supplementary materials


Acta Cryst. (2013). E69, i72    [ doi:10.1107/S1600536813026433 ]

The monoclinic form of trilithium dichromium(III) tris(orthophosphate)

J. Sun, P. Kim and H. Yun

Abstract top

The monoclinic form of trilithium dichromium(III) tris(orthophosphate), Li3Cr2(PO4)3, was prepared by the reactive halide flux method. The structure of the title compound is composed of a three-dimensional anionic framework with composition [infinity] 3[Cr2(PO4)3]3- and Li+ ions situated in the empty channels. The rigid framework built up from CrO6 octahedra and PO4 tetrahedra is the same as that found in other monoclinic Li3M2(PO4)3 (M = Fe, Sc, V) phases. The three Li+ cations of Li3Cr2(PO4)3 are unequally disordered over six crystallographically different sites. The classical charge balance of the title compound can be represented as [Li+]3[Cr3+]2[P5+]3[O2-]12. Solid-state UV/Vis spectra indicate that the crystal filed splitting ([Delta]0) of the Cr3+ ion is around 2.22 eV.

Comment top

The structures of trilithium dimetal tris(orthophosphates), Li3M2(PO4)3 (M = Fe, Sc, Cr, V) have been widely investigated due to their ion transport properties and temperature-dependent phase transitions (d'Yvoire et al., 1983; Verin et al., 1985; Maksimov et al., 1986). For Li3Cr2(PO4)3, the structure of the orthorhombic phase has been studied based on single-crystal diffraction data (Genkina et al., 1991). The monoclinic and rhombohedral phases have been identified by powder diffraction techniques but no detailed structure determinations have been reported yet (d'Yvoire et al., 1983). In attempts to prepare new mixed alkali metal phosphates by using various alkali metal halides, the monoclinic form of Li3Cr2(PO4)3 has been isolated as single crystals and the detailed structural characterization of this phase is reported here.

The anionic framework of Li3Cr2(PO4)3 is the same as that of the previously reported monoclinic Li3V2(PO4)3 structure (Kee & Yun, 2013). The general structural features of this phase have been discussed previously (Patoux et al., 2003; Fu et al., 2010). Figure 1 shows the coordination environment of the Cr and P atoms. CrO6 octahedra are joined to PO4 tetrahedra forming a [Cr2(PO4)3] unit. These units share a terminal oxygen atom to construct the anionic three-dimensional framework, 3[Cr2(PO4)3]3- (Fig. 2). The Cr—O distances (1.9007 (18)–2.0392 (18) Å) are in good agreement with those calculated from their ionic radii (2.00 Å; Shannon, 1976), assuming a valence of +III for Cr.

The Li+ ions in the empty channels are surrounded by four O atoms in distorted tetrahedral coordinations. There are six crystallographically independent Li sites for this phase and three Li+ ions are unequally disordered over them. It has been reported that the positions of Li+ ions in Li3V2(PO4)3 can vary depending on the synthetic conditions while those of the V, P, and O atoms comprising the rigid framework remain intact (Yang et al., 2010). The positions of the Li1, Li3, and Li4 sites in this work are very close to those of the ordered Li sites found in Li3V2(PO4)3 (Kee & Yun, 2013).

The classical charge balance of the title compound can be represented as [Li+]3[Cr3+]2[P5+]3[O2-]12. Solid-state UV/Vis spectra indicate that the crystal filed splitting(Δ0) of the Cr3+ ion is around 2.22 eV, which is in agreement with the green color of the crystals.

Related literature top

For the structures of Li3M2(PO4)3 (M = Fe, Sc, Cr, V), see: d'Yvoire et al. (1983); Verin et al. (1985); Maksimov et al. (1986). The structures of the orthorhombic form of Li3Cr2(PO4)3 have been investigated by Genkina et al. (1991). Structural studies of Li3V2(PO4)3 based on single-crystal data have been reported previously by Kee & Yun (2013). The general structural features of the monoclinic phases have been discussed by Patoux et al. (2003); Fu et al. (2010); Yang et al. (2010). For ionic radii, see: Shannon (1976).

Experimental top

The title compound, Li3Cr2(PO4)3, was prepared by the reaction of the elements with the use of the reactive halide-flux technique. A combination of the pure elements, Cr powder (Cerac, 99.95%) and P powder (Aldrich, 99%), were mixed in a fused silica tube in a molar ratio of Cr:P = 1:1 and then LiCl (Cerac, 99.8%) and CsCl (Alfa, 99.9%) mixed in molar ratio of LiCl:CsCl = 4:1 were added. The mass ratio of the reactants and the halides was 1:3. The tube was evacuated to 0.133 Pa, sealed, and heated gradually (30 K/h) to 1123 K, where it was kept for 48 h. The tube was cooled to room temperature at a rate of 4 K/h. The excess halide was removed with water and greenish block-shaped crystals were obtained. The crystals are stable in air and water. A qualitative X-ray fluorescence analysis of selected crystals indicated the presence of Cr and P. The final composition of the compound was determined by single-crystal X-ray diffraction.

Refinement top

After the positions of heavy elements (Cr, P, and O) had been established, six significant residual peaks suitable for Li+ sites were revealed by difference Fourier maps. A model including disorder for these sites was applied. The sum of the Li+ occupancies was fixed to 3 to meet the charge balance of the compound; the temperature factors of all Li sites were refined isotropically. The highest peak (0.71 e Å-3) and the deepest hole (-0.49 e Å-3) are 0.57 Å and 0.81 Å from atom Li4 and Cr1, respectively.

Computing details top

Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. A view showing the local coordination environments of Cr and P atoms with the atom labeling scheme. Displacement ellipsoids for Cr, P, and O atoms are drawn at the 70% probability level. [Symmetry codes: (ii) -x, y+1/2, -z+1/2; (iii) -x+1, y+1/2, -z+1/2; (iv) -x+1, y-1/2, -z+1/2; (v) -x+1, -y+1, -z; (vi) -x+1, -y+1, -z+1; (vii) -x, -y+1, -z; (viii) x, -y+1/2, z-1/2. ].
[Figure 2] Fig. 2. The polyhedral representation of the anionic framework structure built up from [Cr2(PO4)3] units. The disordered Li+ cations are located in the channels of this framework.
Trilithium dichromium(III) tris(orthophosphate) top
Crystal data top
Li3Cr2(PO4)3F(000) = 792
Mr = 409.73Dx = 3.164 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 8071 reflections
a = 8.4625 (4) Åθ = 3.4–27.7°
b = 8.5560 (3) ŵ = 3.16 mm1
c = 14.5344 (5) ÅT = 290 K
β = 125.186 (2)°Block, green
V = 860.08 (6) Å30.36 × 0.12 × 0.10 mm
Z = 4
Data collection top
Rigaku R-AXIS RAPID S
diffractometer
1962 independent reflections
Radiation source: Sealed X-ray tube1887 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
ω scansθmax = 27.5°, θmin = 3.4°
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
h = 1010
Tmin = 0.688, Tmax = 1.000k = 1110
8163 measured reflectionsl = 1818
Refinement top
Refinement on F21 restraint
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.026Secondary atom site location: difference Fourier map
wR(F2) = 0.068 w = 1/[σ2(Fo2) + (0.0319P)2 + 1.8772P]
where P = (Fo2 + 2Fc2)/3
S = 1.14(Δ/σ)max < 0.001
1962 reflectionsΔρmax = 0.71 e Å3
184 parametersΔρmin = 0.71 e Å3
Crystal data top
Li3Cr2(PO4)3V = 860.08 (6) Å3
Mr = 409.73Z = 4
Monoclinic, P21/cMo Kα radiation
a = 8.4625 (4) ŵ = 3.16 mm1
b = 8.5560 (3) ÅT = 290 K
c = 14.5344 (5) Å0.36 × 0.12 × 0.10 mm
β = 125.186 (2)°
Data collection top
Rigaku R-AXIS RAPID S
diffractometer
1962 independent reflections
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
1887 reflections with I > 2σ(I)
Tmin = 0.688, Tmax = 1.000Rint = 0.021
8163 measured reflectionsθmax = 27.5°
Refinement top
R[F2 > 2σ(F2)] = 0.026Δρmax = 0.71 e Å3
wR(F2) = 0.068Δρmin = 0.71 e Å3
S = 1.14Absolute structure: ?
1962 reflectionsAbsolute structure parameter: ?
184 parametersRogers parameter: ?
1 restraint
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Li10.4750 (10)0.2119 (8)0.1752 (6)0.022 (2)*0.71 (2)
Li20.104 (2)0.208 (2)0.3364 (14)0.022 (6)*0.30 (2)
Li30.1164 (11)0.5885 (9)0.1920 (7)0.017 (3)*0.59 (2)
Li40.1935 (14)0.1892 (12)0.2627 (8)0.036 (3)*0.64 (3)
Li50.672 (3)0.227 (2)0.2586 (15)0.019 (6)*0.27 (2)
Li60.273 (3)0.059 (3)0.1835 (19)0.072 (8)*0.48 (3)
Cr10.36305 (5)0.53352 (4)0.11142 (3)0.00608 (11)
Cr20.13604 (5)0.53218 (5)0.38801 (3)0.00787 (11)
P10.46068 (8)0.39077 (7)0.35382 (5)0.00707 (13)
P20.75261 (8)0.38724 (7)0.14717 (5)0.00693 (13)
P30.04107 (8)0.25059 (7)0.00513 (5)0.00717 (13)
O10.6057 (2)0.4162 (2)0.17588 (15)0.0129 (4)
O20.2909 (3)0.3809 (2)0.36484 (16)0.0138 (4)
O30.5955 (3)0.0119 (2)0.23933 (16)0.0181 (4)
O40.0766 (3)0.0017 (2)0.27885 (15)0.0124 (3)
O50.6674 (3)0.4170 (2)0.02547 (15)0.0135 (4)
O60.3515 (3)0.5558 (2)0.54233 (16)0.0197 (4)
O70.1224 (3)0.6330 (2)0.06579 (16)0.0135 (4)
O80.0340 (2)0.1757 (2)0.09856 (15)0.0135 (4)
O90.2391 (2)0.3295 (2)0.06304 (17)0.0166 (4)
O100.0217 (3)0.3652 (2)0.41922 (16)0.0156 (4)
O110.4784 (2)0.2282 (2)0.31441 (14)0.0106 (3)
O120.1852 (3)0.7155 (2)0.32091 (15)0.0140 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cr10.00427 (18)0.00702 (19)0.00645 (19)0.00016 (12)0.00280 (15)0.00019 (13)
Cr20.00503 (18)0.0106 (2)0.00828 (19)0.00115 (13)0.00402 (15)0.00151 (14)
P10.0064 (3)0.0078 (3)0.0061 (3)0.0019 (2)0.0030 (2)0.0007 (2)
P20.0054 (3)0.0085 (3)0.0063 (3)0.0014 (2)0.0031 (2)0.0000 (2)
P30.0053 (3)0.0063 (3)0.0100 (3)0.0001 (2)0.0045 (2)0.0001 (2)
O10.0089 (8)0.0216 (9)0.0095 (8)0.0060 (7)0.0060 (7)0.0022 (7)
O20.0112 (8)0.0133 (8)0.0197 (9)0.0001 (7)0.0106 (7)0.0023 (7)
O30.0348 (11)0.0105 (8)0.0154 (9)0.0066 (8)0.0182 (9)0.0043 (7)
O40.0105 (8)0.0128 (8)0.0095 (8)0.0013 (7)0.0033 (7)0.0010 (7)
O50.0140 (8)0.0171 (9)0.0089 (8)0.0027 (7)0.0062 (7)0.0018 (7)
O60.0117 (9)0.0235 (10)0.0146 (9)0.0025 (8)0.0023 (8)0.0065 (8)
O70.0117 (8)0.0122 (8)0.0186 (9)0.0053 (7)0.0099 (7)0.0053 (7)
O80.0100 (8)0.0180 (9)0.0108 (8)0.0009 (7)0.0050 (7)0.0038 (7)
O90.0076 (8)0.0083 (8)0.0302 (11)0.0018 (7)0.0087 (8)0.0017 (8)
O100.0115 (8)0.0191 (9)0.0157 (9)0.0037 (7)0.0075 (7)0.0043 (7)
O110.0125 (8)0.0081 (8)0.0086 (8)0.0038 (6)0.0045 (7)0.0002 (6)
O120.0216 (9)0.0100 (8)0.0151 (8)0.0057 (7)0.0133 (8)0.0041 (7)
Geometric parameters (Å, º) top
Li1—O31.934 (7)Cr1—O5v1.9007 (18)
Li1—O91.977 (7)Cr1—O71.9380 (17)
Li1—O112.011 (7)Cr1—O91.9471 (18)
Li1—O12.066 (7)Cr1—O11.9709 (17)
Li2—O41.908 (17)Cr1—O3iii1.9965 (18)
Li2—O22.028 (17)Cr1—O11iii2.0172 (17)
Li2—O102.170 (17)Cr2—O61.9192 (19)
Li2—O12i2.184 (17)Cr2—O101.9208 (18)
Li3—O71.902 (8)Cr2—O8ii1.9847 (18)
Li3—O121.943 (8)Cr2—O22.0041 (18)
Li3—O4ii2.049 (8)Cr2—O122.0129 (18)
Li3—O3iii2.137 (8)Cr2—O4ii2.0392 (18)
Li4—O81.953 (10)P1—O6vi1.4994 (19)
Li4—O41.969 (10)P1—O21.5368 (18)
Li4—O22.040 (10)P1—O111.5443 (17)
Li4—O112.098 (10)P1—O3iii1.5463 (19)
Li5—O11.900 (18)P2—O51.4979 (18)
Li5—O31.916 (18)P2—O12iv1.5394 (18)
Li5—O12iv2.103 (18)P2—O11.5424 (17)
Li5—O112.206 (18)P2—O4iii1.5532 (18)
Li5—O7iv2.252 (18)P3—O7vii1.5248 (18)
Li6—O81.93 (2)P3—O10viii1.5268 (19)
Li6—O1iv2.08 (2)P3—O91.5319 (18)
Li6—O112.22 (2)P3—O81.5337 (18)
Li6—O32.39 (2)
O5v—Cr1—O793.57 (8)O2—Cr2—O1294.84 (8)
O5v—Cr1—O995.83 (9)O6—Cr2—O4ii175.15 (8)
O7—Cr1—O991.63 (8)O10—Cr2—O4ii88.07 (8)
O5v—Cr1—O194.97 (8)O8ii—Cr2—O4ii90.18 (7)
O7—Cr1—O1171.08 (8)O2—Cr2—O4ii86.09 (8)
O9—Cr1—O184.97 (8)O12—Cr2—O4ii79.09 (8)
O5v—Cr1—O3iii172.27 (8)O6vi—P1—O2115.09 (11)
O7—Cr1—O3iii84.53 (8)O6vi—P1—O11112.02 (11)
O9—Cr1—O3iii91.72 (9)O2—P1—O11106.60 (10)
O1—Cr1—O3iii87.34 (8)O6vi—P1—O3iii106.84 (12)
O5v—Cr1—O11iii91.32 (8)O2—P1—O3iii107.11 (11)
O7—Cr1—O11iii93.70 (8)O11—P1—O3iii108.98 (10)
O9—Cr1—O11iii170.80 (8)O5—P2—O12iv111.51 (10)
O1—Cr1—O11iii88.66 (8)O5—P2—O1112.18 (10)
O3iii—Cr1—O11iii81.34 (8)O12iv—P2—O1105.13 (10)
O6—Cr2—O1094.07 (9)O5—P2—O4iii109.45 (11)
O6—Cr2—O8ii94.27 (8)O12iv—P2—O4iii111.89 (10)
O10—Cr2—O8ii86.83 (8)O1—P2—O4iii106.55 (10)
O6—Cr2—O289.50 (8)O7vii—P3—O10viii104.06 (10)
O10—Cr2—O291.50 (8)O7vii—P3—O9111.22 (10)
O8ii—Cr2—O2175.97 (8)O10viii—P3—O9107.65 (11)
O6—Cr2—O1299.31 (8)O7vii—P3—O8112.88 (10)
O10—Cr2—O12165.23 (8)O10viii—P3—O8114.36 (11)
O8ii—Cr2—O1285.96 (8)O9—P3—O8106.63 (11)
Symmetry codes: (i) x, y1/2, z+1/2; (ii) x, y+1/2, z+1/2; (iii) x+1, y+1/2, z+1/2; (iv) x+1, y1/2, z+1/2; (v) x+1, y+1, z; (vi) x+1, y+1, z+1; (vii) x, y+1, z; (viii) x, y+1/2, z1/2.

Experimental details

Crystal data
Chemical formulaLi3Cr2(PO4)3
Mr409.73
Crystal system, space groupMonoclinic, P21/c
Temperature (K)290
a, b, c (Å)8.4625 (4), 8.5560 (3), 14.5344 (5)
β (°) 125.186 (2)
V3)860.08 (6)
Z4
Radiation typeMo Kα
µ (mm1)3.16
Crystal size (mm)0.36 × 0.12 × 0.10
Data collection
DiffractometerRigaku R-AXIS RAPID S
diffractometer
Absorption correctionMulti-scan
(ABSCOR; Higashi, 1995)
Tmin, Tmax0.688, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
8163, 1962, 1887
Rint0.021
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.068, 1.14
No. of reflections1962
No. of parameters184
No. of restraints1
Δρmax, Δρmin (e Å3)0.71, 0.71

Computer programs: RAPID-AUTO (Rigaku, 2006), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1999), WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

Acknowledgements top

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (grant No. 2011– 0011309).

references
References top

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