A monoclinic polymorph of KY(PO₃)₄

The title compound, potassium yttrium polyphosphate, KY(PO₃)₄, was synthesized using the flux method. The atomic arrangement consists of an infinite long-chain polyphosphate organization. Chains, with a period of four PO₄ tetra­hedra, run along the a-axis direction. Two other polymorphs of this phosphate are known, in space groups P21/n and C2/c.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](P-O) = 0.006 Å
• R factor = 0.048
• wR factor = 0.138
• Data-to-parameter ratio = 12.2

checkCIF/PLATON results

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Alert level C
PLAT395_ALERT_2_C Deviating  X-O-Y  Angle from 120 Deg for      O7     147.40 Deg.

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           27.49
           From the CIF: _reflns_number_total               2011
           Count of symmetry unique reflns         1157
           Completeness (_total/calc)            173.81%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       854
           Fraction of Friedel pairs measured     0.738
           Are heavy atom types Z>Si present        yes

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Yttrium condensed phosphates have been considered as a crystal hosts for optical materials when doped with lanthanides, due to there high-temperature chemical stability, high yield intrinsic fluorescence and minimal trapping of excitation, rendering them attractive materials for investigations of the energy transfer phenomena and fluorescence quenching(Malinowski, 1990; Malinowski et al., 1988). The literature dealing with these compounds was rather confusing for some time, between cyclic or chain condensed phosphates, but it is currently well established that the M^IY(PO₃)₄ compounds are polyphosphates with infinite chain and M^IYP₄O₁₂ are cyclotetraphosphates (with M^I= monovalent cation) (Durif, 1995). In our laboratory we have synthesized the potassium and yttrium polyphosphates to establish the solid–liquid equilibrium diagram of the KPO₃–Y(PO₃)₃ system (Jouini et al., 2003). Three allotropic phases with the space groups P2₁, P2₁/n and C2/c were isolated and characterized. The three monoclinic allotropes are: i) KY(PO₃)₄ polyphosphate with the P2₁ space group, isostructural with KNd(PO₃)₄ (Hong, 1975). ii) KY(PO₃)₄ polyphosphate belongs to P2₁/n space group, and is isostructural with TlNd(PO₃)₄ (Palkina et al., 1977). In these two forms the phosphate anion has a chain structure. iii) The third allotropic form is KYP₄O₁₂ which crystallizes in the C2/c space group, only this structure was investigated (Hamady, 1995). This paper is devoted to the crystal structure of the first polymorph KY(PO₃)₄ (P2₁). The atomic arrangement of this srtucture is characterized by a three-dimensional framework built of (PO₃)_n chains that are formed by corner-sharing of PO₄ tetrahedra (Figs 1,2). The chains run along the a axis , with four PO₄ tetrahedra in a repeating unit. KY(PO₃)₄ is isostructural with KNd(PO₃)₄ , but not with CsLa(PO₃)₄ (Sun et al., 2004) although they belong to the same space group, P2₁. In the latter, the infinite screw (PO₃)_n chains are repeated after every eighth PO₄ group along the b axis. The chains (two per unit cell) are joined to each other by YO₈ polyhedra (Fig 3.), no O atom is shared with the adjacent YO₈ polyhedra. The K atoms are in an eightfold coordination.

Related literature

For related structures, see: Durif (1995); Hamady et al. (1995); Hong et al. (1975); Malinowski (1990); Malinowski et al. (1988); Palkina et al. (1977). For earlier work on KY(PO₃)₄, see: Jouini et al. (2003). For related literature, Sun et al. (2004).

S2. Experimental

Single crystal of KY(PO₃)₄ was prepared by flux method. Homogeneous solution of potassium carbonate K₂CO₃ (6 g) and yttrium oxide Y₂O₃ (0.5 g) containing a large excess of orthophosphoric acid H₃PO₄ (16 ml, 85% concentration) was heated in a vitreous carbon crucible at 473 K for 1 day. Then the temperature of the furnace was slowly raised to the predermined temperature in the range of 573–623 K for 7 days. Crystals were separated from the excess phosphoric acid by washing the product in boiling water.

S3. Refinement

The highest peak and the deepest hole are located 0.09Å and 0.85 Å from Y.

Computing details

Data collection: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); cell refinement: CAD-4 EXPRESS (Duisenberg, 1992; Macíček & Yordanov, 1992); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. : Projection of KY(PO3)4 with anisotropic displacement parameters drawn at the 50% probability level.
	Fig. 2. : The structural arrangement of KY(PO3)4 along the b axis.
	Fig. 3. : Projection of KY(PO3)4 along the a axis, showing isolated YO8 polyhedra joined to (PO3)n chains.

Potassium yttrium polyphosphate

Crystal data

KY(PO3)4	F(000) = 428
Mr = 443.89	Dx = 3.138 Mg m^−3
Monoclinic, P21	Melting point: 760 K
Hall symbol: P 2yb	Mo Kα radiation, λ = 0.71073 Å
a = 7.2244 (3) Å	Cell parameters from 25 reflections
b = 8.2825 (3) Å	θ = 2.6–27.5°
c = 7.854 (4) Å	µ = 7.40 mm^−1
β = 91.735 (3)°	T = 298 K
V = 469.7 (2) Å^3	Prism, colourless
Z = 2	0.16 × 0.14 × 0.13 mm

Data collection

Enraf–Nonius CAD-4 diffractometer	1904 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.081
Graphite monochromator	θmax = 27.5°, θmin = 2.6°
ω/2θ scans	h = −7→9
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	k = −8→10
Tmin = 0.321, Tmax = 0.376	l = −8→10
3651 measured reflections	2 standard reflections every 150 reflections
2011 independent reflections	intensity decay: 2%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0908P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.048	(Δ/σ)max < 0.001
wR(F^2) = 0.138	Δρmax = 1.19 e Å^−3
S = 1.13	Δρmin = −2.67 e Å^−3
2011 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
165 parameters	Extinction coefficient: 0.065 (7)
1 restraint	Absolute structure: Flack (1983), with 867 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.002 (9)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
Y	0.23704 (8)	0.75897 (9)	0.24245 (8)	0.0086 (3)
K	0.2703 (3)	0.4566 (3)	−0.2812 (3)	0.0303 (6)
P1	0.4367 (3)	0.3830 (2)	0.0947 (3)	0.0091 (4)
P2	0.0994 (3)	0.1755 (2)	0.0978 (2)	0.0086 (4)
P3	−0.0018 (3)	0.4085 (2)	0.3809 (2)	0.0088 (4)
P4	0.6161 (3)	0.5114 (2)	0.3992 (2)	0.0084 (4)
O1	0.3212 (8)	0.5292 (7)	0.0721 (7)	0.0140 (12)
O2	0.5736 (8)	0.3558 (8)	−0.0387 (8)	0.0184 (13)
O3	0.3126 (7)	0.2261 (7)	0.1093 (8)	0.0169 (13)
O4	0.5360 (8)	0.3706 (7)	0.2789 (7)	0.0139 (12)
O5	0.0239 (8)	0.2062 (7)	−0.0776 (7)	0.0150 (12)
O6	0.0880 (8)	0.0105 (7)	0.1732 (7)	0.0163 (12)
O7	−0.0076 (8)	0.2991 (7)	0.2159 (8)	0.0189 (13)
O8	0.1660 (7)	0.5100 (7)	0.3846 (7)	0.0124 (11)
O9	−0.0337 (8)	0.3109 (7)	0.5348 (8)	0.0167 (12)
O10	−0.1755 (8)	0.5225 (7)	0.3407 (7)	0.0121 (11)
O11	0.5258 (8)	0.6648 (7)	0.3514 (7)	0.0138 (11)
O12	0.6118 (7)	0.4535 (7)	0.5773 (7)	0.0121 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Y	0.0092 (4)	0.0103 (4)	0.0067 (4)	−0.0004 (3)	0.0048 (2)	−0.0001 (2)
K	0.0180 (10)	0.0601 (16)	0.0129 (8)	0.0108 (9)	0.0031 (7)	−0.0019 (10)
P1	0.0100 (9)	0.0098 (10)	0.0080 (9)	−0.0003 (7)	0.0044 (7)	−0.0004 (6)
P2	0.0084 (9)	0.0095 (9)	0.0082 (9)	−0.0008 (6)	0.0034 (7)	−0.0004 (7)
P3	0.0090 (9)	0.0107 (10)	0.0070 (9)	−0.0009 (7)	0.0055 (7)	0.0003 (7)
P4	0.0086 (9)	0.0088 (9)	0.0081 (8)	0.0003 (6)	0.0032 (7)	0.0001 (6)
O1	0.018 (3)	0.012 (3)	0.012 (3)	0.001 (2)	0.003 (2)	−0.001 (2)
O2	0.021 (3)	0.021 (3)	0.014 (3)	0.007 (2)	0.011 (2)	−0.001 (2)
O3	0.010 (3)	0.018 (3)	0.023 (3)	−0.003 (2)	0.000 (2)	−0.004 (2)
O4	0.016 (3)	0.015 (3)	0.011 (3)	0.001 (2)	−0.002 (2)	0.000 (2)
O5	0.014 (3)	0.020 (3)	0.011 (3)	0.004 (2)	0.002 (2)	−0.003 (2)
O6	0.019 (3)	0.011 (3)	0.019 (3)	0.003 (2)	−0.002 (2)	0.004 (2)
O7	0.018 (3)	0.020 (3)	0.019 (3)	0.003 (2)	0.008 (2)	−0.010 (2)
O8	0.008 (3)	0.016 (3)	0.013 (3)	−0.004 (2)	0.004 (2)	0.004 (2)
O9	0.017 (3)	0.019 (3)	0.015 (3)	0.003 (2)	0.010 (2)	0.007 (2)
O10	0.011 (3)	0.015 (3)	0.011 (3)	−0.002 (2)	0.005 (2)	0.003 (2)
O11	0.012 (3)	0.015 (3)	0.014 (3)	0.003 (2)	0.000 (2)	0.002 (2)
O12	0.010 (2)	0.019 (3)	0.008 (2)	0.005 (2)	0.002 (2)	0.000 (2)

Geometric parameters (Å, º)

Y—O2^i	2.282 (6)	P1—O1	1.479 (6)
Y—O5^ii	2.296 (6)	P1—O2	1.480 (6)
Y—O9^iii	2.358 (6)	P1—O3	1.585 (6)
Y—O11	2.363 (5)	P1—O4	1.599 (5)
Y—O12^iv	2.387 (5)	P2—O5	1.488 (6)
Y—O6^v	2.400 (6)	P2—O6	1.492 (6)
Y—O8	2.408 (6)	P2—O3	1.597 (6)
Y—O1	2.415 (6)	P2—O7	1.597 (6)
Y—K^i	3.921 (2)	P3—O8	1.474 (6)
K—O12^vi	2.736 (6)	P3—O9	1.478 (6)
K—O8^vi	2.744 (6)	P3—O7	1.581 (6)
K—O6^ii	2.785 (6)	P3—O10	1.594 (6)
K—O1	2.852 (6)	P4—O11	1.472 (6)
K—O9^vi	2.859 (7)	P4—O12	1.480 (6)
K—O11^vii	2.892 (7)	P4—O10^viii	1.590 (6)
K—O2	2.979 (6)	P4—O4	1.598 (6)
K—O5	3.194 (6)
O2^i—Y—O5^ii	99.8 (2)	O9^vi—K—O11^vii	86.49 (17)
O2^i—Y—O9^iii	148.9 (2)	O12^vi—K—O2	66.57 (16)
O5^ii—Y—O9^iii	86.2 (2)	O8^vi—K—O2	146.32 (18)
O2^i—Y—O11	80.1 (2)	O6^ii—K—O2	121.50 (18)
O5^ii—Y—O11	147.3 (2)	O1—K—O2	50.68 (17)
O9^iii—Y—O11	110.8 (2)	O9^vi—K—O2	138.0 (2)
O2^i—Y—O12^iv	84.6 (2)	O11^vii—K—O2	61.22 (17)
O5^ii—Y—O12^iv	144.7 (2)	O12^vi—K—O5	136.07 (19)
O9^iii—Y—O12^iv	73.79 (19)	O8^vi—K—O5	116.25 (17)
O11—Y—O12^iv	67.98 (19)	O6^ii—K—O5	54.12 (17)
O2^i—Y—O6^v	79.1 (2)	O1—K—O5	72.96 (18)
O5^ii—Y—O6^v	71.5 (2)	O9^vi—K—O5	63.10 (17)
O9^iii—Y—O6^v	74.0 (2)	O11^vii—K—O5	81.22 (17)
O11—Y—O6^v	138.9 (2)	O2—K—O5	84.71 (17)
O12^iv—Y—O6^v	75.09 (19)	O1—P1—O2	115.3 (4)
O2^i—Y—O8	140.1 (2)	O1—P1—O3	111.2 (3)
O5^ii—Y—O8	85.16 (19)	O2—P1—O3	108.5 (4)
O9^iii—Y—O8	70.5 (2)	O1—P1—O4	113.4 (3)
O11—Y—O8	75.39 (19)	O2—P1—O4	109.9 (3)
O12^iv—Y—O8	113.77 (19)	O3—P1—O4	97.0 (3)
O6^v—Y—O8	138.4 (2)	O5—P2—O6	120.0 (3)
O2^i—Y—O1	73.9 (2)	O5—P2—O3	109.5 (3)
O5^ii—Y—O1	75.7 (2)	O6—P2—O3	106.4 (3)
O9^iii—Y—O1	136.7 (2)	O5—P2—O7	104.9 (3)
O11—Y—O1	72.9 (2)	O6—P2—O7	108.9 (4)
O12^iv—Y—O1	137.92 (19)	O3—P2—O7	106.4 (3)
O6^v—Y—O1	132.6 (2)	O8—P3—O9	116.4 (4)
O8—Y—O1	69.1 (2)	O8—P3—O7	110.1 (3)
O12^vi—K—O8^vi	80.69 (17)	O9—P3—O7	110.9 (4)
O12^vi—K—O6^ii	169.5 (2)	O8—P3—O10	107.9 (3)
O8^vi—K—O6^ii	91.99 (17)	O9—P3—O10	110.2 (3)
O12^vi—K—O1	107.81 (17)	O7—P3—O10	100.1 (3)
O8^vi—K—O1	156.9 (2)	O11—P4—O12	120.0 (3)
O6^ii—K—O1	76.31 (17)	O11—P4—O10^viii	107.0 (3)
O12^vi—K—O9^vi	118.63 (18)	O12—P4—O10^viii	109.8 (3)
O8^vi—K—O9^vi	53.15 (16)	O11—P4—O4	109.3 (3)
O6^ii—K—O9^vi	60.95 (18)	O12—P4—O4	107.7 (3)
O1—K—O9^vi	130.90 (19)	O10^viii—P4—O4	101.5 (3)
O12^vi—K—O11^vii	56.23 (17)	P1—O3—P2	139.3 (4)
O8^vi—K—O11^vii	94.54 (19)	P4—O4—P1	129.2 (4)
O6^ii—K—O11^vii	132.5 (2)	P3—O7—P2	147.4 (4)
O1—K—O11^vii	108.06 (18)	P4^ix—O10—P3	130.9 (4)

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