Structure and properties of NaBH4·2H2O and NaBH4

Article abstract of DOI:10.1002/ejic.200800053

NaBH₄·2H₂O and NaBH₄ were studied by single-crystal Xray diffraction and vibrational spectroscopy. In NaBH ₄·2H₂O, the BH₄^- anion has a nearly ideal tetrahedral geometry and is bridged with two Na⁺ ions through the tetrahedral edges. The structure does not contain classical hydrogen bonds, but reveals strong dihydrogen bonds of 1.77-1.95 A. Crystal structures and vibrational spectra of NaBr·2H₂O and NaBH ₄·2H₂O reveal many similarities. The unit cell volume of NaBH₄·2H₂O increases linearly with temperature between 200 and 313 K. At 313-315 K, the hydrate decomposes into NaBH₄ and H₂O, which react to release hydrogen. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800053

FULL PAPER
DOI: 10.1002/ejic.200800053
Structure and Properties of NaBH ·2H O and NaBH
4
2
4
[a]
[b]
Yaroslav Filinchuk* and Hans Hagemann
Keywords: X-ray diffraction / Vibrational spectroscopy / Hydrides / Hydrates / Hydrogen bonds
NaBH
4
·2H
2
O and NaBH
4
were studied by single-crystal X-
·2H O,
4
anion has a nearly ideal tetrahedral geometry and
NaBH
of NaBH
200 and 313 K. At 313–315 K, the hydrate decomposes into
NaBH and H O, which react to release hydrogen.
4
·2H
2
O reveal many similarities. The unit cell volume
ray diffraction and vibrational spectroscopy. In NaBH
the BH
is bridged with two Na ions through the tetrahedral edges.
The structure does not contain classical hydrogen bonds, but
reveals strong dihydrogen bonds of 1.77–1.95 Å. Crystal
4
2
4
·2H
2
O increases linearly with temperature between
–
+
4
2
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
2
structures and vibrational spectra of NaBr·2H O and
Introduction
Results and Discussion
Light-metal hydrides are considered as prospective en-
Although neutron powder diffraction is known as the
ergy carriers for future mobile applications. Hydrogen can main technique to study structure of metal hydrides,[ as
11]
be produced from metal hydrides by thermal decomposition it reveals some of the most complex structures of transition
[
1]
[2]
[12]
(
pyrolysis) or in a reaction with water (hydrolysis).
metal hydrides,
neutron diffraction studies of metal
Borohydrides of alkaline metals, such as LiBH4 and borohydrides are hindered by the incoherent scattering by
NaBH , readily evolve hydrogen by hydrolysis, both upon H and the high absorption of natural B isotopes. To over-
4
direct reaction with water[3] and through a fuel cell. Al- come these drawbacks, isotopically labelled borohydride
[4]
[
13]
though the reactions with water are usually fast, the reac- samples are prepared and neutron and X-ray diffraction
[
14]
tion kinetics under practical conditions is rather slow, thus techniques are combined.
On the other hand, in light
suggesting the use of expensive catalysts.[ Catalytically ac- hydrides X-ray diffraction on its own was shown to be a
5]
celerated NaBH hydrolysis for the generation of hydrogen powerful tool to locate hydrogen atoms and was applied to
4
[6]
[15,16]
has been studied since the 1950s, and it is now under in- potential hydrogen storage materials.
tensive investigation, leading to a number of recent appli- tal structures, including hydrogen atoms’ positions, of anhy-
cations. However, until now, there is no experimental drous and hydrated NaBH4 were accurately determined
structural information on intermediate phases or reaction from synchrotron diffraction on single crystals.
pathways in the NaBH + H O system.
In this work crys-
[5]
[
7]
[17]
Anhydrous NaBH at temperatures above ≈190 K has
4
2
4
The first report on a solid sodium borohydride dihydrate a cubic structure isomorphous to NaCl, previously de-
was published over 50 years ago.[8] Recently, the existence scribed either in Fm3m
¯
[18]
or F43m
¯
[19,20]
space groups. The
of short dihydrogen bonds has been reported for two models differ only by the absence of the inversion cen-
[
9]
¯
NaBH ·2H O from neutron diffraction, but a full account tre in F43m. Although the centrosymmetric structure is in-
4
2
–
of the structural data has not been published until now. trinsically disordered, showing two orientations of the BH4
Hydrogen elimination from LiBH and NaBH complexes group, the noncentrosymmetric model allows the BH4–
4
4
with less-reactive proton donors, such as alcohols, has been anion to be fully ordered. A peak of heat capacity below
[
10]
[17]
[21]
reported, whereas the study of the NaBH complex with ≈190 K is consistent with an order–disorder transition
4
[
18]
water would be very important for hydrogen storage. This from cubic to tetragonal structure. This thermodynamic
work is focused on the crystal structure of NaBH ·2H O data suggests that the high-temperature phase is disordered;
4
2
¯
and its anhydrous counterpart and will contribute to a bet- therefore, the higher-symmetry space group Fm3m has to
ter understanding of the mechanism of borohydride hydrol- be assumed for its structure. We note that the fully disor-
¯
[20]
ysis.
dered F43m model assumed in ref. is completely identical
¯
to the Fm3m model. It is important also to understand that
the nonresonant single-crystal or any powder diffraction
studies are not able to determine whether the BH
in cubic NaBH is ordered or disordered. However, crystal-
chemical analysis shows that the shortest, repulsive H···H
interactions favour the disorder: a number of the shortest
[
[
a] Swiss-Norwegian Beam Lines, European Synchrotron Radia-
tion Facility,
–
6
rue Jules Horowitz, B. P. 220, 38043 Grenoble, France
4
anion
Fax: +33-47-688-26-94
4
E-mail: Yaroslav.Filinchuk@esrf.fr
b] Département de Chimie Physique, Université de Genève,
3
0 quai Ernest Ansermet, 1211 Geneva 4, Switzerland
Eur. J. Inorg. Chem. 2008, 3127–3133
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3127

Y. Filinchuk, H. Hagemann
H···H distances between BH anions in the disordered Table 1. Interatomic distances [Å] and angles [°] in NaBH ·2H O.
FULL PAPER
–
4
4
2
¯
Fm3m structure is two times smaller than in a hypothetical
1
00 K
150 K
¯
[21]
ordered F43m structure.
Thus, among the two possible
Intramolecular contacts
¯
¯
models, the disordered Fm3m and the ordered F43m, only
the first one agrees both with crystallographic and thermo-
dynamic data.
O–H (4ϫ)
H–O–H (2ϫ)
B–H (4ϫ)
0.755(18)–0.792(16)
0.756(16)–0.814(17)
99.9(15)–100.4(17)
1.068(15)–1.123(16)
105.5(10)–112.5(11)
105.5(16)–105.9(15)
1.110(15)–1.134(13)
106.8(9)–112.4(10)
H–B–H (6ϫ)
The crystal structure of NaBH ·2H O contains sodium
4
2
cations having a nearly octahedral coordination made up of Coordination sphere of the sodium atom
four water molecules and two borohydride anions (Fig-
Na–O (4ϫ)
2.3811(8)–2.4689(9)
2.9533(12)–3.0059(13)
2.455(12)–2.670(12)
2.3908(9)–2.4816(10)
2.9635(13)–3.0100(14)
2.464(12)–2.662(13)
81.89(3)–169.19(4)
86.75(4)–175.54(3)
96.42(4)
ure 1). The Na–O bonds are ≈2.4 Å long and the Na···B Na···B (2ϫ)
distances are around 3.0 Å (Table 1). The orientation of the Na–H (4ϫ)
BH4– tetrahedron is such that it is bridged with two Na+
ions through the tetrahedral edges. The Na···µ -H B coor-
O–Na–O (6ϫ) 81.92(3)–169.45(3)
B–Na–O (8ϫ) 86.39(3)–175.51(3)
B···Na···B
2
2
96.51(4)
dination is somewhat asymmetric, with one shorter and one
longer Na–H distances of 2.46–2.67 Å (Table 1). The
3
Na···B···Na angle is ≈96°. In anhydrous NaBH , the disor- 106.9 Å at 295 K). The use of even larger iodine anion re-
4
dered BH4 anion symmetrically µ -coordinates Na atoms sults in a different structure of NaI·2H O (V = 124.5 Å3
–
2
2
f.u.
[
24]
at Na–H distances of 2.59 Å. Although Na···B contacts in at 295 K). The unit cell volumes suggest that the size of
anions change according to the sequence I Ͼ BH Ͼ Br–
–
–
NaBH ·2H O are only slightly shorter than in NaBH
4
2
4
4
–
[
3.0654(1) Å], the Na···Na distances are considerably short- Ͼ Cl . The final product of NaBH hydrolysis, the isosto-
4
[
25]
ened from 4.34 to 3.61–3.80 Å. This is due to the fact that ichiometric Na[B(OH) ]·2H O,
contains Na (H O)
4
2
n 2 n
sodium atoms in NaBH ·2H O do not form a close-packed chains linked by anions into layers, similar to those in
4
2
substructure as in the anhydrous NaBH , but instead they NaI·2H O.
4
2
form flat honeycomb layers in the ab plane.
Isostoichiometric compounds containing tetrahedral
anions other than BH4– reveal 3D framework structures
where ligands display a different denticity. For example, the
dihydrogenphosphate anion in Na[H (PO )]·2H O acts as a
2
4
2
tridentate ligand, and moreover, one water molecule is
[
26]
bridging and the other is terminal. In the group of com-
pounds with a general formula A(BO )·2H O (A = Fe, Al,
4
2
In, Ga; B = P, As), the anions act as tetradentate and water
[
27]
molecules as terminal ligands.
NaBH ·2H O is the first-known hydrated borohydride,
4
2
but it is also the third-known structure containing borohyd-
ride anions and oxygen atoms. The other two compounds,
Na (GaSiO ) (BH ) and Na (AlGeO ) (BH ) , have been
8
4 6
4 2
8
4 6
4 2
recently synthesized under mild hydrothermal conditions
[
28]
and studied by powder diffraction.
They were proposed
–
as BH -containing model compounds that could release
4
hydrogen. However, the NaBH /H O system has a higher
4
2
H capacity and, at present, is the cheapest source of hydro-
4 2
Figure 1. Projection of the NaBH ·2H O structure on the ab plane.
gen. The LiBH –LiNH system is an important alternative,
4
2
Anisotropic thermal ellipsoids at 100 K are drawn at the 80% prob-
ability level. Coordination of sodium atoms (light-grey spheres) is
highlighted by dashed lines.
as it can produce hydrogen under much milder condi-
[
29]
tions.
–
In NaBH ·2H O, the BH anion has a nearly ideal tetra-
4
2
4
As shown in Figure 1, Na atoms and one type of water hedral geometry with an average B–H bond length of
molecules form centrosymmetric Na O units, which are ≈1.12 Å (see Table 1). This value is completely consistent
2
2
–
linked by the second type of water molecules into an infinite with recent single-crystal X-ray data on the BH anion in
4
[
15]
layer located in the ab plane. The Na–O1–Na and Na–O2– a light-metal hydride. The O–H distances have an average
Na angles in the 12-membered Na O rings are nearly the value of 0.77 Å. The nearly ideal tetrahedral configuration
6
6
same, and are, respectively, 98.08(3) and 101.68(3)° at of the BH group and proper H–O–H angles in the H O
4
2
100 K.
molecules confirm that the hydrogen atoms are located
Very similar layers were observed in the monoclinic from synchrotron data with a high accuracy. However, the
[22]
[23]
structures of NaCl·2H O
and NaBr·2H O.
The vol- observed O–H and B–H distances are systematically under-
2
2
ume of the NaX·2H O formulae units (V ) shows that the estimated. Apart from a small effect of libration, this differ-
2
f.u.
–
3
3
BH4 anion (Vf.u. = 106.7 Å at 100 K, and 110.4 Å at ence comes from a displacement of the electron cloud (seen
95 K) is considerably larger than the Cl anion (V
4.8 Å at 105 K) and larger than the Br anion (V
–
2
9
=
=
by X-ray analysis) relative to an average nuclear position
(seen by neutron diffraction and determined by DFT calcu-
f.u.
3
–
f.u.
3128
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3127–3133

4 2 4
Structure and Properties of NaBH ·2H O and NaBH
lations). In order to evaluate better the geometry of the di- distance is longer than the average of the other three B–H
hydrogen bonds, the apparent hydrogen atom positions at distances by 0.02 Å, and the O1–Hw1 bond (forming the
100 K were corrected by “extending” the average O–H shortest dihydrogen bond of 1.77 Å) is longer than the
(
0.77 Å) and B–H (1.12 Å) bond lengths to the ideal values other O–H distances by almost 0.04 Å. These differences
[
20]
of 0.96 and 1.22 Å. Below we will discuss characteristics are within the limits of two standard uncertainties. How-
of the H···H bonds assuming corrected coordinates of the ever, the lengthening of the B–H and O–H bonds in the B–
H atoms.
H···H–O fragments was found in similar systems by ab ini-
[
30]
The structure of NaBH ·2H O does not show classical tio calculations.
4
2
hydrogen bonds, but reveals dihydrogen bonding. Their
As can be seen from Table 2, the O–H vectors are well
geometric characteristics, calculated for the 100 K data by directed towards the B and H3 atoms. However, they are
using corrected positions of the H atoms, are listed in not clearly pointed toward the middle of the B–H bond, as
[
9]
Table 2. The H···H distances are much shorter than twice suggested. The O–H vectors are even less directed with
the value of the van der Waals radius of a hydrogen atom respect to the H–B bonds for a number of additional O–
(2.4 Å) and are very close to those preliminary reported for H···H–B contacts (not shown in Table 2), where the H···H
this compound from single-crystal neutron diffraction distances are less than ≈2.4 Å. This suggests that the
9]
–
δ+
(
1.79, 1.86 and 1.94 Å).[ The latter shows that by assuming BH ···H (O) interaction is somewhat similar to the inter-
4
–
proper corrections, hydrogen atoms in light-metal hydrides action of the BH4 anion with a spherical cation, as, for
can be determined from X-ray diffraction data with accu- instance, BH ···Na in the title compounds or BH ···Li
racy similar to the neutron diffraction study. It is remark- in Li BN H . The observed flexibility is in line with the
–
+
–
+
4
4
[
15]
4
3
10
δ+ δ–
able that the three intermolecular O–H ··· H–B dihydro- conclusion that there is no sharp borderline between dihy-
gen bonds are shorter than H···H distances within the BH4– drogen bonds and van der Waals interactions.
[31]
anion (≈2.0 Å). The interaction between neighbouring BH4–
In order to see whether short dihydrogen bonds enable
anions is reduced to the minimum: the corresponding short- hydrogen release directly from NaBH ·2H O, we studied its
4
2
est H···H contact is 2.72(2) Å in length. The shortest dihy- thermal decomposition by in situ diffraction. To analyze
drogen bond of 1.77 Å connects the layers (Figure 1) along the data collected upon heating the powder of
the c axis. The layers are associated only through dihydro- NaBH ·2H O, its single-crystal structure was used as an in-
4
2
gen bonds, and this is probably the reason why the crystals put for the sequential Rietveld refinement in Fullprof.[
32]
3
grow as thin plates.
We found that within 196–313 K the unit cell volume (Å )
of NaBH ·2H O increases linearly with temperature (K): V
4
2
Table 2. Geometric characteristics of dihydrogen bonds in
=
825.3(1) + 0.1969(4) T. The unit cell parameters a and c
NaBH
4
·2H
2
O (100 K data, corrected positions of H atoms).
also show a linear temperature dependence, whereas the b
parameter can be approximated by a quadratic dependence:
Distance [Å]
Angle [°]
Hw1···H3
Hw2···H3
Hw4···H3
1.77(2)
1.90(2)
1.95(2)
O1–Hw1···H3/B 170.1(14)/157.4(12)
O1–Hw2···H3/B 151.1(18)/162.8(17)
O2–Hw4···H3/B 156.8(13)/171.7(12)
a = 10.1427(7) + 1.080(3)ϫ10–4
T
b = 6.8857(5) – 2.3(4)ϫ10–4 T + 9.5(7)ϫ10–7 T2
Figure 2 shows the coordination environment for the
BH4– anion in NaBH ·2H O. The three shortest dihydrogen c = 11.9308(9) + 1.040(4)ϫ10–3
T
4
2
bonds involve the same hydrogen atom (H3) of the BH4
group. The H3 atom does not interact with sodium atoms,
and the H1, H2 and H4 atoms are coordinated by sodium
Under the experimental conditions (heating NaBH4·
2
H O at 60 K per hour in a glass capillary), the structure
2
decomposes at 313–315 K into NaBH and H O. This is
4
2
atoms through the edges of the BH tetrahedra. The B–H3
4
consistent with an earlier observation that NaBH ·2H O,
4
2
NaBH4 and H O coexist in equilibrium at 1 bar and
2
[
8]
35(1) °C. Upon heating to higher temperatures above that
required for NaBH ·2H O decomposition, we observed that
4
2
NaBH and H O slowly react to release hydrogen. Thus,
4
2
the hydrate NaBH ·2H O does not directly release hydro-
4
2
gen, even upon thermal decomposition, but decomposes
into anhydrous NaBH and water. The latter react to pro-
4
duce hydrogen.
Figure 3 compares the IR spectra of NaBH in solution
4
with the spectra of the solid NaBH , NaBH ·2H O and
4
4
2
NaBr·2H O. The observed bands in the Raman and IR
2
spectra at room temperature are collected in Table 3. These
data confirm that NaBH is stable in alkaline aqueous solu-
4
4 2
Figure 2. Coordination of the borohydride anion in NaBH ·2H O
tion at room temperature. The spectra show that the BH4
ions are unaltered, both in alkaline aqueous solution of
NaBH and in solid NaBH ·2H O. The spectra show very
by two sodium atoms and three water molecules. Interatomic dis-
tances are shown in Å for the corrected hydrogen atom positions
at 100 K.
4
4
2
Eur. J. Inorg. Chem. 2008, 3127–3133
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3129

Y. Filinchuk, H. Hagemann
FULL PAPER
Table 3. Vibrational frequencies in NaBr·2H
2
O, NaBH
4
·2H
2
O, NaBH
4
·2D
2
O and NaBH
4
. Raman bands above 2700 cm–1 could not be
observed with our experimental setup.
NaBr·2H
2
O
NaBH
IR
4
·2H
2
O
NaBH
IR
4
·2D
2
O
NaBH
4
Assignment
IR
Raman
Raman
Raman
IR
Raman
5
156
051
544
460
404
3544+1612 ?
3404+1635 ?
O–H
5
3
3
3
3565
3502
3462
3554
3497
3479
stretching
3
3
374 (sh.)
234 (w)
3241
2
2
648
616
2650
2615
O–D
stretching
2
2
586 (w)
570 (w)
2
2
554
540
2560
2313
2300 (sh.)
2233
2
553
2
380 (sh.)
2319
2299 (sh.)
2233
2346 (w, sh.)
2267
2225
2188 (sh.)
2416
2340
2321
2231
B–H stretching
2
2
268
221
2396
2282
2216
2190 (sh.)
2170
2178
2197
1
1
635
612
1650
1636
1621
1613
1642
1635
HOH bend
1
1
1
434
197
190
HOD bend
DOD bend
1210
1
264
1265
1245
1132
1106
458
1274
1124
B–H def E
1
248 (sh.)
1133
1106
595
1
1
124
097
1125
1097
1110
B–H def F
2
6
20 (sh.)
630 (sh.)
579
616
566
libration
595
489
443
2
H O
4
3
43
83
407
357
282
2
38 (w, sh.)
213
similar absorption frequencies as in the anhydrous NaBH4,
a small splitting of the deformation bands suggests an al- tion (Figure 4) show that the hydrogen atoms of the
most tetrahedral symmetry of the borohydride group. borohydride ion and the water molecules do not exchange
The vibrational spectra of NaBH in alkaline D O solu-
4 2
Figure 3. Room-temperature IR spectra of solid NaBH
NaBH ·2H O, solid NaBr·2H O and alkaline (pH Ͼ 13) 8.8 
aqueous solution of NaBH
4
, solid
4
2
2
Figure 4. IR and Raman spectra of NaBH
purity) at room temperature.
4 2
·2D O (95% D isotope
4
.
3130
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3127–3133

4 2 4
Structure and Properties of NaBH ·2H O and NaBH
significantly at 20 °C. This agrees with the recent observa- tions. This sets new standards for experimental studies of
tion made in a detailed kinetic NMR spectroscopic study light hydrides and opens new routes to characterize them,
[33]
of Pd-catalyzed hydrolysis of NaBH4.
such as single-crystal X-ray diffraction at multiple tempera-
The O–H stretching in NaBH ·2H O reveals a sharp tures and inelastic X-ray scattering on single crystals. Such
4
2
–
1
–1
band at 3553 cm and a strong band at 3478 cm with a experiments on NaBH are in progress.
4
–
1
shoulder at 3490 cm . This is consistent with the presence
of the strong dihydrogen bonds for three O–H groups and
the absence of the dihydrogen bonding for the fourth one Conclusions
O2–Hw3). In comparison, the spectra for NaBr·2H O are
spread over a wider range (3404–3544 cm ), but show a
similar intensity pattern (see Figure 3). The librational
modes of the water molecules in NaBr·2H O and
NaBH ·2H O are found at around 600 cm and below.
(
2
In this work, the positions of hydrogen atoms were un-
ambiguously determined from synchrotron diffraction on
single crystals of anhydrous and hydrated NaBH , which
–
1
4
2
are potential hydrogen storage materials. In NaBH ·2H O,
–
1
4
2
4
2
the BH4– anion has a nearly ideal tetrahedral geometry and
–
1
The F deformation band of BH (≈1100 cm , shoulder
2
4
+
is bridged with two Na ions through the tetrahedral edges.
at higher energy), and the F stretching band together with
2
The structure does not contain classical hydrogen bonds,
but reveals strong dihydrogen bonds of 1.77–1.95 Å. The
crystal structures and vibrational spectra of NaBr·2H O
–
1
other bands arising from Fermi resonances (2300 cm ) ap-
pear at similar positions as in NaBH4.[
34,35]
The positions
–1
2
of the totally symmetrical stretching mode at 2340 cm in
NaBH and 2319 cm in NaBH ·2H O are similar, suggest-
ing a similar B–H bond length in the hydrated and the an-
hydrous form. Under the experimental conditions of the
diffraction experiments, the B–H bond lengths in hydrated
and anhydrous NaBH are similar: the average length of the
B–H bonds in NaBH ·2H O at 100 K is 1.12(1) Å, whereas
in anhydrous NaBH4 at 200 K the B–H bond length is
and NaBH ·2H O show many similarities. It appears that
–
1
4
2
4
4
2
the BH4– ion is rather robust in alkaline aqueous solutions,
as no isotopic exchange was observed in D O at a pH value
of ca. 11. The unit-cell volume of NaBH ·2H O increases
linearly with temperature between 200 and 313 K. At 313–
15 K, NaBH ·2H O decomposes into NaBH and H O,
2
4
2
4
3
4
2
4
2
4
2
which react to release hydrogen.
1
.09(2) Å. The B–D distance determined in NaBD from
4
neutron powder diffraction at room temperature is
[
20]
Experimental Section
≈
1.17 Å. If we assume for NaBH the same 0.10 Å differ-
4
ence between the centre of an electron cloud and an average Crystal growth: Single crystals of NaBH4 were obtained by slow
nuclear position of an H atom, as in the case of NaBH4· evaporation of a saturated solution in isopropylamine under nitro-
gen flow by varying slightly the crystal growth procedure described
2
H O, the effect of the libration would be responsible for a
2
earlier.[ Single crystals of NaBH
8]
4 2
·2H O were obtained by
sensible 0.02 Å decrease in the apparent B–H distance from
00 K (1.09 + 0.10 = 1.19 Å) to room temperature (1.17 Å).
recrystallization of NaBH from an aqueous solution of NaOH.
The crystals can be kept at 0 °C in a closed container. In open air
they take up water from the atmosphere and dissolve.
4
2
Thus, the 0.10-Å correction for the positions of the H
atoms as determined by X-ray diffraction appears to be
practical and may be applied to structures of other borohy-
drides.
4 2
Single-Crystal Diffraction: One crystal of NaBH ·2H O was mea-
sured at 100 K by using synchrotron radiation and MAR345 image
plate detector, and the other at 150 K on a Stoe IPDS dif-
fractometer equipped with an image plate detector and Mo X-ray
tube. Diffraction intensities were indexed and integrated
orthorhombic cell. A single crystal of NaBH
A small part of the 0.10-Å correction originates from a
geometric effect caused by libration of the BH unit. An
4
[37,38]
in an
–
extent of the BH4 libration is not only temperature-de-
4
was measured at
pendent (at higher temperature the motion of the BH4–
200 K by using a KM-6 goniometer, Onyx CCD detector and syn-
chrotron radiation. The data were corrected for Lorentz factor and
groups is more pronounced) but also specific to each crystal
structure. However, a larger part of the 0.10-Å correction polarization effects. Absorption correction was not applied. The
comes from the well-known displacement of the electron structures were solved by direct methods,[ hydrogen atoms were
cloud relative to an average nuclear position, and it is tem- located from difference Fourier maps. A full least-squares refine-
39]
2
ment on F was performed on positional and thermal parameters
perature independent. Thus, the 0.10 Å increment can be
for all atoms (anisotropic for Na, O and B) by using SHELXL-
used as an empirical correction for the B–H distances,
[39]
97.
Neutral atom scattering factors were used, yielding refined
which brings H atom positions determined from X-ray dif-
fraction in borohydrides to a direct comparison with those
derived from neutron diffraction. Such estimates are known
for systems containing N–H or O–H bonds,[ but not for
those containing B–H bonds. Correction of systematic er-
occupancies that were very close to 100%. Crystal data and details
of data collection and structure refinement are given in Table 4.
Further details of the crystal-structure investigations may be ob-
tained from the Fachinformationszentrum Karlsruhe, 76344 Egg-
enstein-Leopoldshafen, Germany, on quoting the depository num-
36]
rors for H positions determined from X-ray diffraction ber(s) CSD-419040, -419045, -419041 and -419039.
leads to an increased accuracy of this technique being ap-
plied to low-Z hydride systems. Nonoverlapped three-di-
mensional information uncovered by the scattering of X-
4 2
In Situ Powder Diffraction: Single crystals of NaBH ·2H O were
rapidly ground in air and sealed in a glass capillary of 0.3-mm
diameter. Capillary was heated from 196 to 336 K at a 60 K per
rays on single crystals gives an advantage over the neutron hour heating rate, and synchrotron powder diffraction data were
powder diffraction, which gives one-dimensional projec- collected in situ. The temperature was controlled with an Oxford
Eur. J. Inorg. Chem. 2008, 3127–3133
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3131

Y. Filinchuk, H. Hagemann
FULL PAPER
4 2 4
Table 4. Crystal data, details of data collection and structure refinement for NaBH ·2H O and NaBH .
NaBH
4
·2H
2
O
NaBH
4
·2H
2
O
NaBH
4
ICSD No.
Radiation
λ [Å]
Detector
T [K]
419045
synchrotron
0.71053
MAR345 IP
100
419041
X-ray, Mo-K
0.71073
STOE IPDS
150
419039
α
synchrotron
0.71700
Onyx CCD
200
Fw
73.86
Pbca
73.86
Pbca
10.3390(16)
6.8894(12)
12.1434(18)
865.0(2)
8, 1.134
56.0, 98.9
0.0523, 0.0447
4441, 1028
37.83
Fm3m
6.13080(10)
¯
Space group
a [Å]
b [Å]
10.2870(9)
6.8759(7)
12.0651(12)
853.39(14)
8, 1.150
51.3, 99.8
0.0264, 0.0095
5607, 813
813, 0, 69
c [Å]3
V [Å ]
230.437(7)
4, 1.090
79.7, 98.2
0.036, 0.011
996, 55
–3
Z, Dcalcd. [gcm ]
max [°], completeness [%]
2
R
θ
int, R
σ
Reflections collected, unique
Data, restraints, parameters
Final R indices
1028, 0, 69
55, 0, 6
R
1
= 0.0212
wR = 0.0397
= 0.0263
wR = 0.0456
R
1
= 0.0242
wR = 0.0460
= 0.0442
wR = 0.0489
R
1
= 0.0158
wR = 0.0176
= 0.0350
wR = 0.0358
[
IϾ2σ(I)]
2
2
2
R indices (all data)
R
1
R
1
R
1
2
2
2
GOF on F2
1.177
0.000
0.18(4), –0.16(4)
0.845
0.001
0.14(4), –0.15(4)
1.282
0.000
0.06(2), –0.06(2)
(∆/σ)max
–3
Largest Fourier diff. [eÅ ]
Cryostream 700+. The data were collected by using MAR345 im-
age plate detector at the BM01A line of SNBL (ESRF). The data
were measured at a sample-to-detector distance of 150 mm by using
the radiation with λ = 0.718320 Å. Data collection time: 60 s per
image, readout ≈83 s per image. 64 images were collected in total.
The data were integrated by using Fit2D program[ and a cali-
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Published Online: March 19, 2008
Eur. J. Inorg. Chem. 2008, 3127–3133
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3133