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Acta Cryst. (2008). E64, i24-i25    [ doi:10.1107/S1600536808010441 ]

Redetermination of the borax structure from laboratory X-ray data at 145 K

G. J. Gainsford, T. Kemmitt and C. Higham

Abstract top

The title compound, sodium tetraborate decahydrate (mineral name: borax), Na2[B4O5(OH)4]·8H2O, has been studied previously using X-ray [Morimoto (1956). Miner. J. 2, 1-18] and neutron [Levy & Lisensky (1978). Acta Cryst. B34, 3502-3510] diffraction data. The structure contains tetraborate anions [B4O5(OH)4]2- with twofold rotation symmetry, which form hydrogen-bonded chains, and [Na(H2O)6] octahedra that form zigzag chains [Na(H2O)4/2(H2O)2/1]. The O-H bond distances obtained from the present redetermination at 145 K are shorter than those in the neutron study by an average of 0.127 (19) Å.

Comment top

The crystal structure of the title compound was previously studied by Morimoto (1956) using X-ray and later by Levy & Lisensky (1978, hereafter LL) using neutron diffraction data.

There are 8 other compounds with free tetraborate anions [B4O5(OH)4]2- reported in the Cambridge Structural Database [C.S.D., version 5.29 with November 2007 updates (Allen, 2002)] with most containing protonated amine-based cations, e.g. DALQEN (Wang et al., 2004) and SIBDIR (Pan et al., 2007). The tetraborate anion in borax has 2-fold symmetry with the axis passing through O1 (Fig. 1) as is observed in five of the related structures. Both Na1 and Na2 cations are on special positions (centre of symmetry and 2-fold axis, respectively) so that they elegantly bind via shared water molecules in a typical zigzag cationic chain [Na(H2O)4/2(H2O)2/1] parallel to the c axis (e.g. DARNOA, Yi et al., 2005), as shown in Figure 2. As is found through a C.S.D. search of similar Na+/H2O cation chains, the Na–O distances to the bridging water molecules are longer than those to non-bridging water molecules, where the trans related Na–O distances belong to non-bridging water molecules.

The results of the present study and the LL model are essentially superimposable, but do reflect expected differences associated with the H atom positions: The systematic pairwise study (Allen, 1986) gave a difference for O–H (X-ray versus neutron) of -0.155 (10) Å, while a more recent study of levoglucosan (Smrčok et al., 2006) averaged at -0.016 (6) Å. The mean O—H distance here (0.843 (17) Å) is significantly shorter than for the neutron set (0.97 (1) Å). As the O···O distances involved in the hydrogen bonding are very similar for both studies (Table 1), the observed H···O distances are correspondingly longer here than in the LL model. We also note that average Na–O distances are marginally longer (0.006 (6) Å) and the B–O distances marginally shorter (-0.005 (2) Å) in the LL model, e.g. Na–O6, B1–O2 are 2.458 (3), 1.500 (2) Å compared with 2.4441 (6), 1.5075 (8) Å, respectively, in the present study. These latter differences are barely significant given that the neutron data set was collected at 296.5 K.

Cell cohesion is provided by strong O—H···O hydrogen bonds of two types: (1) tetraborate anions "head to tail" link via the O5–H and O2 atoms (entry 1, Table 1) to form anionic chains as also seen in DALQEN (Wang et al., 2004); (2) the anionic and cationic chains crosslink through the water & tetraborate strong O–H···O hydrogen bond interactions (entries 2–10; see also Fig. 2 and diagrams in the LL study).

Related literature top

For previous studies of the borax structure, see: Morimoto (1956); Levy & Lisenky (1978). For other structures listed in the Cambridge Structural Database (Allen, 2002) that contain the [B4O5(OH)4]2- anion, see: Wang et al. (2004); Pan et al. (2007). For related structures, see: Yi et al. (2005). For comparative studies of hydrogen bonds obtained from X-ray and neutron data, see: Allen (1986); Smrčok et al. (2006).

Experimental top

To a tetrahydrofuran (thf) solution (90 ml) of sodium tetrahydridoborate (0.31 g, 8.4 mmol) was added 0.5 g (4.2 mmol) of diaminomethane dihydrochloride. After 24 h, the solvent was removed and the remaining product dissolved in water. Methanol was added and the solution was left in a refrigerator. A small clump of colourless crystals of the title compound appeared after several days in the bottom of the flask.

Refinement top

A total of 13 reflections (below 50°/2θ) were not collected. In the present re-determination the same atomic labels and atomic coordinates have been used as in the previous studies (Morimoto, 1956; Levy & Lisensky, 1978). The positions of the H atoms were fully refined with isotropic thermal parameters for each H atom.

Computing details top

Data collection: APEX2 (Bruker, 2006); cell refinement: APEX2 (Bruker, 2006); data reduction: APEX2 (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures top
[Figure 1] Fig. 1. Molecular structure of the tetraborate anion shown with displacement ellipsoids at the 50% probability level. [Symmetry code: i) -x, y, 1/2 - z.]
[Figure 2] Fig. 2. Part of the crystal structure showing the zigzag [Na(H2O)4/2(H2O)2/1] chain, the hydrogen bonded tetraborate chain and some interlinking hydrogen bonds, shown as dashed lines. For clarity, only selected atoms and one of each chain is shown. [Symmetry codes: i) -x, y 1/2 - z; ii) x, 1 + y, z.]
sodium tetraborate decahydrate top
Crystal data top
Na2[B4O5(OH)4]·8H2OF000 = 792
Mr = 381.38Dx = 1.720 Mg m−3
Monoclinic, C2/cMo Kα radiation
λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 6688 reflections
a = 11.8843 (5) Åθ = 2.6–31.9º
b = 10.6026 (4) ŵ = 0.22 mm−1
c = 12.2111 (5) ÅT = 145 (2) K
β = 106.790 (2)ºPrism, colourless
V = 1473.06 (10) Å30.65 × 0.36 × 0.26 mm
Z = 4
Data collection top
Bruker–Nonius APEX2 CCD area-detector
diffractometer		2275 independent reflections
Radiation source: fine-focus sealed tube2137 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.018
Detector resolution: 8.192 pixels mm-1θmax = 33.2º
T = 145(2) Kθmin = 2.6º
φ and ω scansh = −17→16
Absorption correction: multi-scan
(SADABS; Bruker, 2006)		k = −15→15
Tmin = 0.813, Tmax = 0.94l = −16→17
8429 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.025All H-atom parameters refined
wR(F2) = 0.076  w = 1/[σ2(Fo2) + (0.0482P)2 + 0.3901P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.001
2275 reflectionsΔρmax = 0.37 e Å−3
147 parametersΔρmin = −0.22 e Å−3
Primary atom site location: structure-invariant direct methodsExtinction correction: none
Crystal data top
Na2[B4O5(OH)4]·8H2OV = 1473.06 (10) Å3
Mr = 381.38Z = 4
Monoclinic, C2/cMo Kα
a = 11.8843 (5) ŵ = 0.22 mm−1
b = 10.6026 (4) ÅT = 145 (2) K
c = 12.2111 (5) Å0.65 × 0.36 × 0.26 mm
β = 106.790 (2)º
Data collection top
Bruker–Nonius APEX2 CCD area-detector
diffractometer		2275 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2006)		2137 reflections with I > 2σ(I)
Tmin = 0.813, Tmax = 0.94Rint = 0.018
8429 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.025147 parameters
wR(F2) = 0.076All H-atom parameters refined
S = 1.08Δρmax = 0.37 e Å−3
2275 reflectionsΔρmin = −0.22 e Å−3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
Na10.00000.00000.00000.01676 (10)
Na20.00000.84795 (4)0.25000.01796 (11)
B10.08552 (6)0.34499 (6)0.21553 (5)0.01044 (13)
B20.09847 (6)0.45643 (6)0.39269 (6)0.01154 (13)
O10.00000.26659 (6)0.25000.01094 (13)
O20.15546 (4)0.41927 (4)0.31574 (4)0.01276 (11)
O30.01964 (4)0.43573 (4)0.12445 (4)0.01339 (11)
O40.16140 (4)0.27014 (5)0.16772 (4)0.01570 (11)
O50.16369 (4)0.51522 (5)0.49130 (4)0.01815 (12)
O60.12357 (5)0.84607 (5)0.44846 (5)0.01851 (12)
O70.12296 (5)0.00117 (5)0.19548 (5)0.01799 (12)
O80.11919 (5)0.16556 (5)0.46252 (5)0.02067 (12)
O90.11746 (5)0.70654 (6)0.17227 (5)0.02187 (12)
H40.7717 (12)0.2622 (11)0.2876 (12)0.032 (3)*
H50.1187 (13)0.4667 (13)0.0305 (12)0.040 (3)*
H6A0.3089 (13)0.3828 (14)0.0413 (12)0.042 (4)*
H6B0.8662 (14)0.2018 (16)0.4941 (13)0.051 (4)*
H7A0.3098 (13)0.4817 (11)0.3051 (12)0.030 (3)*
H7B0.1304 (12)0.0776 (14)0.2014 (12)0.039 (3)*
H8A0.9099 (12)0.1906 (13)0.1075 (11)0.036 (3)*
H8B0.8131 (12)0.1365 (12)0.0352 (11)0.034 (3)*
H9A0.4018 (13)0.1300 (15)0.3385 (12)0.046 (4)*
H9B0.6140 (15)0.2331 (15)0.1058 (14)0.053 (4)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na10.0165 (2)0.01812 (19)0.0158 (2)0.00057 (13)0.00485 (15)0.00047 (13)
Na20.0179 (2)0.0201 (2)0.0176 (2)0.0000.00773 (16)0.000
B10.0100 (3)0.0121 (3)0.0096 (3)0.0012 (2)0.0035 (2)−0.00028 (19)
B20.0108 (3)0.0133 (3)0.0111 (3)−0.0014 (2)0.0040 (2)−0.0014 (2)
O10.0117 (3)0.0104 (3)0.0111 (3)0.0000.0037 (2)0.000
O20.0103 (2)0.0168 (2)0.0122 (2)−0.00223 (15)0.00493 (16)−0.00376 (15)
O30.0103 (2)0.0180 (2)0.0130 (2)0.00309 (15)0.00519 (16)0.00559 (15)
O40.0119 (2)0.0209 (2)0.0142 (2)0.00489 (17)0.00365 (17)−0.00434 (16)
O50.0132 (2)0.0275 (3)0.0150 (2)−0.00595 (18)0.00593 (19)−0.00949 (18)
O60.0146 (2)0.0219 (2)0.0186 (2)−0.00109 (18)0.00414 (19)0.00229 (18)
O70.0151 (3)0.0160 (2)0.0232 (3)0.00012 (17)0.0061 (2)0.00003 (17)
O80.0185 (3)0.0242 (3)0.0184 (3)0.00116 (19)0.0039 (2)0.00608 (19)
O90.0217 (3)0.0196 (2)0.0229 (3)−0.00047 (19)0.0041 (2)−0.00352 (19)
Geometric parameters (Å, °) top
Na1—O8i2.3815 (6)Na2—O6ii2.4441 (6)
Na1—O8ii2.3815 (6)Na2—O62.4441 (6)
Na1—O6iii2.3979 (5)B1—O41.4451 (8)
Na1—O6iv2.3979 (5)B1—O11.4657 (7)
Na1—O7v2.4121 (6)B1—O21.4902 (8)
Na1—O72.4121 (6)B1—O31.5075 (8)
Na2—O7vi2.4041 (6)B2—O21.3655 (8)
Na2—O7vii2.4041 (6)B2—O3ii1.3757 (8)
Na2—O92.4214 (6)B2—O51.3784 (8)
Na2—O9ii2.4214 (6)
O8i—Na1—O8ii180.00 (2)O9—Na2—O6ii81.696 (19)
O8i—Na1—O6iii90.45 (2)O9ii—Na2—O6ii97.72 (2)
O8ii—Na1—O6iii89.55 (2)O7vi—Na2—O688.29 (2)
O8i—Na1—O6iv89.55 (2)O7vii—Na2—O692.34 (2)
O8ii—Na1—O6iv90.45 (2)O9—Na2—O697.72 (2)
O6iii—Na1—O6iv180.00 (3)O9ii—Na2—O681.70 (2)
O8i—Na1—O7v91.717 (19)O6ii—Na2—O6179.07 (3)
O8ii—Na1—O7v88.283 (19)O4—B1—O1111.72 (5)
O6iii—Na1—O7v89.177 (19)O4—B1—O2110.91 (5)
O6iv—Na1—O7v90.823 (19)O1—B1—O2109.42 (4)
O8i—Na1—O788.283 (19)O4—B1—O3107.71 (5)
O8ii—Na1—O791.717 (19)O1—B1—O3108.56 (5)
O6iii—Na1—O790.823 (19)O2—B1—O3108.43 (5)
O6iv—Na1—O789.177 (19)O2—B2—O3ii122.44 (6)
O7v—Na1—O7180.000 (16)O2—B2—O5117.78 (6)
O7vi—Na2—O7vii94.98 (3)O3ii—B2—O5119.78 (6)
O7vi—Na2—O9172.90 (2)B1ii—O1—B1110.90 (6)
O7vii—Na2—O981.05 (2)B2—O2—B1116.59 (5)
O7vi—Na2—O9ii81.05 (2)B2ii—O3—B1120.25 (5)
O7vii—Na2—O9ii172.90 (2)Na1vi—O6—Na290.952 (19)
O9—Na2—O9ii103.49 (3)Na2viii—O7—Na191.581 (19)
O7vi—Na2—O6ii92.34 (2)Na2viii—O7—H7B134.8 (10)
O7vii—Na2—O6ii88.29 (2)Na1—O7—H7B96.4 (10)
O4—B1—O1—B1ii−172.74 (6)O7vi—Na2—O6—Na1vi−0.355 (19)
O2—B1—O1—B1ii64.05 (4)O7vii—Na2—O6—Na1vi94.56 (2)
O3—B1—O1—B1ii−54.12 (3)O9—Na2—O6—Na1vi175.84 (2)
O3ii—B2—O2—B1−4.91 (9)O9ii—Na2—O6—Na1vi−81.56 (2)
O5—B2—O2—B1174.23 (5)O6ii—Na2—O6—Na1vi−132.911 (15)
O4—B1—O2—B2−156.88 (5)O8i—Na1—O7—Na2viii−89.93 (2)
O1—B1—O2—B2−33.19 (7)O8ii—Na1—O7—Na2viii90.07 (2)
O3—B1—O2—B285.06 (6)O6iii—Na1—O7—Na2viii179.640 (19)
O4—B1—O3—B2ii136.95 (6)O6iv—Na1—O7—Na2viii−0.360 (19)
O1—B1—O3—B2ii15.82 (7)O7v—Na1—O7—Na2viii−122 (44)
O2—B1—O3—B2ii−102.97 (6)
Symmetry codes: (i) x, −y, z−1/2; (ii) −x, y, −z+1/2; (iii) x, −y+1, z−1/2; (iv) −x, y−1, −z+1/2; (v) −x, −y, −z; (vi) −x, y+1, −z+1/2; (vii) x, y+1, z; (viii) x, y−1, z.
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O5—H5ix···O3ix0.836 (15)1.895 (15)2.7300 (7)176.3 (15)
O4x—H4···O9xi0.828 (14)2.049 (14)2.8658 (8)168.4 (12)
O6—H6Axii···O5xiii0.868 (16)1.978 (16)2.8323 (8)167.9 (14)
O6xiv—H6B···O4x0.846 (16)2.040 (15)2.8624 (8)163.9 (16)
O7xii—H7A···O20.827 (16)1.989 (16)2.8135 (8)174.1 (12)
O7—H7B···O40.816 (15)2.135 (15)2.9233 (8)162.3 (14)
O8x—H8A···O1xv0.866 (13)1.936 (13)2.7865 (6)167.0 (14)
O8x—H8B···O5xvi0.855 (15)2.341 (14)3.1320 (8)154.2 (12)
O9—H9Axii···O30.843 (16)2.253 (16)3.0894 (8)171.7 (15)
O9—H9Bxvii···O8iii0.849 (17)2.069 (16)2.9034 (8)167.4 (15)
Symmetry codes: (ix) x, −y+1, z+1/2; (x) −x+1, y, −z+1/2; (xi) x+1/2, y−1/2, z; (xii) −x+1/2, y+1/2, −z+1/2; (xiii) −x+1/2, −y+3/2, −z+1; (xiv) −x+1, −y+1, −z+1; (xv) x+1, y, z; (xvi) x+1/2, −y+1/2, z−1/2; (xvii) x−1/2, y+1/2, z; (iii) x, −y+1, z−1/2.
Table 1
Selected geometric parameters (Å) top
Na1—O8i2.3815 (6)B1—O11.4657 (7)
Na1—O6ii2.3979 (5)B1—O21.4902 (8)
Na1—O72.4121 (6)B1—O31.5075 (8)
Na2—O7iii2.4041 (6)B2—O21.3655 (8)
Na2—O92.4214 (6)B2—O3i1.3757 (8)
Na2—O62.4441 (6)B2—O51.3784 (8)
B1—O41.4451 (8)
Symmetry codes: (i) −x, y, −z+1/2; (ii) −x, y−1, −z+1/2; (iii) −x, y+1, −z+1/2.
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O5—H5iv···O3iv0.836 (15)1.895 (15)2.7300 (7)176.3 (15)
O4v—H4···O9vi0.828 (14)2.049 (14)2.8658 (8)168.4 (12)
O6—H6Avii···O5viii0.868 (16)1.978 (16)2.8323 (8)167.9 (14)
O6ix—H6B···O4v0.846 (16)2.040 (15)2.8624 (8)163.9 (16)
O7vii—H7A···O20.827 (16)1.989 (16)2.8135 (8)174.1 (12)
O7—H7B···O40.816 (15)2.135 (15)2.9233 (8)162.3 (14)
O8v—H8A···O1x0.866 (13)1.936 (13)2.7865 (6)167.0 (14)
O8v—H8B···O5xi0.855 (15)2.341 (14)3.1320 (8)154.2 (12)
O9—H9Avii···O30.843 (16)2.253 (16)3.0894 (8)171.7 (15)
O9—H9Bxii···O8xiii0.849 (17)2.069 (16)2.9034 (8)167.4 (15)
Symmetry codes: (iv) x, −y+1, z+1/2; (v) −x+1, y, −z+1/2; (vi) x+1/2, y−1/2, z; (vii) −x+1/2, y+1/2, −z+1/2; (viii) −x+1/2, −y+3/2, −z+1; (ix) −x+1, −y+1, −z+1; (x) x+1, y, z; (xi) x+1/2, −y+1/2, z−1/2; (xii) x−1/2, y+1/2, z; (xiii) x, −y+1, z−1/2.
Acknowledgements top

We thank Dr J. Wikaira of the University of Canterbury, New Zealand, for her assistance with the data collection.

references
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