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The title compound, poly[[μ-trihydro­(isoprop­oxy)­borato]­sodium(I)], [Na(C3H10BO)]n, forms unique polymeric layers normal to the c axis via Na+...O [2.3405 (15) Å] and Na+...H(borane) [2.22 (3) and 2.28 (3) Å] inter­actions. This arrangement builds on distorted tetra­hedral Na+, oxygen and boron environments, with one of the borane hydride units uncoordinated, and highlights potential H3B—O-based chemistry.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010901172X/dn3110sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010901172X/dn3110Isup2.hkl
Contains datablock I

CCDC reference: 735102

Comment top

This study is part of a programme aimed at investigating boron diolates and alkoxides with potential applications in hydrogen storage/recycling systems (Kemmitt & Gainsford, 2009; Gainsford & Kemmitt, 2005). There are no previous reports of boron trihydride (BH3) structures where the boron is bonded to oxygen, although there are 113 compounds containing C—BH3 (principally cyano-boranes) and 186 reports of N—BH3 adducts [Cambridge Structural Database (CSD); Version 5.30 with February 2009 updates; Allen, 2002]. Likewise, BH3 units bound to P are common (324 hits), whilst the S—BH3 entity is only found three times.

The asymmetric unit contents of the title compound, with formula [Na(C3H10BO)], (I), are shown in Fig. 1. The polymeric unit is built around a highly distorted tetrahedral arrangement of the sodium cations through bridging O atoms (Table 1 and Fig. 2) and adjacent BH3 hydride atoms. The mean Na···O and Na···H distances are 2.3405 (15) and 2.25 (2) Å, with angles subtended at the Na atoms ranging from 97.8 (11) to 133.6 (7)° (Fig. 2). Bridging hydrides (B—H···A) (where A is an alkali metal) are well known in tetrahydroborates (Ruiz et al., 2008). The Na···H distance parameters in (I) are within the ranges noted by Ruiz et al. (2008) {e.g. CSD refcodes HIWXUH [2.28 (2) Å] and HIWZOD (2.32–2.39 Å)} and in the singly-bound Na···H contact in WOCMAD (2.38 Å; Wagler & Hill, 2008). In sodium salts of boron trihydride compounds containing S—B and P—B bonds, the Na···H single contacts are similar at 2.35 (LATSAA; Binder et al., 1993) and 2.32 Å (YILJOT; Izod et al., 2007). The B—O—C angle, and B—O, O—C and Na···O distances, are within the ranges noted previously (Gainsford & Kemmitt, 2004) (XEPPIUE; Knizek et al., 2006).

The unique polymeric structure can be described as layers, running parallel to the ab plane, generated by the 4-coordinated Na, B and O atoms, based on the centrosymmetically related B and O atoms (Figs. 2 and 3) and linked through two of the BH3 hydride atoms. These rings can be delineated as R23(8) rings, taking the BH3 H atoms as donors (Bernstein et al., 1995). This arrangement with sodium ions and BH3 substituents appears unique, with all other reported structures involving tetrahydroborates. The aliphatic isopropyl groups act as spacer units along the c axis (Fig. 3), being involved only in van der Waals interactions.

The B···Na distances average 2.904 (2) Å, consistent with the general observation that such longer interactions indicate less bridging of multiple metal atoms by the hydride atoms (Ruiz et al., 2008). This first reported example of a compound containing the O—BH3 group adds a new dimension to the prolific chemistry of boron hydrides.

Related literature top

For related literature, see: Allen (2002); Bernstein et al. (1995); Binder et al. (1993); Gainsford & Kemmitt (2004, 2005); Izod et al. (2007); Kemmitt & Gainsford (2009); Knizek et al. (2006); Ruiz et al. (2008); Wagler & Hill (2008).

Experimental top

NaAlH4 (0.65 g, 12 mmol) was added in small aliquots over a period of 15 min to a rapidly stirred flask containing NaB[OCH(CH3)2]4 (2.70 g, 10 mmol) in tetrahydrofuran (100 ml)at 273 K. The reaction mixture was allowed to return to room temperature and was stirred for 16 h. The reaction mixture was filtered and the volume reduced under partial vacuum. After the reaction mixture had been left in a freezer (261 K) for 16 h, the product appeared as colourless needles, which were filtered off and dried in vacuo (yield 0.8 g, 84%). 1H NMR (d6-DMSO): δ 0.9, (d, 6.1 Hz, CH3, 6H), 2.01 (q, 88 Hz, BH3, 3H), 3.17(sept, CH, 1H) p.p.m. 13C NMR (d6-DMSO): δ 24.72 (CH3), 61.84 (CH) p.p.m. 11B NMR (d6-DMSO): δ -9.7 p.p.m. (88 Hz).

Refinement top

The positional parameters of all H atoms were freely refined, with Uiso(H) fixed at 1.5 or 1.2 (for H4) times Ueq of their carrier atoms. A total of 37 of the 1077 expected reflections within the sinθ/λ limit of 0.60 either could not be processed correctly (25) or were omitted as outliers (12).

Computing details top

Data collection: CrystalClear (Rigaku, 2005); cell refinement: FSProcess in Process-Auto (Rigaku, 1998); data reduction: FSProcess in Process-Auto (Rigaku, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP in WinGX (Farrugia, 1999); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. An ORTEP (Farrugia, 1999) view showing the asymmetric unit, with 30% probabilility ellipsoids.
[Figure 2] Fig. 2. An ORTEP (Farrugia, 1999) view showing the fourfold coordination of the Na atoms. Atoms not involved in the coordination environment, except isopropyl atom C2, have been omitted for clarity. [Symmetry codes: (i) -x + 1, -y + 1, -z + 1; (ii) x - 1, y, z; (iii) x - 1/2, -y + 1/2, -z + 1.]
[Figure 3] Fig. 3. An ORTEP (Farrugia, 1999) view of the cell contents down the a axis, showing the cross-linked layers normal to the c axis.
Poly[[µ-trihydro(isopropoxy)borato]sodium(I)] top
Crystal data top
[Na(C3H10BO)]F(000) = 416
Mr = 95.91Dx = 1.073 Mg m3
Orthorhombic, PbcaCu Kα radiation, λ = 1.54178 Å
Hall symbol: -P 2ac 2abCell parameters from 4075 reflections
a = 5.5071 (11) Åθ = 6.8–72.0°
b = 11.094 (2) ŵ = 1.19 mm1
c = 19.438 (4) ÅT = 173 K
V = 1187.6 (4) Å3Rod, colourless
Z = 80.5 × 0.05 × 0.02 mm
Data collection top
Rigaku Spider
diffractometer
1119 independent reflections
Radiation source: Rigaku MM007 rotating anode849 reflections with I > 2σ(I)
Rigaku VariMax-HF Confocal Optical System monochromatorRint = 0.104
Detector resolution: 10 pixels mm-1θmax = 72.2°, θmin = 8.0°
ω–scansh = 66
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
k = 1313
Tmin = 0.492, Tmax = 1.0l = 2122
9917 measured reflections
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)] = 0.070Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.194Only H-atom coordinates refined
S = 1.08 w = 1/[σ2(Fo2) + (0.1163P)2]
where P = (Fo2 + 2Fc2)/3
1119 reflections(Δ/σ)max < 0.001
85 parametersΔρmax = 0.49 e Å3
0 restraintsΔρmin = 0.35 e Å3
Crystal data top
[Na(C3H10BO)]V = 1187.6 (4) Å3
Mr = 95.91Z = 8
Orthorhombic, PbcaCu Kα radiation
a = 5.5071 (11) ŵ = 1.19 mm1
b = 11.094 (2) ÅT = 173 K
c = 19.438 (4) Å0.5 × 0.05 × 0.02 mm
Data collection top
Rigaku Spider
diffractometer
1119 independent reflections
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
849 reflections with I > 2σ(I)
Tmin = 0.492, Tmax = 1.0Rint = 0.104
9917 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0700 restraints
wR(F2) = 0.194Only H-atom coordinates refined
S = 1.08Δρmax = 0.49 e Å3
1119 reflectionsΔρmin = 0.35 e Å3
85 parameters
Special details top

Experimental. Because of the small crystal size, X-ray data collection was not possible on a standard sealed tube/CCD system, but was achieved with a microfocus rotating anode system (Rigaku MM007) with confocal optics (Osmic-Rigaku) delivering copper K-alpha radiation to the sample, coupled with a wrap-around image-plate detector (Rigagu Spider).

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
Na10.29141 (16)0.39362 (9)0.49521 (5)0.0498 (5)
O10.6138 (3)0.45558 (14)0.42507 (8)0.0472 (6)
C10.4338 (6)0.5736 (3)0.33565 (17)0.0645 (8)
H50.423 (6)0.585 (3)0.288 (2)0.097*
H60.493 (7)0.642 (3)0.358 (2)0.097*
H70.260 (8)0.558 (3)0.3569 (19)0.097*
C20.5954 (4)0.4665 (2)0.35194 (13)0.0490 (7)
H40.769 (5)0.483 (2)0.3363 (12)0.059*
C30.5002 (6)0.3528 (3)0.31911 (18)0.0636 (8)
H80.494 (7)0.357 (3)0.272 (2)0.095*
H90.335 (7)0.331 (3)0.3394 (18)0.095*
H100.609 (6)0.286 (3)0.3333 (16)0.095*
B10.7916 (4)0.3656 (3)0.45085 (18)0.0509 (8)
H10.824 (7)0.379 (3)0.5120 (17)0.076*
H20.971 (6)0.374 (3)0.4219 (14)0.076*
H30.723 (5)0.270 (3)0.4416 (15)0.076*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na10.0453 (6)0.0586 (8)0.0456 (9)0.0045 (4)0.0024 (3)0.0002 (4)
O10.0451 (9)0.0592 (10)0.0373 (12)0.0048 (6)0.0011 (6)0.0020 (7)
C10.0811 (19)0.0673 (16)0.045 (2)0.0029 (14)0.0133 (15)0.0038 (15)
C20.0495 (12)0.0648 (14)0.0328 (16)0.0033 (10)0.0027 (9)0.0024 (11)
C30.0690 (16)0.0741 (18)0.048 (2)0.0009 (14)0.0045 (13)0.0091 (15)
B10.0438 (13)0.0641 (17)0.045 (2)0.0041 (11)0.0002 (10)0.0064 (14)
Geometric parameters (Å, º) top
Na1—O1i2.3393 (19)C1—H60.94 (4)
Na1—O12.3416 (17)C1—H71.05 (4)
Na1—H2ii2.28 (3)C2—C31.508 (4)
Na1—H3iii2.22 (3)C2—H41.02 (3)
Na1—B1ii2.901 (3)C3—H80.92 (4)
Na1—B1i2.906 (3)C3—H91.02 (4)
O1—C21.430 (3)C3—H101.00 (4)
O1—B11.486 (3)B1—Na1iv3.060 (3)
O1—Na1i2.3393 (19)B1—H11.21 (3)
C1—C21.517 (4)B1—H21.14 (3)
C1—H50.93 (4)B1—H31.14 (3)
O1i—Na1—O190.38 (6)O1—C2—C1108.4 (2)
O1—Na1—H2ii104.5 (8)C3—C2—C1111.2 (2)
O1—Na1—H3iii133.6 (7)O1—C2—H4104.2 (14)
H2ii—Na1—H3iii97.8 (11)C3—C2—H4110.3 (14)
C2—O1—B1116.04 (19)C1—C2—H4110.5 (15)
C2—O1—Na1i127.83 (12)C2—C3—H8113 (2)
B1—O1—Na1i96.32 (16)C2—C3—H9110 (2)
C2—O1—Na1123.36 (13)H8—C3—H9111 (3)
B1—O1—Na196.09 (14)C2—C3—H10107 (2)
Na1i—O1—Na189.62 (6)H8—C3—H10109 (3)
C2—C1—H5111 (2)H9—C3—H10105 (3)
C2—C1—H6110 (2)O1—B1—H1110.2 (16)
H5—C1—H6111 (3)O1—B1—H2110.4 (15)
C2—C1—H7109 (2)H1—B1—H2110 (2)
H5—C1—H7111 (3)O1—B1—H3110.7 (14)
H6—C1—H7106 (3)H1—B1—H3109 (2)
O1—C2—C3112.0 (2)H2—B1—H3107 (2)
O1i—Na1—O1—C2136.89 (16)Na1—O1—C2—C352.8 (2)
O1i—Na1—O1—B196.32 (16)B1—O1—C2—C1172.1 (2)
O1i—Na1—O1—Na1i0.0Na1i—O1—C2—C149.8 (3)
B1—O1—C2—C364.8 (3)Na1—O1—C2—C170.3 (2)
Na1i—O1—C2—C3172.85 (16)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x1, y, z; (iii) x1/2, y+1/2, z+1; (iv) x+1/2, y+1/2, z+1.

Experimental details

Crystal data
Chemical formula[Na(C3H10BO)]
Mr95.91
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)173
a, b, c (Å)5.5071 (11), 11.094 (2), 19.438 (4)
V3)1187.6 (4)
Z8
Radiation typeCu Kα
µ (mm1)1.19
Crystal size (mm)0.5 × 0.05 × 0.02
Data collection
DiffractometerRigaku Spider
diffractometer
Absorption correctionMulti-scan
(ABSCOR; Higashi, 1995)
Tmin, Tmax0.492, 1.0
No. of measured, independent and
observed [I > 2σ(I)] reflections
9917, 1119, 849
Rint0.104
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.070, 0.194, 1.08
No. of reflections1119
No. of parameters85
H-atom treatmentOnly H-atom coordinates refined
Δρmax, Δρmin (e Å3)0.49, 0.35

Computer programs: CrystalClear (Rigaku, 2005), FSProcess in Process-Auto (Rigaku, 1998), SHELXS97 (Sheldrick, 2008), ORTEP in WinGX (Farrugia, 1999), SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Selected geometric parameters (Å, º) top
Na1—O1i2.3393 (19)Na1—H3iii2.22 (3)
Na1—O12.3416 (17)O1—B11.486 (3)
Na1—H2ii2.28 (3)C1—C21.517 (4)
O1i—Na1—O190.38 (6)H2ii—Na1—H3iii97.8 (11)
O1—Na1—H2ii104.5 (8)Na1i—O1—Na189.62 (6)
O1—Na1—H3iii133.6 (7)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x1, y, z; (iii) x1/2, y+1/2, z+1.
 

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