NASICON-type Li_2.5K_0.16Na_0.34Cr₂(PO₄)₃

A new NASICON-type chromium(III) phosphate, K_0.16Na_0.34Li_2.5Cr₂(PO₄)₃, lithium sodium potassium dichrom­ate tris­(phosphate), has been prepared by solid-state reaction. It consists of CrO₆ octa­hedra and PO₄ tetra­hedra sharing corners to form a three-dimensional framework. The monovalent cations are located in the M1 (six-coordinate) and M2 (four-coordinate) sites of the framework. The M1 site is occupied by Na⁺ and K⁺ cations with 69 (3) and 31 (3)% occupancy, respectively. The Li⁺ ions, Li1 and Li2, are split over two M2 sites in general positions, with 60 (2) and 40 (2)% occupancy, respectively. Atom Li2 is disordered around a threefold inversion axis.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](P-O) = 0.002 Å
• Disorder in solvent or counterion
• R factor = 0.025
• wR factor = 0.072
• Data-to-parameter ratio = 9.7

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT068_ALERT_1_C Reported F000 Differs from Calcd (or Missing)...          ?
PLAT077_ALERT_4_C Unitcell contains non-integer number of atoms ..          ?
PLAT088_ALERT_3_C Poor Data / Parameter Ratio ....................       9.67
PLAT199_ALERT_1_C Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_C Check the Reported _diffrn_ambient_temperature .        293 K
PLAT202_ALERT_3_C Isotropic non-H Atoms in Anion/Solvent .........          1
PLAT302_ALERT_4_C Anion/Solvent Disorder .........................      42.00 Perc.

Alert level G
CELLZ01_ALERT_1_G Difference between formula and atom_site contents detected.
CELLZ01_ALERT_1_G ALERT: check formula stoichiometry or atom site occupancies.
           From the CIF: _cell_formula_units_Z    6
           From the CIF: _chemical_formula_sum  Cr2 K0.16 Li2.50 Na0.34 O12 P3
           TEST: Compare cell contents of formula and atom_site data

           atom    Z*formula  cif sites diff
           Cr        12.00     12.00    0.00
           K          0.96      0.93    0.03
           Li        15.00     14.99    0.01
           Na         2.04      2.07   -0.03
           O         72.00     72.00    0.00
           P         18.00     18.00    0.00

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   8 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   6 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97.

Li_2.5Na_0.34K_0.16Cr₂(PO₄)₃

Crystal data

Li2.5Na0.34K0.16Cr2(PO4)3	Dx = 3.124 Mg m^−3
Mr = 420.31	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, R3	Cell parameters from 25 reflections
Hall symbol: -R 3	θ = 10–16°
a = 8.300 (2) Å	µ = 3.13 mm^−1
c = 22.469 (5) Å	T = 293 K
V = 1340.5 (5) Å^3	Hexagon, green
Z = 6	0.15 × 0.12 × 0.08 mm
F(000) = 1220

Data collection

Enraf–Nonius CAD-4 diffractometer	572 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.027
Graphite monochromator	θmax = 26.9°, θmin = 2.7°
ω/2θ scans	h = −10→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→10
Tmin = 0.644, Tmax = 0.779	l = −28→28
2047 measured reflections	2 standard reflections every 120 min
648 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.025	w = 1/[σ^2(Fo^2) + (0.0328P)^2 + 7.8382P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.072	(Δ/σ)max < 0.001
S = 1.13	Δρmax = 0.89 e Å^−3
648 reflections	Δρmin = −0.48 e Å^−3
67 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997)
2 restraints	Extinction coefficient: 0.0016 (4)

Special details

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cr1	0.6667	0.3333	−0.02212 (3)	0.0070 (3)
Cr2	0.6667	0.3333	0.18177 (4)	0.0073 (3)
P	0.66663 (10)	0.62046 (10)	0.08315 (3)	0.0064 (2)
K	0.0000	0.0000	0.0000	0.0406 (15)	0.31 (3)
Na	0.0000	0.0000	0.0000	0.0406 (15)	0.69 (3)
O1	0.6759 (3)	0.5335 (3)	0.02513 (10)	0.0171 (5)
O2	0.5368 (3)	0.7028 (3)	0.07835 (9)	0.0114 (5)
O3	0.8649 (3)	0.7770 (3)	0.09910 (9)	0.0111 (5)
O4	0.5811 (3)	0.4765 (3)	0.13478 (10)	0.0145 (5)
Li1	0.3053 (13)	0.3534 (13)	0.1160 (4)	0.006 (2)*	0.504 (15)
Li2	0.236 (2)	0.565 (2)	0.1678 (8)	0.012 (5)*	0.329 (15)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr1	0.0071 (3)	0.0071 (3)	0.0069 (4)	0.00354 (15)	0.000	0.000
Cr2	0.0066 (3)	0.0066 (3)	0.0086 (4)	0.00328 (15)	0.000	0.000
P	0.0061 (4)	0.0053 (4)	0.0076 (4)	0.0027 (3)	−0.0017 (3)	−0.0011 (2)
K	0.0572 (19)	0.0572 (19)	0.0075 (16)	0.0286 (10)	0.000	0.000
Na	0.0572 (19)	0.0572 (19)	0.0075 (16)	0.0286 (10)	0.000	0.000
O1	0.0226 (13)	0.0172 (12)	0.0153 (11)	0.0128 (11)	−0.0048 (10)	−0.0081 (9)
O2	0.0118 (10)	0.0135 (11)	0.0127 (10)	0.0093 (9)	−0.0041 (8)	−0.0030 (8)
O3	0.0065 (10)	0.0075 (10)	0.0167 (10)	0.0016 (8)	−0.0015 (8)	−0.0032 (8)
O4	0.0103 (11)	0.0146 (11)	0.0190 (11)	0.0065 (9)	0.0017 (9)	0.0078 (9)

Geometric parameters (Å, º)

Cr1—O1^i	1.940 (2)	P—O4	1.559 (2)
Cr1—O1^ii	1.940 (2)	K—O3^ii	2.751 (2)
Cr1—O1	1.940 (2)	K—O3^ix	2.751 (2)
Cr1—O2^iii	2.008 (2)	K—O3^x	2.751 (2)
Cr1—O2^iv	2.008 (2)	K—O3^xi	2.751 (2)
Cr1—O2^v	2.008 (2)	K—O3^xii	2.751 (2)
Cr2—O4^ii	1.968 (2)	K—O3^v	2.751 (2)
Cr2—O4^i	1.968 (2)	Li1—O4	2.031 (10)
Cr2—O4	1.968 (2)	Li1—O2^ix	1.983 (10)
Cr2—O3^vi	1.999 (2)	Li1—O3^ii	1.991 (10)
Cr2—O3^vii	1.999 (2)	Li1—O4^viii	2.221 (10)
Cr2—O3^viii	1.999 (2)	Li2—O2^ix	2.145 (17)
P—O1	1.511 (2)	Li2—O2^xiii	2.323 (19)
P—O2	1.542 (2)	Li2—O2^viii	2.438 (19)
P—O3	1.545 (2)	Li2—O4^ix	2.570 (19)
O1—P—O2	111.44 (13)	O3^x—K—O3^xi	118.88 (7)
O1—P—O3	108.35 (13)	O3^ii—K—O3^xii	118.88 (7)
O2—P—O3	109.28 (12)	O3^ix—K—O3^xii	180.00 (11)
O1—P—O4	112.85 (14)	O3^x—K—O3^xii	61.12 (7)
O2—P—O4	103.92 (12)	O3^xi—K—O3^xii	118.88 (7)
O3—P—O4	110.94 (12)	O3^ii—K—O3^v	118.88 (7)
O3^ii—K—O3^ix	61.12 (7)	O3^ix—K—O3^v	118.88 (7)
O3^ii—K—O3^x	180.00 (5)	O3^x—K—O3^v	61.12 (7)
O3^ix—K—O3^x	118.88 (7)	O3^xi—K—O3^v	180.00 (10)
O3^ii—K—O3^xi	61.12 (7)	O3^xii—K—O3^v	61.12 (7)
O3^ix—K—O3^xi	61.12 (7)

Symmetry codes: (i) −x+y+1, −x+1, z; (ii) −y+1, x−y, z; (iii) y, −x+y, −z; (iv) x−y+1, x, −z; (v) −x+1, −y+1, −z; (vi) x−y+2/3, x−2/3, −z+1/3; (vii) −x+5/3, −y+4/3, −z+1/3; (viii) y−1/3, −x+y+1/3, −z+1/3; (ix) −x+y, −x+1, z; (x) y−1, −x+y, −z; (xi) x−1, y−1, z; (xii) x−y, x−1, −z; (xiii) −x+2/3, −y+4/3, −z+1/3.