inorganic compounds
KPr(PO_{3})_{4}
^{a}Université Cadi Ayyad, Laboratoire de la Matière Condensée et de l'Environnement, Faculté des Sciences Semlalia, Département de Chimie, BP 2390, 40000 Marrakech, Morocco, and ^{b}Université Blaise Pascal, Laboratoire des Matériaux Inorganiques, UMR CNRS 6002, 24 Avenue des Landais, 63177 Aubière, France
^{*}Correspondence email: daniel.avignant@univbpclermont.fr
Single crystals of the title compound, potassium praseodymium(III) polyphosphate, were obtained by solidstate reaction. The monoclinic noncentrosymmetric structure is isotypic with all other KLn(PO_{3})_{4} analogues from Ln = La to Er, inclusive. The of these longchain polyphosphates is built up from infinite crenelated polyphosphate chains of cornersharing PO_{4} tetrahedra with a repeating unit of four tetrahedra. These chains, running along [100], are arranged in a pseudotetragonal rod packing and are further linked by isolated PrO_{8} square antiprisms [Pr—O = 2.3787 (9)–2.5091 (8) Å], forming a threedimensional framework. The K^{+} ions reside in channels parallel to [010] and exhibit a highly distorted coordination sphere by eight O atoms at distances ranging from 2.7908 (9) to 3.1924 (11) Å.
Related literature
Longchain polyphosphates with general formula A^{I}B^{III}(PO_{3})_{4} have been classified into seven structural types, labelled from I to VII (Jaoudi et al., 2003). All KLn(PO_{3})_{4} polyphosphates (Ln is a trivalent rare earth element) reported up to now adopt type III except for KYb(PO_{3})_{4} (Palkina et al., 1981). For corresponding isotypic crystal structures, see: Zhu et al. (2009) for Ce and Eu; HorchaniNaifer et al. (2008) for Y; Parreu et al. (2006) for Gd and Nd; Xing et al. (1987) for Tb; Ninghai et al. (1984) for Eu; Lin et al. (1983) for La; Krutik et al. (1980) for Er; Hong et al. (1975) for Nd. For a review of the crystal chemistry of phosphates, see: Durif (1995). For the cyclophosphate structure with the same composition, KPr(PO_{3})_{4}, see: Zhou et al. (1987).
Experimental
Crystal data

Data collection: APEX2 (Bruker, 2008); cell SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: CaRine (Boudias & Monceau, 1998) and ORTEP3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
Supporting information
https://doi.org//10.1107/S1600536810026942/wm2370sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org//10.1107/S1600536810026942/wm2370Isup2.hkl
Crystals of the title compound were synthesized by reacting Pr_{6}O_{11} with (NH_{4})H_{2}PO_{4} and K_{2}CO_{3} in a platinum crucible. A mixture of these reagents in the molar ratio 14: 66: 20 was used for the synthesis. The mixture has first been heated at 473 K for 12 h and then the temperature has been increased up to 573 K and maintained for 12 h before to be raised at 853 K and kept for 24 additional hours. At the end of this heating step, the muffle furnace was cooled down first to 673 K at the rate of 2 K h^{1} and subsequently to room temperature by switching the power off. Single crystals were extracted from the batch by leaching with hot water.
The highest residual peak in the final difference Fourier map was located 0.46 Å from atom Pr and the deepest hole was located 0.47 Å from atom K.
Long chains polyphosphates with general formula A^{I}B^{III}(PO_{3})_{4} have been classified into seven structural types, labelled from I to VII (Durif, 1995; Jaoudi et al. 2003). All longchains polyphosphates of formula KLn(PO_{3})_{4} (Ln = rare earth elements) reported up to now (Zhu et al., 2009; HorchaniNaifer et al., 2008; Parreu et al., 2006; Xing et al., 1987; Ninghai et al., 1984; Lin et al., 1983; Krutik et al., 1980; Hong et al., 1975) adopt type III except for KYb(PO_{3})_{4} (Palkina et al. 1981) which is the only presently known member of type V. Most of these potassium polyphosphates are dimorphic and crystallize with both the type III and the type IV polymorphs. KCe(PO_{3})_{4} which has been shown to crystallize with either the type II and the type III is the first exception. The second exception is concerned with the Er member of this series presenting the type VII polymorph besides both type III and type IV polymorphs. Moreover, type III longchain polyphosphates do not exist for monovalent cations other than K^{+}. The structure of the title compound also fits in this type III isotypic series.
The _{∞} chains stacked in a pseudotetragonal rod packing as shown in Fig. 2. Figure 2 also shows that within this pseudotetragonal rod packing, two adjacent chains are twisted by ca. 90 ° whereas two opposite chains are parallel. The relative disposition of the chains running along the [100] direction accounts for the strong noncentrosymmetric character of the structure. Figure 3 displays details of the connections between the PrO_{8} square antiprisms and the four chains surrounding each antiprism. One of the four chains (labelled C_{1}) is attached in a tridentate fashion on a triangular face of the square antiprism whereas the opposite and parallel chain (labelled C_{2}) is connected only through a vertex (Fig. 3a). The two other chains which are adjacent to the first one are attached in a bidentate fashion. The first of these two chains (labelled C_{3}) is linked through a bidentate diphosphate group attached on one side of one square face of the square antiprism (Fig. 3b). The second chain (labelled C_{4}) is connected at the ends of one diagonal of the second square face of the antiprism (Fig. 3c) through corners of the terminal PO_{4} groups of the crenelshaped tetraphosphate group corresponding to the repeating unit of the chain. This polyhedral linkage delimits channels running along [010] where the K^{+}ions lie in a highly distorted environment defined by eight oxygen atoms at distances ranging from 2.7908 (9) to 3.1924 (11) Å.
of the title compound is built from crenelated chains with a repeating unit of four cornersharing tetrahedra, as displayed in Fig. 1. The chains are further linked by isolated PrO_{8} square antiprisms to form the threedimensional framework. Each PrO_{8} polyhedron (Pr—O distances range from 2.3787 (9) to 2.5091 (8) Å) is connected through vertices to four (PO_{3})For the cyclophosphate structure with the same composition KPr(PO_{3})_{4}, see: (Zhou et al., 1987).
Longchain polyphosphates with general formula A^{I}B^{III}(PO_{3})_{4} have been classified into seven structural types, labelled from I to VII (Jaoudi et al., 2003). All KLn(PO_{3})_{4} polyphosphates (Ln is a trivalent rare earth element) reported up to now adopt type III except for KYb(PO_{3})_{4} (Palkina et al., 1981). For corresponding isotypic crystal structures, see: Zhu et al. (2009) for Ce and Eu; HorchaniNaifer et al. (2008) for Y; Parreu et al. (2006) for Gd and Nd; Xing et al. (1987) for Tb; Ninghai et al. (1984) for Eu; Lin et al. (1983) for La; Krutik et al. (1980) for Er; Hong et al. (1975) for Nd. For a review of the crystal chemistry of phosphates, see: Durif (1995). For the cyclophosphate structure with the same composition, KPr(PO_{3})_{4}, see: Zhou et al. (1987).
Data collection: APEX2 (Bruker, 2008); cell
SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: CaRine (Boudias & Monceau, 1998) and ORTEP3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).Fig. 1. View of the repeating unit of the (PO_{3})_{∞} chains. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (vi) x + 1, y + 1/2, z + 1; (vii) x, y, z  1; (viii) x, y + 1/2, z + 1; (ix) x  1, y, z.]  
Fig. 2. Projection along [100] showing the pseudotetragonal rod packing of the infinite (PO_{3}) chains.  
Fig. 3. Details of the connections between the (PO_{3})_{∞} chains and the PrO_{8} square antiprisms: a) view showing the tridentate attachement of one chain (C_{1}) and the connection of the second chain (C_{2}) parallel and opposite to the first one. b) view showing the bidentate attachement of the third chain (C_{3}) adjacent and orthogonal to the first one. c) view showing the bidentate attachement of the fourth chain (C_{4}) also orthogonal and adjacent to the first one. 
KPr(PO3)_{4}  F(000) = 468 
M_{r} = 495.89  D_{x} = 3.331 Mg m^{−}^{3} 
Monoclinic, P2_{1}  Mo Kα radiation, λ = 0.71073 Å 
Hall symbol: P 2yb  Cell parameters from 9960 reflections 
a = 7.2872 (2) Å  θ = 2.8–57.3° 
b = 8.4570 (3) Å  µ = 6.06 mm^{−}^{1} 
c = 8.0268 (2) Å  T = 296 K 
β = 91.994 (1)°  Prism, green 
V = 494.37 (3) Å^{3}  0.29 × 0.21 × 0.16 mm 
Z = 2 
Bruker APEXII CCD diffractometer  13443 independent reflections 
Radiation source: finefocus sealed tube  13257 reflections with I > 2σ(I) 
Graphite monochromator  R_{int} = 0.034 
Detector resolution: 8.3333 pixels mm^{1}  θ_{max} = 57.4°, θ_{min} = 3.7° 
ω and φ scans  h = −17→17 
Absorption correction: multiscan (SADABS; Bruker, 2008)  k = −19→20 
T_{min} = 0.448, T_{max} = 0.751  l = −18→18 
45940 measured reflections 
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  w = 1/[σ^{2}(F_{o}^{2}) + (0.P)^{2} + 0.0715P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
R[F^{2} > 2σ(F^{2})] = 0.018  (Δ/σ)_{max} = 0.004 
wR(F^{2}) = 0.043  Δρ_{max} = 2.86 e Å^{−}^{3} 
S = 1.07  Δρ_{min} = −2.42 e Å^{−}^{3} 
13443 reflections  Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
164 parameters  Extinction coefficient: 0.0305 (6) 
1 restraint  Absolute structure: Flack (1983), 6278 Friedel pairs 
0 constraints  Absolute structure parameter: 0.022 (3) 
Primary atom site location: structureinvariant direct methods 
KPr(PO3)_{4}  V = 494.37 (3) Å^{3} 
M_{r} = 495.89  Z = 2 
Monoclinic, P2_{1}  Mo Kα radiation 
a = 7.2872 (2) Å  µ = 6.06 mm^{−}^{1} 
b = 8.4570 (3) Å  T = 296 K 
c = 8.0268 (2) Å  0.29 × 0.21 × 0.16 mm 
β = 91.994 (1)° 
Bruker APEXII CCD diffractometer  13443 independent reflections 
Absorption correction: multiscan (SADABS; Bruker, 2008)  13257 reflections with I > 2σ(I) 
T_{min} = 0.448, T_{max} = 0.751  R_{int} = 0.034 
45940 measured reflections 
R[F^{2} > 2σ(F^{2})] = 0.018  1 restraint 
wR(F^{2}) = 0.043  Δρ_{max} = 2.86 e Å^{−}^{3} 
S = 1.07  Δρ_{min} = −2.42 e Å^{−}^{3} 
13443 reflections  Absolute structure: Flack (1983), 6278 Friedel pairs 
164 parameters  Absolute structure parameter: 0.022 (3) 
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 F^{2} against ALL reflections. The weighted Rfactor wR and goodness of fit S are based on F^{2}, conventional Rfactors R are based on F, with F set to zero for negative F^{2}. The threshold expression of F^{2} > σ(F^{2}) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. Rfactors based on F^{2} are statistically about twice as large as those based on F, and R factors based on ALL data will be even larger. 
x  y  z  U_{iso}*/U_{eq}  
K  0.77227 (5)  0.31500 (7)  0.72001 (4)  0.02909 (8)  
Pr  0.265282 (4)  0.119995 (8)  0.757982 (4)  0.00552 (1)  
P1  0.50137 (3)  0.26677 (3)  0.38019 (3)  0.00690 (3)  
P2  0.93476 (3)  0.24280 (3)  0.09865 (3)  0.00685 (3)  
P3  0.12252 (3)  0.37267 (3)  0.39531 (3)  0.00674 (3)  
P4  0.60346 (3)  0.04117 (3)  0.10444 (3)  0.00675 (3)  
O1  1.04301 (12)  0.23711 (10)  0.27436 (11)  0.01360 (11)  
O2  0.81354 (11)  0.08886 (10)  0.12702 (13)  0.01412 (12)  
O3  −0.03801 (11)  0.02642 (9)  0.65100 (11)  0.01191 (10)  
O4  0.11151 (11)  0.31458 (11)  0.56903 (9)  0.01188 (10)  
O5  0.33093 (10)  0.38001 (9)  0.34329 (10)  0.01061 (9)  
O6  0.66909 (10)  0.36646 (10)  0.38630 (10)  0.01127 (9)  
O7  0.18250 (12)  −0.11539 (10)  0.92653 (10)  0.01172 (10)  
O8  0.41427 (12)  0.38104 (10)  0.82424 (13)  0.01527 (12)  
O9  0.53826 (12)  0.07174 (11)  0.93036 (10)  0.01395 (12)  
O10  0.49263 (14)  0.16280 (13)  0.21526 (13)  0.01754 (15)  
O11  1.06463 (16)  0.21154 (13)  −0.03535 (13)  0.01866 (16)  
O12  0.46952 (13)  0.16652 (11)  0.52829 (11)  0.01411 (12) 
U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23}  
K  0.01717 (11)  0.0542 (3)  0.01579 (10)  0.00955 (13)  −0.00159 (8)  −0.00090 (12) 
Pr  0.00546 (1)  0.00563 (1)  0.00548 (1)  −0.00032 (1)  0.00021 (1)  0.00006 (1) 
P1  0.00666 (7)  0.00665 (7)  0.00750 (7)  0.00002 (5)  0.00174 (5)  0.00055 (5) 
P2  0.00649 (6)  0.00695 (7)  0.00716 (7)  −0.00010 (5)  0.00069 (5)  −0.00144 (5) 
P3  0.00623 (6)  0.00685 (7)  0.00704 (7)  0.00079 (5)  −0.00105 (5)  0.00031 (5) 
P4  0.00704 (7)  0.00576 (6)  0.00735 (7)  −0.00051 (5)  −0.00141 (5)  −0.00019 (5) 
O1  0.0159 (3)  0.0098 (2)  0.0145 (3)  0.0010 (2)  −0.0082 (2)  −0.00244 (18) 
O2  0.0083 (2)  0.0108 (2)  0.0229 (3)  −0.00354 (17)  −0.0037 (2)  0.0027 (2) 
O3  0.0102 (2)  0.0084 (2)  0.0168 (3)  −0.00284 (17)  −0.00320 (19)  −0.00037 (18) 
O4  0.0114 (2)  0.0160 (3)  0.0082 (2)  0.0013 (2)  0.00038 (16)  0.00301 (18) 
O5  0.00730 (18)  0.0111 (2)  0.0135 (2)  0.00173 (16)  0.00166 (16)  0.00354 (18) 
O6  0.00779 (19)  0.0116 (2)  0.0145 (2)  −0.00191 (17)  0.00084 (16)  0.00167 (19) 
O7  0.0141 (2)  0.0103 (2)  0.0106 (2)  −0.00433 (19)  −0.00116 (18)  0.00117 (17) 
O8  0.0131 (3)  0.0090 (2)  0.0235 (4)  0.00183 (19)  −0.0015 (2)  −0.0067 (2) 
O9  0.0143 (3)  0.0186 (3)  0.0087 (2)  0.0028 (2)  −0.00406 (18)  0.0001 (2) 
O10  0.0157 (3)  0.0201 (3)  0.0169 (3)  0.0020 (3)  0.0016 (2)  −0.0106 (3) 
O11  0.0206 (4)  0.0191 (3)  0.0171 (3)  0.0030 (3)  0.0121 (3)  −0.0029 (3) 
O12  0.0141 (3)  0.0144 (3)  0.0142 (3)  0.0033 (2)  0.0059 (2)  0.0074 (2) 
K—O4^{i}  2.7908 (9)  P2—O7^{vi}  1.4822 (8) 
K—O6  2.7909 (9)  P2—O1  1.5926 (8) 
K—O8  2.8231 (10)  P2—O2  1.5941 (8) 
K—O3^{i}  2.8684 (10)  P2—K^{vii}  3.2805 (4) 
K—O7^{ii}  2.9050 (9)  P3—O3^{viii}  1.4806 (8) 
K—O12  2.9285 (11)  P3—O4  1.4832 (8) 
K—O11^{iii}  2.9781 (13)  P3—O5  1.5902 (8) 
K—O9  3.1924 (11)  P3—O1^{ix}  1.5980 (8) 
K—P2^{iii}  3.2805 (4)  P4—O8^{v}  1.4777 (8) 
K—P1  3.3360 (4)  P4—O9^{vii}  1.4829 (8) 
Pr—O11^{iv}  2.3787 (9)  P4—O2  1.5874 (8) 
Pr—O9  2.4180 (8)  P4—O10  1.5973 (9) 
Pr—O12  2.4414 (8)  O1—P3^{i}  1.5980 (8) 
Pr—O3  2.4731 (7)  O3—P3^{x}  1.4806 (8) 
Pr—O4  2.4791 (8)  O3—K^{ix}  2.8684 (10) 
Pr—O6^{v}  2.4912 (8)  O4—K^{ix}  2.7908 (9) 
Pr—O7  2.4928 (8)  O6—Pr^{vi}  2.4912 (8) 
Pr—O8  2.5091 (8)  O7—P2^{v}  1.4822 (8) 
P1—O6  1.4841 (8)  O7—K^{xi}  2.9051 (9) 
P1—O12  1.4850 (8)  O8—P4^{vi}  1.4776 (8) 
P1—O5  1.5881 (7)  O9—P4^{iii}  1.4829 (8) 
P1—O10  1.5887 (9)  O11—Pr^{xii}  2.3787 (9) 
P2—O11  1.4810 (9)  O11—K^{vii}  2.9782 (13) 
O4^{i}—K—O6  78.26 (2)  O12—Pr—O8  75.38 (3) 
O4^{i}—K—O8  166.08 (3)  O3—Pr—O8  136.89 (3) 
O6—K—O8  91.87 (3)  O4—Pr—O8  74.26 (3) 
O4^{i}—K—O3^{i}  58.32 (3)  O6^{v}—Pr—O8  140.10 (3) 
O6—K—O3^{i}  93.61 (3)  O7—Pr—O8  134.32 (3) 
O8—K—O3^{i}  133.01 (3)  O11^{iv}—Pr—K^{ix}  48.64 (3) 
O4^{i}—K—O7^{ii}  110.62 (3)  O9—Pr—K^{ix}  147.29 (2) 
O6—K—O7^{ii}  157.42 (3)  O12—Pr—K^{ix}  116.78 (2) 
O8—K—O7^{ii}  75.23 (3)  O3—Pr—K^{ix}  46.23 (2) 
O3^{i}—K—O7^{ii}  108.78 (3)  O4—Pr—K^{ix}  44.44 (2) 
O4^{i}—K—O12  115.71 (3)  O6^{v}—Pr—K^{ix}  120.771 (19) 
O6—K—O12  52.38 (2)  O7—Pr—K^{ix}  97.96 (2) 
O8—K—O12  63.48 (3)  O8—Pr—K^{ix}  91.99 (2) 
O3^{i}—K—O12  83.86 (3)  O11^{iv}—Pr—K  120.16 (3) 
O7^{ii}—K—O12  131.14 (3)  O9—Pr—K  51.68 (2) 
O4^{i}—K—O11^{iii}  70.23 (2)  O12—Pr—K  45.47 (3) 
O6—K—O11^{iii}  147.28 (3)  O3—Pr—K  155.08 (2) 
O8—K—O11^{iii}  120.66 (3)  O4—Pr—K  94.44 (2) 
O3^{i}—K—O11^{iii}  62.54 (3)  O6^{v}—Pr—K  97.156 (19) 
O7^{ii}—K—O11^{iii}  50.31 (2)  O7—Pr—K  127.02 (2) 
O12—K—O11^{iii}  136.81 (3)  O8—Pr—K  43.25 (2) 
O4^{i}—K—O9  136.58 (3)  K^{ix}—Pr—K  130.558 (15) 
O6—K—O9  118.49 (3)  O6—P1—O12  116.70 (5) 
O8—K—O9  56.95 (3)  O6—P1—O5  107.54 (5) 
O3^{i}—K—O9  79.85 (3)  O12—P1—O5  110.52 (5) 
O7^{ii}—K—O9  70.04 (3)  O6—P1—O10  110.55 (5) 
O12—K—O9  66.11 (2)  O12—P1—O10  110.38 (6) 
O11^{iii}—K—O9  81.08 (3)  O5—P1—O10  99.78 (5) 
O4^{i}—K—P2^{iii}  96.054 (18)  O6—P1—K  55.97 (3) 
O6—K—P2^{iii}  174.10 (2)  O12—P1—K  61.30 (4) 
O8—K—P2^{iii}  94.00 (2)  O5—P1—K  121.03 (3) 
O3^{i}—K—P2^{iii}  81.93 (2)  O10—P1—K  138.98 (4) 
O7^{ii}—K—P2^{iii}  26.858 (16)  O11—P2—O7^{vi}  115.17 (6) 
O12—K—P2^{iii}  130.40 (2)  O11—P2—O1  109.17 (6) 
O11^{iii}—K—P2^{iii}  26.821 (17)  O7^{vi}—P2—O1  114.25 (5) 
O9—K—P2^{iii}  64.676 (17)  O11—P2—O2  109.22 (6) 
O4^{i}—K—P1  98.784 (19)  O7^{vi}—P2—O2  111.14 (5) 
O6—K—P1  26.147 (16)  O1—P2—O2  96.24 (5) 
O8—K—P1  74.92 (2)  O11—P2—K^{vii}  65.14 (5) 
O3^{i}—K—P1  90.78 (2)  O7^{vi}—P2—K^{vii}  62.31 (3) 
O7^{ii}—K—P1  150.12 (2)  O1—P2—K^{vii}  167.90 (4) 
O12—K—P1  26.409 (16)  O2—P2—K^{vii}  95.76 (4) 
O11^{iii}—K—P1  153.20 (3)  O3^{viii}—P3—O4  119.42 (5) 
O9—K—P1  92.400 (19)  O3^{viii}—P3—O5  107.01 (5) 
P2^{iii}—K—P1  156.78 (2)  O4—P3—O5  110.07 (4) 
O4^{i}—K—P4^{vi}  148.57 (3)  O3^{viii}—P3—O1^{ix}  109.79 (4) 
O6—K—P4^{vi}  96.19 (2)  O4—P3—O1^{ix}  107.65 (5) 
O8—K—P4^{vi}  21.809 (17)  O5—P3—O1^{ix}  101.41 (5) 
O3^{i}—K—P4^{vi}  152.95 (2)  O3^{viii}—P3—K^{ix}  90.09 (4) 
O7^{ii}—K—P4^{vi}  65.122 (18)  O5—P3—K^{ix}  150.30 (3) 
O12—K—P4^{vi}  82.33 (2)  O1^{ix}—P3—K^{ix}  95.04 (4) 
O11^{iii}—K—P4^{vi}  115.28 (2)  O8^{v}—P4—O9^{vii}  119.69 (6) 
O9—K—P4^{vi}  73.308 (19)  O8^{v}—P4—O2  106.59 (5) 
P2^{iii}—K—P4^{vi}  89.502 (11)  O9^{vii}—P4—O2  109.84 (5) 
P1—K—P4^{vi}  87.099 (10)  O8^{v}—P4—O10  108.77 (6) 
O4^{i}—K—P3^{i}  20.271 (16)  O9^{vii}—P4—O10  105.12 (6) 
O6—K—P3^{i}  58.589 (17)  O2—P4—O10  106.09 (5) 
O8—K—P3^{i}  147.16 (3)  O8^{v}—P4—K^{v}  45.22 (4) 
O3^{i}—K—P3^{i}  68.374 (19)  O9^{vii}—P4—K^{v}  103.55 (4) 
O7^{ii}—K—P3^{i}  126.64 (2)  O2—P4—K^{v}  145.07 (4) 
O12—K—P3^{i}  102.092 (19)  O10—P4—K^{v}  73.90 (4) 
O11^{iii}—K—P3^{i}  90.45 (2)  P2—O1—P3^{i}  132.40 (6) 
O9—K—P3^{i}  147.36 (2)  P4—O2—P2  136.74 (6) 
P2^{iii}—K—P3^{i}  115.882 (11)  P3^{x}—O3—Pr  136.64 (5) 
P1—K—P3^{i}  81.085 (10)  P3^{x}—O3—K^{ix}  126.63 (4) 
P4^{vi}—K—P3^{i}  137.479 (17)  Pr—O3—K^{ix}  95.26 (3) 
O11^{iv}—Pr—O9  99.75 (4)  P3—O4—Pr  139.19 (5) 
O11^{iv}—Pr—O12  151.63 (3)  P3—O4—K^{ix}  119.05 (4) 
O9—Pr—O12  87.04 (3)  Pr—O4—K^{ix}  97.10 (3) 
O11^{iv}—Pr—O3  77.45 (4)  P1—O5—P3  132.48 (5) 
O9—Pr—O3  148.45 (3)  P1—O6—Pr^{vi}  130.14 (5) 
O12—Pr—O3  110.50 (3)  P1—O6—K  97.89 (4) 
O11^{iv}—Pr—O4  86.26 (3)  Pr^{vi}—O6—K  122.05 (3) 
O9—Pr—O4  143.85 (3)  P2^{v}—O7—Pr  136.16 (5) 
O12—Pr—O4  72.87 (3)  P2^{v}—O7—K^{xi}  90.83 (4) 
O3—Pr—O4  67.70 (3)  Pr—O7—K^{xi}  132.10 (3) 
O11^{iv}—Pr—O6^{v}  137.47 (3)  P4^{vi}—O8—Pr  147.72 (6) 
O9—Pr—O6^{v}  87.33 (3)  P4^{vi}—O8—K  112.97 (5) 
O12—Pr—O6^{v}  69.86 (3)  Pr—O8—K  99.24 (3) 
O3—Pr—O6^{v}  75.34 (3)  P4^{iii}—O9—Pr  143.02 (6) 
O4—Pr—O6^{v}  112.14 (3)  P4^{iii}—O9—K  116.82 (5) 
O11^{iv}—Pr—O7  73.45 (4)  Pr—O9—K  91.87 (3) 
O9—Pr—O7  76.38 (3)  P1—O10—P4  144.49 (7) 
O12—Pr—O7  134.75 (3)  P2—O11—Pr^{xii}  171.29 (7) 
O3—Pr—O7  72.70 (3)  P2—O11—K^{vii}  88.04 (5) 
O4—Pr—O7  138.54 (3)  Pr^{xii}—O11—K^{vii}  94.52 (4) 
O6^{v}—Pr—O7  67.60 (3)  P1—O12—Pr  144.39 (5) 
O11^{iv}—Pr—O8  80.66 (4)  P1—O12—K  92.29 (5) 
O9—Pr—O8  71.69 (3)  Pr—O12—K  98.06 (3) 
Symmetry codes: (i) x+1, y, z; (ii) −x+1, y+1/2, −z+2; (iii) x, y, z+1; (iv) x−1, y, z+1; (v) −x+1, y−1/2, −z+1; (vi) −x+1, y+1/2, −z+1; (vii) x, y, z−1; (viii) −x, y+1/2, −z+1; (ix) x−1, y, z; (x) −x, y−1/2, −z+1; (xi) −x+1, y−1/2, −z+2; (xii) x+1, y, z−1. 
Experimental details
Crystal data  
Chemical formula  KPr(PO3)_{4} 
M_{r}  495.89 
Crystal system, space group  Monoclinic, P2_{1} 
Temperature (K)  296 
a, b, c (Å)  7.2872 (2), 8.4570 (3), 8.0268 (2) 
β (°)  91.994 (1) 
V (Å^{3})  494.37 (3) 
Z  2 
Radiation type  Mo Kα 
µ (mm^{−}^{1})  6.06 
Crystal size (mm)  0.29 × 0.21 × 0.16 
Data collection  
Diffractometer  Bruker APEXII CCD 
Absorption correction  Multiscan (SADABS; Bruker, 2008) 
T_{min}, T_{max}  0.448, 0.751 
No. of measured, independent and observed [I > 2σ(I)] reflections  45940, 13443, 13257 
R_{int}  0.034 
(sin θ/λ)_{max} (Å^{−}^{1})  1.186 
Refinement  
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S  0.018, 0.043, 1.07 
No. of reflections  13443 
No. of parameters  164 
No. of restraints  1 
Δρ_{max}, Δρ_{min} (e Å^{−}^{3})  2.86, −2.42 
Absolute structure  Flack (1983), 6278 Friedel pairs 
Absolute structure parameter  0.022 (3) 
Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), CaRine (Boudias & Monceau, 1998) and ORTEP3 for Windows (Farrugia, 1997), SHELXTL (Sheldrick, 2008).
P1—O6  1.4841 (8)  P3—O3^{ii}  1.4806 (8) 
P1—O12  1.4850 (8)  P3—O4  1.4832 (8) 
P1—O5  1.5881 (7)  P3—O5  1.5902 (8) 
P1—O10  1.5887 (9)  P3—O1^{iii}  1.5980 (8) 
P2—O11  1.4810 (9)  P4—O8^{iv}  1.4777 (8) 
P2—O7^{i}  1.4822 (8)  P4—O9^{v}  1.4829 (8) 
P2—O1  1.5926 (8)  P4—O2  1.5874 (8) 
P2—O2  1.5941 (8)  P4—O10  1.5973 (9) 
Symmetry codes: (i) −x+1, y+1/2, −z+1; (ii) −x, y+1/2, −z+1; (iii) x−1, y, z; (iv) −x+1, y−1/2, −z+1; (v) x, y, z−1. 
References
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This is an openaccess article distributed under the terms of the Creative Commons Attribution (CCBY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Long chains polyphosphates with general formula A^{I}B^{III}(PO_{3})_{4} have been classified into seven structural types, labelled from I to VII (Durif, 1995; Jaoudi et al. 2003). All longchains polyphosphates of formula KLn(PO_{3})_{4} (Ln = rare earth elements) reported up to now (Zhu et al., 2009; HorchaniNaifer et al., 2008; Parreu et al., 2006; Xing et al., 1987; Ninghai et al., 1984; Lin et al., 1983; Krutik et al., 1980; Hong et al., 1975) adopt type III except for KYb(PO_{3})_{4} (Palkina et al. 1981) which is the only presently known member of type V. Most of these potassium polyphosphates are dimorphic and crystallize with both the type III and the type IV polymorphs. KCe(PO_{3})_{4} which has been shown to crystallize with either the type II and the type III is the first exception. The second exception is concerned with the Er member of this series presenting the type VII polymorph besides both type III and type IV polymorphs. Moreover, type III longchain polyphosphates do not exist for monovalent cations other than K^{+}. The structure of the title compound also fits in this type III isotypic series.
The crystal structure of the title compound is built from crenelated chains with a repeating unit of four cornersharing tetrahedra, as displayed in Fig. 1. The chains are further linked by isolated PrO_{8} square antiprisms to form the threedimensional framework. Each PrO_{8} polyhedron (Pr—O distances range from 2.3787 (9) to 2.5091 (8) Å) is connected through vertices to four (PO_{3})_{∞} chains stacked in a pseudotetragonal rod packing as shown in Fig. 2. Figure 2 also shows that within this pseudotetragonal rod packing, two adjacent chains are twisted by ca. 90 ° whereas two opposite chains are parallel. The relative disposition of the chains running along the [100] direction accounts for the strong noncentrosymmetric character of the structure. Figure 3 displays details of the connections between the PrO_{8} square antiprisms and the four chains surrounding each antiprism. One of the four chains (labelled C_{1}) is attached in a tridentate fashion on a triangular face of the square antiprism whereas the opposite and parallel chain (labelled C_{2}) is connected only through a vertex (Fig. 3a). The two other chains which are adjacent to the first one are attached in a bidentate fashion. The first of these two chains (labelled C_{3}) is linked through a bidentate diphosphate group attached on one side of one square face of the square antiprism (Fig. 3b). The second chain (labelled C_{4}) is connected at the ends of one diagonal of the second square face of the antiprism (Fig. 3c) through corners of the terminal PO_{4} groups of the crenelshaped tetraphosphate group corresponding to the repeating unit of the chain. This polyhedral linkage delimits channels running along [010] where the K^{+}ions lie in a highly distorted environment defined by eight oxygen atoms at distances ranging from 2.7908 (9) to 3.1924 (11) Å.
For the cyclophosphate structure with the same composition KPr(PO_{3})_{4}, see: (Zhou et al., 1987).