Novel alkali earth borohydride Sr(BH4)2 and borohydride-chloride Sr(BH4)Cl

Article abstract of DOI:10.1021/ic400862s

Two novel alkali earth borohydrides, Sr(BH₄)₂ and Sr(BH₄)Cl, have been synthesized and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and Raman spectroscopy. Strontium borohydride, Sr(BH₄)₂, was synthesized via a metathesis reaction between LiBH₄ and SrCl₂ by two complementary methods, i.e., solvent-mediated and mechanochemical synthesis, while Sr(BH₄)Cl was obtained from mechanochemical synthesis, i.e., ball milling. Sr(BH₄)₂ crystallizes in the orthorhombic crystal system, a = 6.97833(9) A, b = 8.39651(11) A, and c = 7.55931(10) A (V = 442.927(10) A³) at RT with space group symmetry Pbcn. The compound crystallizes in α-PbO₂ structure type and is built from half-occupied brucite-like layers of slightly distorted [Sr(BH₄)₆] octahedra stacked in the a-axis direction. Strontium borohydride chloride, Sr(BH₄)Cl, is a stoichiometric, ordered compound, which also crystallizes in the orthorhombic crystal system, a = 10.8873(8) A, b = 4.6035(3) A, and c = 7.4398(6) A (V = 372.91(3) A³) at RT, with space group symmetry Pnma and structure type Sr(OH)₂. Sr(BH₄)Cl dissociates into Sr(BH₄)₂ and SrCl₂ at ～170 C, while Sr(BH₄)₂ is found to decompose in multiple steps between 270 and 465 C with formation of several decomposition products, e.g., SrB ₆. Furthermore, partly characterized new compounds are also reported here, e.g., a solvate of Sr(BH₄)₂ and two Li-Sr-BH ₄ compounds.

Full text of DOI:10.1021/ic400862s

Article
pubs.acs.org/IC
Novel Alkali Earth Borohydride Sr(BH ) and Borohydride-Chloride
4
2
Sr(BH )Cl
4
D. B. Ravnsbæk,* E. A. Nickels, R. Cerny,
́
C. H. Olesen, W. I. F. David, P. P. Edwards,§
,
†,‡
§,∥
#
‡
§,∥
̌
⊥
‡
Y. Filinchuk, and T. R. Jensen
†Department of Material Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge,
Massachusetts 02139, United States
‡
Center for Materials Crystallography (CMC), Interdisciplinary Nanoscience Center (iNANO), and Department of Chemistry,
University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark
§
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR, United Kingdom
∥ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
⊥Institute of Condensed Matter and Nanosciences, Universite
́
Catholique de Louvain, Place L. Pasteur, B-1348, Louvain-la-Neuve,
Belgium
#
Laboratory of Crystallography, Department of Condensed Matter Physics, University of Geneva, 1211 Geneva, Switzerland
S Supporting Information
*
ABSTRACT: Two novel alkali earth borohydrides, Sr(BH4)2
and Sr(BH )Cl, have been synthesized and investigated by in-
4
situ synchrotron radiation powder X-ray diffraction (SR-PXD)
and Raman spectroscopy. Strontium borohydride, Sr(BH ) ,
4
2
was synthesized via a metathesis reaction between LiBH and
4
SrCl by two complementary methods, i.e., solvent-mediated
2
and mechanochemical synthesis, while Sr(BH )Cl was
4
obtained from mechanochemical synthesis, i.e., ball milling.
Sr(BH ) crystallizes in the orthorhombic crystal system, a =
4
2
6
4
.97833(9) Å, b = 8.39651(11) Å, and c = 7.55931(10) Å (V =
42.927(10) Å ) at RT with space group symmetry Pbcn. The
3
compound crystallizes in α-PbO structure type and is built
2
from half-occupied brucite-like layers of slightly distorted
[
Sr(BH ) ] octahedra stacked in the a-axis direction. Strontium borohydride chloride, Sr(BH )Cl, is a stoichiometric, ordered
4
6
4
compound, which also crystallizes in the orthorhombic crystal system, a = 10.8873(8) Å, b = 4.6035(3) Å, and c = 7.4398(6) Å
3
(
V = 372.91(3) Å ) at RT, with space group symmetry Pnma and structure type Sr(OH) . Sr(BH )Cl dissociates into Sr(BH )
2 4 4 2
and SrCl at ∼170 °C, while Sr(BH ) is found to decompose in multiple steps between 270 and 465 °C with formation of
2
4 2
several decomposition products, e.g., SrB . Furthermore, partly characterized new compounds are also reported here, e.g., a
6
solvate of Sr(BH ) and two Li−Sr−BH compounds.
4
2
4
INTRODUCTION
structural diversity within this class of material and bonding in
metal borohydrides that can range from ionic to partly covalent
or exhibit a combination of both, resulting in complex
structures. In bimetallic borohydrides, metal atoms of the
■
Hydrogen is widely recognized as a potential energy carrier in a
future sustainable and reliable energy system. However,
development of safe, compact, robust, and efficient means of
hydrogen storage is a major challenge in the realization of a
more electronegative elements and BH groups tend to form
4
−
1
,2
partly covalent complex anions, such as [Zn (BH ) ] and
2
4 5
future hydrogen-based energy system. Borohydride-based
materials have received much attention during the past decade
as potential hydrogen storage materials due to their high
−
[
(
Sc(BH ) ] in MZn (BH ) (M = Li or Na) and MSc(BH )
4 4 2 4 5 4 4
1
3−18
M = Li, Na or K), respectively.
Furthermore, the monometallic alkali earth metal borohy-
drides, Mg(BH ) and Ca(BH ) , have been widely investigated
3
,4
hydrogen densities, e.g., gravimetric density, ρ = 18.5 wt %
m
5
4
2
4 2
H , and volumetric density, ρ = 121 g H /L for LiBH , and
tunable decomposition temperatures, e.g., T = 585 and 80
2
V
2
4
6
,7
due to their high hydrogen contents (14.9 and 11.6 wt %,
dec
3
,6
respectively) and rich crystal polymorphism, i.e., four
°
C for KBH and KCd(BH ) , respectively.
4 4 3
4,19−22
polymorphs are known for both compounds.
Recently,
Recently, a wide range of novel borohydrides have been
prepared combining different metals, filling the gap between the
thermally stable alkali and the unstable transition metal
Received: April 8, 2013
Published: September 19, 2013
4
,8−12
borohydrides.
These studies have revealed an interesting
©
2013 American Chemical Society
10877
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
Table 1. Reaction Products Observed by SR-PXD Measured at RT for Sample Prepared by Solvent-Mediated (SM) Synthesis
(Sample A) and Mechanochemical Synthesis, i.e., Ball Milling (BM) (samples B−E)
SM, sample A
starting composition LiBH :NaBH :SrCl
2
3:1.5:1
4
4
a
reaction products
Sr(BH ) , 1, LiCl
4 2
BM
sample B
1:1
sample C
2:1
sample D
3:1
sample E
4:1
starting composition
LiBH :SrCl2
4
b
b
reaction products
Sr(BH )Cl, Sr(BH ) , LiCl,
Sr(BH ) , 2 (P2/m), 3 (P2 /m), LiCl, Sr(BH ) , 3 (P2 /m), LiCl,
3 (P2 /m), LiCl,
4
4
2
4
2
1
4
2
1
1
SrCl2
SrCl2
SrCl2
SrCl2
a
b
Orthorhombic unit cell (see text). Observed in small amounts.
two novel magnesium borohydride polymorphs were discov-
radiation powder X-ray diffraction (SR-PXD) data were collected at
the beamline ID31, the European Synchrotron Radiation Facility
20,21
ered, γ- and δ-Mg(BH ) .
The former, γ-Mg(BH4)2,
4
2
(ESRF) in Grenoble, France, using a wavelength and step size of
represents a novel nanoporous zeolite-type framework
structure, which has the capability to absorb small gas
molecules, while the dense δ-Mg(BH ) polymorph has the
0
.799888 Å and 0.003°, respectively. The sample was mounted in a
sealed glass capillary with an outer diameter (o.d.) of 1 mm. A variable-
temperature experiment was carried out collecting data at 25 °C
intervals from 25 to 375 °C heating with a hot air blower. To avoid
radiation damage during the variable-temperature experiment, the
capillary containing the sample was moved 2 mm along its axis
between each scan so that each data set was collected from a heated
but not previously exposed part of the sample. Diffraction patterns
between 200 and 375 °C were collected in a second experiment using
a new sample.
4
2
second highest volumetric hydrogen density ρ = 147 g H /L
V
2
among all known hydrides (slightly lower than ρ (Mg FeH ) =
V
2
6
1
50 g H /L), which is more than twice that of liquid hydrogen,
2
ρ (H ) = 71 g/L.
V
2
Hence, the synthesis and characterization of strontium
borohydride is of wide interest. Here we report on the
synthesis, characterization, and thermal decomposition of two
For samples B−E SR-PXD data were collected at the Swiss-
Norwegian Beamlines (SNBL), ESRF. Data were collected using a
MAR345 image plate detector and radiation with selected wavelengths
of 0.700130 and 0.832117 Å. Samples were mounted in glass
capillaries (o.d. 0.5 mm) sealed with glue. The capillary was oscillated
by 60° during exposure to the X-ray beam for 60 s, followed by
readout for ∼83 s. During the variable-temperature experiments
samples were heated from RT to 223 or 500 °C at selected heating
rates ranging from 1 to 4 °C/min. Temperature was controlled with an
Oxford Cryostream 700+ or a hot air blower. Notice that data sets
measured using a selected wavelength below λ = 0.7699 Å
unfortunately suffer from high background due to the excitation of
Kα Sr absorption edge.
novel alkali earth borohydrides Sr(BH4)2 and Sr(BH )Cl,
4
synthesized by two complementary methods, i.e., solvent-
mediated and mechanochemical synthesis. The novel com-
pounds are studied by in-situ synchrotron radiation powder X-
ray diffraction (SR-PXD) and Raman spectroscopy.
EXPERIMENTAL SECTION
■
Synthesis. Two synthesis methods were employed aiming at
preparing Sr(BH ) , i.e., solvent-mediated synthesis and mechano-
4
2
2
3,24
chemical synthesis.
Sample A (prepared at University of Oxford) was prepared
25
according to the method used by Mikheeva et al. Within an
Furthermore, a SR-PXD data set has been collected for sample C at
the beamline I711 of the synchrotron MAX II, Lund, Sweden, in the
research laboratory MAX-Lab. Data were collected using a MAR165
CCD detector system and selected wavelength of 1.0970 Å. The CCD
camera exposure time was 30 s. The sample cell was specially
developed for studies of gas/solid reactions and allows high pressure
argon-filled glovebox (O < 20 ppm) 2.75 g of strontium chloride,
2
SrCl (99.99%, Sigma Aldrich), 1 g of sodium borohydride, NaBH
2
4
(
(
1
98%, Sigma Aldrich), and 1.15 g of lithium borohydride, LiBH4
>95.0%, Sigma Aldrich), were loaded into a Schlenk flask (see Table
). The flask was sealed, removed from the glovebox, and attached to a
nitrogen Schlenk line. Anhydrous tetrahydrofuran (THF) was added
to the flask, and the solution was stirred at room temperature (RT)
under nitrogen for 2 days. The solution was filtered, and the filtrate
was concentrated by evaporation under reduced pressure. Diethyl
2
6
and temperature to be applied. Powdered samples were mounted in
a sapphire single-crystal tube (o.d. 1.09 mm, i.d. 0.79 mm) in an argon-
filled glovebox (p(O , H O) < 1 ppm). The sample holder was sealed
2
2
inside the glovebox. Temperature was controlled with a thermocouple
placed in the sapphire tube ∼1 mm from the sample. Samples were
typically heated from RT to 500 °C with a selected heating rate of 5
ether (Et O) was added to the filtrate, causing a white precipitate to
2
form. The precipitate was filtered and dried under dynamic vacuum,
initially at RT via the Schlenk line before being transferred to a vertical
tube furnace and heated to 70 °C for 1 h and 100 °C for a further 30
min.
°
C/min.
All obtained raw images were transformed to 2D powder diffraction
2
7
patterns using the FIT2D program, which was also used to remove
diffraction spots from the single-crystal sapphire tube used as sample
holder.
For samples B−E (prepared at Aarhus University) anhydrous SrCl2
(
≥99.99%, Sigma Aldrich) and LiBH (≥95.0%, Sigma Aldrich) were
4
combined in molar ratios of LiBH :SrCl of 1:1, 2:1, 3:1, and 4:1 (see
4
2
Structure Solution and Refinement. The structure of Sr(BH4)
2
Table 1) and ball milled in a Fritch Pulverisette No. 4 using 80 mL of
tungsten carbide steel containers and an approximate 1:35 weight ratio
of sample to 10 mm tungsten carbide steel balls. All samples were ball
milled using the same procedure, i.e., high-energy ball milling under
inert conditions (argon atmosphere) comprised of 60 times 2 min of
milling each intervened by 2 min breaks to avoid heating of the
sample. Preparation and manipulation of all samples were performed
in an argon-filled glovebox with a circulation purifier (p(O , H O) < 1
was solved simultaneously and independently from SR-PXD data
measured for the sample prepared by solvent-mediated synthesis
(sample A) and those prepared by mechanochemical synthesis
(samples B−E) yielding the same solution.
The structure of Sr(BH ) was solved from the HR SR-PXD data
4 2
measured at 175 °C for sample A, in which only diffraction from
Sr(BH (98 wt %) and a small amount of LiCl (2 wt %) is observed.
Peaks were indexed to the orthorhombic Pbna space group using the
)
4 2
2
2
ppm).
2
8
29
In-Situ Time-Resolved Synchrotron Powder Diffraction. For
sample A high-resolution (HR) in-situ time-resolved synchrotron
program DASH. Subsequent analysis using TOPAS confirmed this
solution. However, manual comparison of the observed reflections to
1
0878
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
the reflection conditions of the more favorable space groups identified
by TOPAS analysis (Pbna, Pbcn, Pbca, and Pnma) indicated that the
space group Pbcn could be more favorable. A comparison of the
structure has been checked with the routine ADDSYM in the program
PLATON, and the space group Pbcn was confirmed. The structure
3
9
was solved with the BH group as a rigid ideal tetrahedron with one
4
3
indexed cell volume (V ≈ 456 Å ) with volume per formula unit of α-
common B−H distance of 1.13 Å. The orientation of the BH group
4
3
30,31
and β-Mg(BH ) (V/Z = 114.5(3) and 117.9(5) Å )
as well as α-
was not refined; however, it was optimized in FOX by two antibump
distance restraints (Sr−H = 2.5 Å and H−H = 2.5 Å) to minimize the
4
2
3
32,33
and β-Ca(BH4)2 (V/Z = 108.269(1) and 105.3497(1) Å )
suggested Z = 4 for Sr(BH ) . Using TOPAS, atoms were placed on
repulsive H−H interactions, and only the position of BH was refined
4
2
4
the special crystallographic positions with multiplicity of four
in the Rietveld refinement. B and H positions refined to 0.81(3)
occupancy, completed by 0.19(3) chlorine occupancy on the B site.
Two displacement parameters (one for Sr and the other for the BH4
group) have been refined isotropically. The impurities LiCl and SrCl2
have been refined with their lattice parameters and isotropic
displacement parameters. The profile function has been modeled for
each phase by an independent pseudo-Voigt function. Agreement
factors are Rwp (not corrected for background) = 0.558%, Rwp
3
4
according to the International Tables for Crystallography. The 4c
site (0, y, 0.25) refined to a single occupancy of a strontium atom. The
4a (0, 0, 0) and 4b (0, 0.5, 0) sites refined to zero occupancy. A boron
atom was subsequently inserted into the unit cell at random
coordinates with the site occupancy fixed to unity. The position of
the boron atom was refined in order to find a reasonable position
resulting in the best fit to the data. Hydrogen atoms were added using
tetrahedral rigid bodies centered on the boron atoms and fixed B−H
distances of 1.12 Å. The resulting structure contains one Sr atom
(corrected for background) = 5.47%, R
χ = 876. Crystallographic information and atomic coordinates can be
(Sr(BH ) ) = 2.57%, and
Bragg
4 2
2
(
position 4c) and one BH4 group (general position 8d) in the
found in Table S2, Supporting Information.
asymmetric unit. BH4 tetrahedra were allowed to rotate freely;
however, accurate hydrogen positions could not be determined. Final
refinement was performed using the Rietveld method in the program
SR-PXD data measured at RT for the ball-milled sample of LiBH −
4
SrCl in a molar ratio of 1:1 (sample B) was used for structure solution
2
of the novel ordered borohydride/chloride Sr(BH )Cl. The structure
solution procedure was similar to that for Sr(BH ) using 19 peaks for
4
35
GSAS. Incorporation of 9.8 mol % Cl on the BH site is detected.
4
4 2
This was modeled by introducing a Cl atom on the position of B and
constraining the sum of their occupancies to 1. Refined unit cell
parameters for Sr(BH4)2 (space group Pbcn) at 175 °C are a =
indexing, giving an orthorhombic lattice with unit cell parameters from
the final Rietveld refinement a = 10.8873(5) Å, b = 4.6036(2) Å, and c
3
= 7.4407(4) Å (V = 372.91(3) Å ). The systematic absences suggested
7
.02444(8) Å, b = 8.50969(10) Å, and c = 7.62214(9) Å (V =
space group Pnma or its noncentrosymetric subgroup Pn2 a. The
1
3
2
4
55.620(9) Å , Z = 4). Agreement factors are χ = 1.28, R = 7.71%,
structure was solved in the first of these two possible space groups.
The resulting structure contains one Sr atom (position 4c), one BH4
group (position 4c), and one chlorine atom (position 4c) in the
asymmetric unit. B and H positions refined to 0.932(7) occupancy,
completed by 0.068(7) chlorine occupancy on the B site. As an
impurity also Sr(BH ) phase (5.6(3) wt%) was observed and refined
exp
Rwp = 9.89%, and R = 8.28% (see Figure 1). Complete crystallo-
p
4
2
with the structural model fixed to that from sample C. Agreement
factors are Rwp (not corrected for background) = 0.38%, R
wp
2
(corrected for background) = 4.39%, χ = 373, and R
(Sr(BH )Cl)
Bragg 4
=
9.95%. Crystallographic information is shown in Table 2, while
atomic coordinates can be found in Table S3, Supporting Information.
The high values of χ (for samples B and C) reflect mainly the
2
extremely high counting statistics of the powder diffraction data
obtained from modern 2D detectors.
Raman Spectroscopy. Room-temperature Raman spectra were
recorded on a Jobin Yvon Dilor Labram 300 confocal spectrometer,
fitted with an Olympus microscope using the 10-fold magnification
objective. A 20 mW He−Ne laser (633 nm) was used. The
spectrometer is fitted with an 1800 L/mm (lines per mm) grating
−
1
−1
which gives a resolution ranging from 1.0 cm at 200 cm to 0.5
−
1
−1
cm at 3600 cm . The spectrometer was calibrated with a silicon
−1
Figure 1. Rietveld plot for sample prepared by solvent-mediated
standard, and the sharp Raman shifts are accurate to ±2 cm . Samples
were contained inside melting point tubes which were loaded within
an argon-filled glovebox and temporarily sealed with vacuum grease
before being removed from the glovebox and flame sealed.
synthesis (sample A) containing Sr(BH ) (upper blue marks) and
4
2
small amounts of LiCl (lower blue marks). Data are measured at 175
C (λ = 0.799888 Å): observed data (Yobs, red curve), Rietveld
°
refinement profile (Ycalc, black curve), and difference plot (Yobs − Ycalcd
blue curve).
,
RESULTS AND DISCUSSION
■
Synthesis and Initial Phase Analysis. SR-PXD data for
the sample prepared by solvent-mediated synthesis (sample A)
show two sets of Bragg peaks, one of which is assigned to
Sr(BH ) , while the other originates from an unidentified
graphic information is shown in Table 2, while atomic coordinates can
be found in Table S1, Supporting Information. Subsequently, unit cell
parameters were refined from data measured for sample A at RT: a =
4
2
6
4
.97833(9) Å, b = 8.39651(11) Å, and c = 7.55931(10) Å (V =
42.927(10) Å ). Due to the presence of an unknown compound
3
compound, denoted 1 (see Figure 2 and Table 1).
Furthermore, a small amount of LiCl is observed. This
indicates that the following reactions occur during synthesis
(eqs 1 and 2).
(denoted 1), atomic positions in Sr(BH ) were not refined at RT.
4 2
Simultaneously, the structure of Sr(BH ) was solved from SR-PXD
4
2
data measured for the ball-milled sample of LiBH −SrCl in a molar
4
2
ratio of 2:1 (sample C) at 227 °C. The 17 observed peaks assigned to
36
Sr(BH ) were indexed with DICVOL04 in an orthorhombic lattice
2MBH (THF) + SrCl (THF) → Sr(BH ) (THF)
4
2
4
2
4 2
with unit cell parameters (values from final Rietveld refinement of the
data measured at 230 °C) a = 6.9415(11) Å, b = 8.3770(14) Å, and c =
7
group Pbcn, and the structure was solved with the direct space method
program FOX and subsequently refined with the Rietveld method
using the FULLPROF program. The symmetry of the refined
+
2MCl(s)
3
.5532(11) Å (V = 439.21(12) Å ). Systematic absences led to space
(
(
1)
2)
M = Li or Na
37
Et2O
38
Sr(BH ) (THF) ⎯⎯⎯ →⎯ Sr(BH ) (s)
4 2
4 2
1
0879
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
Table 2. Structural Data Extracted by Rietveld Refinement of SR-PXD Data Measured at RT along with the Hydrogen Content
for Sr(BH ) (Sample A) and Sr(BH )Cl (Sample B)
4
2
4
Sr(BH4)2
Sr(BH )Cl
4
space group
structure type
a (Å)
Pbcn
Pnma
α-PbO2
Sr(OH)2
6.97833(9)
8.39651(11)
7.55931(10)
10.8873(5)
4.6036(2)
7.4407(4)
2.705(2)−3.109(4)
2.965(3)−3.092(8)
115.233(2)−116.630(1)
110.403(2)
4
b (Å)
c (Å)
Sr−B (Å)
Sr−Cl (Å)
B−Sr−B (deg)
Sr−B−Sr (deg)
Z
2.96(3)−3.12(3)
83.7(7)−97.3(7) 169.2(7)−173.9(7)
96.3(7)−129.9(9)
4
3
V/Z (Å )
110.73(10)
1.80
93.225(7)
2.45
ρ (g cm−3)
ρ (H ) (kg H m−3)
123.1
6.85
71.8
v
2
2
ρm (H ) (wt %)
2.92
2
from two novel strontium borohydrides, Sr(BH4)2 and
Sr(BH )Cl, as well as LiCl and unreacted SrCl (see Table 1
4
2
and Figure 2). The weight fractions extracted from Rietveld
refinement reveal that the sample consists of 27.2(6) mol %
Sr(BH )Cl (40.2(9) wt%), while only 4.5(2) mol % Sr(BH )
4
4 2
(
5.7(3) wt%) is observed. This suggests that the dominant
reaction occurring for this sample composition during
mechanochemical synthesis can be described according to
reaction eq 3.
LiBH (s) + SrCl (s) → Sr(BH )Cl(s) + LiCl(s)
(3)
4
2
4
Furthermore, observation of a small amount of Sr(BH4)2
indicates that the reaction shown in eq 4 occurs as a minor side
reaction.
2
LiBH (s) + SrCl (s) → Sr(BH ) (s) + 2LiCl(s)
(4)
4
2
4 2
Comparing the stoichiometry of reaction eq 4
2LiBH :SrCl ) to the sample composition (LiBH :SrCl )
(
4
2
4
2
also explains why no LiBH is observed, while some unreacted
Figure 2. SR-PXD data measured at RT for (a) sample prepared by
solvent-mediated synthesis (sample A, λ = 0.799888 Å) and ball-milled
samples of LiBH −SrCl in molar composition (b) 1:1 (sample B, λ =
4
SrCl (18.5(4) mol %, 31.5(6) wt%) remains in the sample
2
after ball milling.
4
2
0
.700130 Å), (c) 2:1 (sample C, λ = 0.832117 Å), (d) 3:1 (sample D,
As the content of LiBH in the starting composition is
4
λ = 0.796201 Å), and (e) 4:1 (sample E, λ = 0.796201 Å). Symbols:
increased to LiBH :SrCl = 2:1 (sample C), mechanochemical
4
2
(
◊) Sr(BH )Cl (⧫) Sr(BH ) , (○) LiCl, (*) SrCl , while 1, 2, and 3
4
4
2
2
synthesis yields higher amounts of Sr(BH ) , LiCl and two
4 2
correspond to the unknown compounds described in the text.
unidentified compounds, denoted 2 and 3 (see Figure 1).
Hence, reaction eq 4 is occurring to a high extent. The
unidentified compounds, 2 and 3, have both been indexed in
monoclinic unit cells, i.e., a = 10.015(2) Å, b = 5.811(2) Å, c =
8.666(3) Å, and β = 93.90(2)° for 2 and a = 10.726(4) Å, b =
6.832(3) Å, c = 7.251(3) Å, and β = 101.24(3)° for 3. Le Bail
Even though both LiBH and NaBH were used as starting
4
4
materials for the solvent-mediated synthesis no NaCl was
observed by SR-PXD. This suggests either that NaBH did not
4
participate in reaction eq 1 to a significant extent or that NaCl
formed in the metathesis reaction did not precipitate during
addition of diethyl ether.
fitting suggests space groups P2/m and P2 /m for 2 and 3,
1
respectively. Increasing the content of LiBH in the starting
4
The unidentified compound, 1, might be a strontium
borohydride solvate, i.e., Sr(BH ) ·nEt O or Sr(BH ) ·nTHF,
composition further, i.e., LiBH :SrCl ≥ 3:1 (samples D and E),
4
2
results in a significant decrease in the yield of Sr(BH ) and 2,
4
2
2
4 2
4 2
remaining after removing the solvent. The unit cell of 1 has
and for the sample of LiBH −SrCl in a molar ratio of 4:1
4
2
been indexed as orthorhombic with a = 21.0792(6) Å, b =
(sample E) these compounds are not formed and only
3
6
.8986(2 Å), c = 4.51839(11) Å, and V = 657.04(3) Å . Bremer
diffraction from 3, LiCl, and unreacted SrCl is observed (see
2
et al. reported unit cell parameters for Sr(BH ) ·2THF of a =
Table 1 and Figure 2). The fact that unreacted SrCl is present
4
2
2
40
4
.405(1) Å, b = 7.997(2) Å, and c = 18.826(5) Å, suggesting
in all samples, while no diffraction from LiBH is observed even
4
that 1 may be Sr(BH ) ·nEt O. However, it has not been
possible to solve the structure of 1 from the data obtained in
this study.
in the samples of highest LiBH :SrCl ratio, might suggest that
4
2
2
4
2
LiBH is consumed to a higher extent than by the metathesis
4
shown in eq 4. Hence, formation of 2 and 3 possibly consumes
For the ball-milled sample of LiBH −SrCl in a molar ratio of
LiBH . The decreasing yield of Sr(BH ) upon increasing
4
2
4
4 2
1
:1 (sample B), SR-PXD data measured at RT show diffraction
LiBH content in the starting composition might indicate that 2
4
1
0880
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
and 3 are lithium strontium borohydrides, i.e., Li Sr(BH )
83.7(7)−97.3(7)°. The Sr−B−Sr angles within the nonplanar
x
4 2+x
formed by an addition reaction between Sr(BH ) and xLiBH .
[BSr ] triangle range from 96.3(7)° to 129.9(9)°, and the
4
2
4
3
Furthermore, sample compositions after milling suggest that x
in Li Sr(BH ) is higher for 3 than for 2, since 3 is formed in
distance of the B atom from the Sr plane is 0.36(3) Å.
Hydrogen positions determined from antibump restraints in
FOX suggest mixed bi- and tridentate coordination of the BH4
x
4 2+x
higher yields in samples of higher LiBH :SrCl molar ratios.
4
2
Some chloride substitution in Sr(BH ) is found to occur
units to Sr, i.e., four BH units coordinating via the tetrahedral
4
2
4
from both synthesis methods, i.e., a solid solution Sr-
BH4)2−xCl is formed. This effect is most pronounced in the
edge and two via the tetrahedral face. Thus, Sr seems to
coordinate to 14 hydrogen atoms.
(
x
ball-milled samples, where Rietveld refinements suggest
substitution degrees ranging from 16 to 31 mol %. The
substitution degree, x, decreases with decreasing amounts of
SrCl in the reaction mixture, i.e., LiBH :SrCl = 1:1 (sample
The novel strontium borohydride chloride, Sr(BH )Cl,
crystallizes in an orthorhombic unit cell with space group
symmetry Pnma (see Table 2). The structural drawing of the
4
2
4
2
Sr(BH )Cl viewed approximately along the b axis is shown in
4
B) exhibits the highest Cl substitution in Sr(BH4)2−xCl . For
Figure 4a. The chloride/borohydride Sr(BH )Cl is a stoichio-
x
4
42
the sample prepared by solvent-mediated synthesis only 9.8
mol % Cl substitution is observed.
metric, ordered compound with structure type Sr(OH)2. The
same structure type was reported for HT-SrBr and metastable
2
Crystal Structures of Sr(BH ) and Sr(BH )Cl. Strontium
SrI ; however, it was later discovered that both compounds
4
2
4
2
borohydride, Sr(BH ) , crystallizes in an orthorhombic unit cell
were hydrated, i.e., SrX ·H O, X = Br and I. The fact that the
4
2
2
2
with space group symmetry Pbcn (see Table 2). The structural
structure of SrCl is not preserved is likely due to incorporation
2
of the BH4− anions, which is significantly larger than Cl ,
−
drawing of the strontium borohydride Sr(BH ) is shown in
4
2
Figure 3. The basic building unit for the structure of Sr(BH4)2
facilitating an expansion of the structure likely to cause
structural rearrangement. The Sr(BH )Cl structure is built
4
from (011) layers of edge-sharing slightly distorted [Sr-
(
BH ) Cl ] monocapped trigonal prisms stacked in the a-axis
4 3 4
direction (Figure 4b). Each prism shares eight edges and one
vertex with nine other polyhedra in total. The BH units keep
4
the coordination by three Sr in a nonplanar triangle also found
in Sr(BH ) . Cl atoms coordinate to four Sr atoms in a
4
2
distorted tetrahedral fashion similar to the coordination in
43
cubic strontium chloride. The Sr−Cl distances ranging from
2
.95(1) to 3.03(1) Å are also similar to those in SrCl of 3.019
2
Å. Sr−B distances are within 2.92(1)−2.93(1) Å, which is
similar to those found in Sr(BH ) . Sr−Cl−Sr angles cover a
4
2
relatively wide range from 99.06(1)° to 136.9(1)°, while the
Sr−B−Sr angles are within 103.97(1)−109.74(1)°. The
distance of the B atom from the Sr plane in the [BSr ] trigonal
3
coordination is 1.051(3) Å.
Table 3 lists the coordination numbers of Sr (CN(Sr))
4
3−49
within the series of strontium halides
as well as the anionic
50,51
radii of the halides and the BH ¯ anion.
Anionic radii
4
−
−
−
−
−
increase as r(F ) < r(Cl ) < r(Br ) < r(BH ) < r(I ). By
4
comparing these values it becomes clear that CN(Sr) within the
strontium borohydrides is not only determined by the anionic
Figure 3. Crystal structures of Sr(BH ) (structure type α-PbO ).
size, as that would imply a coordination between those in SrI2
4
2
2
Blue: Sr and red polyhedra, BH units. For clarity, Sr−B coordinations
and SrBr , i.e., between 7 and 8. The lower CN(Sr) of 6 in
2
4
are shown while Sr−H bonds are omitted. Basic building unit in
Sr(BH ) reflects that the H−H repulsive forces between
4
2
−
Sr(BH ) is half-occupied brucite-like layer (011) of SrB octahedra
neighboring BH4 anions play a significant role for the
4
2
6
(
blue) stacked in the a-axis direction. Second layer is shown in light
structural topology. For Sr(BH )Cl the coordination number
4
blue.
of strontium is 7, which indicates that the presence of Cl in the
coordination sphere somewhat reduces the H−H repulsive
forces.
−
is the borohydride anion BH , which is a regular tetrahedron.
4
Strontium borohydride Sr(BH ) crystallizes in structure type
Raman Spectroscopy. Raman spectra of Sr(BH )
4 2
4
2
4
1
α-PbO2. The structure is built from half-occupied brucite-like
(sample A) are shown in Figure 5. For comparison, the
layers of slightly distorted [Sr(BH ) ] octahedra stacked in the
Raman spectra of α-Ca(BH ) is also shown. The B atom in the
4
6
4 2
a-axis direction (Figure 3). The octahedra share two edges and
structure of Sr(BH ) is located on a general position (8d) with
4
2
all vertices with eight other octahedra in total. BH units are
coordinated by three Sr in a nonplanar triangle.
There are three different strontium−boron distances, each
appearing twice within an octahedron either adjacent or
opposite to each other; these are 2.96(3) (adjacent),
site symmetry 1. Thus, there are no symmetry elements apart
from the identity associated with the local symmetry of the
BH4 anion. Consequently, the BH4− anion has point group C1
and all of the 3N − 6 = 9 vibrational modes would be expected
to have A-type symmetry.
4
−
3
.058(6) (opposite), and 3.12(3) Å (adjacent). These
The strongest Raman signal for Sr(BH ) , observed around
4
2
−1
strontium−boron distances are consistent with the distance of
2300 cm , is assigned to symmetric B−H stretching mode, υ .
1
40
2
.960 Å reported by Bremer et al. in Sr(BH ) ·2THF. There
The other strong signal in the B−H stretching region is
4
2
are 3 B−Sr−B angles within 169.2(7)−173.9(7)° and 12 within
assigned to the asymmetric B−H stretching, υ observed at
3
1
0881
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
Figure 4. Crystal structure of Sr(BH )Cl (a) shown along the b axis: blue, Sr; green, Cl; red polyhedra, BH units. Basic building unit is (011) layer
4
4
of an edge-sharing Sr(BH ) (Cl) monocapped trigonal prism (light) stacked in the a-axis direction. Structures of Sr(OH) (b) and SrBr ·H O (c)
4
3
4
2
2
2
are shown for comparison.
Table 3. Anionic Radius of the Halides and the BH4− Anion50,51 (top) and Comparison of Structure Types, Space Groups,
43−49
Strontium Coordination Number (CN(Sr)), and Geometry for a Series of Strontium Halides
and Sr(BH ) and
4 2
a
Sr(BH )Cl
4
anion
F−
Cl−
Br−
BH4−
2.05
I−
radius (Å)
1.33
1.81
1.96
2.20
b
compound
structure type
space group
CN(Sr)
Sr coordination
ref
Sr(BH4)2
α-PbO2
Sr(OH)2
CaF2
Pbcn
6
7
8
8
7
9
9
octahedron
This work
This work
43 44
45
Sr(BH )Cl
Pnma
Fm-3m
P4/n
Pbca
monocapped trigonal prism [Sr(BH ) Cl ]
4 3 4
4
SrF SrCl2
cube
2
SrBr2
SrI2
SrBr2
square antiprism
SrI2
monocapped trigonal prism
tricapped trigonal prism
46
high pressure/temperature SrI2
PbCl2
Pnma
Pnma
47
SrBr ·H O, SrI ·H O
BaCl ·H O
tricapped trigonal prism [SrX (H O) ], X = Br or I
48, 49
2
2
2
2
2
2
7
2
2
a
Note the low CN(Sr) of 6 in Sr(BH ) , which reflects that not only the anionic radius but to a high extent also the H−H repulsive forces are
4
2
b
important for coordination in Sr(BH ) and Sr(BH )Cl. In the coordination number (CN) a Sr−BH coordination counts as 1.
4
2
4
4
suggest that the symmetric B−H bond bending vibrations, υ ,
2
−
1
are around 1280 cm , and the asymmetric B−H bond bending
−1
vibrations, υ , are around 1090 cm .
4
The fact that no significant splitting is observed for the
stretching mode confirms the framework topology of the
Sr(BH4)2 structure containing only bridging BH . Similar
4
observations have been reported for other framework structures
3
0,54,55
such as α-Mg(BH4)2 and Mn(BH ) .
In contrast,
4
2
structures containing isolated anions or polymeric units exhibit
several modes within the stretching region due to the presence
of terminal BH units, e.g., for LiZn (BH ) stretching modes
4
2
4 5
for both the bridging and terminal B−H units within the
−
complex anion [Zn (BH ) ] are observed, giving rise to four
2
4 5
−1
18,56
modes between 2100 and 2458 cm .
Furthermore,
observation of the relatively strong bending mode at 1280
−
1
57,58
cm confirms the presence of tridentate BH −Sr bonding.
Figure 5. Raman spectra measured at RT for Sr(BH ) prepared by
3
4
2
solvent-mediated synthesis (black, sample A) and α-Ca(BH ) (red).
This band is comparable to the bands observed around 1200
4
2
−1
cm for MSc(BH ) (M = Li, Na, or K) and NaY(BH ) Cl in
4
4
4 2
2
3
13,15,16,59
−1
which the BH units also act as η -ligands.
2
280 cm . In other borohydrides, υ vibrations have been
4
3
No peaks are observed corresponding to either THF or
diethyl ether, which is likely present in compound 1 in sample
A. This may be due to the small amount of 1 in the sample
observed on either or both sides of υ ; hence, the presence of υ3
1
on the opposite side of υ compared to Ca(BH ) is not
1
4 2
particularly significant. Comparison with the Raman spectrum
5
2
53
of Ca(BH4)2 and the alkali metal borohydrides would
compared to Sr(BH ) and LiCl.
4 2
1
0882
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
Decomposition Analysis by in-Situ SR-PXD. Thermal
indicates that these might be borohydrides, since chloride salts
are expected to be significantly more stable. Furthermore,
decomposition of Sr(BH )Cl was investigated by in-situ SR-
4
PXD for the ball-milled sample of LiBH −SrCl in a molar ratio
formation of Sr(BH ) from decomposition of 3 suggests that
4
2
4 2
of 1:1 (sample B), shown in Figure 6. From RT to ∼170 °C
this is entailed in the structure of 3, i.e., it might be a
Li Sr(BH ) . After decomposition of Sr(BH ) diffraction,
x
4 2+x
4 2
most likely from several compounds, is observed. The
diffraction shows significant “spotty” character, likely due to
the fact that these compounds form from a melt, causing
formation of small single crystals rather than a powder. This
complicates data analysis, and these compounds have not been
identified. As the temperature reaches ∼410 °C slow formation
of SrB is initiated as well as formation of an unknown
6
decomposition product, which has been indexed in an
orthorhombic cell (a = 7.1156 Å, b = 6.8124 Å, and c =
5
.3032 Å). Formation of SrB might suggest formation of SrH
6
2
(
<
e.g., 3Sr(BH ) → SrB + 2SrH + 10 H ), which is stable at T
4
2
6
2
2
60
675 °C. However, diffraction from SrH has not been
2
observed in any of the conducted experiments. From these
observations it is evident that decomposition of Sr(BH ) is
4
2
relatively complex and cannot be deduced in detail from the
present data. Furthermore, higher boranes, e.g., SrB H , might
1
2
12
form as decomposition intermediates, as suggested for other
6
1,62
borohydrides including Ca(BH4)2 and LiBH4.
The
63
existence of SrB H ·7H O has been previously reported.
The high stability of SrB may hamper reversible hydrogen
12
12
2
6
Figure 6. In-situ SR-PXD data for a sample containing Sr(BH )Cl
4
storage in Sr(BH4)2.
(
1
LiBH −SrCl , 1:1, sample B) measured from RT to 230 °C, ΔT/Δt =
4
2
°C/min (BM01A, ESRF, λ = 0.832117 Å): (◊) Sr(BH )Cl, (○)
4
⧫
) Sr(BH ) .
CONCLUSIONS
LiCl, (*) SrCl , (
2
4
2
■
The synthesis, crystal structure, and thermal decomposition
have been investigated for two novel metal borohydrides,
Sr(BH ) and Sr(BH )Cl. The former was obtained from a
diffraction from Sr(BH )Cl, SrCl , and LiCl is observed. At
4
2
∼
170 °C all diffraction from Sr(BH )Cl vanishes simulta-
4
4 2
4
neously with formation of Sr(BH ) and SrCl . Hence, Sr(BH )
metathesis reaction between MBH (M = Li or Na) and SrCl
by solvent-mediated as well as mechanochemical synthesis, i.e.,
4
2
2
4
4
2
Cl dissociates according to the reaction shown in eq 5.
ball milling, while Sr(BH )Cl was only obtained by ball milling
4
Sr(BH )Cl(s) → Sr(BH ) (s) + SrCl (s)
(5)
4
4 2
2
LiBH −SrCl in a molar ratio of 1:1. The latter compound
4
2
For the remainder of the experiment, i.e., in the temperature
range from 170 to 230 °C, no significant changes in the
diffraction from Sr(BH ) and SrCl are observed.
forms from an addition reaction between Sr(BH ) and SrCl .
4 2 2
Furthermore, three additional compounds were discovered: 1 is
most likely a strontium borohydride solvate, while 2 and 3 may
4
2
2
Thermal decomposition of Sr(BH ) is investigated by in-situ
be Li
Sr(BH
[Sr(BH
layers along the a axis. The Sr(BH
(011) layers of edge-sharing slightly distorted [Sr(BH
x 4 2+x
Sr(BH ) .
4
2
SR-PXD for samples A, C, and D. These data also provide some
insight into the behavior of the unknown compounds observed
after solvent-mediated synthesis (1) and ball milling (2 and 3).
For the sample prepared by solvent-mediated synthesis (sample
A) diffraction from Sr(BH ) and 1 is observed from RT to 100
4
)
)
2
consists of a framework of slightly distorted
] octahedra stacked in half-occupied brucite-like
)Cl framework is built from
Cl ]
4
4 6
4
)
4
3
monocapped trigonal prisms stacked along the a axis.
Comparison of these novel borohydride structures to a series
of strontium halides reveals the large effect of H−H repulsive
forces on the strontium coordination numbers.
4
2
°
C, where 1 vanishes simultaneously with an increase in the
diffracted intensity from Sr(BH ) . Hence, it underlines that 1
4
2
might be a strontium borohydride solvate, i.e., Sr(BH ) ·nEt O
4
2
2
or Sr(BH ) ·nTHF. From 100 to 350 °C only diffraction from
Investigation of the thermal decomposition by in-situ SR-
4
2
Sr(BH ) and a small amount of LiCl is observed. Between 200
PXD showed that Sr(BH
at ∼170 °C, while Sr(BH
formation of multiple decomposition intermediates and SrB
the final decomposition product. The fact that SrB
4
)Cl dissociates to Sr(BH
4
)
2
and SrCl
2
4
2
and 300 °C, Sr(BH ) seems to be annealed and the Bragg
4
)
2
decomposes at ∼350 °C with
4
2
peaks become sharper. At 350 °C diffraction from Sr(BH4)2
disappears and a new set of broad peaks is observed. This set of
Bragg peaks was indexed in an orthorhombic unit cell with a =
6
as
was
6
observed among the final decomposition products may suggest
that boron is kept in the solid state during hydrogen release
1
1
8.4808(9) Å, b = 5.7526(2) Å, c = 14.3600(6) Å, and V =
3
526.65(11) Å .
from Sr(BH ) , which is a prerequisite for safe, reversible
4 2
For the ball-milled sample of LiBH −SrCl in a molar ratio of
hydrogen storage.
4
2
3
:1 (sample D), diffraction from 3, SrCl , LiCl, and a small
2
ASSOCIATED CONTENT
Supporting Information
Figure of in-situ SR-PXD data of a ball-milled sample of
amount of Sr(BH4)2 is observed at RT (see Figure S1,
Supporting Information). Upon heating to ∼125 °C, diffraction
from 3 vanishes simultaneously with formation of Sr(BH ) . It
■
*
S
4
2
should also be noted that the unknown compound, 2, is
observed to decompose at ∼105 °C (from data of sample C).
The relatively low decomposition temperature of 2 and 3
LiBH −SrCl (3:1); tables of atomic coordinates of Sr(BH ) ,
4
2
4 2
Sr(BH ) , and Sr(BH )Cl. This material is available free of
4
2
4
charge via the Internet at http://pubs.acs.org.
1
0883
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
(
20) Filinchuk, Y.; Richter, B.; Jensen, T. R.; Dmitriev, V.;
AUTHOR INFORMATION
■
*
Chernyshov, D.; Hagemann, H. Angew. Chem. 2011, 123, 11358−
Corresponding Author
Phone: 617-253-5308. E-mail: dorthe@mit.edu.
1
1362; Angew. Chem., Int. Ed. 2011, 50, 11162−11166.
(21) David, W. I. F.; Callear, S. K.; Jones, M. O.; Aeberhard, P. C.;
Culligan, S. D.; Pohl, A. H.; Johnson, S. R.; Ryan, K. R.; Parker, J. E.;
Edwards, P. P.; Nuttall, C. J.; Amieiro-Fonseca, A. Phys. Chem. Chem.
Phys. 2012, 14, 11800−11807.
Notes
The authors declare no competing financial interest.
(
22) Paskevicius, M.; Pitt, M.; Webb, C. J.; Sheppard, D. A.; Filsø, U.;
ACKNOWLEDGMENTS
Gray, E. M.; Buckley, C. E. J. Phys. Chem. C 2012, 116, 15231−15240.
■
̂
(
23) Hagemann, H.; Cerny,
́
R. Dalton Trans. 2010, 39, 6006−6012.
D.B.R. and T.R.J. thank the Danish Research Council for
Nature and Universe (Danscatt), the Danish National Research
Foundation (Centre for Materials Crystallography), the Danish
Strategic Research Council (HyFillFast), and the Carlsberg
Foundation for funding. E.A.N. acknowledges EPSRC and
STFC for funding. We are also grateful to SNBL, ESRF, and
MAX-lab for the provision of beam time. This work was
supported by the Swiss National Science Foundation.
(24) Huot, J.; Ravnsbæk, D. B.; Zhang, J.; Cuevas, F.; Latroche, M.;
Jensen, T. R. Prog. Mater. Sci. 2013, 58, 30−75.
(25) Mikheeva, V. I.; Sizareva, A. S. Zh. Neorg. Khim. 1977, 22, 1706.
(26) Jensen, T. R.; Nielsen, T. K.; Filinchuk, Y.; Jørgensen, J.-E.;
Cerenius, Y.; Mac. Gray, E.; Webb, C. J. J. Appl. Crystallogr. 2010, 43,
1
(
456−1463.
27) Hammersley, A. P.; Svensson, S. O.; Hanfland, M.; Fitch, A. N.;
Hausermann, D. High Pressure Res. 1996, 14, 235−248.
28) David, W. I. F.; Shankland, K.; van de Streek, J.; Pidcock, E.;
Motherwell, W. D. S.; Cole, J. C. J. Appl. Crystallogr. 2006, 39, 910−
15.
29) Coelho, A. A. TOPAS; Academic Press: New York, 2004.
̈
(
REFERENCES
9
(
■
(
1) Eberle, U.; Felderhoff, M.; Schu
̈
th, F. Angew. Chem. 2009, 121,
̂
(
30) Cerny,
Int, Ed. 2007, 46, 5765−5767.
31) Her, J.-H.; Stephens, P. W.; Gao, Y.; Soloveichik, G. L.;
́
R.; Filinchuk, Y.; Hagemann, H.; Yvon, K. Angew. Chem.
6
732−6757.
(
(
2) Schlapbach, L. Nature 2009, 460, 809−811.
(
3) Orimo, S.; Nakamori, Y.; Eliseo, J. R.; Zuttel, A.; Jensen, C. M.
Rijssenbeek, J.; Andrus, M.; Zhao, J.-C. Acta Crystallogr., Sect. B: Struct.
Sci. 2007, 63, 561−568.
Chem. Rev. 2007, 107, 4111−4132.
4) Rude, L. H.; Nielsen, T. K.; Ravnsbæk, D. B.; Bosenberg, U.; Ley,
M. B.; Richter, B.; Arnbjerg, L. M.; Dornheim, M.; Filinchuk, Y.;
Besenbacher, F.; Jensen, T. R. Phys. Status Solidi A 2011, 208, 1754−
(
̈
(32) Miwa, K.; Aoki, M.; Noritake, T.; Ohba, N.; Nakamori, Y.;
Towata, S.; Zuttel, A.; Orimo, S. Phys. Rev. B: Condens. Matter 2006,
4, 155122.
33) Buchter, F.; Łodziana, Z.; Remhof, A.; Friedrichs, O.;
Borgschulte, A.; Mauron, P.; Zuttel, A.; Sheptyakov, D.;
7
(
1
(
773.
5) Zu
Emmenegger, Ch. J. Power Sources 2003, 118, 1−7.
6) Ravnsbæk, D. B.; Sørensen, L. H.; Filinchuk, Y.; Besenbacher, F.;
Jensen, T. R. Angew. Chem., Int. Ed. 2012, 51, 3582−3586.
7) Nickels, E. A.; Jones, M. O.; David, W. I. F.; Johnson, S. R.;
Lowton, R. L.; Sommariva, M.; Edwards, P. P. Angew. Chem., Int. Ed.
008, 47, 2817−2819.
̈
ttel, A.; Wenger, P.; Rentsch, S.; Sudan, P.; Mauron, Ph.;
̈
Barkhordarian, G.; Bormann, R.; Chlopek, K.; Fichtner, M.; Sorby,
(
M. H.; Riktor, M. D.; Hauback, B. C.; Orimo, S. J. Phys. Chem. B 2008,
1
(
12, 8042.
34) Hahn, T. International Tables for Crystallography; Springer for
(
International Union of Crystallography: Dordrecht, The Netherlands,
2005; Vol. A.
2
(
(
̂
8) Cerny,
9) Ley, M. B.; Ravnsbæk, D. B.; Filinchuk, Y.; Lee, Y.-S.; Janot, R.;
Cho, Y. W.; Skibsted, J.; Jensen, T. R. Chem. Mater. 2012, 24, 1654−
663.
10) Ley, M. B.; Boulineau, S.; Janot, R.; Filinchuk, Y.; Jensen, T. R. J.
Phys. Chem. C 2012, 116, 21267−21276.
́
R.; Filinchuk, Y. Z. Kristallogr. 2011, 226, 882−891.
(35) Larson, A. C.; Von Dreele, R. B. Los Alamos National Laboratory
Report LAUR 1994, 86−748.
(36) Boultif, A.; Louer, D. J. Appl. Crystallogr. 2004, 37, 724.
1
(
̂
(37) Favre-Nicolin, V.; Cerny,
(38) Rodrigues-Carvajal, J. Physica B 1993, 192, 55. For a more
recent version, see: Rodrıguez-Carvajal, J. Recent developments of the
́
R. J. Appl. Crystallogr. 2002, 35, 734.
̂
́
(
11) Cerny,
Y.; Teyssier, J.; Smrco
563−1571.
12) Schouwink, P.; D’Anna, V.; Ley, M. B.; Daku, L. M. L.; Richter,
́
R.; Ravnsbæk, D. B.; Schouwink, P.; Filinchuk, Y.; Penin,
̌
k, L.; Jensen, T. R. J. Phys. Chem. C 2012, 116,
program FULLPRO; Commission on Powder Diffraction Newsletters
(IUCr), Chester, England, 2001; Vol. 26, pp 12−19. The complete
program and documentation can be obtained at http://www.iucr.
org/__data/assets/pdf_file/0019/21628/cpd26.pdf.
(39) Spek, A. L. PLATON; University of Utrecht: The Netherlands,
2006.
1
(
̂
B.; Jensen, T. R.; Hagemann, H.; Cerny,
0829−10840.
13) Hagemann, H.; Longhini, M.; Kaminski, J. W.; Wesolowski, T.
́
R. J. Phys. Chem. C 2012, 116,
1
(
̂
(40) Bremer, M.; No
1995, 128, 455−460.
̈
th, H.; Thomann, M.; Schmidt, M. Chem. Ber.
A.; Cerny,
Jensen, C. M. J. Phys. Chem. A 2008, 112, 7551−7555.
14) Hwang, S. -J.; Bowman, R. C., Jr.; Reiter, J. W.; Rijssenbeek, J.;
́
R.; Penin, N.; Sørby, M. H.; Hauback, B. C.; Severa, G.;
(
(41) Zaslavskii, A. I.; Kondrashev, Yu. D.; Tolkachev, S. S. Dokl.
Akad. Nauk SSSR 1950, 75, 559−561.
Soloveichik, G. L.; Zhao, J.-C.; Kabbour, H.; Ahn, C. C. J. Phys. Chem.
C 2008, 112, 3164−3169.
(42) (a) Partin, D. E.; O’Keeffe, M. J. Solid State Chem. 1995, 119,
157−160. (b) Engelen, B.; Kellersohn, T.; Kuske, P.; Lutz, H. D. Z.
Anorg. Allg. Chem. 1988, 566, 49−54.
̂
́
15) Cerny, R.; Severa, G.; Ravnsbæk, D. B.; Filinchuk, Y.; d’Anna,
(
V.; Hagemann, H.; Haase, D.; Jensen, C. M.; Jensen, T. R. J. Phys.
Chem. C 2010, 114, 1357−1364.
(43) Ott, H. Z. Kristallogr. Krist. 1926, 63, 222−230.
(44) Greis, O.; Petzel, T. Z. Anorg. Allg. Chem. 1974, 403, 1−96.
(45) Sass, R. L.; Brackett, T. E.; Brackett, E. B. J. Phys. Chem. 1963,
67, 2862−2863.
(46) Hodorowicz, S. A.; Eick, H. A. J. Solid State Chem. 1983, 46,
313−320.
(47) Liu, G.; Eick, H. A. J. Less-Common Met. 1989, 156, 237−245.
(48) Dyke, M.; Sass, R. L. J. Phys. Chem. 1964, 68, 3259−3262.
(49) Lutz, H. D.; Buchmeier, W.; Engelen, B. Acta Crystallogr., Sect. B
1987, 43, 71−75.
(50) Lide, D. R. CRC Handbook of Chemistry and Physics, 88th ed.;
CRC: Boca Raton, FL, 2007.
̂
́
16) Cerny, R.; Ravnsbæk, D. B.; Severa, G.; Filinchuk, Y.; d’Anna,
(
V.; Hagemann, H.; Haase, D.; Skibsted, J.; Jensen, C. M.; Jensen, C. M.
J. Phys. Chem. C 2010, 114, 19540−19549.
17) Ravnsbæk, D.; Filinchuk, Y.; Cerenius, Y.; Jakobsen, H. J.;
Besenbacher, F.; Skibsted, J.; Jensen, T. R. Angew. Chem., Int. Ed. 2009,
8, 6659−6663.
18) Ravnsbæk, D. B.; Frommen, C.; Reed, D.; Filinchuk, Y.; Sørby,
M.; Hauback, B. C.; Jakobsen, H. J.; Book, D.; Besenbacher, F.;
Skibsted, J.; Jensen, T. R. J. Alloys Compd. 2011, 509, S698−S704.
19) Filinchuk, Y.; Chernyshov, D.; Dmitriev, V. Z. Kristallogr. 2008,
(
4
(
(
2
23, 649−659.
1
0884
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885

Inorganic Chemistry
Article
(
51) Barron, A. R.; Hursthouse, M. B.; Motevalli, G.; Wilkinson, G.
Chem. Commun. 1986, 81−82.
52) Fichtner, M.; Chłopek, K.; Longhini, M.; Hagemann, H. J. Phys.
Chem. C 2008, 112, 11575.
53) Orimo, S.; Nakamori, Y.; Zuttel, A. Mater. Sci. Eng. 2004, B104,
1.
54) Filinchuk, Y.; Cerny,
25−933.
(
(
5
(
̂
́
R.; Hagemann, H. Chem. Mater. 2009, 21,
9
(
̂
55) Cerny,
́
R.; Penin, N.; Hagemann, H.; Filinchuk, Y. J. Phys. Chem.
C 2009, 113, 9003−9007.
(
Sholl, D. S. J. Phys. Chem. C 2010, 114, 19127−19133.
(
̂
́
56) Cerny, R.; Kim, K. C.; Penin, N.; D’Anna, V.; Hagemann, H.;
57) Marks, T. J.; Kolb, J. R. Chem. Rev. 1977, 77, 263−293.
58) Reed, D.; Book, D. Curr. Opin. Solid State Mater. Sci. 2011, 15,
(
6
2−72.
59) Ravnsbæk, D. B.; Ley, M. B.; Lee, Y.-S.; Hagemann, H.; D’Anna,
V.; Cho, Y. W.; Filinchuk, Y.; Jensen, T. R. Int. J. Hydrogen Energy
(
2
(
(
012, 37, 8428−8438.
60) Grochala, W.; Edwards, P. P. Chem. Rev. 2004, 104, 1283−1315.
61) Wang, L.-L.; Graham, D. D.; Robertson, I. M.; Johnson, D. D. J.
Phys. Chem. C 2009, 113, 20088.
(
62) Her, J.-H.; Yousufuddin, M.; Zhou, W.; Jalisatgi, S. S.; Kulleck, J.
G.; Zan, J. A.; Hwang, S.-J.; Bowman, R. C, Jr.; Udovic, T. J. Inorg.
Chem. 2008, 47, 9757.
(
63) Solntsev, K. A.; Kuznetsov, N. T.; Kol’ba, L. N.; Agre, V. M.;
Ponomarev, V. I. Russ. J. Inorg. Chem. 1977, 22, 313.
1
0885
dx.doi.org/10.1021/ic400862s | Inorg. Chem. 2013, 52, 10877−10885