Related literature {#sec1}
==================

For isotypic structures, see: Rochère *et al.* ( 1985[@bb5]); Stus *et al.* ( 2001[@bb7]). 

Experimental {#sec2}
============

 {#sec2.1}

### Crystal data {#sec2.1.1}

Na~7~Al~4~(P~2~O~7~)~4~(PO~4~)*M* *~r~* = 1059.58Tetragonal,*a* = 14.054 (3) Å*c* = 6.1718 (16) Å*V* = 1219.1 (4) Å^3^*Z* = 2Mo *K*α radiationμ = 1.06 mm^−1^*T* = 296 K0.15 × 0.05 × 0.05 mm

### Data collection {#sec2.1.2}

Rigaku Saturn70 CCD diffractometerAbsorption correction: multi-scan (*ABSCOR*; Higashi, 1995[@bb3]) *T* ~min~ = 0.857, *T* ~max~ = 0.9495562 measured reflections1347 independent reflections1287 reflections with *I* \> 2σ(*I*)*R* ~int~ = 0.024

### Refinement {#sec2.1.3}

*R*\[*F* ^2^ \> 2σ(*F* ^2^)\] = 0.017*wR*(*F* ^2^) = 0.047*S* = 1.081347 reflections118 parametersΔρ~max~ = 0.22 e Å^−3^Δρ~min~ = −0.29 e Å^−3^Absolute structure: Flack (1983[@bb2]), 540 Friedel pairsFlack parameter: −0.04 (9)

 {#d5e469}

Data collection: *CrystalClear* (Rigaku, 2004[@bb4]); cell refinement: *CrystalClear*; data reduction: *CrystalClear*; program(s) used to solve structure: *SHELXS97* (Sheldrick, 2008[@bb6]); program(s) used to refine structure: *SHELXL97* (Sheldrick, 2008[@bb6]); molecular graphics: *DIAMOND* (Brandenburg, 2004[@bb1]); software used to prepare material for publication: *SHELXTL* (Sheldrick, 2008[@bb6]). 

Supplementary Material
======================

Crystal structure: contains datablock(s) I, global.  DOI: [10.1107/S1600536811041729/wm2530sup1.cif](http://dx.doi.org/10.1107/S1600536811041729/wm2530sup1.cif)

Structure factors: contains datablock(s) I. DOI: [10.1107/S1600536811041729/wm2530Isup2.hkl](http://dx.doi.org/10.1107/S1600536811041729/wm2530Isup2.hkl)

Additional supplementary materials: [crystallographic information](http://scripts.iucr.org/cgi-bin/sendsupfiles?wm2530&file=wm2530sup0.html&mime=text/html); [3D view](http://scripts.iucr.org/cgi-bin/sendcif?wm2530sup1&Qmime=cif); [checkCIF report](http://scripts.iucr.org/cgi-bin/paper?wm2530&checkcif=yes)

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: [WM2530](http://scripts.iucr.org/cgi-bin/sendsup?wm2530)). 

The author acknowledges the Doctoral Foundation of Henan Polytechnic University (B2010--92, 648483). 

Comment
=======

Metal phosphates possessing open-framework structures with defined tunnels have been extensively investigated for their structural diversity, properties, and potential applications in shape-selective catalysis, adsorbents, ion exchangers, and molecular sieves.  Among them, a series of isotypic ortho-diphosphates Na~7~(MP~2~O~7~)~4~PO~4~ (M = Al, Cr, Fe) (Rochère et al.,  1985) and Na~7~(InP~2~O~7~)~4~PO~4~ (Stus et al.,  2001) were synthesized, and their ion exchange and conductivity properties studied.  However, for compound Na~7~(AlP~2~O~7~)~4~PO~4~, a detailed crystal structure analysis has not been reported so far.  In this work, the synthesis and results of the crystal structure refinement of this compound is reported.  In comparison with the unit cell parameters reported by Rochère from X-ray powder data (a = 14.046 (3), c = 6.169 (2) Å; Rochère et al.,  1985), the determined unit cell parameters from the single crystal X-ray study are slighty larger. 

As shown in Figs 1 and 2, the structure of the title compound consists of a three-dimensional framework of isolated PO~4~ tetrahedra, AlO~6~ octahedra and P~2~O~7~ groups, the conformation of the latter more eclipsed than staggered.  The sodium cations are located in sites within cavities in the framework, exhibiting coordination numbers of 7 (Na1), 6 (Na2) and 4 (Na3).  There are three crystallography distinct P atoms in the structure of the title compound.  P1 and P2 atoms are located in general positions and their corresponding P1O~4~ and P2O~4~ tetrahedra are connected by the bridging O5 atom to form a P~2~O~7~ group, which is further linked to four AlO~6~ octahedra.  P3 atoms are located on 4 axes, forming isolated P3O~4~ tetrahedra which are further connected to four AlO~6~ octahedra.  The P3O~4~ tetrahedra are regular with a P---O bond length of 1.5351 (18) Å, while the P--O distances in the P~2~O~7~ group are irregular, showing the characteristic variance of smaller P--O~terminal~ bonds (1.4862 (14) to 1.5199 (14) Å) and larger P--O~bridging~ bonds (1.6097 (14) and 1.6284 (15) Å) as typically observed for diphosphate unit.  The title structure differs in their P--O--P bridging angle of the diphosphate group and the average metal--O distances from those of the isotypic congeners.  For the Al compound, the interatomic distances in the MO~6~ octahedron are decreasing (Fe--O~6~ 1.968--2.021 Å, InO~6~ 2.091--2.146 Å, AlO~6~ 1.8391 (15)--1.9278 (16) Å), as expected from the smaller ionic radius of Al^3+^ comparerd to Fe^3+^ and In^3+^. With a decrease of the unit-cell parameters a trend in a likewise decreasing P--O--P bridging angle of the diphosphate groups is observed: (Na~7~(FeP~2~O~7~)~4~PO~4~: 136.6 (3)°; Na~7~(InP~2~O~7~)~4~PO~4~: 136.7 (3)°, Na~7~(AlP~2~O~7~)~4~PO~4~: 127.92 (9)°. 

Experimental {#experimental}
============

The finely ground reagents Na~2~CO~3~, Al~2~O~3~ and NH~4~H~2~PO~4~ were mixed in the molar ratio Na: Al: P = 2: 1: 8, were placed in a Pt crucible, and heated at 673 K for 4 h. The mixture was then re-ground and heated at 1173 K for 20 h, then cooled to 673 K at a rate of 3 K h^-1^, and finally quenched to room temperature.  A few colorless crystals of the title compound with prismatic shape were obtained. 

Refinement {#refinement}
==========

The highest peak in the difference electron density map equals to 0.22 e/Å^3^ at the distance of 0.63 Å from O4 site while the deepest hole equals to -0.29 e/Å^3^ at the distance of 0.68 Å from the P3 site. 

Figures
=======

![ The expanded asymmetric unit of Na7(AlP2O7)4PO4 showing the coordination environments of the P and Al atoms.  The displacement ellipsoids are drawn at the 50% probability level.  \[Symmetry codes: (iii) -y + 1, x, -z + 1; (vii) -x + 1, -y + 1, z; (viii) -y + 1, x, -z + 2; (ix) x - 1/2, -y + 3/2, -z + 3/2; (x) y, -x + 1, -z + 1.\]](e-67-00i64-fig1){#Fap1}

![ View of the crystal structure of Na7(AlP2O7)4PO4.  PO4 and AlO6 units are given in the polyhedral representation.](e-67-00i64-fig2){#Fap2}

Crystal data {#tablewrapcrystaldatalong}
============

  -------------------------------- ---------------------------------------
  Na~7~Al~4~(P~2~O~7~)~4~(PO~4~)   *D*~x~ = 2.887 Mg m^−3^
  *M~r~* = 1059.58                 Mo *K*α radiation, λ = 0.71073 Å
  Tetragonal, *P*42~1~*c*          Cell parameters from 3720 reflections
  Hall symbol: P -4 2n             θ = 2.9--27.5°
  *a* = 14.054 (3) Å               µ = 1.06 mm^−1^
  *c* = 6.1718 (16) Å              *T* = 296 K
  *V* = 1219.1 (4) Å^3^            Prism, colourless
  *Z* = 2                          0.15 × 0.05 × 0.05 mm
  *F*(000) = 1040                  
  -------------------------------- ---------------------------------------

Data collection {#tablewrapdatacollectionlong}
===============

  ------------------------------------------------------------- --------------------------------------
  Rigaku Saturn70 CCD diffractometer                            1347 independent reflections
  Radiation source: fine-focus sealed tube                      1287 reflections with *I* \> 2σ(*I*)
  Graphite Monochromator                                        *R*~int~ = 0.024
  Detector resolution: 14.6306 pixels mm^-1^                    θ~max~ = 27.5°, θ~min~ = 3.2°
  ω scans                                                       *h* = −18→17
  Absorption correction: multi-scan (*ABSCOR*; Higashi, 1995)   *k* = −18→16
  *T*~min~ = 0.857, *T*~max~ = 0.949                            *l* = −7→7
  5562 measured reflections                                     
  ------------------------------------------------------------- --------------------------------------

Refinement {#tablewraprefinementdatalong}
==========

  ------------------------------------- ------------------------------------------------------------------------------------------------
  Refinement on *F*^2^                  Primary atom site location: structure-invariant direct methods
  Least-squares matrix: full            Secondary atom site location: difference Fourier map
  *R*\[*F*^2^ \> 2σ(*F*^2^)\] = 0.017   *w* = 1/\[σ^2^(*F*~o~^2^) + (0.0297*P*)^2^ + 0.278*P*\] where *P* = (*F*~o~^2^ + 2*F*~c~^2^)/3
  *wR*(*F*^2^) = 0.047                  (Δ/σ)~max~ = 0.001
  *S* = 1.08                            Δρ~max~ = 0.22 e Å^−3^
  1347 reflections                      Δρ~min~ = −0.29 e Å^−3^
  118 parameters                        Absolute structure: Flack (1983), 540 Friedel pairs
  0 restraints                          Flack parameter: −0.04 (9)
  ------------------------------------- ------------------------------------------------------------------------------------------------

Special details {#specialdetails}
===============

  -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  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 *R*-factor *wR* and goodness of fit *S* are based on *F*^2^, conventional *R*-factors *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 *R*-factors(gt) *etc*.  and is not relevant to the choice of reflections for refinement. * R*-factors 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. 
  -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^2^) {#tablewrapcoords}
==================================================================================================

  ----- -------------- -------------- -------------- -------------------- --
        *x*            *y*            *z*            *U*~iso~\*/*U*~eq~   
  Na1   0.42251 (6)    0.75865 (7)    0.09314 (15)   0.0200 (2)           
  Na2   0.5000         1.0000         0.3156 (2)     0.0268 (3)           
  Na3   0.5000         0.5000         1.0000         0.0411 (6)           
  Al1   0.32097 (4)    0.62225 (4)    0.63747 (9)    0.00558 (13)         
  P1    0.62752 (3)    0.74207 (3)    0.84990 (8)    0.00573 (11)         
  P2    0.46166 (3)    0.79988 (3)    0.60041 (8)    0.00656 (11)         
  P3    0.5000         0.5000         0.5000         0.00535 (19)         
  O1    0.42717 (10)   0.89936 (10)   0.5600 (2)     0.0117 (3)           
  O2    0.54197 (10)   0.81323 (10)   0.7882 (2)     0.0109 (3)           
  O3    0.38751 (10)   0.73621 (10)   0.7038 (2)     0.0128 (3)           
  O4    0.51085 (9)    0.75581 (10)   0.4067 (2)     0.0104 (3)           
  O5    0.71136 (9)    0.80522 (10)   0.8791 (2)     0.0129 (3)           
  O6    0.59683 (10)   0.69263 (10)   1.0575 (2)     0.0113 (3)           
  O7    0.63718 (10)   0.66852 (9)    0.6721 (2)     0.0087 (3)           
  O8    0.43148 (9)    0.55247 (10)   0.6522 (2)     0.0100 (3)           
  ----- -------------- -------------- -------------- -------------------- --

Atomic displacement parameters (Å^2^) {#tablewrapadps}
=====================================

  ----- ------------ ------------ ------------ --------------- --------------- ---------------
        *U*^11^      *U*^22^      *U*^33^      *U*^12^         *U*^13^         *U*^23^
  Na1   0.0224 (4)   0.0242 (5)   0.0133 (4)   −0.0060 (3)     −0.0034 (4)     0.0031 (4)
  Na2   0.0280 (7)   0.0405 (9)   0.0118 (6)   −0.0216 (6)     0.000           0.000
  Na3   0.0561 (9)   0.0561 (9)   0.0111 (9)   0.000           0.000           0.000
  Al1   0.0049 (2)   0.0063 (3)   0.0055 (3)   0.0010 (2)      0.0002 (2)      0.0000 (2)
  P1    0.0056 (2)   0.0069 (2)   0.0047 (2)   −0.00024 (16)   0.00004 (17)    0.00036 (18)
  P2    0.0064 (2)   0.0068 (2)   0.0064 (2)   0.00048 (16)    −0.00085 (19)   −0.00024 (18)
  P3    0.0053 (3)   0.0053 (3)   0.0054 (4)   0.000           0.000           0.000
  O1    0.0133 (7)   0.0101 (6)   0.0117 (8)   0.0030 (6)      −0.0018 (6)     0.0007 (6)
  O2    0.0106 (7)   0.0123 (7)   0.0097 (7)   0.0043 (5)      −0.0043 (6)     −0.0034 (6)
  O3    0.0139 (7)   0.0127 (7)   0.0118 (7)   −0.0066 (6)     0.0023 (6)      −0.0033 (6)
  O4    0.0086 (6)   0.0138 (7)   0.0088 (6)   0.0027 (5)      0.0000 (5)      −0.0019 (6)
  O5    0.0101 (7)   0.0166 (7)   0.0121 (8)   −0.0056 (5)     −0.0004 (6)     −0.0012 (6)
  O6    0.0149 (7)   0.0134 (7)   0.0055 (7)   −0.0024 (5)     0.0008 (6)      0.0021 (5)
  O7    0.0119 (7)   0.0076 (7)   0.0065 (7)   0.0015 (5)      −0.0005 (5)     0.0007 (5)
  O8    0.0081 (6)   0.0135 (7)   0.0084 (6)   0.0039 (5)      0.0000 (6)      −0.0014 (5)
  ----- ------------ ------------ ------------ --------------- --------------- ---------------

Geometric parameters (Å, °) {#tablewrapgeomlong}
===========================

  -------------------------- ------------- -------------------------- -------------
  Na1---O4                   2.2998 (17)   P1---O7                    1.5136 (14)
  Na1---O1^i^                2.3993 (17)   P1---O6                    1.5199 (14)
  Na1---O3^ii^               2.4730 (18)   P1---O2                    1.6097 (14)
  Na1---O7^iii^              2.5789 (17)   P2---O1                    1.5006 (14)
  Na1---O6^ii^               2.6291 (18)   P2---O4                    1.5134 (14)
  Na1---O2^ii^               2.6363 (18)   P2---O3                    1.5145 (15)
  Na1---O6^iii^              2.9419 (18)   P2---O2                    1.6284 (15)
  Na2---O1^iv^               2.3072 (16)   P3---O8^iii^               1.5341 (14)
  Na2---O1                   2.3072 (17)   P3---O8^x^                 1.5341 (14)
  Na2---O1^i^                2.3532 (17)   P3---O8                    1.5341 (14)
  Na2---O1^v^                2.3532 (17)   P3---O8^vii^               1.5341 (14)
  Na2---O2^i^                2.6957 (15)   O1---Na2^xi^               2.3532 (17)
  Na2---O2^v^                2.6957 (15)   O1---Na1^xii^              2.3993 (17)
  Na3---O8^vi^               2.4655 (16)   O2---Na1^xiii^             2.6363 (18)
  Na3---O8                   2.4655 (16)   O2---Na2^xi^               2.6957 (15)
  Na3---O8^vii^              2.4655 (16)   O3---Na1^xiii^             2.4730 (18)
  Na3---O8^viii^             2.4655 (16)   O4---Al1^x^                1.9210 (15)
  Al1---O8                   1.8391 (15)   O5---Al1^xiv^              1.8500 (15)
  Al1---O5^ix^               1.8500 (15)   O6---Al1^vi^               1.9258 (16)
  Al1---O3                   1.8993 (16)   O6---Na1^xiii^             2.6291 (18)
  Al1---O4^iii^              1.9210 (15)   O6---Na1^x^                2.9419 (18)
  Al1---O6^viii^             1.9258 (16)   O7---Al1^x^                1.9278 (16)
  Al1---O7^iii^              1.9278 (16)   O7---Na1^x^                2.5789 (17)
  P1---O5                    1.4862 (14)                              
                                                                      
  O4---Na1---O1^i^           99.33 (6)     O3---Al1---O6^viii^        89.69 (7)
  O4---Na1---O3^ii^          157.36 (7)    O4^iii^---Al1---O6^viii^   86.10 (7)
  O1^i^---Na1---O3^ii^       90.92 (6)     O8---Al1---O7^iii^         92.43 (7)
  O4---Na1---O7^iii^         77.49 (5)     O5^ix^---Al1---O7^iii^     87.07 (6)
  O1^i^---Na1---O7^iii^      129.35 (6)    O3---Al1---O7^iii^         94.82 (7)
  O3^ii^---Na1---O7^iii^     111.27 (6)    O4^iii^---Al1---O7^iii^    89.49 (6)
  O4---Na1---O6^ii^          63.97 (5)     O6^viii^---Al1---O7^iii^   175.36 (7)
  O1^i^---Na1---O6^ii^       117.88 (6)    O5---P1---O7               115.13 (8)
  O3^ii^---Na1---O6^ii^      93.38 (6)     O5---P1---O6               113.31 (8)
  O7^iii^---Na1---O6^ii^     106.00 (5)    O7---P1---O6               108.92 (9)
  O4---Na1---O2^ii^          105.20 (6)    O5---P1---O2               104.47 (8)
  O1^i^---Na1---O2^ii^       74.83 (5)     O7---P1---O2               108.65 (8)
  O3^ii^---Na1---O2^ii^      58.00 (5)     O6---P1---O2               105.76 (8)
  O7^iii^---Na1---O2^ii^     155.46 (6)    O1---P2---O4               113.43 (9)
  O6^ii^---Na1---O2^ii^      56.60 (5)     O1---P2---O3               113.46 (8)
  O4---Na1---O6^iii^         123.33 (6)    O4---P2---O3               113.91 (8)
  O1^i^---Na1---O6^iii^      131.42 (6)    O1---P2---O2               103.58 (8)
  O3^ii^---Na1---O6^iii^     59.00 (5)     O4---P2---O2               107.01 (8)
  O7^iii^---Na1---O6^iii^    52.62 (5)     O3---P2---O2               104.19 (8)
  O6^ii^---Na1---O6^iii^     102.31 (6)    O8^iii^---P3---O8^x^       104.48 (11)
  O2^ii^---Na1---O6^iii^     110.46 (5)    O8^iii^---P3---O8          112.02 (6)
  O1^iv^---Na2---O1          98.36 (9)     O8^x^---P3---O8            112.02 (6)
  O1^iv^---Na2---O1^i^       166.32 (7)    O8^iii^---P3---O8^vii^     112.02 (6)
  O1---Na2---O1^i^           84.54 (5)     O8^x^---P3---O8^vii^       112.02 (6)
  O1^iv^---Na2---O1^v^       84.54 (5)     O8---P3---O8^vii^          104.48 (11)
  O1---Na2---O1^v^           166.32 (7)    P1---O2---P2               127.92 (9)
  O1^i^---Na2---O1^v^        95.80 (8)     P1---O2---Na1^xiii^        97.23 (7)
  O1^iv^---Na2---O2^i^       109.82 (5)    P2---O2---Na1^xiii^        91.90 (7)
  O1---Na2---O2^i^           75.12 (5)     P1---O2---Na2^xi^          138.90 (8)
  O1^i^---Na2---O2^i^        57.84 (5)     P2---O2---Na2^xi^          90.30 (6)
  O1^v^---Na2---O2^i^        116.61 (6)    Na1^xiii^---O2---Na2^xi^   95.69 (5)
  O1^iv^---Na2---O2^v^       75.12 (5)     P2---O3---Al1              138.27 (10)
  O1---Na2---O2^v^           109.82 (5)    P2---O3---Na1^xiii^        101.37 (7)
  O1^i^---Na2---O2^v^        116.61 (6)    Al1---O3---Na1^xiii^       114.51 (7)
  O1^v^---Na2---O2^v^        57.84 (5)     P2---O4---Al1^x^           135.59 (9)
  O2^i^---Na2---O2^v^        172.79 (8)    P2---O4---Na1              114.27 (8)
  O8^vi^---Na3---O8          139.29 (4)    Al1^x^---O4---Na1          109.28 (7)
  O8^vi^---Na3---O8^vii^     139.29 (4)    P1---O5---Al1^xiv^         169.27 (10)
  O8---Na3---O8^vii^         58.94 (7)     P1---O6---Al1^vi^          144.77 (10)
  O8^vi^---Na3---O8^viii^    58.94 (7)     P1---O6---Na1^xiii^        100.00 (7)
  O8---Na3---O8^viii^        139.29 (4)    Al1^vi^---O6---Na1^xiii^   97.24 (6)
  O8^vii^---Na3---O8^viii^   139.29 (4)    P1---O6---Na1^x^           76.46 (6)
  O8---Al1---O5^ix^          178.73 (7)    Al1^vi^---O6---Na1^x^      96.37 (6)
  O8---Al1---O3              91.33 (7)     Na1^xiii^---O6---Na1^x^    160.22 (7)
  O5^ix^---Al1---O3          87.55 (7)     P1---O7---Al1^x^           131.02 (9)
  O8---Al1---O4^iii^         92.68 (6)     P1---O7---Na1^x^           89.48 (7)
  O5^ix^---Al1---O4^iii^     88.48 (6)     Al1^x^---O7---Na1^x^       131.83 (7)
  O3---Al1---O4^iii^         173.98 (7)    P3---O8---Al1              139.13 (10)
  O8---Al1---O6^viii^        86.36 (7)     P3---O8---Na3              98.29 (7)
  O5^ix^---Al1---O6^viii^    94.23 (6)     Al1---O8---Na3             122.17 (7)
  -------------------------- ------------- -------------------------- -------------

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