inorganic compounds
K0.53Mn2.37Fe1.24(PO4)3
aFaculté des Sciences de Monastir, 5019 Monastir, Tunisia
*Correspondence e-mail: mourad_hidouri@yahoo.fr
During an attempt to crystallize potassium manganese diiron phosphate KMnFe2(PO4)3 by the method, a new phase, potassium dimanganese iron triphosphate, K0.53Mn2.37Fe1.24(PO4)3, was isolated. This phase, whose composition was confirmed by ICP analysis, is isotypic with the alluaudite-like phosphates, thus it exhibits the (A2)(A′2)(A1)(A′1)(A′′1)(M1)(M2)2(PO4)3 general formula. The site occupancies led to the following cation distribution: 0.53 K on A′2 (site symmetry 2), 0.31 Mn on A′′1, 1.0 Mn on M1 (site symmetry 2) and (0.62 Fe + 0.38 Mn) on M2. The structure is built up from infinite chains of edge-sharing M1O6 and M2O6 octahedra. These chains run along [10] and are connected by two different PO4 tetrahedra, one of which exhibits 2 symmetry. The resulting three-dimensional framework delimits large tunnels parallel to [001], which are partially occupied by the K+ and Mn2+ cations.
Related literature
For the alluaudite structure, see: Fisher (1955); Moore (1971); Chouaibi et al. (2001); Corbin et al. (1986); Lee & Ye (1997); Hidouri et al. (2003, 2004, 2008) Antenucci et al. (1993, 1995); For P—O distances, see: Baur (1974). For bond-valence sums, see: Brown & Altermatt (1985). For ionic radii, see: Shannon (1976).
Experimental
Crystal data
|
Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536810051238/br2150sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810051238/br2150Isup2.hkl
Single crystals of the title phase were extracted from a mixture of nominal composition KMnFe2(PO4)3. The latter was prepared by the
method starting from a mixture of 2.042 g of KNO3, 2.589 g of Mn(NO3)2.6H2O, 8.245 g of Fe(NO3)3.9H2O, 4.002 g of (NH4)2HPO4 and 0.719 g of MoO3. These reactants were dissolved in nitric acid and the solution obtained was dried for 24 h at 353 K. The obtained dry residue was ground in an agate mortar to ensure its best then heated in a platinum crucible to 673 K for 24 h in order to remove the decomposition products: NH3 and H2O. The sample was then reground, melted at 1173 K for 1 h and subsequently cooled at a 10 °.h-1 rate to 673 K. The final product was washed with warm water in order to dissolve the From the mixture, dark brown and hexagonally shaped crystals were extracted. Their analysis using ICP confirmed the presence of only K, Mn, Fe and P in atomic ratio of 0.53:2.37:1.24:3, in accordance with the K0.53Mn2.37Fe1.24(PO4)3 composition.The term alluaudite is referred to both natural and synthetic phosphates of compositions (Na+)(Na+, Ca2+)(M2+)(Fe2+,Fe3+)2(PO4)3 where M2+ is a divalent cation. The first detailed structural description was reported in 1971 by Moore (Moore, 1971) who proposed the ~0, 1/4) in a tunnel at (0, 0, z) and X1 has three distinct positions, labeled A1 (1/2, 0, 0), A'1 (0,~1/2, 1/4) and A''1 (x, y, z) in a tunnel at (1/2, 0, z). The general formula of Moore was then reformulated as [(A2)(A'2)][(A1)(A'1)(A''1)](M1)(M2)2(PO4)3. The consists of M22O10 bioctahedral units of edge-sharing M2O6 octahedra, sharing opposite edges with M1O6 octahedra that form zigzag chains of a sequence –M(2)—M(2)—M(1)-, running along the [1 0 - 1] direction. Adjacent chains are linked by the phosphate tetrahedra leading to what have been described as "pleated sheets" perpendicular to the [0 1 0] direction (Fig. 1(b)). These sheets are connected by the phosphate groups giving rise to a three-dimensional framework with two sets of tunnels parallel to [001] (Fig. 1(b)).
(X2)(X1)(M1)(M2)2(PO4)3. X1 and X2 are cationic sites available to large monovalent and divalent cations such as Na+ and Ca2+ while M1 and M2 are octahedral sites containing a distribution of divalent and trivalent cations of moderate size such as Mn2+, Fe2+ or Fe3+. More recently, detailed structural analysis of several alluaudites demonstrated that the X2 site has two distinct positions labeled A2 (0, 0, 0) and A'2 (0,The title phase K0.53Mn2.37Fe1.24(PO4)3 was isolated during an attempt to synthesize KMnFe2(PO4)3 and its structure has shown to be of the alluaudite type. The site occupancy factors indicated to the following cation distribution: 0.53 K on A'2, 0.31 Mn on A''1, 1.0 Mn on M1 and (0.62 Fe + 0.38 Mn) on M2. The partial occupancy of the large A sites has already been observed in several alluaudites being attributed to the great flexibility of these sites which allows them to be filled totally, partially or left vacant without significant influence on the alluaudite framework. Assuming a maximum gap in the cation-oxygen distances, the envronment of the A'2 site (figure 2) consists of eight oxygen atoms forming what has been called by Moore as a gable desphenoid (Moore, 1971). That of the A''1 site (figure 2) onsists of five O atoms forming a distorted trigonal bipyramid. The fivefold coordination of this site which is, to the best of our knowledge, observed for the first time in an alluaudite-like compound can be attributed to the small size of the Mn2+ cation. Both the M1 and M2 sites are octahedrally coordinated (figure 2). From the M1—O distances and cis O—M1—O angles, one can deduce that the M1O6 octahedron is strongly distorted. However, the mean M1—O> mean distance of 2.238 Å is close to that 2.23 Å predicted by Shannon for octahedral Mn2+ cations (Shannon, 1976). The M2—O distances and cis O—M2—O angles show the M2O6 octahedron to be less distorted than M1O6. The <M(2)—O> mean distance (2.068 Å) is between 2.03 Å and 2.23 Å, calculated by Shannon (Shannon, 1976) for the Fe3+ and Mn2+ cations, respectively. This result confirms the presence of both atoms on the M(2) site. The PO4 tetrahedra have classical P—O distances with an overall value of 1.537 Å close to that 1.537 Å, assigned by Baur for the monophosphate groups (Baur, 1974). The Bond Valence Sums (BVS) were calculated for all cationic sites by the Brown and Altermatt method (Brown et al., 1985). The analysis of the sums for the M2 site, around Fe3+ and Mn2+ led to valence sums of 2.87 and 2.64, respectively which corresponds to occupation numbers of 0.71 and 0.29, very close to the x-ray values of 0.62 and 0.38. The sum around Mn3 is 1.34 and around K is 0.42. These are poor because of the partial occupancy but unfortunately these values cannot be used to estimate the occupancy. The sums around P1 and P2 of 4.92 and 4.98, respectively around the O sites (from 1.91 to 2.12) are consistent with the predicted ones of 5 for P and 2 for O. In summery, the valence calculation results gave a good confirmation of the structure, including the assigned oxidation states which cannot be determined by x-ray analysis.
For the alluaudite structure, see: Fisher (1955); Moore (1971); Chouaibi et al. (20016); Corbin et al. (19867); Lee & Ye (19974); Hidouri et al. (20031, 20042, 20083). For related literature [on what subject?], see: Antenucci et al. (1993, 1995); For P—O distances, see: Baur (1974). For bond-valence sums, see: Brown & Altermatt (1985). For ionic radii, see: Shannon (1976).
For related literature, see: Hidouri et al. (2004, 2008).
Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell
CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).K0.53Mn2.37Fe1.24(PO4)3 | F(000) = 957 |
Mr = 505.28 | Dx = 3.727 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 25 reflections |
a = 12.272 (2) Å | θ = 9.8–14.4° |
b = 12.606 (2) Å | µ = 6.07 mm−1 |
c = 6.416 (4) Å | T = 293 K |
β = 114.87 (2)° | Hexagonal, brown |
V = 900.5 (6) Å3 | 0.43 × 0.09 × 0.02 mm |
Z = 4 |
Enraf–Nonius TurboCAD-4 diffractometer | 1047 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.042 |
Graphite monochromator | θmax = 30.0°, θmin = 2.4° |
non–profiled ω/2θ scans | h = −17→15 |
Absorption correction: part of the (Parkin et al., 1995) | model (ΔF) k = 0→17 |
Tmin = 0.42, Tmax = 0.81 | l = 0→9 |
1754 measured reflections | 2 standard reflections every 120 min |
1308 independent reflections | intensity decay: 1% |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.037 | w = 1/[σ2(Fo2) + (0.0451P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.089 | (Δ/σ)max = 0.001 |
S = 1.07 | Δρmax = 0.78 e Å−3 |
1308 reflections | Δρmin = −0.68 e Å−3 |
102 parameters | Extinction correction: SHELXL97 (Sheldrick, 2008) |
2 restraints | Extinction coefficient: 0.0009 (4) |
K0.53Mn2.37Fe1.24(PO4)3 | V = 900.5 (6) Å3 |
Mr = 505.28 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 12.272 (2) Å | µ = 6.07 mm−1 |
b = 12.606 (2) Å | T = 293 K |
c = 6.416 (4) Å | 0.43 × 0.09 × 0.02 mm |
β = 114.87 (2)° |
Enraf–Nonius TurboCAD-4 diffractometer | 1047 reflections with I > 2σ(I) |
Absorption correction: part of the (Parkin et al., 1995) | model (ΔF) Rint = 0.042 |
Tmin = 0.42, Tmax = 0.81 | 2 standard reflections every 120 min |
1754 measured reflections | intensity decay: 1% |
1308 independent reflections |
R[F2 > 2σ(F2)] = 0.037 | 102 parameters |
wR(F2) = 0.089 | 2 restraints |
S = 1.07 | Δρmax = 0.78 e Å−3 |
1308 reflections | Δρmin = −0.68 e Å−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 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. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
K | 0.0000 | −0.0116 (2) | 0.2500 | 0.0229 (7) | 0.531 (5) |
Mn1 | 0.0000 | 0.26376 (7) | 0.2500 | 0.0156 (2) | |
Fe2 | 0.22489 (4) | 0.15521 (4) | 0.13977 (8) | 0.01004 (16) | 0.6217 (6) |
Mn2 | 0.22489 (4) | 0.15521 (4) | 0.13977 (8) | 0.01004 (16) | 0.3783 (7) |
Mn3 | −0.02360 (17) | 0.49774 (17) | 0.0393 (4) | 0.0209 (5) | 0.3064 (12) |
P1 | 0.0000 | 0.28642 (11) | −0.2500 | 0.0096 (3) | |
O11 | 0.0479 (2) | 0.2160 (2) | −0.0331 (4) | 0.0138 (5) | |
O12 | −0.0942 (3) | 0.3615 (2) | −0.2314 (6) | 0.0251 (7) | |
P2 | 0.24436 (8) | 0.10810 (7) | 0.63905 (15) | 0.0093 (2) | |
O21 | 0.2272 (2) | 0.1782 (2) | 0.8220 (4) | 0.0156 (6) | |
O22 | 0.1735 (3) | 0.1629 (2) | 0.4048 (4) | 0.0169 (6) | |
O23 | 0.3783 (2) | 0.1019 (2) | 0.6976 (6) | 0.0255 (7) | |
O24 | 0.1930 (2) | −0.0019 (2) | 0.6349 (5) | 0.0178 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
K | 0.0093 (10) | 0.0218 (13) | 0.0260 (13) | 0.000 | −0.0040 (9) | 0.000 |
Mn1 | 0.0115 (4) | 0.0202 (4) | 0.0154 (4) | 0.000 | 0.0058 (3) | 0.000 |
Fe2 | 0.0065 (2) | 0.0138 (3) | 0.0065 (3) | 0.00016 (18) | −0.00043 (19) | 0.0008 (2) |
Mn2 | 0.0065 (2) | 0.0138 (3) | 0.0065 (3) | 0.00016 (18) | −0.00043 (19) | 0.0008 (2) |
Mn3 | 0.0156 (12) | 0.0164 (9) | 0.0165 (11) | −0.0002 (9) | −0.0070 (7) | 0.0014 (9) |
P1 | 0.0060 (5) | 0.0140 (6) | 0.0038 (5) | 0.000 | −0.0028 (4) | 0.000 |
O11 | 0.0087 (11) | 0.0193 (13) | 0.0066 (11) | −0.0027 (10) | −0.0033 (9) | 0.0028 (10) |
O12 | 0.0149 (13) | 0.0245 (15) | 0.0301 (17) | 0.0025 (12) | 0.0037 (13) | −0.0119 (14) |
P2 | 0.0065 (4) | 0.0123 (4) | 0.0050 (4) | 0.0004 (3) | −0.0016 (3) | 0.0012 (3) |
O21 | 0.0128 (12) | 0.0235 (14) | 0.0078 (11) | −0.0030 (11) | 0.0017 (10) | −0.0038 (11) |
O22 | 0.0244 (14) | 0.0141 (14) | 0.0048 (11) | 0.0003 (11) | −0.0010 (10) | −0.0007 (10) |
O23 | 0.0114 (13) | 0.0189 (15) | 0.047 (2) | 0.0003 (11) | 0.0132 (14) | −0.0018 (15) |
O24 | 0.0127 (12) | 0.0184 (14) | 0.0171 (13) | −0.0013 (11) | 0.0012 (11) | 0.0030 (11) |
K—O24 | 2.608 (3) | Mn1—O22i | 2.315 (3) |
K—O24i | 2.608 (3) | Mn1—O22 | 2.315 (3) |
K—O24ii | 2.767 (3) | Fe2—O24ii | 1.970 (3) |
K—O24iii | 2.767 (3) | Fe2—O12x | 2.027 (3) |
K—O11iv | 2.869 (4) | Fe2—O22 | 2.049 (3) |
K—O11v | 2.869 (4) | Fe2—O21xi | 2.071 (3) |
K—O22 | 2.929 (3) | Fe2—O11 | 2.123 (3) |
K—O22i | 2.929 (3) | Fe2—O21vi | 2.167 (3) |
Mn3—O23vi | 2.253 (4) | P1—O12xii | 1.537 (3) |
Mn3—O23vii | 2.256 (4) | P1—O12 | 1.537 (3) |
Mn3—O12viii | 2.294 (4) | P1—O11xii | 1.544 (3) |
Mn3—O12 | 2.335 (4) | P1—O11 | 1.544 (3) |
Mn3—O23ix | 2.400 (4) | P2—O24 | 1.519 (3) |
Mn1—O23vi | 2.189 (3) | P2—O23 | 1.526 (3) |
Mn1—O23vii | 2.189 (3) | P2—O22 | 1.547 (3) |
Mn1—O11 | 2.215 (3) | P2—O21 | 1.553 (3) |
Mn1—O11i | 2.215 (3) | ||
O24—K—O24i | 174.63 (16) | O23vi—Mn1—O11 | 86.39 (11) |
O24—K—O24ii | 73.24 (8) | O23vii—Mn1—O11 | 118.95 (12) |
O24i—K—O24ii | 106.42 (8) | O23vi—Mn1—O11i | 118.95 (12) |
O24—K—O24iii | 106.42 (8) | O23vii—Mn1—O11i | 86.39 (11) |
O24i—K—O24iii | 73.24 (8) | O11—Mn1—O11i | 148.43 (15) |
O24ii—K—O24iii | 172.95 (16) | O23vi—Mn1—O22i | 159.42 (10) |
O24—K—O11iv | 114.87 (10) | O23vii—Mn1—O22i | 85.06 (10) |
O24i—K—O11iv | 70.34 (8) | O11—Mn1—O22i | 90.70 (10) |
O24ii—K—O11iv | 87.10 (9) | O11i—Mn1—O22i | 71.87 (10) |
O24iii—K—O11iv | 99.26 (10) | O23vi—Mn1—O22 | 85.06 (10) |
O24—K—O11v | 70.34 (8) | O23vii—Mn1—O22 | 159.42 (10) |
O24i—K—O11v | 114.87 (10) | O11—Mn1—O22 | 71.87 (10) |
O24ii—K—O11v | 99.26 (10) | O11i—Mn1—O22 | 90.70 (10) |
O24iii—K—O11v | 87.10 (9) | O22i—Mn1—O22 | 113.36 (14) |
O11iv—K—O11v | 52.22 (11) | O24ii—Fe2—O12x | 94.65 (12) |
O24—K—O22 | 53.32 (8) | O24ii—Fe2—O22 | 86.05 (12) |
O24i—K—O22 | 121.80 (11) | O12x—Fe2—O22 | 109.44 (13) |
O24ii—K—O22 | 57.49 (9) | O24ii—Fe2—O21xi | 101.92 (12) |
O24iii—K—O22 | 116.43 (11) | O12x—Fe2—O21xi | 87.13 (12) |
O11iv—K—O22 | 144.11 (8) | O22—Fe2—O21xi | 161.16 (11) |
O11v—K—O22 | 122.58 (8) | O24ii—Fe2—O11 | 101.11 (11) |
O24—K—O22i | 121.80 (11) | O12x—Fe2—O11 | 162.62 (11) |
O24i—K—O22i | 53.32 (8) | O22—Fe2—O11 | 79.18 (11) |
O24ii—K—O22i | 116.43 (11) | O21xi—Fe2—O11 | 82.52 (11) |
O24iii—K—O22i | 57.49 (9) | O24ii—Fe2—O21vi | 174.59 (11) |
O11iv—K—O22i | 122.58 (8) | O12x—Fe2—O21vi | 81.71 (11) |
O11v—K—O22i | 144.11 (8) | O22—Fe2—O21vi | 91.37 (11) |
O22—K—O22i | 82.66 (13) | O21xi—Fe2—O21vi | 81.97 (11) |
O23vi—Mn3—O23vii | 75.91 (14) | O11—Fe2—O21vi | 83.04 (10) |
O23vi—Mn3—O12viii | 84.68 (13) | O12xii—P1—O12 | 104.0 (3) |
O23vii—Mn3—O12viii | 121.62 (16) | O12xii—P1—O11xii | 107.33 (17) |
Mn1viii—Mn3—O12 | 76.0 (3) | O12—P1—O11xii | 114.23 (15) |
O23vi—Mn3—O12 | 94.38 (14) | O12xii—P1—O11 | 114.23 (15) |
O23vii—Mn3—O12 | 79.85 (14) | O12—P1—O11 | 107.33 (17) |
O12viii—Mn3—O12 | 157.20 (11) | O11xii—P1—O11 | 109.7 (2) |
Mn1viii—Mn3—O23ix | 69.7 (3) | O24—P2—O23 | 110.71 (16) |
O23vi—Mn3—O23ix | 157.58 (11) | O24—P2—O22 | 109.32 (15) |
O23vii—Mn3—O23ix | 123.93 (15) | O23—P2—O22 | 111.67 (18) |
O12viii—Mn3—O23ix | 91.62 (14) | O24—P2—O21 | 110.22 (17) |
O12—Mn3—O23ix | 80.58 (13) | O23—P2—O21 | 108.50 (16) |
O23vi—Mn1—O23vii | 78.61 (15) | O22—P2—O21 | 106.32 (16) |
Symmetry codes: (i) −x, y, −z+1/2; (ii) x, −y, z−1/2; (iii) −x, −y, −z+1; (iv) −x, −y, −z; (v) x, −y, z+1/2; (vi) −x+1/2, −y+1/2, −z+1; (vii) x−1/2, −y+1/2, z−1/2; (viii) −x, −y+1, −z; (ix) x−1/2, y+1/2, z−1; (x) x+1/2, −y+1/2, z+1/2; (xi) x, y, z−1; (xii) −x, y, −z−1/2. |
Experimental details
Crystal data | |
Chemical formula | K0.53Mn2.37Fe1.24(PO4)3 |
Mr | 505.28 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 12.272 (2), 12.606 (2), 6.416 (4) |
β (°) | 114.87 (2) |
V (Å3) | 900.5 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 6.07 |
Crystal size (mm) | 0.43 × 0.09 × 0.02 |
Data collection | |
Diffractometer | Enraf–Nonius TurboCAD-4 |
Absorption correction | Part of the refinement model (ΔF) (Parkin et al., 1995) |
Tmin, Tmax | 0.42, 0.81 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1754, 1308, 1047 |
Rint | 0.042 |
(sin θ/λ)max (Å−1) | 0.703 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.089, 1.07 |
No. of reflections | 1308 |
No. of parameters | 102 |
No. of restraints | 2 |
Δρmax, Δρmin (e Å−3) | 0.78, −0.68 |
Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1994), XCAD4 (Harms & Wocadlo, 1995), SIR92 (Altomare et al., 1993), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
References
Altomare, A., Cascarano, G., Giacovazzo, C. & Guagliardi, A. (1993). J. Appl. Cryst. 26, 343–350. CrossRef Web of Science IUCr Journals Google Scholar
Antenucci, D., Fransolet, A. M., Miehe, G. & Tarte, P. (1995). Eur. J. Mineral. 7, 175–181. CAS Google Scholar
Antenucci, D., Miehe, G., Tarte, P., Shmahl, W. W. & Fransolet, A. M. (1993). Eur. J. Mineral. 5, 207–213. CAS Google Scholar
Baur, W. H. (1974). Acta Cryst. B30, 1195–1215. CrossRef CAS IUCr Journals Web of Science Google Scholar
Brown, I. D. & Altermatt, D. (1985). Acta Cryst. B41, 244–247. CrossRef CAS Web of Science IUCr Journals Google Scholar
Chouaibi, N., Daidouh, A., Pico, C., Strantrich, A. & Veiga, M. L. (2001). J. Solid State Chem. 159, 46–50. Web of Science CrossRef CAS Google Scholar
Corbin, D. R., Whitney, J. F., Fulz, W. C., Stucky, G. D., Eddy, M. M. & Cheetham, A. K. (1986). Inorg. Chem. 25, 2279–2280. CrossRef CAS Web of Science Google Scholar
Enraf–Nonius (1994). CAD-4 EXPRESS. Enraf–Nonius, Delft, The Netherlands. Google Scholar
Fisher, D. J. (1955). Am. Mineral. 40, 1100–1109. CAS Google Scholar
Harms, K. & Wocadlo, S. (1995). XCAD4. University of Marburg, Germany. Google Scholar
Hidouri, M., Lajmi, B., Driss, A. & Ben Amara, M. (2003). Acta Cryst. E59, i7–i9. Web of Science CSD CrossRef IUCr Journals Google Scholar
Hidouri, M., Lajmi, B., Wattiaux, A., Fournes, L., Darriet, J. & Amara, M. B. (2004). J. Solid State Chem. 177, 55–60. Web of Science CrossRef CAS Google Scholar
Hidouri, M., Lajmi, B., Wattiaux, A., Fournes, L., Darriet, J. & Amara, M. B. (2008). J. Alloys Compd, 450, 301–305. Web of Science CrossRef CAS Google Scholar
Lee, K.-H. & Ye, J. (1997). J. Solid State Chem. 131, 131–137. CrossRef Web of Science Google Scholar
Moore, P. B. (1971). Am. Mineral. 56, 1955–1975. CAS Google Scholar
Parkin, S., Moezzi, B. & Hope, H. (1995). J. Appl. Cryst. 28, 53–56. CrossRef CAS Web of Science IUCr Journals Google Scholar
Shannon, R. D. (1976). Acta Cryst. A32, 751–767. CrossRef CAS IUCr Journals Web of Science Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
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The term alluaudite is referred to both natural and synthetic phosphates of compositions (Na+)(Na+, Ca2+)(M2+)(Fe2+,Fe3+)2(PO4)3 where M2+ is a divalent cation. The first detailed structural description was reported in 1971 by Moore (Moore, 1971) who proposed the structural formula (X2)(X1)(M1)(M2)2(PO4)3. X1 and X2 are cationic sites available to large monovalent and divalent cations such as Na+ and Ca2+ while M1 and M2 are octahedral sites containing a distribution of divalent and trivalent cations of moderate size such as Mn2+, Fe2+ or Fe3+. More recently, detailed structural analysis of several alluaudites demonstrated that the X2 site has two distinct positions labeled A2 (0, 0, 0) and A'2 (0,~0, 1/4) in a tunnel at (0, 0, z) and X1 has three distinct positions, labeled A1 (1/2, 0, 0), A'1 (0,~1/2, 1/4) and A''1 (x, y, z) in a tunnel at (1/2, 0, z). The general formula of Moore was then reformulated as [(A2)(A'2)][(A1)(A'1)(A''1)](M1)(M2)2(PO4)3. The crystal structure consists of M22O10 bioctahedral units of edge-sharing M2O6 octahedra, sharing opposite edges with M1O6 octahedra that form zigzag chains of a sequence –M(2)—M(2)—M(1)-, running along the [1 0 - 1] direction. Adjacent chains are linked by the phosphate tetrahedra leading to what have been described as "pleated sheets" perpendicular to the [0 1 0] direction (Fig. 1(b)). These sheets are connected by the phosphate groups giving rise to a three-dimensional framework with two sets of tunnels parallel to [001] (Fig. 1(b)).
The title phase K0.53Mn2.37Fe1.24(PO4)3 was isolated during an attempt to synthesize KMnFe2(PO4)3 and its structure has shown to be of the alluaudite type. The site occupancy factors indicated to the following cation distribution: 0.53 K on A'2, 0.31 Mn on A''1, 1.0 Mn on M1 and (0.62 Fe + 0.38 Mn) on M2. The partial occupancy of the large A sites has already been observed in several alluaudites being attributed to the great flexibility of these sites which allows them to be filled totally, partially or left vacant without significant influence on the alluaudite framework. Assuming a maximum gap in the cation-oxygen distances, the envronment of the A'2 site (figure 2) consists of eight oxygen atoms forming what has been called by Moore as a gable desphenoid (Moore, 1971). That of the A''1 site (figure 2) onsists of five O atoms forming a distorted trigonal bipyramid. The fivefold coordination of this site which is, to the best of our knowledge, observed for the first time in an alluaudite-like compound can be attributed to the small size of the Mn2+ cation. Both the M1 and M2 sites are octahedrally coordinated (figure 2). From the M1—O distances and cis O—M1—O angles, one can deduce that the M1O6 octahedron is strongly distorted. However, the mean M1—O> mean distance of 2.238 Å is close to that 2.23 Å predicted by Shannon for octahedral Mn2+ cations (Shannon, 1976). The M2—O distances and cis O—M2—O angles show the M2O6 octahedron to be less distorted than M1O6. The <M(2)—O> mean distance (2.068 Å) is between 2.03 Å and 2.23 Å, calculated by Shannon (Shannon, 1976) for the Fe3+ and Mn2+ cations, respectively. This result confirms the presence of both atoms on the M(2) site. The PO4 tetrahedra have classical P—O distances with an overall value of 1.537 Å close to that 1.537 Å, assigned by Baur for the monophosphate groups (Baur, 1974). The Bond Valence Sums (BVS) were calculated for all cationic sites by the Brown and Altermatt method (Brown et al., 1985). The analysis of the sums for the M2 site, around Fe3+ and Mn2+ led to valence sums of 2.87 and 2.64, respectively which corresponds to occupation numbers of 0.71 and 0.29, very close to the x-ray values of 0.62 and 0.38. The sum around Mn3 is 1.34 and around K is 0.42. These are poor because of the partial occupancy but unfortunately these values cannot be used to estimate the occupancy. The sums around P1 and P2 of 4.92 and 4.98, respectively around the O sites (from 1.91 to 2.12) are consistent with the predicted ones of 5 for P and 2 for O. In summery, the valence calculation results gave a good confirmation of the structure, including the assigned oxidation states which cannot be determined by x-ray analysis.