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The structure of strontium magnesium diphosphate, SrMgP2O7, belongs to the α-Ca2P2O7 isotypical pyrophos­phates series SrMP2O7 (M = Cr, Mn, Fe, Co, Ni, Cu, Zn). MgII atoms occupy square-pyramidal coordination and are isolated in the structure. [MgO5] units and the [P2O7] groups form a three-dimensional framework with channels along [100] and [010], in which are located Sr2+ ions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801020633/br6032sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801020633/br6032Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](Mg-O) = 0.003 Å
  • R factor = 0.036
  • wR factor = 0.071
  • Data-to-parameter ratio = 17.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


Yellow Alert Alert Level C:
ABSTM_02 Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10 Tmin and Tmax reported: 0.604 0.662 Tmin and Tmax expected: 0.548 0.662 RR = 1.104 Please check that your absorption correction is appropriate.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

Systematic preparative and structural studies of pyrophosphates M2P2O7 and (A,M)2P2O7 with A and/or M an alkaline earth or divalent 3 d-metal ion, have been undertaken during the last two decades. The pseudo-binary system Sr2P2O7–Mg2P2O7 has been investigated by Calvo who reported the α-Ca2P2O7 (Calvo, 1968a) isostructural pyrophosphate SrMgP2O7, but with no sufficient crystal data (Calvo, 1968b). We undertook the study of this system to achieve the crystal structure of SrMgP2O7. Those of the limit phases are known: Sr2P2O7 (Hagman, 1968), Mg2P2O7 [α- (Calvo, 1967) and β- (Calvo, 1965)]. Mixed pyrophosphates SrMP2O7 form a series of compounds all isostructural to α-Ca2P2O7. The main feature of these pyrophosphates, compared to the structure of α-Ca2P2O7, is that A and M occupy respectively the Ca(1) and Ca(2) positions of the Ca in the structure. The result of such `substitution' is a decrease of coordination passing from 8 to 5 for M, which leads to isolated [MO5] groups instead of [Ca2Ox] dimers. Known isotypic pyrophosphates SrMP2O7 [M = Cr (Maa\&s & Glaum, 2000), Mn (Maa\&s et al., 1999), Fe (LeMeins & Courbion, 1999), Co (Riou & Raveau, 1991), Ni (El-Bali et al., 2001), Cu (Moqine et al., 1993), Zn (Murashova et al., 1991)] all show square-pyramidal [MO5] units. To complete this investigation, we report in this paper the synthesis of SrMgP2O7 and its crystal structure refinement from X-ray single-crystal data.

The structure of the title pyrophosphate can be described as an association of [MgO5] and [P2O7] groups. Corner-sharing of these two building units results in a three-dimensional framework with tunnels running along [001] and [010] in which Sr+2 ions are located. Fig. 1 depicts an ATOMS projection (Dowty, 1999), onto [100], of the asymmetric unit cell of SrMgP2O7. This structure joins the previously mentioned set of pyrophosphates SrMP2O7, it is thus isostructural to α-Ca2P2O7. Mg behaves like the other M atoms in this series showing a square-pyramidal coordination. Each Mg2+ is coordinated by five O atoms from five of the [P2O7]4- counter-ions. The five short Mg—O contacts range from 1.986 to 2.116 Å, with an average dMg—O of 2.046 Å. This latter value can be compared to the similar distance found in the homologous coordination in α-Mg2P2O7 of 2.044 Å. The MgO5 polyhedra are isolated in the structure, where two nearest Mg2+ ions are at 3.768 Å from each other. Fig. 2 is a projection, onto [010], showing the repartition of Mg in the structure of SrMgP2O7. The asymmetric unit contains two crystallographically independent phosphorus centers tetrahedrally coordinated, the two PO4 share O(1) to form the P2O7 group (Fig. 3). Average bridging and terminal P—O distances are 1.601 and 1.516 Å. A bridging angle ϕ(P,O,P) = 129.8 (2)° is observed for P2O7. All these values are quite usual in the series SrMP2O7 [d(P—O) and angle ϕ(P,O,P): SrCrP2O7 (1.600 Å, 128.1°), SrNiP2O7 (1.597 Å, 128.3°)]. The strontium ion is surrounded by eight O atoms. Mean distance Sr—O in the polyhedra SrO8 is 2.641 Å which is close to 2.622 Å found in SrNiP2O7.

Experimental top

Powder has been prepared, according to the chemical formulae SrMgP2O7, starting from equimolar mixtures of the starting materials SrCO3, MgCO3 and (NH4)2HPO4. The mixture was heated progressively in air at increasing temperatures up to 1173 K. An X-ray diagram of the resulting powder shows it is isotypic to the homologous SrMP2O7 pyrophosphates. However, the direct melting seems to not provide sufficient quality crystals for X-ray data collection. For this, we have tried the following method: ca 200 mg powder of SrMgP2O7 was mixed with 100 mg iodine and 10 mg red phosphorous and the mixture sealed in an evacuated silica ampoule (l ~10 cm and d ~1.6 cm). The ampoule was transferred to a tubular furnace where it was heated for 5 d at 1073 K. The reaction products have been washed with dilute NaOH and water and dried at 373 K. It results in small prismatic crystals from which we have selected the one used for the present crystal structure determination.

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty,1999) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Projection of the crystal structure of SrMgP2O7 along the a axis. Sr and Mg are shown as green and blue balls respectively. PO4 tetrahedra are yellow.
[Figure 2] Fig. 2. Projection of the crystal structure along the b axis with Mg polyhedra (blue). Sr atoms are shown as green balls and PO4 as yellow tetrahedra.
[Figure 3] Fig. 3. Atomic displacement ellipsoids at 50% probability.
Strontium Magnesium Diphosphate top
Crystal data top
SrMgP2O7F(000) = 544
Mr = 285.87Dx = 3.394 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 5.3046 (8) ÅCell parameters from 1188 reflections
b = 8.3053 (13) Åθ = 5.9–57.1°
c = 12.700 (2) ŵ = 10.30 mm1
β = 90.502 (3)°T = 293 K
V = 559.48 (15) Å3Prism, colorless
Z = 40.06 × 0.05 × 0.04 mm
Data collection top
Bruker CCD area-detector
diffractometer
1798 independent reflections
Radiation source: fine-focus sealed tube1317 reflections with I > 2α(I)
Graphite monochromatorRint = 0.069
ω scansθmax = 31.7°, θmin = 2.9°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 77
Tmin = 0.604, Tmax = 0.662k = 1212
7156 measured reflectionsl = 1718
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.036 w = 1/[σ2(Fo2) + (0.0286P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.071(Δ/σ)max = 0.001
S = 0.95Δρmax = 0.82 e Å3
1798 reflectionsΔρmin = 0.77 e Å3
101 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0029 (6)
Crystal data top
SrMgP2O7V = 559.48 (15) Å3
Mr = 285.87Z = 4
Monoclinic, P21/nMo Kα radiation
a = 5.3046 (8) ŵ = 10.30 mm1
b = 8.3053 (13) ÅT = 293 K
c = 12.700 (2) Å0.06 × 0.05 × 0.04 mm
β = 90.502 (3)°
Data collection top
Bruker CCD area-detector
diffractometer
1798 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
1317 reflections with I > 2α(I)
Tmin = 0.604, Tmax = 0.662Rint = 0.069
7156 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.036101 parameters
wR(F2) = 0.0710 restraints
S = 0.95Δρmax = 0.82 e Å3
1798 reflectionsΔρmin = 0.77 e Å3
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.

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 (Å2) top
xyzUiso*/Ueq
Sr10.21537 (7)0.33976 (4)0.72107 (3)0.0100 (1)
Mg10.6784 (2)0.1493 (2)0.8910 (1)0.0096 (3)
P10.7459 (2)0.0357 (1)0.66719 (8)0.0076 (2)
P20.6868 (2)0.2999 (1)0.51986 (8)0.0076 (2)
O10.7331 (5)0.1157 (3)0.5530 (2)0.0107 (6)
O20.6831 (5)0.1393 (3)0.6533 (2)0.0105 (6)
O31.0063 (5)0.0652 (3)0.7126 (2)0.0152 (6)
O40.5471 (5)0.1158 (3)0.7348 (2)0.0103 (6)
O50.8049 (5)0.3115 (3)0.4118 (2)0.0111 (6)
O70.4046 (5)0.3309 (3)0.5233 (2)0.0111 (6)
O60.8275 (5)0.4043 (3)0.6000 (2)0.0105 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Sr10.0081 (2)0.0104 (2)0.0116 (2)0.00044 (14)0.0006 (1)0.0011 (2)
Mg10.0097 (7)0.0093 (6)0.0098 (7)0.0003 (5)0.0019 (5)0.0002 (5)
P10.0081 (5)0.0076 (4)0.0071 (5)0.0004 (3)0.0000 (4)0.0002 (4)
P20.0072 (5)0.0086 (4)0.0070 (5)0.0001 (3)0.0008 (4)0.0003 (4)
O10.0151 (15)0.0086 (12)0.0085 (14)0.0024 (11)0.0021 (12)0.0006 (11)
O20.0128 (14)0.0072 (12)0.0115 (14)0.0012 (10)0.0003 (11)0.0000 (10)
O30.0099 (14)0.0160 (14)0.0196 (16)0.0012 (11)0.0059 (12)0.0007 (12)
O40.0111 (14)0.0116 (12)0.0081 (14)0.0003 (10)0.0016 (11)0.0022 (10)
O50.0091 (14)0.0172 (14)0.0070 (14)0.0005 (10)0.0036 (11)0.0002 (10)
O70.0082 (13)0.0127 (13)0.0123 (15)0.0016 (11)0.0006 (11)0.0013 (11)
O60.0125 (14)0.0093 (12)0.0096 (14)0.0010 (11)0.0024 (11)0.0006 (10)
Geometric parameters (Å, º) top
Sr1—O3i2.525 (3)Mg1—O7vi2.062 (3)
Sr1—O3ii2.537 (3)Mg1—O42.116 (3)
Sr1—O42.565 (3)P1—O21.501 (3)
Sr1—O6ii2.613 (3)P1—O31.512 (3)
Sr1—O2iii2.665 (3)P1—O41.519 (3)
Sr1—O72.714 (3)P1—O11.596 (3)
Sr1—O4iii2.743 (3)P2—O51.516 (3)
Sr1—O5iv2.766 (3)P2—O71.520 (3)
Mg1—O2i1.986 (3)P2—O61.527 (3)
Mg1—O5iv2.027 (3)P2—O11.605 (3)
Mg1—O6v2.038 (3)
O3i—Sr1—O3ii159.19 (6)O2—P1—O3113.77 (15)
O3i—Sr1—O496.68 (8)O2—P1—O4109.64 (15)
O3ii—Sr1—O469.55 (8)O3—P1—O4110.46 (15)
O3i—Sr1—O6ii119.94 (8)O2—P1—O1106.78 (15)
O3ii—Sr1—O6ii79.51 (8)O3—P1—O1108.10 (15)
O4—Sr1—O6ii136.44 (8)O4—P1—O1107.85 (14)
O3i—Sr1—O2iii102.50 (8)O5—P2—O7115.47 (16)
O3ii—Sr1—O2iii74.64 (8)O5—P2—O6111.32 (16)
O4—Sr1—O2iii123.62 (8)O7—P2—O6111.11 (15)
O6ii—Sr1—O2iii73.42 (8)O5—P2—O1103.57 (15)
O3i—Sr1—O796.25 (9)O7—P2—O1107.61 (15)
O3ii—Sr1—O795.84 (9)O6—P2—O1107.09 (15)
O4—Sr1—O777.54 (8)P1—O1—P2129.84 (17)
O6ii—Sr1—O775.91 (8)P1—O2—Mg1v143.78 (17)
O2iii—Sr1—O7149.04 (8)P1—O2—Sr1vii99.72 (13)
O3i—Sr1—O4iii66.93 (8)Mg1v—O2—Sr1vii114.17 (11)
O3ii—Sr1—O4iii122.50 (8)P1—O3—Sr1v122.43 (14)
O4—Sr1—O4iii160.27 (4)P1—O3—Sr1viii124.02 (15)
O6ii—Sr1—O4iii63.28 (8)Sr1v—O3—Sr1viii113.48 (10)
O2iii—Sr1—O4iii54.31 (7)P1—O3—Mg177.81 (12)
O7—Sr1—O4iii113.84 (8)Sr1v—O3—Mg1105.44 (10)
O3i—Sr1—O5iv87.10 (8)Sr1viii—O3—Mg190.88 (9)
O3ii—Sr1—O5iv72.57 (8)P1—O4—Mg1111.29 (15)
O4—Sr1—O5iv59.93 (8)P1—O4—Sr1139.32 (15)
O6ii—Sr1—O5iv137.45 (8)Mg1—O4—Sr1100.86 (10)
O2iii—Sr1—O5iv68.66 (8)P1—O4—Sr1vii96.06 (12)
O7—Sr1—O5iv137.41 (8)Mg1—O4—Sr1vii94.68 (10)
O4iii—Sr1—O5iv106.50 (8)Sr1—O4—Sr1vii105.72 (9)
O2i—Mg1—O5iv105.02 (12)P2—O5—Mg1ix122.67 (16)
O2i—Mg1—O6v154.70 (13)P2—O5—Sr1ix133.99 (14)
O5iv—Mg1—O6v97.91 (12)Mg1ix—O5—Sr1ix96.85 (10)
O2i—Mg1—O7vi86.92 (12)P2—O7—Mg1x123.79 (16)
O5iv—Mg1—O7vi116.32 (12)P2—O7—Sr1113.80 (14)
O6v—Mg1—O7vi92.46 (11)Mg1x—O7—Sr1122.31 (11)
O2i—Mg1—O488.28 (11)P2—O6—Mg1i126.64 (16)
O5iv—Mg1—O480.17 (11)P2—O6—Sr1viii130.79 (14)
O6v—Mg1—O485.20 (11)Mg1i—O6—Sr1viii100.62 (10)
O7vi—Mg1—O4163.51 (12)
O2—P1—O1—P2156.4 (2)O6—P2—O1—P138.6 (3)
O3—P1—O1—P280.8 (2)O2—P1—P2—O558.6 (2)
O4—P1—O1—P238.6 (3)O3—P1—P2—O637.33 (16)
O5—P2—O1—P1156.3 (2)O4—P1—P2—O737.85 (15)
O7—P2—O1—P180.9 (2)
Symmetry codes: (i) x+3/2, y+1/2, z+3/2; (ii) x1, y, z; (iii) x+1/2, y+1/2, z+3/2; (iv) x1/2, y+1/2, z+1/2; (v) x+3/2, y1/2, z+3/2; (vi) x+1/2, y+1/2, z+1/2; (vii) x+1/2, y1/2, z+3/2; (viii) x+1, y, z; (ix) x+1/2, y+1/2, z1/2; (x) x1/2, y+1/2, z1/2.

Experimental details

Crystal data
Chemical formulaSrMgP2O7
Mr285.87
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)5.3046 (8), 8.3053 (13), 12.700 (2)
β (°) 90.502 (3)
V3)559.48 (15)
Z4
Radiation typeMo Kα
µ (mm1)10.30
Crystal size (mm)0.06 × 0.05 × 0.04
Data collection
DiffractometerBruker CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.604, 0.662
No. of measured, independent and
observed [I > 2α(I)] reflections
7156, 1798, 1317
Rint0.069
(sin θ/λ)max1)0.738
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.071, 0.95
No. of reflections1798
No. of parameters101
Δρmax, Δρmin (e Å3)0.82, 0.77

Computer programs: SMART (Bruker, 1999), SAINT (Bruker, 1999), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty,1999) and ORTEP-3 (Farrugia, 1997), SHELXL97.

Selected geometric parameters (Å, º) top
Sr1—O3i2.525 (3)Mg1—O7vi2.062 (3)
Sr1—O3ii2.537 (3)Mg1—O42.116 (3)
Sr1—O42.565 (3)P1—O21.501 (3)
Sr1—O6ii2.613 (3)P1—O31.512 (3)
Sr1—O2iii2.665 (3)P1—O41.519 (3)
Sr1—O72.714 (3)P1—O11.596 (3)
Sr1—O4iii2.743 (3)P2—O51.516 (3)
Sr1—O5iv2.766 (3)P2—O71.520 (3)
Mg1—O2i1.986 (3)P2—O61.527 (3)
Mg1—O5iv2.027 (3)P2—O11.605 (3)
Mg1—O6v2.038 (3)
O2—P1—O1—P2156.4 (2)O3—P1—P2—O637.33 (16)
O5—P2—O1—P1156.3 (2)O4—P1—P2—O737.85 (15)
O2—P1—P2—O558.6 (2)
Symmetry codes: (i) x+3/2, y+1/2, z+3/2; (ii) x1, y, z; (iii) x+1/2, y+1/2, z+3/2; (iv) x1/2, y+1/2, z+1/2; (v) x+3/2, y1/2, z+3/2; (vi) x+1/2, y+1/2, z+1/2.
 

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