NaFe(TeO₃)₂

The hydro­thermally prepared title compound, sodium iron(III) bis­[trioxotellurate(IV)], is isotypic with its Ga^III analogue and consists of corrugated layers with an overall composition of [FeTe₂O₆]^- together with Na⁺ cations. The layers extend parallel to (001) and are made up of [Fe₂O₁₀] edge-shared octa­hedral dimers and TeO₃ trigonal pyramids sharing vertices. The Na⁺ cations are located in the cavities of this arrangement and link adjacent [FeTe₂O₆]^- layers via distorted [NaO₈] polyhedra.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Te-O) = 0.004 Å
• R factor = 0.027
• wR factor = 0.061
• Data-to-parameter ratio = 17.6

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S1. Comment

The present communication is part of our ongoing studies of the phase formation and structures of Te(IV)-containing oxocompounds formed under hydrothermal conditions (e.g. Weil, 2005, 2007; Weil & Stöger, 2007).

The crystal structure of the title compound, (I), is built up of layers with an overall composition [FeTe₂O₆]^- extending parallel to (001). Adjacent layers are linked by Na⁺ cations that are located in the voids of this arrangement (Fig. 1).

The anionic layers consists of octahedral [FeO₆] and trigonal-pyramidal TeO₃ units as simple building blocks (Table 1). Two edge-sharing [FeO₆] octahedra [mean Fe—O = 2.017 Å] form a centrosymmetric [Fe₂O₁₀] dimer which is connected to eight TeO₃ units via oxygen-atom corners. The equatorial oxygen atoms of the dimer are linked to six Te1O₃ groups whereas the axial oxygen atoms of the dimer are part of two Te2O₃ groups capping both Fe atoms at the top and at the bottom (Fig. 2). Each of the free corners of the Te1O₃ groups are further linked to adjacent [Fe₂O₁₀] dimers thus establishing the layered arrangement. The lone-pair electrons of the tellurium(IV) atoms point towards the free space and are aligned approximately parallel to [001]. The Na⁺ cations are surrounded by eight oxygen atoms, leading to distorted polyhedra with a mean Na—O of 2.650 Å. The Te—O bond lengths and mean O—Te—O angle of 96.3° are typical values for trigonal-pyramidal TeO₃ units (Dolgikh, 1991). The next nearest O sites relative to the Te centres are outside of the first coordination spheres with distances of Te1—O2 = 2.549 (4) Å, Te1—O1[x + 1/2, -y + 1/2, z] = 2.570 (4) Å and Te2—O5 = 2.703 (4) Å.

The crystal structure of NaFe(TeO₃)₂ is isotypic with the Ga^III analogue, NaGa(TeO₃)₂ (Miletich & Pertlik, 1998), and exhibits similar interatomic distances and angles.

Related literature

For the isotypic structure NaGa(TeO₃)₂, see: Miletich & Pertlik (1998). For related structures, see: Weil (2005, 2007); Weil & Stöger (2007). For a review on the crystal chemistry of tellurate(IV) oxocompounds, see: Dolgikh (1991).

S2. Experimental

All chemicals used were of analytical grade (Merck, p.A.) and employed without further purification: 20 mg (0.5 mmol) NaOH, 53 mg (0.33 mmol) Fe₂O₃ and 160 mg (1 mmol) TeO₂ were placed in a 5-ml Teflon-lined steel autoclave that was filled with 2 ml demineralized water. The autoclave was heated at 493 K for 6 d and then cooled to room temperature within 3 h. The reaction product consisted mainly of a mixture of unreacted Fe₂O₃ and TeO₂. Only few colourless crystals of (I) with unspecific habit were obtained.

S3. Refinement

For better comparison with the isotypic NaGa(TeO₃)₂ structure, the refinement was carried out in the non-standard setting Pcab of space group No. 61 (standard setting Pbca). The atomic coordinates of the Ga analogue were taken as starting parameters. The highest remaining peak in the final difference Fourier map is 0.71 Å from Te2 and the deepest hole is 0.79 Å from O4.

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: coordinates taken from an isotypic structure; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

Fig. 1. The crystal structure of NaGa(TeO3)2 in projection along [110].

Fig. 2. The [Fe2O10] dimer with the corner-sharing TeO3 trigonal-pyramids attached. Atoms are drawn as displacement ellipsoids at the 90% probability level. [Symmetry operators: (i) -x + 1, -y + 1, z; (ii) -x + 1/2, y + 1/2, -z + 1; (iii) x + 1/2, -y + 1/2, z - 1; (iv) x - 1/2, -y + 1, -z + 1/2; (v) -x + 1/2, -y + 1/2, z - 1; (vi) -x + 1, -y + 1/2, z - 1/2; (vii) x, y + 1/2, -z + 1/2; (viii) -x + 1.5, y, z - 1/2; (ix) x + 1/2, -y + 1, -z + 1/2.]

sodium iron(III) bis[trioxotellurate(IV)]

Crystal data

NaFe(TeO3)2	F(000) = 1512
Mr = 430.04	Dx = 5.182 Mg m^−3
Orthorhombic, Pcab	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2bc 2ac	Cell parameters from 2569 reflections
a = 7.8530 (15) Å	θ = 3.0–30.0°
b = 10.448 (2) Å	µ = 13.15 mm^−1
c = 13.438 (3) Å	T = 293 K
V = 1102.5 (4) Å^3	Prism, colourless
Z = 8	0.08 × 0.02 × 0.01 mm

Data collection

Bruker SMART APEX CCD diffractometer	1598 independent reflections
Radiation source: fine-focus sealed tube	1329 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
ω scans	θmax = 30.0°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2002)	h = −11→9
Tmin = 0.405, Tmax = 0.858	k = −14→14
11127 measured reflections	l = −18→18

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: isomorphous structure methods
R[F^2 > 2σ(F^2)] = 0.027	w = 1/[σ^2(Fo^2) + (0.0323P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.061	(Δ/σ)max < 0.001
S = 1.03	Δρmax = 1.77 e Å^−3
1598 reflections	Δρmin = −0.96 e Å^−3
91 parameters

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Te1	0.54652 (4)	0.28714 (3)	0.42454 (2)	0.00780 (9)
Te2	0.08184 (4)	0.00810 (3)	0.76667 (2)	0.00932 (9)
Fe	0.30472 (10)	0.49980 (6)	−0.02064 (5)	0.00866 (15)
Na	0.8320 (3)	0.2417 (2)	0.64216 (19)	0.0254 (6)
O1	0.3210 (4)	0.3435 (3)	0.4480 (3)	0.0122 (7)
O2	0.4293 (5)	0.1849 (4)	0.2665 (3)	0.0169 (8)
O3	0.3696 (4)	0.1292 (3)	0.0402 (3)	0.0106 (7)
O4	0.4983 (4)	0.1292 (3)	0.4888 (3)	0.0104 (7)
O5	0.3769 (5)	0.0296 (3)	0.6643 (3)	0.0107 (7)
O6	0.2625 (5)	0.4796 (3)	0.1281 (3)	0.0119 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te1	0.00751 (16)	0.00640 (14)	0.00950 (15)	−0.00033 (11)	0.00003 (11)	0.00063 (11)
Te2	0.00962 (16)	0.00905 (15)	0.00928 (16)	0.00021 (11)	0.00013 (11)	−0.00144 (11)
Fe	0.0085 (3)	0.0069 (3)	0.0106 (4)	0.0000 (3)	−0.0002 (3)	−0.0005 (2)
Na	0.0326 (15)	0.0142 (11)	0.0294 (13)	−0.0056 (10)	−0.0082 (11)	0.0034 (10)
O1	0.0065 (17)	0.0113 (16)	0.0188 (19)	0.0005 (14)	0.0010 (14)	−0.0019 (14)
O2	0.022 (2)	0.0110 (17)	0.0175 (19)	−0.0020 (15)	−0.0020 (16)	0.0000 (14)
O3	0.0087 (17)	0.0094 (16)	0.0138 (17)	−0.0030 (14)	−0.0017 (14)	0.0023 (13)
O4	0.0074 (17)	0.0085 (16)	0.0152 (17)	0.0012 (13)	−0.0020 (13)	0.0028 (13)
O5	0.0096 (17)	0.0156 (17)	0.0071 (17)	0.0007 (14)	−0.0014 (13)	−0.0017 (14)
O6	0.0119 (18)	0.0154 (17)	0.0084 (17)	−0.0003 (14)	0.0003 (14)	−0.0006 (13)

Geometric parameters (Å, º)

Na—O5^i	2.434 (4)	Fe—O5^vi	2.036 (3)
Na—O6^ii	2.436 (4)	Fe—O6	2.037 (4)
Na—O3^ii	2.491 (4)	Fe—O4^vii	2.055 (4)
Na—O2^iii	2.581 (5)	Fe—O4^vi	2.078 (4)
Na—O2^ii	2.755 (5)	Te1—O1	1.893 (4)
Na—O1^i	2.758 (4)	Te1—O3^ii	1.901 (4)
Na—O4^i	2.788 (4)	Te1—O4	1.901 (4)
Na—O3^iii	2.958 (4)	Te2—O2^viii	1.849 (4)
Fe—O3^iv	1.942 (4)	Te2—O6^ix	1.892 (4)
Fe—O1^v	1.955 (4)	Te2—O5^x	1.899 (4)
O1—Te1—O3^ii	92.59 (15)	O6^ii—Na—O4^i	123.02 (15)
O1—Te1—O4	90.44 (15)	O3^ii—Na—O4^i	68.23 (12)
O3^ii—Te1—O4	95.54 (16)	O2^iii—Na—O4^i	104.45 (14)
O2^viii—Te2—O6^ix	100.85 (16)	O2^ii—Na—O4^i	131.48 (14)
O2^viii—Te2—O5^x	99.64 (16)	O1^i—Na—O4^i	58.10 (12)
O6^ix—Te2—O5^x	98.64 (16)	O5^i—Na—O3^iii	109.39 (14)
O3^iv—Fe—O1^v	101.34 (15)	O6^ii—Na—O3^iii	80.11 (13)
O3^iv—Fe—O5^vi	87.79 (15)	O3^ii—Na—O3^iii	117.64 (17)
O1^v—Fe—O5^vi	93.64 (15)	O2^iii—Na—O3^iii	68.48 (13)
O3^iv—Fe—O6	95.17 (15)	O2^ii—Na—O3^iii	168.98 (14)
O1^v—Fe—O6	92.48 (15)	O1^i—Na—O3^iii	57.21 (11)
O5^vi—Fe—O6	172.55 (15)	O4^i—Na—O3^iii	58.59 (11)
O3^iv—Fe—O4^vii	174.47 (15)	Te1—O1—Fe^viii	140.2 (2)
O1^v—Fe—O4^vii	81.12 (15)	Te1—O1—Na^xi	91.60 (15)
O5^vi—Fe—O4^vii	87.11 (14)	Fe^viii—O1—Na^xi	94.66 (14)
O6—Fe—O4^vii	89.65 (14)	Te2^v—O2—Na^xii	105.36 (18)
O3^iv—Fe—O4^vi	95.20 (15)	Te2^v—O2—Na^vii	104.09 (17)
O1^v—Fe—O4^vi	163.16 (15)	Na^xii—O2—Na^vii	94.82 (15)
O5^vi—Fe—O4^vi	83.80 (14)	Te1^vii—O3—Fe^xiii	116.98 (18)
O6—Fe—O4^vi	89.11 (14)	Te1^vii—O3—Na^vii	114.90 (17)
O4^vii—Fe—O4^vi	82.13 (15)	Fe^xiii—O3—Na^vii	90.19 (14)
O5^i—Na—O6^ii	170.30 (17)	Te1^vii—O3—Na^xii	85.51 (13)
O5^i—Na—O3^ii	68.14 (13)	Fe^xiii—O3—Na^xii	153.87 (17)
O6^ii—Na—O3^ii	106.13 (15)	Na^vii—O3—Na^xii	91.93 (13)
O5^i—Na—O2^iii	92.37 (15)	Te1—O4—Fe^ii	113.01 (17)
O6^ii—Na—O2^iii	93.05 (14)	Te1—O4—Fe^xiv	143.49 (19)
O3^ii—Na—O2^iii	160.49 (15)	Fe^ii—O4—Fe^xiv	97.87 (15)
O5^i—Na—O2^ii	76.12 (14)	Te1—O4—Na^xi	90.52 (14)
O6^ii—Na—O2^ii	94.86 (14)	Fe^ii—O4—Na^xi	135.71 (17)
O3^ii—Na—O2^ii	73.11 (14)	Fe^xiv—O4—Na^xi	79.65 (12)
O2^iii—Na—O2^ii	102.25 (16)	Te2^xv—O5—Fe^xiv	131.84 (19)
O5^i—Na—O1^i	115.91 (14)	Te2^xv—O5—Na^xi	112.72 (17)
O6^ii—Na—O1^i	67.10 (12)	Fe^xiv—O5—Na^xi	89.63 (14)
O3^ii—Na—O1^i	68.55 (13)	Te2^xvi—O6—Fe	127.7 (2)
O2^iii—Na—O1^i	124.14 (15)	Te2^xvi—O6—Na^vii	106.73 (16)
O2^ii—Na—O1^i	129.82 (15)	Fe—O6—Na^vii	102.93 (15)
O5^i—Na—O4^i	63.09 (12)

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