Structural and Dynamical Properties of Phase I of Solid Ammonia

Article pubs.acs.org/JPCC

Structural and Dynamical Properties of Phase I of Solid Ammonia Borane Liancheng Wang,* Qingchun Wu, and Aiping Zhou Department of Mathematics and Physics, Nanjing Institute of Technology, Nanjing, Jiangsu 211167, P. R. China S Supporting Information *

ABSTRACT: The structural and dynamical properties of phase I of solid ammonia borane were investigated by means of extensive density functional theory calculations. Ab initio molecular dynamics simulation indicates that molecules in phase I are dynamically tilting along the c axis rather than aligning parallel to the c axis. A 12-site static model of phase I was proposed which is different from former models. Our simulation also demonstrates that the hydrogen distribution in phase I is 4-fold instead of the previously suggested 8-fold or 12-fold. The link between dihydrogen bonding network and lattice structure is discussed.

1. INTRODUCTION Ammonia borane (NH3BH3, AB) is a potential hydrogenstorage material which has attracted considerable attention in recent years, due to its high gravimetric and volumetric hydrogen density and moderate dehydrogenation temperature.1−5 Experimental attempts to improve its thermodynamic properties including increasing the H2 releasing rate and lowering the decomposition temperature were carried out extensively.6−11 In order to improve the kinetics of the hydrogen absorption and desorption in AB, experimental and theoretic studies including ab initio modeling were performed extensively in understanding every aspect of the structural and electrical properties of AB at various pressures and temperatures. At ambient pressure, two crystalline phases of AB were studied by various methods. NMR12−15 and neutron scattering experiments16,17 investigated the hydrogen dynamics and indicated that the rotation of the NH3 and BH3 groups distinguish the room-temperature phase from the low-temperature phase. Further, X-ray diffraction18,19 and neutron diffraction20−22 located the atomic positions and determined the lattice symmetries and structures of the two phases. At low temperature, AB crystal has a symmetry of orthorhombic Pmn21 (phase II) in which all atoms are ordered.19−22 At room temperature, AB displays a tetragonal I4mm structure (phase I) in which hydrogen atoms are disordered and form halos surrounding the N and B atoms.19,21,22 To represent the hydrogen disorder in the I4mm phase, an eight-site static model19,21 was suggested in which 3/8 occupancy of hydrogen is used. This eight-site model is consistent with the fourfold lattice symmetry but inconsistent with the C3v molecular symmetry. Later, N. J. Hess et al.22 suggested a 12-site model with 1/4 fractional occupancy in which the hydrogen positions © 2014 American Chemical Society

are spaced 30° apart, thus consistent with the C3v molecular symmetry23,24 and the fourfold lattice symmetry simultaneously. Despite the differences of the hydrogen positions, the AB molecules are all considered parallel to the c axis in these two static structures. In this study, we further explore the structural and dynamical properties of phase I at ambient conditions since it is most widely utilized in experiments attempting hydrogen releasing and related industrial applications. Ab initio molecular dynamics (MD) were performed extensively. A 12-site static structure was proposed with preservation of both molecule symmetry and lattice symmetry. Moreover, our simulations indicate that the AB molecules in phase I are dynamically tilting along the c axis rather than aligning parallel to the c axis and the H distribution in phase I is fourfold which is consistent with the tetragonal lattice of phase I.

2. THEORETICAL METHODS Ab initio molecular dynamics was performed using the Car− Parrinello scheme25 with the CPMD package.26 Gradientcorrected density functional approach27,28 and norm-conserving pseudopotentials29 were used. The valence orbits were expanded in plane waves with an energy cutoff of 120 Ry. Brillouin zone sampling was restricted to the supercell Γ point. A time step of 0.06 fs was used. A supercell with 16 AB molecules (2 × 2 × 2 of the Pmn21 structure in ref 20) was used as the starting structure. MD simulations with NPT ensemble were performed at 100, 200, 300 K, and at a pressure of 0.1 GPa for better convergence. Average lattice constants Received: March 10, 2014 Revised: July 29, 2014 Published: July 29, 2014 19266

dx.doi.org/10.1021/jp502429t | J. Phys. Chem. C 2014, 118, 19266−19272

The Journal of Physical Chemistry C

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GPa and at 300 K, the most probable tilting angle is ∼10°. Our NVT simulation with experimental lattice constants22 at ambient conditions gives similar result. In addition, we found that in the area of tilting angle approaching zero, the distributional probability is also close to zero. This implies that the molecular disorder comes from molecule rotation around the c axis rather than molecule swinging along the c axis. Moreover, it indicates that in the I4mm phase, AB molecules still tend to remain in tilted states. This is an important factor in determining the crystal structure and in understanding the dihydrogen bonding network in the I4mm phase. In a recent study by N. J. Hess et al.,22 the authors first reported that the angle of the N−B bond to the c axis does not become zero in the tetragonal phase and the AB molecule precesses about the c axis in the tetragonal phase. Our simulation results are in close agreement with N. J. Hess et al.’s results. It is worth noting that in the average MD supercells (hydrogen is ignored), which are obtained by simply calculating the average values of lattice parameters and all atoms’ average positions from the two runs at 300 K, the N−B bonds are all parallel to the c axis and the I4mm symmetry is found with maximal coordinate deviation of 0.22 Å (at 0.1 GPa and 300 K) and 0.10 Å (at ambient conditions), respectively. This is not inconsistent with the dynamical tilting of molecules along the c axis since the rotation disorder in the I4mm phase and time averaging can easily erase instantaneous information during MD simulation. 3.2. Hydrogen Dynamics and Lattice Structure. The molecular disorder in the I4mm phase mainly comes from the rotations of the NH3 and BH3 groups around the molecular axis (i.e., the N−B bond) and the rotations of the molecules as a whole around the c axis. Due to the C3v molecular symmetry, the rotations of the two groups around the N−B bond are threefold. Due to the lattice symmetry, the rotations of the molecules around the c axis are fourfold. If these two rotational axes are considered overlapped in the static structure, i.e., AB molecules align parallel to the c axis, it leads to the 12-site model in which the shared rotational axis is 12-fold as N. J. Hess et al. suggested.22 Earlier, M. E. Bowden et al.19 and J. B. Yang et al.21 both suggested a model with eight H positions around each N and B atom. However, this eight-site model is inconsistent with the C3v molecular symmetry. We found that in both models (12-site22 and 8-site19), the hydrogen positions have higher symmetry than the 4-fold lattice symmetry (12-fold and 8-fold). From our simulation, we suggest that by introducing the dynamical tilting of molecules along the c axis, the hydrogen distribution will naturally form a fourfold symmetry. This picture can be demonstrated by the statistical hydrogen distribution derived from the MD trajectories. There are two ways to calculate the hydrogen distribution depending on the reference points we choose, the H distribution with respect to the average positions of molecule mass centers (fixed positions during the simulation for each molecule, type A, Figure 2a) in the supercell or the distribution with respect to the positions of instantaneous molecule mass centers (changing positions with MD steps for every molecule, type B, Figure 2b) in the supercell. The hydrogen distribution can also be calculated with respect to the coordinate origin of the supercell, which is identical to type A. Type B distribution represents the motion of hydrogen in the intramolecular level, while type A distribution describes the correlated motion of hydrogen including NH3 and BH3 groups rotation around the B−N bonds, molecule rotation around the c axis, and the molecule

derived from the NPT simulations were then used in the simulations with NVT ensemble at the same temperature points. Experimental lattice constants for the I4mm phase at ambient conditions from ref 22 were also used in an independent NVT simulation as comparison. Parrinello− Rahman Lagrangian30,31 was used in the variable-cell MD, and the Nosé−Hoover chain thermostats32,33 were used in all MD simulations. Statistical properties were computed on wellequilibrated trajectories of 10 ps for the Pmn21 phase and 30 ps for the I4mm phase, respectively.

3. RESULTS AND DISCUSSION 3.1. Molecular Structure and Orientation. The AB molecular structure in the crystalline phase at ambient pressure has no significant difference compared with the free AB molecule. Since the C3v molecular symmetry is preserved, three intramolecular bond lengths (N−H, B−H, and N−B) and four bond angles (H−N−H, H−B−H, H−N−B, and H−B−N) are required to characterize the intramolecular shape. In this work, we do not intent to investigate the precise values or the temperature dependency for the said quantities. At all three studied temperature points, the calculated average bond lengths are approximately 1.0 Å for N−H bond, 1.2 Å for B−H bond, and 1.6 Å for N−B bond, respectively. The four calculated average bond angles are all close to 109.47° which implies the NH3 and BH3 groups both approximately form regular tetrahedrons. In addition, the averaged intramolecular H−N− B−H dihedral angle is 60° which means only staggered molecular conformation is allowed in the ambient pressure phases. The orientation of AB molecule is mainly represented by the angle between the N−B bond and the c axis (i.e., the tilting angle). In the Pmn21 phase, this tilting angle has a certain value which decreases with rising temperature at ambient pressure.22 In the I4mm phase, because of the molecular orientational disorder, the value of this angle from the average structure is zero which is confirmed by experiments.18,19 However, our calculation indicates the average tilting angle still has a considerable nonzero value. As shown in Figure 1, the calculated tilting angle distribution at various temperatures indicates that most of the time, AB molecules exist in an inclined posture along the c axis even in the I4mm phase. At 0.1

Figure 1. Tilting angle distributions of AB molecules along the c axis in the Pmn21 phase (at 0.1 GPa, 100 K and at 0.1 GPa, 200 K) and in the I4mm phase (at 0.1 GPa, 300 K and at ambient conditions). 19267



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Figure 3. Static structure of the I4mm phase. Blue represents nitrogen, pink represents boron, and white represents hydrogen.

Table 1. Structural Parameters for the I4mm Phase at Ambient Conditions

Figure 2. Density distribution of H atoms in NH3 and BH3 groups with respect to (a) average positions of molecule mass centers and (b) positions of instantaneous molecule mass centers.

translational motion as a whole. If the mass centers of molecules fluctuate insignificantly, these two types of distribution will both look like type B. However, it is not the case for AB in the I4mm phase. In general, type A represents the distribution of hydrogen in space, and type B distribution demonstrates intramolecular motion better. As shown in Figure 2, at 300 K: (i) the hydrogen all forms halos surrounding the mass centers due to the rotational disorder of hydrogen, (ii) all distribution forms fourfold symmetry (i.e., the positions of hydrogen density maxima are spaced 90° apart) which is consistent with the lattice symmetry, (iii) in type B distribution, H atoms prefer to stay in the opposite directions parallel to a or b axis in both the NH3 and BH3 groups, (iv) in type A distribution, H atoms in the BH3 groups form similar distribution compared with type B, whereas H atoms in NH3 groups have very different distribution compared with type B and the density maxima are located in the opposite direction parallel to the diagonals of the a-b plane. The difference of H distribution in the two types is attributed to the thermal fluctuations of the molecule mass centers and is discussed in the Supporting Information. To build the static structure for the I4mm phase at room temperature, we first put one AB molecule parallel to the c axis in the unit cell, with the molecule mass center positioned in the lattice origin and one H atom in the NH3 group oriented along the a axis. The calculated average molecular bond lengths and angles from the MD trajectory are used to build the molecule. Then the molecule is rotated around the b axis with the calculated average tilting angle of 11.6°. Finally, the I4mm symmetry is imposed on the lattice, forming a 12-site model (Figure 3, Table 1). After this procedure, the C3v molecular symmetry and the fourfold lattice symmetry are preserved automatically. Further,

structure

atom

x

I4mm a = 5.216 Å c = 5.005 Å

H

−0.0469

0.1587

y

0.2366

z

H H H N B

0.0598 0.2224 −0.2663 0.0280 −0.0346

−0.1922 0 0 0 0

−0.2711 0.1788 −0.2012 0.1421 −0.1755

the N and B atoms in the structure will also have fractional occupied positions with 1/4 fractional occupancy; however, the four positions for each N or B atom are very close. In addition, we found that the positions of H atoms in our 12-site model are consistent with the density maxima of type B H distribution rather than type A distribution. This is because the anharmonic thermal motion of the molecule mass centers is excluded in the static model and in the calculation of H distribution of type B. 3.3. Dihydrogen Bonding Network. The dihydrogen bonds, formed between protonic (H in NH3) and hydridic (H in BH3) hydrogen atoms on adjacent molecules, have a substantial interaction energy34 of 26 KJ·mol−1 and play a key role in understanding the structural and dynamical properties of AB. Normally, the dihydrogen bonding network is analyzed based on the static structure in which all atoms have certain equilibrium positions such as in the low-temperature Pmn21 phase20 and all high-pressure phases of AB.35,36 In the roomtemperature I4mm phase, since the structure is disordered, fractional occupancy is used to characterize the structure, and one subset of four possible orientations as a local description of the structure is used to analyze the dihydrogen interaction, realizing that the true structure is orientationally disordered occupying all four possible orientations.19,21,22 Further, since the locations of AB molecule centers are restricted by the lattice symmetry in the static structure, the dihydrogen bonding networks including bond lengths and bond angles are mainly determined by the orientations of NH3 and BH3 groups in the subset. In the eight-site model as Bowden et al. suggested,19 the authors suggested a completely different dihydrogen bonding network compared with the low-temperature Pmn21 phase 19268



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Figure 4. (a) Inequivalent adjacent NH3 and BH3 arrangements in the I4mm phase. Five Hδ+···−δH close contacts (dashed lines) within the distances of 2.2 Å are labeled according to distance. (b) Dihydrogen bonding network in the I4mm phase.

In considering the angular relationship, we suggest the type 4 close contact with length of 2.053 Å, angle of 161° for N−H··· H group, and angle of 119° for B−H···H group is the most energy favorable dihydrogen bond. As a result, the apexes of adjacent NH3 and BH3 groups are orientated along the same direction, and the dihydrogen bonding network is formed between adjacent NH3 and BH3 groups via type 4 and type 1 dihydrogen bonds (Figure 4b). It is noticed that although type 1 dihydrogen bond has shorter length, it is weaker than type 4 dihydrogen bond due to its reversed angular relationship from those expected based on Klooster et al. analysis.20 In addition, the dihydrogen bonding network as shown in Figure 4b indicates that the alignment of NH3 and BH3 groups is similar to that in the low-temperature Pmn21 phase, i.e., one of the two groups’ apexes points in the same direction. However, in the Pmn21 phase this dihydrogen bonding network does not change, while in the I4mm phase this network is randomly formed in four directions along the a or b axis. In other words, the dihydrogen bonding network as shown in Figure 4b is not only locally but also temporarily due to the rotation disorder in the room-temperature phase. Moreover, according to our 12site structure (Figure 3), the orientations of the NH3 and BH3 groups are bound to the tilting directions of AB molecules or N−B bonds, i.e., the tilting direction of the N−B bond (described by projection vector of the B−N vector in the a−b plane) and the pointing of one apex of the NH3 group within one molecule are in the same direction. In our model, since the

(Figure 4b in ref 19) in which the apexes of the BH3 groups are oriented in both directions parallel to the original Pmn21 a axis and the apexes of the NH3 groups are aligned with the Pmn21 b axis in both directions. In the 12-site model as N. J. Hess et al. suggested (Figure 1b in ref 22), the orientations of the NH3 and BH3 groups in one subset have no significant difference compared with the low-temperature phase, i.e., one of the three apexes points in the same direction parallel to the a axis or b axis. Despite the orientation difference of NH3 and BH3 groups in Bowden’s and Hess’s models, we found that in both structures AB molecules are considered parallel to the c axis and the molecular rotations have symmetries higher than fourfold which is inconsistent with the fourfold lattice chemical environment. To understand the dihydrogen bonding geometry in borane−ammonia complex, W. T. Klooster et al.20 carried out a Cambridge Structural Database study and suggested the most favorable dihydrogen bonding geometry with characteristic metric data: the H···H distance is in the range 1.7−2.2 Å, and the N−H···H group tends to be linear (angle range 150− 170°) while the B−H···H group tends to be bent (angle range 95−115°). In our model at ambient conditions, there are in total eight inequivalent adjacent BH3 and NH3 spatial arrangements (Figure 4a) in which five Hδ+···−δH close contacts within the distances of 2.2 Å are found (labeled ①−⑤ according to distance). 19269



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Figure 5. Distribution of angle between molecule tilting directions in the Pmn21 phase and I4mm phase. Red circle represents the angle between two molecules from the same layer perpendicular to the c axis. Black square represents the angle between two molecules from adjacent layers.

of the molecules constantly change due to the rotational disorder, the dihydrogen bonds are created and destroyed in a dynamical fashion. This means the angles between tilting directions of molecules will not stay near fixed values. Hence, the angles between tilting directions of molecules from same and adjacent layers are both widely distributed in the angle range of 0−360° in the I4mm phase. Nevertheless, it is clearly seen that in the I4mm phase molecules in the same layers prefer to tilt in the same direction and molecules in adjacent layers prefer to tilt in the opposite direction due to their largest statistical probability at the angle of 0 and angle of 180°, respectively. Hence, the calculation result in Figure 5 ensures that the dihydrogen bonding network determined by Klooster’s rule20 is consistent with our MD simulation and therefore supports our model.

dihydrogen bonding network (Figure 4b) is determined according to the empirical bonding rule,20 the adjacent NH3 and BH3 groups in different molecules must tend to point in the same direction which leads to the conclusion that the nearest AB molecules must tend to tilt in opposite directions. We then calculated the relative tilting distribution of adjacent molecules which is characterized by the angle between B−N vectors projections in the a−b plane. First, the projection vectors of all B−N vectors in the a−b plane are calculated for every MD step from the simulation trajectory; then the angles between the projection vectors are calculated; finally, a statistical distribution for these angles are calculated. We noticed there are two molecules in the unit cell of the I4mm phase (Figure 3). Under transitional operation, these two molecules generate two groups of molecules in alternate parallel planes or layers, respectively. The dihydrogen bonding geometry in Figure 4b then requires that only molecules that form adjacent layers are dihydrogen bonded. This also means AB molecules from adjacent layers must tend to tilt in opposite directions and molecules from the same layer (or alternate layers) must tend to tilt in the same direction. The relative tilting distribution of the low-temperature Pmn21 phase is also calculated for comparison. As shown in Figure 5, in the Pmn21 phase, angles between tilting directions of AB molecules from the same layers are close to 0° and those from adjacent layers are close to 180°, i.e., molecules in same layers are tilting in the same direction and molecules in adjacent layers are tilting in the opposite direction. In the I4mm phase, since the pointing directions of the NH3 and BH3 groups and the tilting directions

4. CONCLUSIONS In summary, we explored the structural and dynamical properties of phase I of ammonia borane by extensive ab initio molecular dynamics. The molecules in phase I are found to be dynamically tilting along the c axis. At ambient conditions, the most probable tilting angle is ∼10°. The I4mm symmetry for phase I is confirmed from the average structure derived from MD trajectory. We also found the hydrogen distribution around the molecule axis in phase I is fourfold which is consistent with the fourfold lattice symmetry. A new 12-site static structure for phase I was proposed. The most energy favorable dihydrogen bonding geometry in phase I is found to be similar to that in the low-temperature Pmn21 phase. 19270



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(15) Cho, H.; Shaw, W. J.; Parvanov, V.; Schenter, G. K.; Karkamkar, A.; Hess, N. J.; Mundy, C.; Kathmann, S.; Sears, J.; Lipton, A. S.; et al. Molecular Structure and Dynamics in the Low Temperature (Orthorhombic) Phase of NH3BH3. J. Phys. Chem. A 2008, 112, 4277−4283. (16) Hess, N. J.; Hartman, M. R.; Brown, C. M.; Mamontov, E.; Karkamkar, A.; Heldebrant, D. J.; Daemen, L. L.; Autrey, T. Quasielastic Neutron Scattering of -NH3 and -BH3 Rotational Dynamics in Orthorhombic Ammonia Borane. Chem. Phys. Lett. 2008, 459, 85−88. (17) Kathmann, S. M.; Parvanov, V.; Schenter, G. K.; Stowe, A. C.; Daemen, L. L.; Hartl, M.; Linehan, J.; Hess, N. J.; Karkamkar, A.; Autrey, T. Experimental and Computational Studies on Collective Hydrogen Dynamics in Ammonia Borane: Incoherent Inelastic Neutron Scattering. J. Chem. Phys. 2009, 130, 024507. (18) Hoon, C. F.; Reynhardt, E. C. Molecular Dynamics and Structures of Amine Boranes of the Type R3N.BH3. I. X-ray Investigation of H3N.BH3 at 295 K and 110 K. J. Phys. C 1983, 16, 6129−6136. (19) Bowden, M. E.; Gainsford, G. J.; Robinson, W. T. RoomTemperature Structure of Ammonia Borane. Aust. J. Chem. 2007, 60, 149−153. (20) Klooster, W. T.; Koetzle, T. F.; Siegbahn, P. E. M.; Richardson, T. B.; Crabtree, R. H. Study of the N−H···H−B Dihydrogen Bond Including the Crystal Structure of BH3NH3 by Neutron Diffraction. J. Am. Chem. Soc. 1999, 121, 6337−6343. (21) Yang, J. B.; Lamsal, J.; Cai, Q.; James, W. J.; Yelon, W. B. Structural Evolution of Ammonia Borane for Hydrogen Storage. Appl. Phys. Lett. 2008, 92, 091916. (22) Hess, N. J.; Schenter, G. K.; Hartman, M. R.; Daemen, L. L.; Proffen, T.; Kathmann, S. M.; Mundy, C. J.; Hartl, M.; Heldebrant, D. J.; Stowe, A. C.; et al. Neutron Powder Diffraction and Molecular Simulation Study of the Structural Evolution of Ammonia Borane from 15 to 340 K. J. Phys. Chem. A 2009, 113, 5723−5735. (23) Hess, N. J.; Bowden, M. E.; Parvanov, V. M.; Mundy, C.; Kathmann, S. M.; Schenter, G. K.; Autrey, T. Spectroscopic Studies of the Phase Transition in Ammonia Borane: Raman Spectroscopy of Single Crystal NH3BH3 as a Function of Temperature from 88 to 330 K. J. Chem. Phys. 2008, 128, 034508. (24) Brown, C. M.; Jacques, T. L.; Hess, N. J.; Daemen, L. L.; Mamontov, E.; Stowe, A. C.; Autrey, T. Dynamics of Ammonia Borane Using Neutron Scattering. Physica B 2006, 385, 266−268. (25) Car, R.; Parrinello, M. Unified Approach for Molecular Dynamics and Density-Functional Theory. Phys. Rev. Lett. 1985, 55, 2471−2474. (26) CPMD, http://www.cpmd.org/, Copyright IBM Corp., 1990− 2008; Copyright MPI für Festkörperforschung Stuttgart, 1997−2001. (27) Becke, A. D. Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior. Phys. Rev. A 1988, 38, 3098−3100. (28) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle− Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37, 785−789. (29) Troullier, N.; Martins, J. L. Efficient Pseudopotentials for PlaneWave Calculations. Phys. Rev. B 1991, 43, 1993−2006. (30) Parrinello, M.; Rahman, A. Crystal Structure and Pair Potentials: A Molecular-Dynamics Study. Phys. Rev. Lett. 1980, 45, 1196−1199. (31) Focher, P.; Chiarotti, G. L.; Bernasconi, M.; Tosatti, E.; Parrinello, M. Structural Phase Transformations via First-Principles Simulation. Europhys. Lett. 1994, 26, 345−351. (32) Nosé, S. A Unified Formulation of the Constant Temperature Molecular Dynamics Methods. J. Chem. Phys. 1984, 81, 511−519. (33) Hoover, W. G. Canonical Dynamics: Equilibrium Phase-Space Distributions. Phys. Rev. A 1985, 31, 1695−1697. (34) Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold, A. L.; Koetzle, T. F. A New Intermolecular Interaction: Unconventional Hydrogen Bonds with Element-Hydride Bonds as Proton Acceptor. Acc. Chem. Res. 1996, 29, 348−354.

ASSOCIATED CONTENT

S Supporting Information *

Discussion about the difference of two types of H distribution and the influence of thermal fluctuation of the molecule mass centers in phase I. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel./Fax: +86-25-86118470. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Scientific Research Foundation of Nanjing Institute of Technology (YKJ201112, ZKJ201204, YKJ201341, and QKJA2011010) and the NSF of the Jiangsu Higher Education Institutions of China (12KJB510004).

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REFERENCES

(1) Wolf, G.; Baumann, J.; Baitalow, F.; Hoffmann, F. P. Calorimetric Process Monitoring of Thermal Decomposition of B−N−H Compounds. Thermochim. Acta 2000, 343, 19−25. (2) Baitalow, F.; Baumann, J.; Wolf, G.; Jaenicke-Rössler, K.; Leitner, G. Thermal Decomposition of B−N−H Compounds Investigated by Using Combined Thermoanalytical Methods. Thermochim. Acta 2002, 391, 159−168. (3) Storozhenko, P. A.; Svitsyn, R. A.; Ketsko, V. A.; Buryak, A. K.; Ulyanov, A. V. Ammineborane: Synthesis and Physicochemical Characterization. Russ. J. Inorg. Chem. 2005, 50, 980−985. (4) Bowden, M.; Autrey, T.; Brown, I.; Ryan, M. The Thermal Decomposition of Ammonia Borane: A Potential Hydrogen Storage Material. Curr. Appl. Phys. 2008, 8, 498−500. (5) Hu, M. G.; Geanangel, R. A.; Wendlandt, W. W. The Thermal Decomposition of Ammonia Borane. Thermochim. Acta 1978, 23, 249−255. (6) Kelly, H. C.; Marriott, V. B. Reexamination of the Mechanism of Acid-Catalyzed Amine−Borane Hydrolysis. The Hydrolysis of Ammonia−Borane. Inorg. Chem. 1979, 18, 2875−2878. (7) Stephens, F. H.; Baker, R. T.; Matus, M. H.; Grant, D. J.; Dixon, D. A. Acid Initiation of Ammonia−Borane Dehydrogenation for Hydrogen Storage. Angew. Chem., Int. Ed. 2007, 46, 746−749. (8) Keaton, R. J.; Blacquiere, J. M.; Baker, R. T. Base Metal Catalyzed Dehydrogenation of Ammonia−Borane for Chemical Hydrogen Storage. J. Am. Chem. Soc. 2007, 129, 1844−1845. (9) Cheng, F. Y.; Ma, H.; Li, Y. M.; Chen, J. Ni1−xPtx (x = 0−0.12) Hollow Spheres as Catalysts for Hydrogen Generation from Ammonia Borane. Inorg. Chem. 2007, 46, 788−794. (10) Bluhm, M. E.; Bradley, M. G.; Butterick, R.; Kusari, U.; Sneddon, L. G. Amineborane-Based Chemical Hydrogen Storage: Enhanced Ammonia Borane Dehydrogenation in Ionic Liquids. J. Am. Chem. Soc. 2006, 128, 7748−7749. (11) Gutowska, A.; Li, L.; Shin, Y.; Wang, C. M.; Li, X. S.; Linehan, J. C.; Smith, R. S.; Kay, B. D.; Schmid, B.; Shaw, W.; et al. Nanoscaffold Mediates Hydrogen Release and the Reactivity of Ammonia Borane. Angew. Chem., Int. Ed. 2005, 44, 3578−3582. (12) Reynhardt, E. C.; Hoon, C. F. Molecular Dynamics and Structures of Amine Boranes of the Type R3N.BH3. II. NMR Investigation of H3N.BH3. J. Phys. C 1983, 16, 6137−6152. (13) Penner, G. H.; Phillis Chang, Y. C.; Hutzal, J. A Deuterium NMR Spectroscopic Study of Solid BH3NH3. Inorg. Chem. 1999, 38, 2868−2873. (14) Gunaydin-Sen, O.; Achey, R.; Dalal, N. S.; Stowe, A.; Autrey, T. High Resolution 15N NMR of the 225 K Phase Transition of Ammonia Borane (NH3BH3): Mixed Order−Disorder and Displacive Behavior. J. Phys. Chem. B 2007, 111, 677−681. 19271



Article

(35) Filinchuk, Y.; Nevidomskyy, A. H.; Chernyshov, D.; Dmitriev, V. High-Pressure Phase and Transition Phenomena in Ammonia Borane NH3BH3 from X-ray Diffraction, Landau Theory, and ab Initio Calculations. Phys. Rev. B 2009, 79, 214111. (36) Wang, L. C.; Bao, K.; Meng, X.; Wang, X. L.; Jiang, T. T.; Cui, T.; Liu, B. B.; Zou, G. T. Structural and Dynamical Properties of Solid Ammonia Borane under High Pressure. J. Chem. Phys. 2011, 134, 024517.

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Structural and Dynamical Properties of Phase I of Solid Ammonia

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