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The title compound, tetrasodium cobalt aluminium hexaarsen­ate, Na4Co7-xAl2/3x(AsO4)6 (x = 1.37), is isostructural with K4Ni7(AsO4)6; however, in its crystal structure, some of the Co2+ ions are substituted by Al3+ in a fully occupied octa­hedral site (site symmetry 2/m) and a partially occupied tetra­hedral site (site symmetry 2). A third octa­hedral site is fully occupied by Co2+ ions only. One of the two independent tetra­hedral As atoms and two of its attached O atoms reside on a mirror plane, as do two of the three independent Na+ cations, all of which are present at half-occupancy. The proposed structural model based on a careful investigation of the crystal data is supported by charge-distribution (CHARDI) analysis and bond-valence-sum (BVS) calculations. The correlation between the X-ray refinement and the validation results is discussed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270110037376/sq3262sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270110037376/sq3262Isup2.hkl
Contains datablock I

Comment top

Metal-substituted aluminophosphates constitute an interesting group of materials widely used as molecular sieves with catalytic and adsorptive properties. The cobalt analogue compounds possess such [the same?] structural properties, for example, the mixed cobalt aluminium phosphate K(CoII,Al)2(PO4)2, which contains only tetrahedrally coordinated Co/Al sites and a three-dimensional system of interconnected tunnels (Chen et al., 1997), and the two ammonium-templated cobalt aluminophosphates (NH4)2[(OH)0.95(H2O)0.05]2[Co0.05Al0.95]2(PO4)2 and (NH4)[(OH)0.95(H2O)0.05][Co0.025Al0.975]2.2H2O with zeolite-like structures (Bontchev & Sevov, 1999). During an exploration of the Na–Co–As–O system, and in an attempt to prepare the arsenic homologue of Na4Co7(PO4)6 (Kobashi et al. 1998), the new compound Na4Co7-xAl2/3x(AsO4)6 (x = 1.37), (I), was isolated and its composition determined by single-crystal X-ray diffraction. It should be noted that, as for the three already mentioned aluminophsphates, the incorporation of aluminium from the reaction container could occur. Herein, we report the synthesis and crystal structure of (I), together with charge-distribution (CHARDI) and bond-valence-sum (BVS) calculations that validate the X-ray composition.

The asymmetric unit (Fig. 1) contains six metallic sites of which three are half-occupied by Na+ cations with eight cations per unit cell, two others (called M1 and M2) are simultaneously shared by Co2+ and Al3+ ions, and one is fully occupied by Co2+ ions. The fact that Co2+ and Al3+ ions are distributed over the two M positions was determined based on examination of the displacement ellipsoids, residual peaks and interatomic distances. Aluminium cations share with cobalt the 2b Wyckoff position at the centre of an octahedron with a fully occupied scheme and this position with overall occupancy Co0.286Al0.714 is denoted as M1. The substitution of the smaller Al3+ cations results in a reduction of the M1—O bond distances compared to what would be found in a pure Co2+ octahedron, thus supporting the mixing of Co2+ and Al3+ at this site.

For the second site, denoted M2, the Co2+/Al3+ ions are tetrahedrally coordinated by oxygen atoms with an arithmetic average distance of <M2—O> = 2.13 Å. As the interatomic distances are notably larger than those of a pure Co2+ tetrahedron [such as that in the phosphorus homologue (Kobashi et al., 1998) in which <Co—O> = 2.01 Å], the displacement parameters were large for a fully occupied cobalt site, and a deep hole of -3.44 e.A-3 was localized in the difference Fourier map at a distance of 0.52 Å from the M2 position; therefore, the M2 site was initially refined as being partially occupied by cobalt ions, yielding an occupancy of just under 72%. This occupancy if only Co2+ is not sufficient to make the obtained compound formula neutral [Na4Co5.715Al0.715(AsO4)6] [words missing from this sentence?].

Many propositions are possible to ensure the electroneutrality: the existence of some vacancies in the oxygen positions, the oxidation of a small amount of Co2+ to Co3+, and aliovalent occupation of the same site other than M1 by Co2+ and Al3+ ions. These hypotheses were then tested one by one. Although the presence of heavy atoms makes the refinement of oxygen atom occupancies not very reliable, these occupancy factors have been refined and did not show significant deviation from full occupation, so the first hypothesis was then excluded.

To check the second proposition, one should first know the thermal decomposition behaviour of the cobalt source, cobalt acetate tetrahydrate (Grimes & Fitch, 1991; Alshehri et al. 2000; Tang & Chen, 2007). The atmospheres used in the decomposition studies include vacuum, flowing gas and self-generated atmospheres and the end product is influenced by the atmosphere and the conditions used.

Assuming the dehydration process produced CoO as a final product, as suggested by Grimes & Fitch (1991), within the Ellingham approximation the oxygen pressure needed to transform CoO to Co3O4 at 1153 K was evaluated from the thermodynamic data to be about 3.27 bar (1 bar = 10 5 Pa). This is much higher than the PO2 in air of 0.2 bar, so we can deduce that the reaction to give partial oxidation of Co2+ to Co3+ is thermodynamically impossible under the conditions of our reaction. This does not exclude the existence of other oxidation reactions, but such a mechanism remains less probable. Indeed, to the best of our knowledge, there is only one cobalt arsenate, Co8As3O16 (Krishnamachari & Calvo, 1970), where this particular transformation has been proposed because of the deviation from stoichiometry.

The third mechanism was then retained to fulfill the electroneutrality. In the final refinement, a fraction of Al3+ was introduced in the M2 site and the two ions were assumed to be statistically distributed in the fractionally occupied M2 site to yield an overall occupancy distribution of Co0.672Al0.1010.230, with □ expressing the vacancy. The result thus obtained corresponds to the formula Na4Co5.63Al0.91(AsO4)6. A similar distribution in a tetrahedral site has been reported in the structure of Co2+-stabilized beta''-alumina, Co0.350Al0.5580.092 (Chen et al. 1986).

The obtained structural model of (I) was submitted to both charge-distribution (CD) (Nespolo et al., 2001; Nespolo, 2001) and BVS analyses (Brown, 2002; Adams, 2003). The cation charges Q from the CD analysis and valences V according to the BVS model are reported in Table 2. The CD method has been mainly used to validate structures, as in the non-stochiometric mixed oxide YbFeMnO4 (Nespolo et al., 2000), the oxygen-deficient arsenate Na7As11O31 (Guesmi et al., 2006) and the mixed-valent cobalt phosphate Li4.03Co1.97(P2O7)2 (Kouass et al., 2010); the bond valence analysis has also been used for structural validation and seems to be an important tool to model ionic conduction pathways (e.g. Mazza, 2001; Adams, 2006; Ouerfelli et al., 2008).

The computed charges (Q) from the CD analysis are in good agreement with the charges of all the cation sites and the structural model is thus validated, as shown by the dispersion factor of 5% which measures the deviation of the computed charges (Q) with respect to the formal oxidation numbers. The rejection of the oxygen vacancy hypothesis to ensure elctroneutrality is also supported, as the computed anion charges are consistent with the expected ones (dispersion factor 9%), with the exception of a slight under- and over- bonding on O1 and O2, respectively [Q(O1) -1.841, Q(O2) -2.095]. Looking to the BVS results, and mainly to the cation valences, although the BVS validation tool does not contain an internal criterion as for the CD analysis (q/Q ratio close to 1), the structural model is supported, particularly the cation distribution on the M1 site. The exception is a significant deviation observed for the partially occupied M2 site. Such a result is expected since the BVS model rarely confirms the valence of sites partially occupied by metal cations such as Al3+ or transition metal ions as in the investigated compound. For example, the valence of the partially occupied Co2+ site (site occupation factor 0.728) in Co6.95As3.62O16 (Krishnamachari & Calvo, 1973) is calculated by BVS to be only 1.30 v.u. (valence unit), lower than the occupancy-based value of 1.46. This is not the case for alkali cations where sometimes it is difficult to distinguish between the first and the second coordination sphere and their BVS valences in most cases are close to the expected values. In summary, the structural model is supported by associating the results of the crystal structure refinement to the CD and BVS investigations.

The investigated compound is a new member of the family of isostructural phases that includes Na4Ni7(PO4)6 (Moring & Kostiner, 1986), Na4Co7(PO4)6 (Kobashi et al., 1998) and K4Ni7(AsO4)6 (Ben Smail et al., 1999). In addition to the Co/Al-centred polyhedra, the structure contains two independent arsenic-centred tetrahedra. All the polyhedra show limited degrees of distortion with respect to ideal geometries, as indicated by their effective coordination numbers (ECoN) (Table 1). The distortion is a bit more pronounced for the octahedra than the tetrahedra based on these results.

The three-dimensional centrosymmetric framework (Fig. 2) delimits tunnels running along the [100] direction and communicating along the b axis through quadrilateral windows. These voids accommodate the Na+ cations which are, as in the isostructural compounds, distributed into three independent positions, one located at the periphery and two special positions at the centre of the tunnels. The dimensions of the hexagonal sections of the tunnels are 4.46 × 4.82 Å measured between oxygen atoms; the O3 oxygen atoms coordinated only to As1 tetrahedra point to the centre of tunnels at a shortest distance of 2.93 Å. The framework of (I) is thus of open character and the motion of sodium cations through the tunnels seems feasible. This possibility is to be confirmed by electrical measurements in future work.

Related literature top

For related literature, see: Brown (2002); Adams (2006); Adams (2003); Alshehri et al. (2000); Ben Smail, Driss & Jouini (1999); Bontchev & Sevov (1999); Chen et al. (1986, 1997); Grimes & Fitch (1991); Guesmi et al. (2006); Kobashi et al. (1998); Kouass et al. (2010); Krishnamachari & Calvo (1970, 1973); Mazza (2001); Moring & Kostiner (1986); Nespolo et al. (2000, 2001); Ouerfelli et al. (2008); Tang & Chen (2007).

Experimental top

A mixture of sodium carbonate, cobalt acetate tetrahydrate and As2O5 in the molar ratio Na:Co:As = 4:7:6 was placed in a porcelain boat and first heated at 673 K in air for 24 h and then heated gradually to 1153 K for 3 d. Some pink, parallelepiped crystals were isolated from the sample. A qualitative EDX analysis detected the presence of Na, Co, Al and O, with the aluminium diffusing from the reaction container. A polycrystalline powder of (I) was obtained by treating a stochiometric mixture of the above reagents with Al2O3 as the aluminium source. The powder X-ray diffraction pattern was in agreement with the single-crystal structure.

Refinement top

The cobalt and aluminium atoms occupying the M1 and M2 sites were constrained (using EXYZ and EADP) to have the same positional and displacement parameters. Two linear free variable restraints (SUMP) were required to restrain the sum of their occupation factors. Noting the difference between the displacement parameters of the M1 and M2 sites, we believe that the relatively large displacement parameters for the latter are reasonable since the M2 site is fractionally occupied. The same relationship has been observed in Co6.95As3.62O16 (Krishnamachari & Calvo, 1973) in which the following parameters were reported: Co1 site occupation factor 0.7275, Ueq 0.0107 (2), Co2 site occupation factor 1.0, Ueq: 0.0075 (2).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1995); cell refinement: CAD-4 EXPRESS (Enraf–Nonius, 1995); 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, 1998); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of (I) with the atom-labelling scheme. Some symmetry-related O atoms are included to show the full coordination polyhedra around the Co/Al and As atoms. Displacement ellipsoids are drawn at the 50% probability level [Symmetry codes: (i) x, -y + 1, z; (ii) -x, -y + 1, -z; (iii) -x, y, -z; (iv) x - 1/2, y - 1/2, z; (v) -x + 1/2, y - 1/2, -z; (vi) -x + 1/2, -y + 1/2, -z + 1; (vii) -x + 1/2, -y + 1/2, -z; (viii) x + 1/2, -y + 1/2, z].
[Figure 2] Fig. 2. The structure of Na4Co5.63Al0.91(AsO4)6 viewed near the [100] direction, showing the tunnels.
tetrasodium cobalt aluminium hexaarsenate top
Crystal data top
Na4Co5.63Al0.91(AsO4)6F(000) = 1196
Mr = 1281.94Dx = 4.121 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yCell parameters from 25 reflections
a = 10.744 (4) Åθ = 11.0–14.5°
b = 14.847 (3) ŵ = 14.20 mm1
c = 6.722 (3) ÅT = 293 K
β = 105.51 (3)°Parallelipiped, pink
V = 1033.2 (6) Å30.25 × 0.25 × 0.22 mm
Z = 2
Data collection top
Enraf–Nonius CAD-4
diffractometer
1042 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.028
Graphite monochromatorθmax = 27.0°, θmin = 2.4°
ω/2θ scansh = 1313
Absorption correction: ψ scan
(North et al., 1968)
k = 118
Tmin = 0.040, Tmax = 0.044l = 82
1584 measured reflections2 standard reflections every 120 min
1157 independent reflections intensity decay: 1%
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)] = 0.026 w = 1/[σ2(Fo2) + (0.0275P)2 + 8.3215P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.068(Δ/σ)max < 0.001
S = 1.13Δρmax = 0.90 e Å3
1157 reflectionsΔρmin = 0.91 e Å3
117 parametersExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
2 restraintsExtinction coefficient: 0.00110 (14)
Crystal data top
Na4Co5.63Al0.91(AsO4)6V = 1033.2 (6) Å3
Mr = 1281.94Z = 2
Monoclinic, C2/mMo Kα radiation
a = 10.744 (4) ŵ = 14.20 mm1
b = 14.847 (3) ÅT = 293 K
c = 6.722 (3) Å0.25 × 0.25 × 0.22 mm
β = 105.51 (3)°
Data collection top
Enraf–Nonius CAD-4
diffractometer
1042 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.028
Tmin = 0.040, Tmax = 0.0442 standard reflections every 120 min
1584 measured reflections intensity decay: 1%
1157 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.026117 parameters
wR(F2) = 0.0682 restraints
S = 1.13Δρmax = 0.90 e Å3
1157 reflectionsΔρmin = 0.91 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*/UeqOcc. (<1)
As10.31961 (6)0.50000.06318 (10)0.00820 (18)
As20.09838 (4)0.32118 (3)0.29005 (7)0.00617 (15)
Co10.00000.50000.00000.0051 (7)0.286 (11)
Al10.00000.50000.00000.0051 (7)0.714 (11)
Co20.00000.16422 (9)0.00000.0121 (4)0.672 (8)
Al20.00000.16422 (9)0.00000.0121 (4)0.101 (8)
Co30.32049 (6)0.18170 (4)0.18184 (9)0.00749 (17)
O10.1805 (5)0.50000.1304 (8)0.0172 (11)
O20.3273 (4)0.5902 (3)0.0882 (6)0.0227 (9)
O30.4410 (5)0.50000.2771 (8)0.0212 (12)
O40.0086 (3)0.2349 (2)0.2760 (5)0.0152 (7)
O50.0126 (3)0.4059 (2)0.2032 (5)0.0103 (6)
O60.1883 (3)0.2907 (2)0.1290 (5)0.0126 (7)
O70.1918 (3)0.3497 (3)0.5228 (5)0.0156 (7)
Na10.0734 (5)0.1155 (3)0.4928 (7)0.0299 (11)0.50
Na20.6821 (6)0.50000.4225 (9)0.0173 (12)0.50
Na30.0708 (12)0.50000.4759 (13)0.064 (4)0.50
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
As10.0048 (3)0.0066 (3)0.0123 (3)0.0000.0007 (2)0.000
As20.0038 (2)0.0087 (2)0.0055 (2)0.00084 (16)0.00055 (17)0.00119 (16)
Co10.0030 (10)0.0051 (10)0.0072 (10)0.0000.0014 (7)0.000
Al10.0030 (10)0.0051 (10)0.0072 (10)0.0000.0014 (7)0.000
Co20.0078 (7)0.0155 (7)0.0130 (7)0.0000.0028 (5)0.000
Al20.0078 (7)0.0155 (7)0.0130 (7)0.0000.0028 (5)0.000
Co30.0054 (3)0.0098 (3)0.0070 (3)0.0006 (2)0.0012 (2)0.0006 (2)
O10.009 (2)0.017 (3)0.025 (3)0.0000.005 (2)0.000
O20.0214 (18)0.024 (2)0.028 (2)0.0132 (16)0.0145 (17)0.0159 (17)
O30.012 (2)0.021 (3)0.024 (3)0.0000.007 (2)0.000
O40.0112 (17)0.0122 (17)0.0188 (18)0.0011 (14)0.0018 (14)0.0045 (14)
O50.0074 (14)0.0086 (15)0.0151 (16)0.0018 (12)0.0034 (13)0.0009 (13)
O60.0147 (17)0.0152 (17)0.0104 (16)0.0088 (14)0.0077 (13)0.0026 (13)
O70.0138 (17)0.0264 (19)0.0056 (15)0.0074 (15)0.0009 (13)0.0027 (14)
Na10.038 (3)0.022 (2)0.023 (2)0.009 (2)0.004 (2)0.0086 (19)
Na20.021 (3)0.017 (3)0.015 (3)0.0000.007 (2)0.000
Na30.169 (11)0.010 (3)0.023 (4)0.0000.042 (7)0.000
Geometric parameters (Å, º) top
As1—O31.663 (5)O4—Co3xiv2.165 (3)
As1—O11.673 (5)O4—Na12.314 (6)
As1—O2i1.698 (4)O4—Na1xv2.573 (6)
As1—O21.698 (4)O5—Co3xiv2.188 (3)
As2—O71.672 (3)O5—Na32.513 (8)
As2—O61.694 (3)O5—Na3xvi2.525 (8)
As2—O41.706 (3)O6—Co3vii2.107 (3)
As2—O51.724 (3)O7—Co3vi2.077 (3)
Co1—O11.902 (5)O7—Na3xvi2.583 (7)
Co1—O1ii1.902 (5)O7—Na2ix2.585 (5)
Co1—O5iii1.984 (3)O7—Na1vi2.604 (6)
Co1—O51.984 (3)Na1—Na1xv1.606 (10)
Co1—O5i1.984 (3)Na1—Na2iv2.196 (6)
Co1—O5ii1.984 (3)Na1—O3vi2.343 (6)
Co2—O2iv2.100 (4)Na1—O3iv2.443 (6)
Co2—O2v2.100 (4)Na1—O4xv2.573 (6)
Co2—O4iii2.155 (4)Na1—O7vi2.604 (6)
Co2—O42.155 (4)Na1—Na2vi3.411 (7)
Co3—O2v2.056 (4)Na2—Na1viii2.196 (6)
Co3—O7vi2.077 (3)Na2—Na1xi2.196 (6)
Co3—O6vii2.107 (3)Na2—Na3xvii2.582 (13)
Co3—O62.119 (3)Na2—O7xviii2.585 (5)
Co3—O4viii2.165 (3)Na2—O7ix2.585 (5)
Co3—O5viii2.188 (3)Na2—O2xii2.595 (6)
O1—Na2ix2.973 (8)Na2—O2xix2.595 (6)
O2—Co3x2.056 (4)Na2—O3ix2.693 (8)
O2—Co2xi2.100 (4)Na2—O1ix2.973 (8)
O2—Al2xi2.100 (4)Na2—Na1vi3.411 (7)
O2—Na2xii2.595 (6)Na3—Na3xvi1.47 (2)
O3—Na1vi2.343 (6)Na3—O5i2.513 (8)
O3—Na1xiii2.343 (6)Na3—O5xv2.525 (8)
O3—Na1viii2.443 (6)Na3—O5xvi2.525 (8)
O3—Na1xi2.443 (6)Na3—Na2xx2.582 (13)
O3—Na22.512 (8)Na3—O7xv2.583 (7)
O3—Na2ix2.693 (8)Na3—O7xvi2.583 (7)
O3—As1—O1108.5 (3)Na2iv—Na1—O4126.7 (3)
O3—As1—O2i111.44 (18)Na1xv—Na1—O3vi73.8 (3)
O1—As1—O2i110.60 (16)Na2iv—Na1—O3vi72.7 (2)
O3—As1—O2111.44 (18)O4—Na1—O3vi153.6 (3)
O1—As1—O2110.60 (16)Na1xv—Na1—O3iv67.1 (2)
O2i—As1—O2104.2 (3)Na2iv—Na1—O3iv65.3 (2)
O7—As2—O6111.32 (17)O4—Na1—O3iv95.8 (2)
O7—As2—O4117.95 (17)O3vi—Na1—O3iv75.3 (2)
O6—As2—O4104.75 (18)Na1xv—Na1—O4xv62.3 (2)
O7—As2—O5108.65 (18)Na2iv—Na1—O4xv156.0 (3)
O6—As2—O5116.09 (16)O4—Na1—O4xv74.6 (2)
O4—As2—O597.71 (16)O3vi—Na1—O4xv91.7 (2)
O1—Co1—O1ii180.0O3iv—Na1—O4xv129.3 (3)
O1—Co1—O5iii93.91 (15)Na1xv—Na1—O7vi168.53 (15)
O1ii—Co1—O5iii86.09 (15)Na2iv—Na1—O7vi64.5 (2)
O1—Co1—O586.09 (15)O4—Na1—O7vi91.9 (2)
O1ii—Co1—O593.91 (15)O3vi—Na1—O7vi114.1 (2)
O5iii—Co1—O590.46 (19)O3iv—Na1—O7vi122.1 (3)
O1—Co1—O5i86.09 (15)O4xv—Na1—O7vi108.0 (2)
O1ii—Co1—O5i93.91 (15)Na1xv—Na1—Co294.9 (3)
O5iii—Co1—O5i180.0Na2iv—Na1—Co287.3 (2)
O5—Co1—O5i89.54 (19)O4—Na1—Co241.02 (12)
O1—Co1—O5ii93.91 (15)O3vi—Na1—Co2142.1 (2)
O1ii—Co1—O5ii86.09 (15)O3iv—Na1—Co267.04 (16)
O5iii—Co1—O5ii89.54 (19)O4xv—Na1—Co2115.35 (18)
O5—Co1—O5ii180.0O7vi—Na1—Co283.65 (15)
O5i—Co1—O5ii90.46 (19)Na1xv—Na1—As1vi93.1 (3)
O2iv—Co2—O2v116.9 (2)Na2iv—Na1—As1vi73.60 (18)
O2iv—Co2—O4iii104.45 (13)O4—Na1—As1vi158.6 (2)
O2v—Co2—O4iii105.05 (14)O3vi—Na1—As1vi26.97 (12)
O2iv—Co2—O4105.05 (14)O3iv—Na1—As1vi100.08 (17)
O2v—Co2—O4104.45 (13)O4xv—Na1—As1vi84.20 (15)
O4iii—Co2—O4121.71 (19)O7vi—Na1—As1vi91.84 (16)
O2v—Co3—O7vi84.45 (15)Co2—Na1—As1vi160.40 (18)
O2v—Co3—O6vii89.92 (15)Na1xv—Na1—As2102.07 (15)
O7vi—Co3—O6vii173.76 (14)Na2iv—Na1—As2120.9 (2)
O2v—Co3—O691.42 (15)O4—Na1—As227.49 (10)
O7vi—Co3—O696.93 (14)O3vi—Na1—As2162.4 (2)
O6vii—Co3—O680.49 (14)O3iv—Na1—As2119.40 (19)
O2v—Co3—O4viii173.13 (14)O4xv—Na1—As271.65 (14)
O7vi—Co3—O4viii96.59 (14)O7vi—Na1—As267.86 (13)
O6vii—Co3—O4viii89.33 (14)Co2—Na1—As254.33 (7)
O6—Co3—O4viii95.19 (14)As1vi—Na1—As2140.52 (15)
O2v—Co3—O5viii100.35 (14)Na1xv—Na1—Na2vi31.00 (12)
O7vi—Co3—O5viii93.67 (14)Na2iv—Na1—Na2vi98.1 (2)
O6vii—Co3—O5viii89.97 (13)O4—Na1—Na2vi107.6 (2)
O6—Co3—O5viii164.87 (13)O3vi—Na1—Na2vi47.41 (17)
O4viii—Co3—O5viii72.81 (13)O3iv—Na1—Na2vi51.61 (19)
O2v—Co3—As2viii137.02 (12)O4xv—Na1—Na2vi83.43 (17)
O7vi—Co3—As2viii94.69 (10)O7vi—Na1—Na2vi159.7 (2)
O6vii—Co3—As2viii91.26 (10)Co2—Na1—Na2vi107.03 (16)
O6—Co3—As2viii131.08 (10)As1vi—Na1—Na2vi72.24 (13)
O4viii—Co3—As2viii36.18 (9)As2—Na1—Na2vi132.45 (17)
O5viii—Co3—As2viii36.70 (8)Na1viii—Na2—Na1xi102.7 (3)
O2v—Co3—Na3xxi76.6 (2)Na1viii—Na2—O362.1 (2)
O7vi—Co3—Na3xxi50.14 (18)Na1xi—Na2—O362.1 (2)
O6vii—Co3—Na3xxi130.96 (16)Na1viii—Na2—Na3xvii123.8 (2)
O6—Co3—Na3xxi145.3 (2)Na1xi—Na2—Na3xvii123.8 (2)
O4viii—Co3—Na3xxi98.8 (2)O3—Na2—Na3xvii165.7 (3)
O5viii—Co3—Na3xxi48.3 (2)Na1viii—Na2—O7xviii65.41 (15)
As2viii—Co3—Na3xxi70.5 (2)Na1xi—Na2—O7xviii158.8 (3)
As1—O1—Co1138.6 (3)O3—Na2—O7xviii120.14 (14)
As1—O1—Na2ix92.0 (2)Na3xvii—Na2—O7xviii59.99 (14)
Co1—O1—Na2ix129.4 (3)Na1viii—Na2—O7ix158.8 (3)
As1—O2—Co3x123.2 (2)Na1xi—Na2—O7ix65.41 (15)
As1—O2—Co2xi115.1 (2)O3—Na2—O7ix120.14 (14)
Co3x—O2—Co2xi107.02 (18)Na3xvii—Na2—O7ix59.99 (14)
As1—O2—Al2xi115.1 (2)O7xviii—Na2—O7ix119.3 (3)
Co3x—O2—Al2xi107.02 (18)Na1viii—Na2—O2xii83.30 (18)
Co2xi—O2—Al2xi0.00 (6)Na1xi—Na2—O2xii133.6 (3)
As1—O2—Na2xii96.58 (19)O3—Na2—O2xii82.3 (2)
Co3x—O2—Na2xii103.16 (19)Na3xvii—Na2—O2xii85.5 (2)
Co2xi—O2—Na2xii109.94 (19)O7xviii—Na2—O2xii64.85 (13)
Al2xi—O2—Na2xii109.94 (19)O7ix—Na2—O2xii117.8 (2)
As1—O3—Na1vi113.3 (2)Na1viii—Na2—O2xix133.6 (3)
As1—O3—Na1xiii113.3 (2)Na1xi—Na2—O2xix83.30 (18)
Na1vi—O3—Na1xiii94.2 (3)O3—Na2—O2xix82.3 (2)
As1—O3—Na1viii135.31 (14)Na3xvii—Na2—O2xix85.5 (2)
Na1vi—O3—Na1viii39.2 (3)O7xviii—Na2—O2xix117.8 (2)
Na1xiii—O3—Na1viii104.7 (2)O7ix—Na2—O2xix64.85 (13)
As1—O3—Na1xi135.31 (14)O2xii—Na2—O2xix62.2 (2)
Na1vi—O3—Na1xi104.7 (2)Na1viii—Na2—O3ix56.15 (18)
Na1xiii—O3—Na1xi39.2 (3)Na1xi—Na2—O3ix56.15 (18)
Na1viii—O3—Na1xi89.2 (3)O3—Na2—O3ix68.3 (2)
As1—O3—Na2145.6 (3)Na3xvii—Na2—O3ix126.0 (3)
Na1vi—O3—Na289.2 (2)O7xviii—Na2—O3ix103.73 (17)
Na1xiii—O3—Na289.2 (2)O7ix—Na2—O3ix103.72 (17)
Na1viii—O3—Na252.60 (17)O2xii—Na2—O3ix137.4 (2)
Na1xi—O3—Na252.60 (17)O2xix—Na2—O3ix137.4 (2)
As1—O3—Na2ix102.7 (3)Na1viii—Na2—O1ix86.1 (2)
Na1vi—O3—Na2ix51.14 (18)Na1xi—Na2—O1ix86.1 (2)
Na1xiii—O3—Na2ix51.14 (18)O3—Na2—O1ix125.1 (3)
Na1viii—O3—Na2ix83.1 (2)Na3xvii—Na2—O1ix69.2 (2)
Na1xi—O3—Na2ix83.1 (2)O7xviii—Na2—O1ix75.91 (15)
Na2—O3—Na2ix111.7 (2)O7ix—Na2—O1ix75.91 (15)
As2—O4—Co2103.30 (18)O2xii—Na2—O1ix140.28 (18)
As2—O4—Co3xiv95.33 (15)O2xix—Na2—O1ix140.28 (18)
Co2—O4—Co3xiv104.78 (14)O3ix—Na2—O1ix56.83 (18)
As2—O4—Na1113.8 (2)Na1viii—Na2—As1xii110.8 (2)
Co2—O4—Na194.17 (19)Na1xi—Na2—As1xii110.8 (2)
Co3xiv—O4—Na1140.6 (2)O3—Na2—As1xii83.2 (2)
As2—O4—Na1xv140.4 (2)Na3xvii—Na2—As1xii82.5 (2)
Co2—O4—Na1xv105.39 (17)O7xviii—Na2—As1xii90.27 (16)
Co3xiv—O4—Na1xv103.00 (17)O7ix—Na2—As1xii90.26 (16)
Na1—O4—Na1xv37.9 (2)O2xii—Na2—As1xii31.15 (10)
As2—O5—Co1125.33 (18)O2xix—Na2—As1xii31.15 (10)
As2—O5—Co3xiv93.97 (14)O3ix—Na2—As1xii151.5 (2)
Co1—O5—Co3xiv125.39 (16)O1ix—Na2—As1xii151.7 (2)
As2—O5—Na3116.3 (3)Na1viii—Na2—Na1vi22.13 (17)
Co1—O5—Na3100.77 (17)Na1xi—Na2—Na1vi81.9 (2)
Co3xiv—O5—Na391.1 (3)O3—Na2—Na1vi43.36 (15)
As2—O5—Na3xvi93.4 (2)Na3xvii—Na2—Na1vi145.09 (16)
Co1—O5—Na3xvi97.14 (17)O7xviii—Na2—Na1vi87.53 (14)
Co3xiv—O5—Na3xvi118.9 (3)O7ix—Na2—Na1vi145.6 (2)
Na3—O5—Na3xvi33.9 (5)O2xii—Na2—Na1vi92.19 (17)
As2—O6—Co3vii134.41 (19)O2xix—Na2—Na1vi123.9 (2)
As2—O6—Co3124.62 (18)O3ix—Na2—Na1vi45.30 (14)
Co3vii—O6—Co399.51 (14)O1ix—Na2—Na1vi92.05 (18)
As2—O7—Co3vi131.4 (2)As1xii—Na2—Na1vi112.20 (17)
As2—O7—Na3xvi92.6 (3)Na3xvi—Na3—O573.5 (5)
Co3vi—O7—Na3xvi91.7 (2)Na3xvi—Na3—O5i73.5 (5)
As2—O7—Na2ix120.8 (2)O5—Na3—O5i67.6 (3)
Co3vi—O7—Na2ix102.87 (18)Na3xvi—Na3—O5xv72.6 (5)
Na3xvi—O7—Na2ix59.9 (3)O5—Na3—O5xv102.4 (2)
As2—O7—Na1vi110.97 (19)O5i—Na3—O5xv146.1 (5)
Co3vi—O7—Na1vi113.13 (17)Na3xvi—Na3—O5xvi72.6 (5)
Na3xvi—O7—Na1vi108.8 (3)O5—Na3—O5xvi146.1 (5)
Na2ix—O7—Na1vi50.07 (17)O5i—Na3—O5xvi102.4 (2)
Na1xv—Na1—Na2iv126.87 (19)O5xv—Na3—O5xvi67.2 (3)
Na1xv—Na1—O479.8 (2)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1, z; (iii) x, y, z; (iv) x1/2, y1/2, z; (v) x+1/2, y1/2, z; (vi) x+1/2, y+1/2, z+1; (vii) x+1/2, y+1/2, z; (viii) x+1/2, y+1/2, z; (ix) x+1, y+1, z+1; (x) x+1/2, y+1/2, z; (xi) x+1/2, y+1/2, z; (xii) x+1, y+1, z; (xiii) x+1/2, y+1/2, z+1; (xiv) x1/2, y+1/2, z; (xv) x, y, z+1; (xvi) x, y+1, z+1; (xvii) x+1, y, z; (xviii) x+1, y, z+1; (xix) x+1, y, z; (xx) x1, y, z; (xxi) x+1/2, y1/2, z.

Experimental details

Crystal data
Chemical formulaNa4Co5.63Al0.91(AsO4)6
Mr1281.94
Crystal system, space groupMonoclinic, C2/m
Temperature (K)293
a, b, c (Å)10.744 (4), 14.847 (3), 6.722 (3)
β (°) 105.51 (3)
V3)1033.2 (6)
Z2
Radiation typeMo Kα
µ (mm1)14.20
Crystal size (mm)0.25 × 0.25 × 0.22
Data collection
DiffractometerEnraf–Nonius CAD-4
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.040, 0.044
No. of measured, independent and
observed [I > 2σ(I)] reflections
1584, 1157, 1042
Rint0.028
(sin θ/λ)max1)0.638
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.068, 1.13
No. of reflections1157
No. of parameters117
No. of restraints2
Δρmax, Δρmin (e Å3)0.90, 0.91

Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1995), XCAD4 (Harms & Wocadlo, 1995), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 1998), WinGX (Farrugia, 1999).

CHARDI and BVS analysis of cation polyhedra in Na4Co5.63Al0.91(AsO4)6. top
Cationq(i).sof(i)Q(i)V(i)CN(i)ECoN(i)
M12.7142.8102.70165.912
M21.6471.5671.02043.978
Co32.001.9901.98165.898
As15.005.0335.01143.990
As25.005.0014.87043.983
Na10.500.4980.47154.589
Na20.500.5010.41376.437
Na30.500.5040.47165.970
M1 = Co0.286Al0.714; M2 = Co0.672Al0.1010.230; q(i): formal oxidation number; sof(i): site occupation factor; sodium CNs for d(Na—O)max=3.00 Å; σ = [Σi(qi-Qi)2/N - 1]1/2 = 0.047.
 

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