of fit | Rp = 0.094, Rwp = 0.125, Rexp = 0.042, RBragg = 0.051, R(F) = 0.038, χ2 = 8.821 |
No. of parameters | 150 |
No. of restraints | 3 |
Computer programs: PCXRD (Shimadzu, 2006), Dicvol (Boultif & Louër, 2004), FULLPROF (Rodriguez-Carvajal, 2006), DIAMOND (Brandenburg, 1999), PLATON (Spek, 2009) and enCIFer (Allen et al., 2004).
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In recent years phosphates which are isotypic with β-Ca3(PO4)2 (whitlockite; Calvo & Gopal, 1975; Yashima et al., 2003) or whitlockite-related structures have attracted a growing interest due to their ferroelectric (Lazoryak et al., 2004), non-linear optical (Teterskii et al., 2005) or luminescent (Dou et al., 2011; Enhai et al., 2011; Zhang et al., 2011) properties. The structure of β-Ca3(PO4)2 contains three phosphorus (P1—P3) and five metal (M1—M5) sites, that are amenable to different types of substitutions, thus yielding a large number of closely related compounds. The Ca sites in the M1 and M2 positions (6a) are prone to substitution by univalent metals under formation of MCa10(PO4)7 compounds (M = Li, Na, K, Cs; Morozov et al., 2000; Sandström & Boström, 2006; Zatovsky et al., 2011), or by trivalent metals under formation of Ca9M(PO4)7 (M = Cr, Fe, In; Lazoryak et al., 1996; Morozov et al., 2002; Zatovsky et al., 2007), or combinations of univalent and trivalent metals (Zatovsky et al., 2010; Zatovsky et al., 2011). The new title compound AgCa10(PO4)7, (I), is likewise isotopic to the family of MCa10(PO4)7 (M = Li, Na, K, Cs) phosphates.
In the crystal structure of (I) four types of Ca sites (three in general positions 18b and one in special position 6a), three P sites (two in 18b one in 6a), ten O atoms (nine in 18b and one in 6a) and one Ag in 6a are present (Fig. 1).
The anionic framework [Ca10(PO4)7]- of (I) is formed by interconnection of four types of [CaOx] and [PO4] tetrahedra (Fig. 2). The silver cations reside in cavities and compensate the charge of the rigid framework.
The Ca—O distances in the three types of [CaOx] polyhedra (one [CaO9] (Ca4) and two [CaO8] (Ca2, Ca3)) are in the range 2.28 (4)–2.97 (4) Å which is close to that in the series of MCa10(PO4)7 structures (M = K, Cs; Sandström & Boström, 2006; Zatovsky et al., 2011). The polyhedron [CaO6] (Ca1) is more irregular with Ca—O distances spread over the range 2.17 (4) to 2.40 (4) Å. In the case of MCa10(PO4)7 (M = K, Cs), the corresponding distances are 2.23–2.31 Å. The nearest oxygen environment of the Ag site corresponds to an almost regular triangular arrangement. The position of the Ag site is slightly shifted by 0.30 (3) Å from the plane of the O3 triangle (Fig. 3). On both sides from the central triangular plane two further groups of Ag—O contacts can be observed. Three O2 atoms, which belong to a single orthophosphate tetrahedron, coordinate the Ag atom from one side of the plane and three O9 atoms, which belong to three different orthophosphate tetrahera, complete the other part of the [AgO9] coordination sphere. Such kind of arrangement of O atoms can be described as a distorted three-capped triangular antiprism (Fig. 3). The lengths of Ag—O contacts are 2.476 (19), 3.15 (4) and 3.35 (4) Å. In comparison with MCa10(PO4)7 (M = Na, Cs) the corresponding M—O distances are: d(Na—O) = 2.452, 2.981, 3.362 (Morozov et al., 2000) and d(Cs—O) = 2.803, 3.200, 3.252 Å (Zatovsky et al., 2011) and the coordination numbers of the alkaline metal are six for Na and nine for Cs (Fig. 4(b,c)). For the Ag atom, the Ag—O2 distance (3.15 (4) Å) significantly exceeds that of Ag—O10 (2.471 (15) Å) thus indicating that the coordination number should rather be described as [3 + 6] (Fig. 4a). Bond valence calculations (Brown, 2002) of the Ag+ cation resulted in 0.60 valence units considering the three close O atoms, and 0.67 v.u. considering also the six remote O atoms, thus indicating a rather low contribution to the overall bonding of the latter O atoms.