Solid-state structure of bromine azide

Article abstract of DOI:10.1002/anie.201108092

A new twist: The single-crystal structural analysis of BrN₃ is described. In contrast to IN₃, which forms chains, BrN₃ forms a helical structure in the solid state (see picture). Such a structural feature has not been previously observed in covalent p-block azide chemistry.

Full text of DOI:10.1002/anie.201108092

.
Angewandte
Communications
DOI: 10.1002/anie.201108092
Halogen Azides
Solid-State Structure of Bromine Azide**
Benjamin Lyhs, Dieter Blꢀser, Christoph Wçlper, Stephan Schulz,* and Georg Jansen
Dedicated to Professor Gꢁnter Schmid on the occasion of his 75th birthday
Covalent azides have been investigated for more than
hundred years. Hydrazoic acid (HN3) for instance was
synthesized for the first time by Curtius in 1890.[1] Since
then, its molecular structure was investigated by use of IR and
microwave spectroscopy as well as electron diffraction.[2–4]
Only very recently, Klapçtke et al. reported on the solid-state
structure of the compound, which was determined by single-
crystal X-ray diffraction, showing that HN3 crystallizes in a
two-layer structure in which almost planar layers, formed by
intermolecular hydrogen bonds between the HN3 molecules,
are stacked parallel to (001) with an ABA stacking
sequence.[5]
synthesis of halogen azides and present the single-crystal X-
ray structure of bromine azide, BrN3 (1).
BrN3 (1) was prepared by reaction of NaN3 with bromine
(Scheme 1). The 14N NMR spectrum of a solution of 1 in
Scheme 1. Synthesis of BrN3.
CDCl3 shows three resonances for Na (d = À324 ppm, Dm1/2
=
118 Hz), Nb (d = À135 ppm, Dm1/2 = 16 Hz), and Ng (d =
À170 ppm, Dm1/2 = 25 Hz; Table 1 and Figure 1). These
values differ from those previously reported for a CDCl3
Aside from HN3, the halogen azides XN3 (X = F, Cl, Br, I)
are the simplest azides.[6] They have been investigated
experimentally and theoretically,
in particular in respect to their
Table 1: 14N chemical shifts [ppm] of BrN3.
bonding situation. IN3 was found
to be monomeric in CFCl3 solution
and forms a trans-bent structure in
the gas phase.[7] In contrast, in the
solid state, IN3 adopts a polymeric
structure, with disordered azide
Sample
Na
Nb
Ng
Ref.
[a]
BrN3
BrN3
BrN3
À324, Dm1/2 =118 Hz
À319, Dm1/2 =288 Hz
À349, Dm1/2 =475 Hz
À328, Dm1/2 =220 Hz
À135, Dm1/2 =16 Hz
À134, Dm1/2 =22 Hz
À122, Dm1/2 =30 Hz
À142, Dm1/2 =65 Hz
À170, Dm1/2 =25 Hz
À172, Dm1/2 =118 Hz
À157, Dm1/2 =90 Hz
À178, Dm1/2 =80 Hz
this work
this work
[7]
[b]
[a]
[c]
BrN3
[14]
À
[a] CDCl3. [b] Pure (without any solvent). [c] CH2Cl2.
groups with almost identical I N
bond
distances
(2.264(23),
2.30(3) ꢀ).[8] Unfortunately, only
IN3 has been structurally characterized by single-crystal X-
ray diffraction to date. The growth of suitable single crystals
of halogen azides in general is difficult owing to their extreme
sensitivity towards small pressure variations. For instance,
bromine azide was reported to explode when Dp ꢀ 0.05 Torr,
and also upon crystallization.[9] However, the gas-phase
structure of BrN3, which adopts a trans-bent structure, could
be determined by electron diffraction,[9] and the experimental
structure parameters agreed well with those obtained from
quantum-chemical calculations.[10]
Figure 1. 14N NMR spectra of the BrN3 in solution (CDCl3; bottom)
and pure (without any solvent; top). The spectra are displaced
vertically for clarity.
We became interested in the synthesis of covalent azides
only recently, and reported on the solid-state structures of
Group 15 triazides (Sb(N3)3, Pyr2Bi(N3)3),[11] a novel pentaa-
zidoantimonite dianion (Sb(N3)52À),[12] and organoantimony
diazides RSb(N3)2.[13] Herein, we expand these studies on the
solution of 1,[7] but correspond well to values reported for a
CH2Cl2 solution of 1,[14] even though the half-widths are
somewhat smaller.[14] In contrast, the 14N NMR spectrum of
pure 1 shows broader resonances.
The Raman spectrum of liquid BrN3 shows strong
adsorption bands that are due to the asymmetric (n˜ =
2146 cmÀ1) and symmetric Na-Nb-Ng stretching mode (n˜ =
1274 cmÀ1) and the Na-Br (n˜ = 451 cmÀ1) stretching mode.
The recording of the spectrum was limited by partial
decomposition of 1 upon irradiation.[15]
[*] B. Lyhs, D. Blꢀser, Dr. C. Wçlper, Prof. S. Schulz, Prof. G. Jansen
Faculty of Chemistry, University of Duisburg-Essen
Universitꢀtsstrasse 5–7, S07 S03 C30, 45117 Essen (Germany)
E-mail: stephan.schulz@uni-due.de
[**] S.S. and B.L. gratefully acknowledge the Fonds der Chemischen
Industrie (FCI) for financial support and a doctoral fellowship (B.L.).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201108092.
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Table 2: Selected structural parameters of 1.
The crystallization of 1 was performed directly on the
diffractometer at a temperature of 150 K using a miniature
zone-melting procedure with focused infrared laser radia-
tion.[16] The IR laser allowed a very controlled heating of
BrN3, thus allowing optimization of the growth conditions.
The successful growth of suitable crystals of 1 clearly
demonstrates the promising potential of this method, even
for the structural characterization of heat- and shock-sensitive
compounds.
ED[a]
SC[b]
ab initio
À
Na Br
À
Na Nb
1.899(6)
1.916(9)
1.265(9)
1.123(12)
172.2(11)
108.6(7)
1.894
1.250
1.134
172.6
108.6
1.231(22)
1.129(22)
170.7(24)
109.7(11)
À
Nb Ng
Na-Nb-Ng
Br-Na-Nb
[a] Electron diffraction. [b] single-crystal determination.
Compound 1 crystallizes in the tetragonal space group
¯
I4cd with 16 molecules in the unit cell and adopts a trans-bent
most significant changes upon neglect of relativistic and core–
structure (Figure 2).[17] The Na-Nb-Ng angle (172.2(11)8) is
valence correlation effects are an elongation of the N Br
À
bond by 0.006 ꢀ and a widening of the Br-N-N angle by 0.38.
The harmonic vibration frequencies for 79Br14N3 (187, 475,
543, 698, 1189, and 2125 cmÀ1) agree to within 23 cmÀ1 with
the measured frequencies, with exception of the symmetric
Na-Nb-Ng stretching mode, which was found to be 85 cmÀ1
lower in the calculations. The disagreement cannot be
attributed to relativistic or core–valence correlation effects,
which change the frequencies by less than 5 cmÀ1, but is rather
due to inharmonic corrections. The reaction energy for the
breakup of BrN3 to Br2 and N2 (À403.5 kJmolÀ1, at 0 K) was
calculated including zero-point vibrational energy correction
(ZPE). The latter (in the harmonic approximation) contrib-
utes À9.0 kJmolÀ1 to this value, while the contribution of
relativistic and core–valence correlation effects amounts to
À0.9 kJmolÀ1.
Figure 2. Solid-state structure of BrN3 (1). Ellipsoids set at 50%
probability.
significantly larger than the Br-Na-Nb angle (108.6(7)8). The
À
Na Br bond (1.916(9) ꢀ) is slightly longer than the sum of the
covalent radii as reported by Pyykkç et al. (1.85 ꢀ),[18] but
corresponds very well to typical values observed for neutral
In remarkable contrast to the solid state structure of IN3,
which was found to form an endless chain-like structure by
compounds containing a direct N Br bond.[19] The difference
À
À
À
À
in the Na Nb (1.265(9) ꢀ) and Nb Ng (1.123(12) ꢀ) bond
lengths clearly shows its covalently bonded nature. The bond
lengths and angles correspond very well with those obtained
from an electron-diffraction study and also with values
previously obtained from HF-MO and MP2 calculations.[9]
Herein, we have further increased the level of theory to that
of coupled-cluster theory with iterative single, double, and
perturbative triple excitations (CCSD(T)). The complete
basis set limit was nearly reached with the explicitly
correlated CCSD(T)-F12a method,[20] and relativistic and
bromine atom core–valence electron correlation effects were
determined using the Douglas–Kroll–Heß Hamiltonian.[21,22]
Geometry optimizations and calculations of harmonic
frequencies with numerical first and second derivatives for
the nitrogen and bromine molecules demonstrate the accu-
racy of this method: a bond distance and harmonic frequency
for 14N2 of 1.099 ꢀ and 2359 cmÀ1 were obtained (experimen-
tal values: 1.09768 ꢀ and 2358.57 cmÀ1),[23] while for 79Br2
values of 2.278 ꢀ and 328.5 cmÀ1 (exptl values: 2.28105 ꢀ and
325.321 cmÀ1) were obtained. Without inclusion of relativity
effects and bromine core–valence correlation, the Br2 bond is
0.019 ꢀ longer and has a harmonic frequency that is lower by
2 cmÀ1. The geometrical parameters obtained for BrN3 are
shown in Table 2. Note that the ab initio bond distances and
angles refer to the equilibrium structure, while the exper-
imental data as shown in Table 2 contain effects of non-zero-
temperature vibrational averaging in case of the electron
diffraction data and also interactions with the environment
for the single-crystal measurements. Despite this, the bond
distances agree within 0.02 ꢀ and the angles within 28. The
bridging iodine atoms with almost identical I Na bond
lengths (2.264(23), 2.30(3) ꢀ), BrN3 forms a helical structure
in the solid state (Figure 3). This structural motif has not been
observed in covalent azide chemistry to date.
Figure 3. Helical structure as observed for 1 owing to intermolecular
interactions between Na and the adjacent bromine atom. The helix is
constituted by a 41 screw axis (yÀ1/2, Àx+1, z+1/4).
À
À
The Br Na (1.916(9) ꢀ) and Br Na’ (2.885(8) ꢀ) bonds
differ by about 0.9 ꢀ, but the value of 2.885(8) ꢀ is clearly
smaller than the sum of the van-der-Waals radii of Br and N
(3.38 ꢀ)[20] and can thus be regarded as an interaction from a
crystallographic point of view. Compared to the other
structurally characterized simple covalent azide, namely
HN3, some striking similarities can be found. While BrN3
forms a helix with a 41 screw axis, HN3 has the same structural
motif with (approximately) fourfold symmetry bar the trans-
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lational component. As a consequence, an eight-membered
ring consisting of four HN3 molecules (see Figure 4a in
Ref. [5]) is formed rather than the helix observed for BrN3.
The same is true for the structural motif shown in Figure 4b in
Ref. [5]. Again, in the packing of 1, the ring is transformed
into a helix. Unlike in the solid-state structure of HN3, the
interactions of this arrangement in 1 are less certain. Weak,
but indisputably existent, hydrogen bonds connect the
molecules in the HN3 structure accompanied by N···N
contacts just less the sum of the van-der-Waals radii,[24]
whereas in
1
Br···N contacts and N···N contacts
(3.094(16) ꢀ) were found. Klapçtke et al. attributed a weak
bonding nature to these contacts to be due to opposite formal
charges of Nb and Ng in one mesomeric structure, even though
this mesomeric form is most likely not the most important
one. Furthermore, these contacts might be random side
effects of the weak hydrogen bonds. However, as these
contacts also appear in 1 where they cannot be related to
hydrogen bonds, a weak attractive interaction seems possible.
Furthermore, they are not observed in the IN3 structure,
which thus might explain why BrN3 forms helices instead of
chains. Unfortunately, attempts to obtain further information
on these contacts by recording a Raman spectrum of the BrN3
crystal led to an immediate explosion of the sample on
irradiation with the Raman laser. Therefore, the character of
these contacts could not be resolved experimentally.
Finally, the third motive identified in the packing of HN3
(Figure 4c in Ref. [5]) also has its counterpart in the packing
of 1. Four BrN3 molecules form a ring with twofold symmetry.
As was observed in HN3, two weak and two strong inter-
actions connect the molecules. Whether the N···N contacts are
attractive or not, combined with the Br···N interactions they
constitute a three-dimensional network (Figure 4), of which
two, related by c-glide-plane symmetry, interleave (Figure 5).
Figure 5. Top: Interleaved networks in the packing of 1. One network
is depicted in blue and the other in red. Gray lines mark the positions
of the 41 screw axes in the center of the helices. The networks are
related by c glide plane symmetry. Bottom: Detail of the interleaved
networks. One helix formed by Br···N interactions (red) is interpene-
trated by another formed by N···N contacts (blue) of the other network
(interactions/contacts indicated as above).
To quantify the stabilizing or destabilizing role of the
N···N and Br···N contacts, the energy of interaction of a BrN3
molecule with its nearest neighbors in the crystal was
determined by CCSD(T)-F12a calculations using the same
ab initio methods already employed to study the monomer
properties.[25] We calculated the energy of interaction of a
dimer with a Br···N contact exactly in the geometry as
observed in the crystal to be À13.1 kJmolÀ1, while for a dimer
with an N···N contact a value of À6.1 kJmolÀ1 was found, thus
demonstrating that the latter indeed stabilizes the crystal.
Relativistic and core-valence correlation effects contribute
À0.8 kJmolÀ1 to the former value, while their influence is
completely negligible for the N···N contact. The intermolec-
ular Br···N interaction is fairly large, amounting to about 60%
of the 21 kJmolÀ1 found for the hydrogen bond in the water
dimer.[26] These strong interactions are the main factor for the
stability of the crystal.
To understand the reasons for the strength of these
interactions DFT-SAPT calculations, that is, symmetry-
adapted intermolecular perturbation theory based on a
density functional theory description of the monomers,[27]
were carried out. In this case the interaction energy is
calculated as the sum of electrostatic, induction, and dis-
persion energy contributions, along with their repulsive
exchange corrections that take the energetic consequences
of the antisymmetry principle into account.[28] In DFT-SAPT,
Figure 4. Packing of 1. Br···N interactions are shown as thick dashed
lines, and N···N contacts of uncertain nature in thin dashed lines. The
helices formed by the Br···N interactions are primitively packed parallel
to the c axis. The N···N contacts (assuming they are bonding inter-
actions) connect the helices to form a three-dimensional network. The
N···N contacts themselves constitute a helix with 41 symmetry. A series
of stacked rings can be observed along the twofold axes parallel to c,
for example, in the center of the ab plane (others only partially shown).
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under Ar in a glove box. CDCl3 was dried over molecular sieves
no multipole approximation is used to calculate these
contributions, which are rather determined from electron
densities, density matrices, and corresponding static and
dynamic response properties. Neglecting relativistic effects,
the interaction energy of the dimer structure with a Br···Na
contact is determined to be À12.6 kJmolÀ1, which is in good
agreement with the non-relatvistic CCSD(T) value of
À12.3 kJmolÀ1. While the partial charges as determined
with a natural population analysis with + 0.19e for the Br
atom and À0.39e for the Na atom suggest that a strong
electrostatic interaction could provide the main contribu-
tion,[29] Figure 6 shows that the dispersion contribution is even
slightly more important. This reflects the large polarizability
(3 ꢀ) and degassed prior to use. The 14N NMR spectrum was recorded
on a Bruker Avance 300 spectrometer at 258C at 21.7 MHz and
referenced to external CH3NO2 (d(14N) = 0). Raman spectra were
recorded with a Bruker FT-Raman spectrometer RFS 100/S using the
1064 nm line of a Nd:YAG laser. The back-scattered (1808) radiation
was sampled and analyzed (Stoke range: 0 to 3500 cmÀ1). The liquid
sample was measured in a sealed capillary (400 scans and a resolution
of 2 cmÀ1) using a laser power of 40 mW. Unfortunately, an attempt to
obtain a Raman spectrum of solid BrN3 on the diffractometer (80 mW
power) resulted in an explosion of the sample immediately upon
radiation.
BrN3 (1): NaN3 (0.14 g, 2.15 mmol) was loaded in the glovebox
into a FEP reaction trap. Pure Br2 (80 mL, 1.55 mmol) was condensed
onto NaN3 at À1968C. The trap was then slowly warmed to ambient
temperature. The reaction mixture was kept at ambient temperature
for 30 min and then slowly cooled to À158C. The resulting BrN3 was
condensed in another FEP trap at À808C. This procedure was
repeated twice to finally yield pure BrN3. Raman (40 mW, 258C, 400
scans): n˜ = 2146, 1273, 451, 303 cmÀ1 14N{1H} NMR (21.7 MHz,
.
CDCl3): d = À135 (s, Nb, Dn1/2 = 16 Hz), À170 (s, Ng, Dn1/2 = 25 Hz),
À324 ppm (s, Na, Dn1/2 = 118 Hz). 14N{1H} NMR (pure BrN3): d =
À134 (s, Nb, Dn1/2 = 22 Hz), À172 (s, Ng, Dn1/2 = 182 Hz), À319 ppm
(s, Na, Dn1/2 = 288 Hz).
Received: November 17, 2011
Published online: January 16, 2012
Keywords: ab initio computations · bromine azide ·
.
covalent azides · solid-state structures
Figure 6. Electrostatic (Eel), exchange (Eexch), induction (Eind), and
dispersion (Edisp) DFT-SAPT contributions to the total interaction
energy (Eint) for dimers with Br···Na and Nb···Ng contacts in the
geometry of the crystal structure.
[1] N. N. Greenwood, A. Earnshaw in Chemistry of the Elements,
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of the bromine atom, which also becomes apparent in the
importance of the induction contribution. For the dimer with
an Nb···Ng contact, the total DFT-SAPT interaction energy is
À6.0 kJmolÀ1, in excellent agreement with the CCSD(T)
result. As to be expected from the charges on the Nb and Ng
atoms of + 0.18 and + 0.02e,[30] respectively, the electrostatic
interaction energy is strongly decreased compared to that of
the Br···Na contact. It is still an attractive contribution owing
to the incomplete screening of the attraction between
electrons and nuclei from the different molecules through
repulsive electron–electron and nucleus–nucleus interactions.
Nevertheless, dispersion clearly is the dominant stabilizing
contribution in case of the Nb···Ng contact.
[11] S. Schulz, B. Lyhs, G. Jansen, D. Blꢁser, C. Wçlper, Chem.
Commun. 2011, 47, 3401 – 3403.
[12] B. Lyhs, G. Jansen, D. Blꢁser, C. Wçlper, S. Schulz, Chem. Eur. J.
2011, 17, 11394 – 11398.
[13] B. Lyhs, D. Blꢁser, C. Wçlper, S. Schulz, Chem. Eur. J. 2011, 17,
4914 – 4920.
[14] T. M. Klapçtke, Polyhedron 1997, 16, 2701 – 2704.
[15] Details are given in the Supporting Information.
[16] “In Situ Crystallisation Techniques”: R. Boese, M. Nussbaumer
in Organic Crystal Chemistry (Ed.: D. W. Jones), Oxford
University Press, Oxford, 1994, pp. 20 – 37.
Experimental Section
Bromine azide is potentially toxic and can decompose explosively
under various conditions! It should be handled only on a scale of less
than 2 mmol with appropriate safety precautions (safety shields,
safety glasses, face shields, leather gloves, protective clothing, such as
leather suits, and ear plugs). Teflon containers should be used,
whenever possible, to avoid hazardous fragmentation. Ignoring safety
precautions can lead to serious injuries. Reactions were carried out in
traps constructed from FEP tubes. Volatile materials were handled in
a
stainless-steel–Teflon-FEP vacuum line; nonvolatile materials
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[17] Bruker AXS SMART diffractometer with APEX2 detector
(MoKa radiation, l = 0.71073 ꢀ; T= 150(1) K). The structure
was solved by Direct Methods (SHELXS-97, G. M. Sheldrick,
Acta Crystallogr. Sect. A 1990, 46, 467) and refined by full-matrix
least-squares on F2. Absorption corrections were performed
semi-empirically from equivalent reflections on basis of multi-
scans (Bruker AXS APEX2). All atoms were refined anisotropi-
cally. Single crystals were formed by an in situ zone melting
Kroll – Heß relativistic Hamiltonian, replacing the basis set for
bromine with aug-cc-pwCVTZ-DK (B. Prascher, D. E. Woon,
K. A. Peterson, T. H. Dunning, Jr., A. K. Wilson, Theor. Chem.
Acc. 2011, 128, 69 – 82) and that for nitrogen with aug-cc-pVTZ-
DK, also correlating the 3d shell of bromine, and finally adding
the variation of the considered property as compared to the
corresponding non-relativistic, valence-only CCSD(T)/aug-cc-
pVTZ result to the CCSD(T)-F12a value. Full details and
(nearly identical) CCSD(T)-F12b results can be found in the
Supporting Information.
process inside
a quartz capillary using an IR laser. The
experimental setup only allows w scans with c set to 08. Any
other orientation would have partially removed the capillary
from the cooling stream and thus led to a melting of the crystals.
This limits the completeness to 65% to 90% depending on the
[23] K. P. Huber, G. Herzberg, “Constants of Diatomic Molecules”
(data prepared by J. W. Gallagher and R. D. Johnson, III) in
NIST Chemistry WebBook, NIST Standard Reference Database
Number 69, Eds. P. J. Linstrom, W. G. Mallard, National Insti-
tute of Standards and Technology, Gaithersburg MD, 20899,
http://webbook.nist.gov.
[24] By the term “contact” we refer to any distance in the range of or
below the sum of the van-der-Waals radii.
[25] The basis set superposition error has been taken into account
through application of the counterpoise correction (S. F. Boys, F.
Bernardi, Mol. Phys. 1970, 19, 553 – 566).
[26] A. D. Buckingham, J. E. Del Bene, S. A. C. McDowell, Chem.
Phys. Lett. 2008, 463, 1 – 10, and references cited therein.
[27] a) G. Jansen, A. Heßelmann, J. Phys. Chem. A 2001, 105, 11156 –
11157; b) A. Heßelmann, G. Jansen, Phys. Chem. Chem. Phys.
2003, 5, 5010 – 5014; c) A. J. Misquitta, R. Podeszwa, B. Jeziorski,
K. Szalewicz, J. Chem. Phys. 2005, 123, 214103.
[28] DFT-SAPT calculations were carried out using the density-
fitting approximation as implemented in Molpro (A.
Heßelmann, G. Jansen, M. Schꢃtz, J. Chem. Phys. 2005, 122,
014103) with the aug-cc-pVTZ and aug-cc-pVQZ orbital basis
sets and their appropriate auxiliary basis sets as described above.
Dispersion and exchange – dispersion energies were obtained
with orbitals from the asymptotically corrected Perdew –
crystal system. 1: BrN3, Mr = 121.94, yellow crystal (0.27 ꢂ 0.05 ꢂ
3
¯
0.03 mm ); tetragonal, space group I4cd; a = 13.1873(12), b =
13.1873(12), c = 7.266(3) ꢀ; V= 1263.6(5) ꢀ3; Z = 16; m =
12.736 mmÀ1; 1calcd = 2.564 gcmÀ3; 3541 reflexes (2qmax = 548),
586 unique (Rint = 0.1904); 37 parameters, 1 restraint; largest
max./min. in the final difference Fourier synthesis 0.620 eꢀÀ3
/
À0.613 eꢀÀ3; max./min. transmission 0.75/0.17; R1 = 0.0423 (I >
2s(I)), wR2 (all data) = 0.0616. Flack absolute structure param-
eter 0.11(6) in the final structure factor calculation (a) H. D.
Flack, Acta Crystallogr. Sect. A 1983, 39, 876 – 881; b) G.
Bernardinelli, H. D. Flack, Acta Crystallogr. Sect. A 1985, 41,
500 – 511). Further details on the crystal structure investigations
for 1 may be obtained from the Fachinformationszentrum
Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax:
(+ 49)7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), on
quoting the depository number CSD-423741.
[18] P. Pyykkç, M. Atsumi, Chem. Eur. J. 2009, 15, 186 – 197.
[19] A Cambridge Structure Database (CSD) search (version 5.32
update August 2011) with ConQuest (version 1.13) gave 41
À
compounds (30 neutral, 11 ionic) containing a N Br bond with
an average bond lengths of 1.89 ꢀ.
[20] a) T. B. Adler, G. Knizia, H.-J. Werner, J. Chem. Phys. 2007, 127,
221106; b) G. Knizia, T. B. Adler, H.-J. Werner, J. Chem. Phys.
2009, 130, 054104.
Burke – Ernzerhof
exchange-correlation
(xc)
potential
(PBEAC) in combination with the adiabatic local density
approximation (ALDA) for the xc kernel, the other DFT-
SAPT contributions and partial atomic charges were calculated
with the corresponding hybrid modifications containing 25% of
exact exchange (PBE0AC; see A. Heßelmann, G. Jansen, Chem.
Phys. Lett. 2002, 357, 464 – 470; A. Heßelmann, G. Jansen, Chem.
Phys. Lett. 2002, 362, 319 – 325). Second-order dispersion and
exchange-dispersion energies were summed to the contribution
Edisp, which was extrapolated to the complete basis set limit using
the standard 1/X3 two-point formula for X = 3 and 4 (A. Halkier,
T. Helgaker, P. Jørgensen, W. Klopper, H. Koch, J. Olsen, A. K.
Wilson, Chem. Phys. Lett. 1998, 286, 243 – 252). The remaining
contributions were directly taken from the aug-cc-pVQZ results.
While Eel and Eexch denote the first-order electrostatic and
exchange contributions, Eind stands for the sum of the second-
order induction and exchange-induction and the d(HF) estimate
of higher-order contributions.
[21] G. Jansen, B. A. Heß, Phys. Rev. A 1989, 39, 6016 – 6017.
[22] CCSD(T)-F12a and F12b calculations were carried out with an
augmented triple-zeta valence Gaussian orbital basis set (aug-cc-
pVTZ; see: R. A. Kendall, T. H. Dunning, Jr., R. J. Harrison, J.
Chem. Phys. 1992, 96, 6796 – 6806) and the appropriate auxiliary
basis sets for the density fitting and resolution of the identity
approximations involved (a) F. Weigend, Phys. Chem. Chem.
Phys. 2002, 4, 4285 – 4291; b) F. Weigend, A. Kçhn, C. Hꢁttig, J.
Chem. Phys. 2002, 116, 3175 – 3183). They were made with the
Molpro program package (MOLPRO, version 2010.1, a package
of ab initio programs, H.-J. Werner, P. J. Knowles, G. Knizia,
F. R. Manby, M. Schꢃtz, P. Celani, T. Korona, R. Lindh, A.
Mitrushenkov, G. Rauhut, K. R. Shamasundar, T. B. Adler, R. D.
Amos, A. Bernhardsson, A. Berning, D. L. Cooper, M. J. O.
Deegan, A. J. Dobbyn, F. Eckert, E. Goll, C. Hampel, A.
Hesselmann, G. Hetzer, T. Hrenar, G. Jansen, C. Kçppl, Y. Liu,
A. W. Lloyd, R. A. Mata, A. J. May, S. J. McNicholas, W. Meyer,
M. E. Mura, A. Nicklass, D. P. OꢄNeill, P. Palmieri, K. Pflꢃger, R.
Pitzer, M. Reiher, T. Shiozaki, H. Stoll, A. J. Stone, R. Tarroni, T.
Thorsteinsson, M. Wang, A. Wolf; see http://www.molpro.net.).
The combined effects of relativity and bromine atom core –
valence correlation have been determined from standard
CCSD(T) calculations employing the second-order Douglas –
[29] a) A. E. Reed, R. B. Weinstock, F. Weinhold, J. Chem. Phys.
1985, 83, 735 – 746; b) A. E. Reed, L. A. Curtis, F. Weinhold,
Chem. Rev. 1988, 88, 899 – 926.
[30] The mesomeric structure with opposite formal charges on Nb and
Ng was postulated by Klapçtke et al. to play a major role for the
structure of HN3, whereas this effect hardly shows up in the
partial charges of BrN3.
1974
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