Synthesis of Ammonia Borane Nanoparticles and the Diammoniate of Diborane by Direct Combination of Diborane and Ammonia

Article abstract of DOI:10.1002/chem.201600367

Pure nanoparticle ammonia borane (NH₃BH₃, AB) was first prepared through a solvent-free, ambient-temperature gas-phase combination of B₂H₆ with NH₃. The prepared AB nanoparticle exhibits improved dehydrogenation behavior giving 13.6 wt. % H₂ at the temperature range of 80-175°C without severe foaming. Ammonia diborane (NH₃BH₂(μ-H)BH₃, AaDB) is proposed as the intermediate in the reaction of B₂H₆ with NH₃ based on theoretical studies. This method can also be used to prepare pure diammoniate of diborane ([H₂B(NH₃)₂][BH₄], DADB) by adjusting the ratio and concentration of B₂H₆ to NH₃.

Full text of DOI:10.1002/chem.201600367

DOI: 10.1002/chem.201600367
Communication
&
Borane Chemistry
Synthesis of Ammonia Borane Nanoparticles and the
Diammoniate of Diborane by Direct Combination of Diborane and
Ammonia
Yuanzhou Song+,[a] Nana Ma+,[b] Xiaohua Ma,[a, c] Fang Fang,[a] Xuenian Chen,*[b] and
Yanhui Guo*[a]
other hand, the pure nanophase of other hydrogen-storage
candidates—metal hydrides—demonstrates improved kinetics
for reversible hydrogen storage in comparison with the bulk
materials.[8] In considering that scaffolds always carry a mass
penalty as a hydrogen-storage method and the nanophase im-
proves dehydrogenation properties of metal hydrides, synthe-
sis and dehydrogenation studies of the pure nanosized AB
nanoparticle will be of great significance. We have found con-
ditions under which AB nanoparticles form. Nanoparticle AB
exhibits promising dehydrogenation behaviour in comparison
with AB formed in the presence of solvent.
Abstract: Pure nanoparticle ammonia borane (NH3BH3,
AB) was first prepared through a solvent-free, ambient-
temperature gas-phase combination of B2H6 with NH3. The
prepared AB nanoparticle exhibits improved dehydrogen-
ation behavior giving 13.6 wt.% H2 at the temperature
range of 80–1758C without severe foaming. Ammonia di-
borane (NH3BH2(m-H)BH3, AaDB) is proposed as the inter-
mediate in the reaction of B2H6 with NH3 based on theo-
retical studies. This method can also be used to prepare
pure diammoniate of diborane ([H2B(NH3)2][BH4], DADB)
by adjusting the ratio and concentration of B2H6 to NH3.
The molecular formula of AB (NH3BH3) invites the conclusion
that AB can be synthesized by direct combination of NH3 and
B2H6. However, as first reported by Stock in 1923,[9] the direct
combination yields the diammoniate of diborane (DADB)
rather than pure AB in the reaction of B2H6 with solid NH3
(below À1008C), or in the reaction of liquid NH3 with gaseous
B2H6 later reported by Shore, et al.[10] These results have puz-
zled the boron chemistry community for decades. Thus, a varie-
ty of indirect methods have been developed to synthesize AB.
The earliest strategy is by the metathesis reaction of ammoni-
um and borohydride salts in an organic solvent developed by
Shore and Parry in 1955,[1] which was improved by Autrey and
Ramachandran.[11] Newer methods include displacement reac-
tions[12] and the decomposition of DADB.[13]
Ammonia borane (AB), first prepared by Shore in 1955,[1] has
attracted significant attention recently as a solid hydrogen-
storage material because of its high hydrogen content
(19.6 wt.%), good stability at ambient temperature, and mod-
erate hydrogen-release temperature.[2] However, AB has severe
limitations as a hydrogen-storage material due to some draw-
backs including high kinetic barriers,[2a] the emission of poison-
ing product (borazine), and material foaming in the dehydro-
genation. Over the past few years, a variety of methods such
as metal-catalyzing,[2b,3] additive-doping,[4] substitution of the
amine hydrogen of AB with metal cations,[5] and size effects,[6]
have been explored to improve the dehydrogenation of AB.
Amongst these methods, size effects have been demonstrated
to have a significant impact on the hydrogen-storage per-
formance of the AB nanoparticle loaded in various scaffolds,
such as mesoporous silica,[6a] microporous carbon framework
(MCF),[7] and metal–organic frameworks (MOFs).[6d] On the
To find a convenient preparation of AB continues to be of
practical and theoretical interest. In a recently developed prac-
tical synthesis technology, a borane displacement reaction in-
volving tetrahydrofuran borane and liquid NH3 produces AB;[10]
this reaction also yielded mechanistic insight into the combina-
tion of NH3 with B2H6.[14] Yet, the production of pure nanosized
AB has not been reported using the previous methods. Direct
combination of NH3 and B2H6 to produce pure AB at ambient
temperature remains a desirable but unrealized preparative
method.
[a] Y. Song,+ Prof. X. Ma, Prof. F. Fang, Prof. Y. Guo
Department of Materials Science
Fudan University, Shanghai, 200433 (P. R. China)
E-mail: gyh@fudan.edu.cn
[b] N. Ma,+ Prof. X. Chen
Meanwhile, DADB the ionic dimer of AB that has also attract-
ed much attention as hydrogen-storage candidate,[15] remains
difficult to synthesize due to the rigorous procedure of the
original synthesis and DADB’s instability in organic solvents at
ambient temperature.[16] Currently, there is no commercial
source of DADB[10,16] and the existing preparative methods, the
reaction of liquid ammonia with borane,[9,10] decomposition of
NH4BH4,[17] or ball milling NaBH4 and NH4F[15a,18] are not suitable
for commercialization. The absence of a facile synthesis has
become a barrier for the comprehensive study of this ad-
School of Chemistry and Chemical Engineering
Henan Normal University, Xinxiang, Henan 453007 (P. R. China)
E-mail: xnchen@htu.edu.cn
[c] Prof. X. Ma
Center of Special Materials and Technology
Fudan University, Shanghai, 200433 (P. R. China)
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201600367.
Chem. Eur. J. 2016, 22, 6228 – 6233
6228
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
vanced material, and a practical synthesis method is still ur-
gently needed.
In this study, it is found that solvent-free combination of
B2H6 with NH3 can produce both nanosized AB and pure DADB
at ambient temperature. Results show that excess B2H6 pro-
motes formation of AB, while excess NH3 leads to formation of
DADB. Nanosized AB shows superior dehydrogenation behav-
iour compared to AB prepared by other methods, improve-
ments that may represent an advantage as investigations of
AB as a solid-state hydrogen-storage material continue.
The synthesis of pure AB nanoparticles and pure DADB was
realized through the reaction of a B2H6 stream with a NH3
stream in apparatus shown in Figure 1. Ammonia was purified
Figure 2. XRD patterns of: a) AB, b) mixture of AB and DADB, and c) DADB.
could be obtained with appropriate adjustment of the ratio of
B2H6 to NH3 and their concentrations. Excess B2H6 was required
to produce pure AB, and excess NH3 was required to produce
pure DADB. Pure AB was synthesized using a B2H6/N2 mixture
(15:85 volume ratio) at a flow rate of 10 mLminÀ1 and a NH3/
N2 mixture (3:97 volume ratio) at a flow rate of 3 mLminÀ1 at
ambient temperature. These conditions created a B2H6/NH3
ratio of 17:1. The purity of AB was confirmed by XRD (Fig-
ure 2a), FTIR spectroscopy (Figure S3, Supporting Information),
NMR (Figure S4, Supporting Information) analyses, and the
content of boron element and active hydrogen in the product
measured by ICP-AES and active hydrogen analysis[19] (Table S1,
Supporting Information). Typically, around 73 mg of white
powder can be collected after 12 h and the theoretical yield of
AB, which was calculated according to the amount of NH3 that
flows into Reactor III (Figure ) is 83 mg. Therefore, the yield of
AB was around 87%. Moreover, the concentration of NH3 in
the NH3/N2 mixtures was found to affect the purity of AB. Re-
sults show that when the NH3 concentration was increased,
a mixture of DADB and AB formed (Figure S1, Supporting Infor-
mation).
Figure 1. Apparatus for the preparation of AB or DADB by direct combina-
tion. Equations (1–3) describe the reactions that occur in Reactors I–III, re-
spectively.
with soda lime and carried on a stream of purified N2. B2H6 was
produced by reacting gaseous HCl (from concentrated H2SO4
dripped into dry NaCl using a peristaltic pump [Eq. (1)]), which
was carried by purified N2 through a layer of LiBH4 powder
[Eq. (2)].
In contrast to the production of AB, excessive NH3 environ-
ment favors the formation of DADB. Pure DADB was synthe-
sized using a 1:40 ratio of B2H6 to NH3 by mixing B2H6/N2 (4:96
volume ratio, flow rate: 10 mLminÀ1) and pure NH3 (flow rate:
4 mLminÀ1) at ambient temperature. The purity of DADB was
confirmed by XRD (Figure 2c), FTIR spectroscopy (Figure S3,
Supporting Information), and the content of boron and active
hydrogen in DADB[19] (Table S1, Supporting Information). In this
case, the concentration of B2H6 will affect the purity of the as-
prepared DADB. Higher concentrations of B2H6 will lead to the
formation of AB impurity (Figure S2, Supporting Information).
Typically, around 131 mg DADB can be collected after 12 h
compared to the theoretical yield of 402 mg calculated accord-
ing to the amount of B2H6 that is introduced into Reactor III.
Therefore, the yield of DADB was around 33%.
NaCl ðsÞ þ H2SO4 ðlÞ ! HCl ðgÞ þ NaHSO4 ðsÞ
2 HClðgÞ þ 2 LiBH4 ðsÞ ! 2 LiCl ðsÞ þ B2H6 ðgÞ þ 2 H2 ðgÞ
B2H6ðgÞ þ 2 NH3ðgÞ ! x NH3BH3þ
ð1Þ
ð2Þ
ð3Þ
ð1Àx=2Þ½NH3BH2NH3Š½BH4Š 0 ꢀ x ꢀ 2
The absence of ClÀ in the B2H6 stream was confirmed by ClÀ
titration analysis. The concentration of B2H6 was controlled by
the H2SO4 drop rate. The amount of N2 diluent controlled the
concentration of NH3. A detailed experimental procedure is
provided in the Supporting Information. Composition of the
powdery solid product isolated from Reactor III (500 mL 3-
necked flask; Figure 1) was determined by XRD measurements
(Figure 2). When reactant ratios were not carefully adjusted
both AB and DADB (Figure 2b) were present, which is consis-
tent with previous reports of the reaction of B2H6 with liquid
NH3.[10] However, it was discovered that pure AB or pure DADB
It is believed that the influence of concentration is compli-
cated by the inhomogeneity of the B2H6/NH3 ratio in the reac-
tor. Diffusion dynamics may lead to a different ratio of the two
starting materials in the center of the flowing gases compared
to the bulk material ratio. Therefore, it is difficult to achieve
Chem. Eur. J. 2016, 22, 6228 – 6233
www.chemeurj.org
6229
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
a consistent reaction environment of stable ratios of B2H6 and
NH3. Presumably inhomogeneity increases the possibility of im-
purity formation.
the particle size of AB would affect its hydrogen-storage prop-
erties.
Currently, the normal strategy to facilitate size effect is scaf-
fold confinement. Autrey et al. have loaded AB within the mes-
oporous silica SBA-15, and the confined nanosized AB showed
an encouraging one-step dehydrogenation peaking at around
1008C (heating rate: 18CminÀ1) with little borazine impurity
evolution.[6a] Yao et al. have confined AB into the metal–organ-
ic framework (MOF) and the MOF-confined AB produced pure
hydrogen peaking at 848C (heating rate:18CminÀ1).[6d] Al-
though significant dehydrogenation improvement has been
achieved using a confinement strategy, the mass penalty of
these methods was quite obvious, which made these methods
less practical. Pure nanoparticle strategy may be a promising
alternative for AB modification due to the comprehensive de-
hydrogenation improvements without a mass penalty. The en-
hanced dehydrogenation properties of nanoparticles in our
study represents an important advance, further optimization
on the particle size or combination of other modification
methods may achieve a more efficient AB-based hydrogen-
storage system with high hydrogen capacity, practical dehy-
drogenation temperature, pure hydrogen evolution, and no
severe material foaming.
Decomposition of the as-prepared DADB and AB was investi-
gated using TGA/MS (Figure S5, Supporting Information), TPD,
and DSC (Figure S6, Supporting Information). Dehydrogenation
of the as-prepared DADB proceeds in the temperature range
of 90–2258C with significant weight loss (33.6 wt.%) and
severe foaming at 3008C. However, for the as-prepared nano-
scale AB, several notable improvements were observed. First,
the dehydrogenation temperature of AB prepared in this work
is lower than that of AB prepared from solution. Two dehydro-
genation peaks were observed by TGA/MS (Figure S7, Support-
ing Information) and DSC at 101 and 1498C, compared to 121
and 1568C for the bulk AB.[20] Second, weight loss of the as-
prepared nanoscale AB (24.9 wt.%) at 3008C is far below that
for AB prepared from solution (around 50 wt.%), suggesting
the release of fewer volatile impurities during dehydrogenation
(Figure S7, Supporting Information). Finally, no severe material
foaming or expansion occurred during the decomposition of
the as-prepared AB (Figure S8, Supporting Information). The
DSC result suggests that no melting phase transition was pres-
ent during decomposition of AB (Figure S6, Supporting Infor-
mation), which indicates that the elimination of foaming may
be attributed to new bonds being formed before the melting
of AB.[21] Furthermore, AB prepared by direct combination
formed nanoscale particles according to their SEM images (Fig-
ure 3b, around 50 nm), which is consistent with the grain-size
The key intermediate in an early proposed mechanism is
ammonia diborane (NH3BH2(m-H)BH3, AaDB), which was first es-
tablished in a report by Shore et al. describing the reaction of
NH3 with THF·BH3 that leads to a mixture of AB and DADB.[14a]
A similar mechanism (Scheme 1) was proposed which is sup-
ported by experimental results and computational studies (see
the Supporting Information for computational details). Initially
NH3 reacts with B2H6 to form AaDB. The reaction is predicted
to be exothermic (À3.8 kcalmolÀ1, Figure S10, Supporting In-
formation) with a calculated activation energy barrier of
8.2 kcalmolÀ1. Subsequent addition of NH3 to AaDB at Ba leads
to DADB (pathway I) or addition of NH3 at Bb results in two
molecules of AB. The calculated energy profile with structures
of reaction complex (RC), transition state (TS), and product
complex (PC) is shown in Table S1, Supporting Information.
Based on calculated energy barriers (Table 1) formation of AB is
Table 1. Calculated free energies (kcalmolÀ1, at 298 K) of the reaction be-
tween NH3 and AaDB in the presence of AB, B2H6, and NH3 molecules at
the M062X/6-311+ +G(d,p) level.
Figure 3. a) MS profiles for the as-prepared nanoscale AB, the as-prepared
nanoscale AB resolved in THF and recrystallized from THF, and AB prepared
from solution at a heating rate of 58CminÀ1. SEM image for: b) the as-pre-
pared nanoscale AB and c) the as-prepared nanoscale AB resolved in THF
and recrystallized from THF.
Pathway I
TS2-I
Pathway II
TS2-II
RC
DADB
RC
2AB
none
one AB
two AB
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
30.2
23.9
19.2
16.6
14.3
27.7
27.3
26.0
27.7
24.9
17.8
17.1
16.9
À0.8
À8.0
À10.6
À3.3
À8.0
À2.9
À4.9
À5.0
À3.2
À7.0
À9.2
À10.6
À14.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
13.6
12.0
10.6
12.2
11.3
12.6
11.3
9.8
10.5
10.8
10.7
11.3
10.6
À12.1
À7.8
À11.5
À4.1
three AB
four AB
one B2H6
two B2H6
three B2H6
one NH3
two NH3
three NH3
four NH3
five NH3
calculated by the XRD result (around 61 nm). It is supposed
that the small size should contribute to the dehydrogenation
improvement of AB. To study the size effect, the as-prepared
AB nanoparticles were recrystallized in THF to produce AB
powder with larger particle size. It shows that apparent incre-
ment of AB particles size (Figure 3c) along with the degrada-
tion of its dehydrogenation performance were present after
the recrystallization (Figure 3a). These results may suggest that
À8.1
À5.8
À8.5
À7.6
À17.1
À5.7
À14.7
À12.6
À12.2
Chem. Eur. J. 2016, 22, 6228 – 6233
www.chemeurj.org
6230
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Scheme 1. Proposed mechanism for the formation of AB and DADB by direct combination of NH3 and B2H6.
strongly favored, 13.6 kcalmolÀ1 (pathway II) versus 30.2 kcal
molÀ1 (pathway I). However, while pure AB has been obtained,
mixtures of AB and DADB (Figure 2b) and pure DABD have
been obtained depending upon reaction conditions. Factors
not represented in the mechanism must be involved.
presence of one NH3 molecule, the calculated activation
energy barrier for AB formation was reduced to 10.5 kcalmolÀ1
,
much lower than the barrier for DADB formation (27.7 kcal
molÀ1) (Table 1, TS structures are shown in Figures S16 and
S17, Supporting Information). As the proportion of NH3 is in-
creased, the activation energy barrier of AB formation changed
little but the barrier to DADB formation decreased significantly.
However, these calculations do not account for the formation
of pure DADB since the energy barrier to DADB formation is
consistently higher than for AB formation. Therefore, other fac-
tors such as dynamic influence might play important roles in
this reaction.
Shore et al. have reported that dihydrogen bonds between
AaDB and AB play a crucial role in DADB formation in the solu-
tion reaction of NH3 with THF·BH3.[14a] In the present case, dihy-
drogen bond interactions between AaDB and AB were intro-
duced resulting in a dramatic decrease (6.3 kcalmolÀ1) in the
calculated activation energy of pathway I, but little change for
pathway II (Table 1). TS structures are shown in Figures S12
and S13, Supporting Information. More dihydrogen bonds
from the more complexed AB slow the calculated activation
barrier further. When four AB molecules are present, the pre-
dicted activation energy for pathway I is 14.3 kcalmolÀ1, com-
parable to the 11.3 kcalmolÀ1 barrier calculated for the path-
way II. It is also observed that DADB formation is calculated to
be more exothermic in the presence of AB.
In the transition-state TS2-I of the pathway I, a six-mem-
bered BaÀNÀH···HÀBbÀH ring is formed through dihydrogen
bonding interactions. The formation of a dihydrogen bond and
the six-membered ring are considered as key factors in this
step. In order to confirm their important roles, trimethylamine
was used to react with B2H6 in which no dihydrogen bond
could be formed after protonic hydrogen had been replaced
When B2H6 is in excess, AaDB forms dihydrogen bond NÀ by a methyl group. Experimental results indicate that in either
H···HÀB and homopolar dihydrogen bond BÀH···HÀB[22] with
excess B2H6 rather than with the small amount of AB present.
Energy barriers of pathways I and II were calculated in the
presence of one, two, and three B2H6 molecules (Table 1) and
the TS structures are provided in Figures S14 and S15, Support-
ing Information. The calculated activation energy barriers of
both pathways I and II were reduced generally with the forma-
tion of dihydrogen bonds. When three B2H6 molecules were
considered to form dihydrogen bonds with AaDB, the energy
barrier for pathway I (26.0 kcalmolÀ1) was significantly higher
than the barrier of pathway II (9.8 kcalmolÀ1) (Table 1). This is
probably the reason for the formation of pure AB in the pres-
ence of excess B2H6.
trimethylamine or B2H6 excess, only pure trimethylamine
borane (Me3NBH3, TMB) was formed. This observation indirectly
proves that the formation of the dihydrogen bond and six-
membered ring may play key roles in the formation of DADB.
In summary, effective synthesis of the pure nanoscale of AB
and pure DADB has been developed by the gas-phase combi-
nation of NH3 and B2H6. The mechanistic implications of the
dependence of product formation on relative ratio and con-
centration of reagents have been analysed. The dehydrogena-
tion properties of pure AB and DADB have been characterized
with encouraging results. Pure AB yields 0.068 mol H2/g
(around 13.6 wt.%) in the temperature range 80–1758C with-
out severe foaming, behaviour that is attributed to its nano-
particle size. This work not only provides a convenient proce-
dure for preparation of pure nanoscale AB and pure DADB, but
At higher NH3 concentrations, dihydrogen bonds and hydro-
gen bonds (NÀH···N) involving AaDB can be expected. In the
Chem. Eur. J. 2016, 22, 6228 – 6233
www.chemeurj.org
6231
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
collected using a TA Q100. Samples were heated from room tem-
perature to 3008C at a heating rate of 58CminÀ1 under nitrogen.
FTIR (Netzch Nicolet Is10) analyses were conducted using the KBr-
pellet method and recorded in the range 500 to 4000 cmÀ1. SEM
images were collected on SUPERSCAN SSX-550. Dried samples with
an ultrathin coating of electrically-conducting material were used
for observation.
also shed light on the relationship of compound properties,
particle size and its synthetic method, which will benefit
a wide range of readers.
Experimental Section
General
NH3BH3 (97%, United boron (Zhengzhou) S&T LLC, China) was
used as received. LiBH4 (95%, Sigma-Aldrich, USA) and NaCl (Sino- Acknowledgements
pharm Chemical Reagent Co., Ltd, China) were ball milled for 1 h
before use. NH3 gas (Alfa Aesar, China) was purified by bubbling
This work was financially supported by National Natural Sci-
through soda lime before use. THF (98%, Sinopharm Chemical Re-
agent Co., Ltd, China) was dried over sodium/benzophenone and
distilled prior to use. All samples, except H2SO4 (95–98%, Zhitang
Chemical Co., Ltd, China), were handled in a nitrogen-filled glove
box that kept water and oxygen concentrations below 1 ppm
during operation. The flow rates of N2 and NH3 were controlled by
gauges (LZB-2 6–60ML/MIN, Yuzhaoweichuang Flow Gauge CO.,
Ltd, China) and peristaltic pump (BS100–1AQ, BAODING SIGNAL
FLUID TECHNOLOGY CO., Ltd, China). The flow rate of B2H6/N2 mix-
ture and NH3/N2 mixture were measured by the flowmeter
(FS4001, Siargo Ltd., America).
ence Foundation of China (51201035, 51471052, U1201241,
21371051), the Doctoral Program of Higher Education of China
(20110071120008) and Key Laboratory of Advanced Energy
Storage Materials of Guangdong Province. The authors are
grateful to Prof. T. Evans for very valuable comments.
Keywords: ammonia borane
diammoniate of diborane
nanotechnology
·
borane chemistry
hydrogen storage
·
·
·
Notice, B2H6 and NH3 are extremely toxic gas and should therefore
only be handled in fumehood with ventilation. Off-gas should be
bubbled into 5% ammonia solution for security.
[1] S. G. Shore, R. W. Parry, J. Am. Chem. Soc. 1955, 77, 6084–6085.
[2] a) G. Wolf, J. Baumann, F. Baitalow, F. P. Hoffmann, Thermochim. Acta
2000, 343, 19–25; b) J.-M. Yan, X.-B. Zhang, S. Han, H. Shioyama, Q. Xu,
Angew. Chem. Int. Ed. 2008, 47, 2287–2289; Angew. Chem. 2008, 120,
2319–2321; c) T. B. Marder, Angew. Chem. Int. Ed. 2007, 46, 8116–8118;
Angew. Chem. 2007, 119, 8262–8264; d) U. Eberle, M. Felderhoff, F.
Schueth, Angew. Chem. Int. Ed. 2009, 48, 6608–6630; Angew. Chem.
2009, 121, 6732–6757; e) G. R. Whittell, I. Manners, Angew. Chem. Int.
Ed. 2011, 50, 10288–10289; Angew. Chem. 2011, 123, 10470–10472;
f) G. R. Whittell, I. Manners, Angew. Chem. 2011, 123, 10470–10472.
[3] a) P.-Z. Li, A. Aijaz, Q. Xu, Angew. Chem. Int. Ed. 2012, 51, 6753–6756;
Angew. Chem. 2012, 124, 6857–6860; b) G. Alcaraz, S. Sabo-Etienne,
Angew. Chem. Int. Ed. 2010, 49, 7170–7179; Angew. Chem. 2010, 122,
7326–7335; c) G. Alcaraz, S. Sabo-Etienne, Angew. Chem. 2010, 122,
7326–7335.
[4] D. J. Heldebrant, A. Karkamkar, N. J. Hess, M. Bowden, S. Rassat, F.
Zheng, K. Rappe, T. Autrey, Chem. Mater. 2008, 20, 5332–5336.
[5] H. V. K. Diyabalanage, R. P. Shrestha, T. A. Semelsberger, B. L. Scott, M. E.
Bowden, B. L. Davis, A. K. Burrell, Angew. Chem. Int. Ed. 2007, 46, 8995–
8997; Angew. Chem. 2007, 119, 9153–9155.
[6] a) A. Gutowska, L. Li, Y. Shin, C. M. Wang, X. S. Li, J. C. Linehan, R. S.
Smith, B. D. Kay, B. Schmid, W. Shaw, M. Gutowski, T. Autrey, Angew.
Chem. Int. Ed. 2005, 44, 3578–3582; b) A. Feaver, S. Sepehri, P. Sham-
berger, A. Stowe, T. Autrey, G. Cao, J. Phys. Chem. B 2007, 111, 7469–
7472; c) Z. Tang, X. Chen, H. Chen, L. Wu, X. Yu, Angew. Chem. Int. Ed.
2013, 52, 5832–5835; Angew. Chem. 2013, 125, 5944–5947; d) Z. Li, G.
Zhu, G. Lu, S. Qiu, X. Yao, J. Am. Chem. Soc. 2010, 132, 1490–1491.
[7] L. Li, X. Yao, C. Sun, A. Du, L. Cheng, Z. Zhu, C. Yu, J. Zou, S. C. Smith, P.
Wang, H.-M. Cheng, R. L. Frost, G. Q. Lu, Adv. Funct. Mater. 2009, 19,
265–271.
All the calculations were performed using Gaussian 09 program.
The structures were fully optimized at the M062X/6–311+ +G(d,p)
level in gas phase. M062X functional was proved to be very accu-
rate for reproducing the thermodynamic data, barrier heights,
isomerization energies. The vibrational frequency was calculated at
the same level to determine whether it is an equilibrium structure
or a transition state (TS). The corresponding normal mode for the
imaginary vibrational frequency then suggested the related reac-
tant and product for that transition state. The Gibbs free energy
(DG, kcalmolÀ1 at 298 K) barriers can be used to discuss the reac-
tion between NH3 and B2H6 to produce DADB and AB. The Cartesi-
an coordinates and vibrational frequencies of the studied models
are provided in this Supporting Information. The active hydrogen
was determined by hydrolysis of the sample in 2m-hydrochloric
acid within a sealed bulb. The amount of hydrogen released
during the hydrolysis was calculated by the pressure variation of
the system. Inductively coupled plasma-atomic emission spectrom-
etry (ICP-AES) measurements were conducted using Hitachi Limit-
ed P-4010. Before the ICP-AES measurements, samples were dis-
solved in 5 wt.% hydrochloric acid to produce a solution with
a concentration of 50–100 mgLÀ1. Powder XRD patterns were ob-
tained by D8 Advance Bruker AXS with CuKa radiation (1600 W).
During the XRD measurement, samples were mounted in a glove
box, and covered by an amorphous polymer tape to avoid oxida-
tion. Temperature-programmed desorption (TPD) and volumetric-
release measurements were carried out using a semiautomatic Sie-
vert’s apparatus, connected with a reactor filled with a sample
(typical weight ꢁ30 mg) under nitrogen atmosphere (ꢁ1 bar). The
sample was heated from 25 to 3008C at a rate of 58CminÀ1. The
11B NMR spectroscopy experiments were recorded using a Bruker
DMX (500 MHz, 11.7 T) at room temperature. All samples were dis-
solved in [D8]THF. Thermogravimetric analysis and mass spectrome-
try (TGA-MS) measurements were conducted from 30 to 3008C
under argon at a heating rate of 58CminÀ1 using TGA Q500
equipped with a quadrupole mass spectrometer for the analysis of
the evolved gas. The targeted evolving gas monitored by MS was
H2 (m/e=2). Differential Scanning Calorimetry (DSC) results were
[8] H. Fujii, S. Orimo, Physica B-Condensed Matter 2003, 328, 77–80.
[9] a) A. Stock, E. Kuss, Ber. Deut. Chem. Ges. 1923, 56, 789–808; b) H. T.
Schlesinger, A. B. Burg, J. Am. Chem. Soc. 1938, 60, 290–299.
[10] S. G. Shore, K. W. Boddeker, Inorg. Chem. 1964, 3, 914–915.
[11] a) P. V. Ramachandran, P. D. Gagare, Inorg. Chem. 2007, 46, 7810–7817;
b) D. J. Heldebrant, A. Karkamkar, J. C. Linehan, T. Autrey, Energy Environ.
Sci. 2008, 1, 156–160.
[12] X. Chen, X. Bao, B. Billet, S. G. Shore, J.-C. Zhao, Chem. Eur. J. 2012, 18,
11994–11999.
[13] E. Mayer, Inorg. Chem. 1973, 12, 1954–1955.
[14] a) X. Chen, X. Bao, J.-C. Zhao, S. G. Shore, J. Am. Chem. Soc. 2011, 133,
14172–14175; b) X. Chen, J.-C. Zhao, S. G. Shore, Acc. Chem. Res. 2013,
46, 2666–2675.
Chem. Eur. J. 2016, 22, 6228 – 6233
www.chemeurj.org
6232
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[15] a) Z. Fang, J. Luo, X. Kang, H. Xia, S. Wang, W. Wen, X. Zhou, P. Wang,
Phys. Chem. Chem. Phys. 2011, 13, 7508–7513; b) M. Bowden, D. J. Hel-
debrant, A. Karkamkar, T. Proffen, G. K. Schenter, T. Autrey, Chem.
Commun. 2010, 46, 8564–8566.
[16] H. K. Lingam, X. Chen, J.-C. Zhao, S. G. Shore, Chem. Eur. J. 2012, 18,
3490–3492.
[20] a) A. Staubitz, A. P. M. Robertson, I. Manners, Chem. Rev. 2010, 110,
4079–4124; b) S. F. Li, Y. H. Guo, W. W. Sun, D. L. Sun, X. B. Yu, J. Phys.
Chem. C 2010, 114, 21885–21890.
[21] T. He, Z. Xiong, G. Wu, H. Chu, C. Wu, T. Zhang, P. Chen, Chem. Mater.
2009, 21, 2315–2318.
[22] a) D. J. Wolstenholme, J. T. Titah, F. N. Che, K. T. Traboulsee, J. Flogeras,
G. S. McGrady, J. Am. Chem. Soc. 2011, 133, 16598–16604; b) D. J. Wol-
stenholme, K. T. Traboulsee, Y. Hua, L. A. Calhoun, G. S. McGrady, Chem.
Commun. 2012, 48, 2597–2599.
[17] A. Karkamkar, S. M. Kathmann, G. K. Schenter, D. J. Heldebrant, N. Hess,
M. Gutowski, T. Autrey, Chem. Mater. 2009, 21, 4356–4358.
[18] W. J. Shaw, J. C. Linehan, N. K. Szymczak, D. J. Heldebrant, C. Yonker,
D. M. Camaioni, R. T. Baker, T. Autrey, Angew. Chem. Int. Ed. 2008, 47,
7493–7496; Angew. Chem. 2008, 120, 7603–7606.
Received: January 26, 2016
Published online on March 21, 2016
[19] P. H. Bird, M. G. H. Wallbridge, J. Chem. Soc. 1965, 3923–3928.
Chem. Eur. J. 2016, 22, 6228 – 6233
www.chemeurj.org
6233
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim