9th Int. Symposium Hydrogen & Energy
Emmetten, Switzerland 2015
SYNTHESIS AND CHARACTERISATION OF NEW AMIDOBORANES
Nikola Biliškova, Ivan Halasza, Elsa Callinib, Andreas Borgschulteb, Andreas Züttelb
Laboratory of Solid State and Complex Compounds Chemistry, Ruđer Bošković Institute, Bijenička c. 54, HR-10000
Zagreb, Croatia
b EMPA, Materials Science and Technology, Dept. Hydrogen and Energy, 8600 Dübendorf, Switzerland
a
A series of single- and bimetallic amidoboranes and their complexes with ammonia borane were prepared by ball milling
from ammonia borane and corresponding metal hydrides. Products are characterised by means of IR spectroscopy and
powder XRD. Dehydrogenation was followed by DSC and variable temperature Raman spectroscopy. All of the prepared
systems dehydrogenate at considerably lower temperature with respect to ammonia borane.
Introduction
Results
Ammonia borane (NH3BH3, further in the text AB) is
extensively investigated due to its extremely high both
gravimetric and volumetric hydrogen density. However,
serious drawbacks make it unfavourable system for
practical onboard hydrogen storage. Its reactivity is
largely determined by intermolecular dihydrogen bonding
interaction of N-H+···-H-B type, which operates in solid
AB. Thus, the flexibility of this interaction is of crucial
importance for fine tuning of properties of AB-based
systems. A very successful approach is its chemical
modification by substitution of one H+ of NH3 moiety by
an electropositive element, such as alkaline or alkaline
earth metal, which gives rise to amidoboranes [1]. This
substitution causes a significant destabilisation of
dihydrogen bonding network, with assistance of
dehydrogenation via hydride transfer by intermediate MH
species. The changes in dehydrogenation mechanism,
as well as opportunity of tuning of thermodynamics [2]
make them highly promising systems for hydrogen
storage. Additionally, complexation of amidoboranes with
hydrogen bond donating species, such as NH3 [3] or AB
[4] further promotes dehydrogenation.
Milling of the LiH with AB in all molar ratios gives rise to
corresponding LiAB∙mAB products. As expected, IR
spectrum of the product obtained by reaction of 1:1
mixture is considerably simpler than those for 1:2 and 1:3
products.
On the other hand, all attempts to obtain NaAB by milling
1:1 mixture of NaH and AB were unsuccessful. The
obtained product was grey, and IR spectra show almost
complete lack of the bands in the (NH) and (BH)
region, which indicates decomposition of the product.
However, milling of the 1:2 ad 1:3 mixture of NaH and AB
readily gives NaAB∙mAB. (BH) region is complex, as in
the case of Li-containing counterparts.
Bimetallic amidoboranes Li2Mg(AB)4 and Na2Mg(AB)4
were successfully prepared. XRD of the product obtained
by milling of the 2:1:4 mixture of NaH, MgH2 and AB
corresponds to the one previously reported for
Na2Mg(AB)4 [5]. Combined evidence from IR spectra and
XRD for prepared M2MgAB4 systems shows that the
bonding in these systems is very similar, but they are not
isostructural, as confirmed by structure of the Li2Mg(AB)4,
solved by Rietveld method. It revealed very similar
coordination of M and Mg atoms in both cases. Attempts
to prepare trimetallic amidoborane LiNaMg(AB)4 as well
as aducts of bimetallic MABs with AB, Li2Mg(AB)4∙AB and
Na2Mg(AB)4∙AB, were unsuccessful. In all cases, just a
physical mixtures were obtained.
Here we report a series of novel complexes of lithium and
sodium amidoborane with AB (MAB·mAB, where M = Li,
Na and m = 1, 2), as well as bimetallic amidoboranes of
M2MgAB4 composition.
Experimental
Samples were prepared by high energy ball milling (Spex
8000M) of stoichiometric mixtures of AB and
corresponding metal hydrides during 30 min in argon
atmosphere. Single-reflection ATR IR spectroscopy,
powder XRD were used for structural characterisation.
Dehydrogenation properties were investigated by DSC
and variable temperature Raman spectroscopy.
References
[1] Y. S. Chua et al. Chem. Commun. 47 (2011) 51165129
[2] Y. S. Chua et al. Chem. Mater. 24 (2012) 3574-3581
[3] Y. S. Chua et al. Inorg. Chem. 51 (2012) 1599-1603
[4] C. Wu et al. Chem. Mater. 22 (2010) 3-5
[5] H. Wu et al. Chem. Commun. 47 (2011) 4102-4104
Born September 17, 1974 in Pula, Croatia.
1999 Masters degree of inorganic chemistry at Faculty of Sciences, University of Zagreb; thesis at
Faculty of Science in Zagreb.
2009 PhD degree in physical chemistry at Ruđer Bošković Institute, Zagreb; thesis “”
2012 Research associate at the Laboratory of Solid State and Complex Compounds Chemistry,
Division of Materials Chemistry, Ruđer Bošković Institute, Zagreb
2014 Visiting scientist at EMPA, Dept. Hydrogen and Energy, Dübendorf, Switzerland
Nikola Biliškov
Corresponding author: Nikola Biliškov, nbilis@irb.hr, Tel. +385 91 7209759