Stabilization of the Pentazolate Anion in a Zeolitic Architecture with Na20N60 and Na24N60 Nanocages

Article abstract of DOI:10.1002/anie.201710602

The experimental detection and synthesis of pentazole (HN₅) and its anion (cyclo-N₅^?) have been actively pursued for the past hundred years. The synthesis of an aesthetic three-dimensional metal–pentazolate framework (denoted as MPF-1) is presented. It consists of sodium ions and cyclo-N₅^? anions in which the isolated cyclo-N₅^? anions are preternaturally stabilized in this inorganic open framework featuring two types of nanocages (Na₂₀N₆₀ and Na₂₄N₆₀) through strong metal coordination bonds. The compound MPF-1 is indefinitely stable at room temperature and exhibits high thermal stability relative to the reported cyclo-N₅^? salts. This finding offers a new approach to create metal–pentazolate frameworks (MPFs) and enables the future exploration of interesting pentazole chemistry and also related functional materials.

Full text of DOI:10.1002/anie.201710602

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Accepted Article
Title: Stabilization of the Pentazolate Anion in a Zeolitic Architecture
with Na20N60 and Na24N60 Nanocages
Authors: Qinghua Zhang, Wenquan Zhang, Kangcai Wang, Juecheng
Li, Zhien Lin, Siwei Song, Shiliang Huang, Yu Liu, and Fude
Nie
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201710602
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10.1002/anie.201710602
Angewandte Chemie International Edition
COMMUNICATION
Stabilization of the Pentazolate Anion in a Zeolitic Architecture with
Na20N60 and Na24N60 Nanocages
Wenquan Zhang,‡a Kangcai Wang,‡a Juecheng Li,a Zhien Lin,b Siwei Song,a Shiliang Huang,a Yu Liu,a Fude Nie,a
and Qinghua Zhang*a
Abstract: The experimental detection and synthesis of pentazole in the arylpentazoles while keeping the considerably weaker N-N
-
(HN5) and its anion (cyclo-N5 ) have been actively pursued for the and N=N bonds of the pentazole ring intact.
past hundred years in worldwide laboratories. In this study, we
In view of great attractions and unprecedented challenges in
-
describe the synthesis of an aesthetical three-dimensional metal- the experimental synthesis of isolated cyclo-N5 anion or its
pentazolate framework (denoted as MPF-1) consisting of sodium parent HN5 molecule, significant efforts have been devoted to
-
-
-
ions and cyclo-N5 anions, in which the isolated cyclo-N5 anions are theoretical studies and experimental detection of the cyclo-N5
preternaturally stabilized in this inorganic open-framework featuring anion in the solution at the start of this study.7-8 Several
-
two types of nanocages (Na20N60 and Na24N60) through strong metal pioneering studies in the experimental detection of cyclo-N5
coordination bonds. The compound MPF-1 is indefinitely stable at anion were achieved through the negative ion electrospray
room temperature and exhibits relatively high thermal stability than ionization mass spectrometry (ESI-MS) and collision-induced
the reported cyclo-N5 salts. This finding offers a new approach to dissociation (CID) as the analytical tool.9-11 Very recently, the
-
-
create metal-pentazolate frameworks (MPFs) and enables the future direct formation of cyclo-N5 in THF solution was successful
exploration of interesting pentazole chemistry and also related through the reductive cleavage of the C-N bond in
functional materials.
phenylpentazole using sodium or potassium metals,12 thereby
providing a viable route towards the exploration of stable cyclo-
N5- salts in the condensed phase.
Pentazole (HN5) as the last member in the azole series has
been attracting worldwide interest over the past century because
of its intriguing aesthetic structure and potential applications as
high-performing explosives or propellants.1-2 A striking feature of
pentazole is that five nitrogen atoms enter a highly symmetric
ring with the aromatic character. However, the inherent
From an experimental point of view, two key factors for
isolating stable bulk materials containing cyclo-N5 anion must be
-
considered: (1) selective cleavage of C-N bond in a stable
arylpentazole without the destruction of pentazole ring; (2) rapid
-
and efficient stabilization of the in-situ generated active cyclo-N5
-
anion in condensed phases through strong interactions (e.g.,
hydrogen bonds), better allowing the formation of a stable
crystal material. Following such experimental guidelines, two
instability of cyclopentazolate anion (cyclo-N5 ), arising from its
high calculated electron affinity of 5.06 eV and five sterically
active free-valence electron pairs in the equatorial plane,3 has
severely hampered the prosperity of pentazole chemistry.
Despite the arylpentazoles have existed for more than half a
-
significant breakthroughs in the bulk synthesis of stable cyclo-N5
salts were achieved by Hu13 and Lu14, respectively. The key to
their success of isolating stable cyclo-N5 species in a series of
-
-
century,4 the experimental synthesis of the isolated cyclo-N5
bulk materials is to precisely cut the C-N bond of 3,5-dimethyl-4-
salts as well as its parent HN5 molecule in condensed phases
still remains a great challenge. In this regard, intensive studies
have demonstrated that the stability of pentazole ring in the
arylpentazoles largely depends on the conjugation of the
attached aryl ring featuring a strong electron-detonation group.5
Theoretical calculations also indicated that the C-N bond that
links the aryl and pentazole group has a rather high dissociation
barrier than either the N-N single bond or N=N double bond in
the pentazole ring.6 As a result, the biggest challenge in
hydroxyphenylentazole
through
treatment
with
m-
chloroperbenzoic acid while rapidly stabilizing the in-situ
-
generated cyclo-N5 species by using the ferrous bisglycinate
-
([Fe(Gly)2]) as the stabilizer. Accordingly, a series of cyclo-N5
salts including (N5)6(H3O)3(NH4)4Cl and five metal pentazolate
hydrate complexes [Na(H2O)(N5)2]·2H2O, [M(H2O)4(N5)2]·4H2O
(M = Mn, Fe and Co) and [Mg(H2O)6(N5)2] · 4H2O, were
successfully synthesized,13,14 and their crystal structures were
also determined by single-crystal X-ray diffraction analysis. In
-
synthesizing a bulk material containing the isolated cyclo-N5
anion is how to selectively cleave the relatively strong C-N bond
-
these salts containing the isolated cyclo-N5 , large amounts of
coordinated water molecules were contained in the crystal
structure, which played an irreplaceable role in stabilizing the
-
cyclo-N5 anion through extensive hydrogen bond interactions.
[a]
[b]
Dr. W. Zhang, Dr.K. Wang, Dr.J. Li, Dr. Z. Lin, Dr. S. Song, Dr. S.
Huang, Dr. Y. Liu, Prof. F. D. Nie, and Prof. Q. H. Zhang
Research Center of Energetic Material Genome Science
Institute of Chemical Materials, China Academy of Engineering
Physics (CAEP), Mianyang, 621900, China
E-mail: qinghuazhang@caep.cn
Prof. Z. Lin
College of Chemistry
Sichuan University, Chengdu 610064, China
Supporting information for this article is given via a link at the end of
the document.
More importantly, most of these pentazolate salts (either the
ammonium salt or metal pentazolate hydrates) exhibited
surprisingly good thermal stability with the decomposition
temperatures higher than 100 oC, highlighting the massive
success of this synthetic approach towards isolating and
-
stabilizing the cyclo-N5 anion. The successful syntheses of
-
above-mentioned stable cyclo-N5 salts have opened a door to
the fascinating pentazole chemistry and related materials
science.15
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10.1002/anie.201710602
Angewandte Chemie International Edition
COMMUNICATION
Encouraged by the successful progresses in well-known
metal azolate frameworks, we expect thatcyclo-N5 anion has a
contained in MPF-1 shared all its faces to twelve nearby 62·512
nanocages, while each 62·512nanocage shares its four pentagon
faces to four adjacent 512 nanocages, and the remaining ten
faces to ten adjacent 62·512 nanocages (Figure S4 and S5). The
packing of the two types of nanocages results in a 3D framework
with a zeolitic MEP topology (Figure 3a and 3b). Viewing along
the [100], [010], and [001] directions, MPF-1 has circular
channels with a pore size of 8.4 Å (Figure 3a, Figure S6 and S7).
The total accessible volume is 33.3% as calculated by PLATON
Program.16 The calculated BET surface area and pore volume
are 743.7 m2 g-1 and 0.34 cm3 g-1, respectively.17 More details
about the theoretical simulation are provided in the supporting
information (Figure S8-S10).
-
great tendency to coordinate with metal ions to form open-
framework architectures. The strong coordination bonds
-
between cyclo-N5 anions and metal ions will help to stabilize the
-
cyclo-N5 anions. During the course of such investigations, a new
open-framework material (denoted as MPF-1) containing stable
-
cyclo-N5 anion was obtained. This compound has an aesthetical
zeolitic architecture with Na20N60 and Na24N60 nanocages.
Notably, it remains stable at room temperature and exhibits
excellent thermal stability with an exothermic peak of 147.5 oC.
Single-crystal X-ray diffraction revealed that MPF-1
crystallizes in the cubic Pm-3n (No. 223) space group with
azeolitic MEP topology. The asymmetric unit contained three
unique sodium ions, which are coordinated by four, five, and six
-
neighboring different cyclo-N5 anions, respectively (Figure 1, a-
-
c). Eachcyclo-N5 anion is bonded to five adjacent sodium ions
through η5-coordination mode to form a regular pentagonal
building block (Figure 1, d). The bond lengths of Na-N and N-N
bonds are in the range of 2.407(3)-2.537(4)Å and 1.309(4)-
1.323(4) Å, respectively, while the distances between two
adjacent sodium ions are in the range of 4.003(11)-4.180(2) Å.
Figure 2. (a) the structure of Na20N60 nanocage; (b) the 512 topology of the
Na20N60 cage; (c) the structure of Na24N60 nanocage; (d) the 62·512 topology of
the Na24N60 cage; (e) the connected mode between 512 and 62·512 nanocages.
So far, a number of open-framework inorganic solids with
zeolitic topologies have been prepared and characterized.18
These compounds are constructed from corner-sharing
tetrahedral building blocks, such as SiO4, AlO4, and PO4.19,20
The discovery of MPF-1 offers a new approach to create
inorganic zeolitic frameworks by using pentagonal building unit
-
(i.e., Na5N5 from one cyclo-N5 anion and five sodium ions). This
synthetic strategy may be effective for the preparation of a new
class of inorganic zeolitic frameworks since the pentagon-liked
building block can be found in many traditional zeolites, e.g.,
DDR, IFU, MTN, and RUT zeolitic structures.
Figure 1. (a)-(c) the three different coordination modes of sodium ions (Na1,
-
-
Na2 and N3) with cyclo-N5 anion; (d) the η5-coordination mode of the cyclo-N5
anion with sodium ions.
-
Until now, the isolated cyclo-N5 anion has been reported in
six crystalline compounds.13,14 In all these compounds, water
-
The framework of MPF-1 features two types of nanocages,
i.e., Na20N60 and Na24N60. As shown in Figure 2a, the small
Na20N60 cage consists of 12 pentagons (made of pentazole ring)
and 28 hexagons (made of two sodium ions and four nitrogen
atoms from two different pentazole rings), the diameter of
Na20N60 nanocage is about 1.2 nm (as measured from two
sodium ions contained in this cage). The Na20N60 nanocage is a
closed cage with a similar ball-like structure to C60 which is
comprised by 12 pentagons and 20 hexagons. As shown in
Figure 2c, the large Na24N60 nanocage consists of 12 pentagons
and 24 hexagons with a diameter of about 1.4 nm. Considered
Na5N5 building unit as an enlarged pentagon, the Na20N60 and
Na24N60 nanocages can be simplified as 512 and 62·512
nanocages, respectively (Figure 2b and 2d). Each 512 nanocage
molecules served the important role in stabilizing the cyclo-N5
anion through extensive hydrogen bonds as N···H-O. To our
surprise, no hydrogen bonds between cyclo-N5 anions and
water molecules were observed in MPF-1, and all of the nitrogen
atoms in the cyclo-N5- anion were coordinated to the sodium ions.
Therefore, the water molecules should be not indispensable to
stabilize the cyclo-N5 anion at room temperature. In MPF-1, all
the nitrogen atoms have the similar coordination environments
which promote the cyclo-N5 anion much regular, with average
N-N bond length values as 1.309(4), 1.319(3), 1.321(3), 1.322(3),
and 1,323(4) Å, respectively. The IR spectroscopy was also
used for analyzing the structure of the MPF-1. As can be seen in
Figure S1, the characteristic absorption of cyclo-N5 anion at
1232 cm-1 was found, which is in agreement with the reported
-
-
-
-
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10.1002/anie.201710602
Angewandte Chemie International Edition
COMMUNICATION
result (ca. 1225 ±10 cm−1) that is generally present in the
pentazole salts. In addition, one additional unassigned signal at
1384cm-1, may be also due to the structural vibrations of the
cyclo-N5- anions.
development of inorganic zeolitic frameworks based on the
cyclo-N5- anions.
Acknowledgements
The authors gratefully acknowledge the supports from the
National Natural Science Foundation of China (No. 21602211,
U1530262), the Science Challenge Project (TZ2018004), the
Development Foundation of CAEP (No.2015B0302057), and the
Thousand Talents Plan of China (Youth).
Keywords: pentazole • stabilization • zeolitic framework •
nanocages • thermal stability
Figure 3. (a) the 3D open-framework of MPF-1; (b) the zeolitic MEP topology
of MPF-1 (the Na20N60 nanocages were represented by deep blue polyhedra;
the Na24N60 nanocages were represented by yellow-green polyhedral).
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COMMUNICATION
COMMUNICATION
An aesthetical 3D open-framework
featuring two types of nanocages
(Na20N60 and Na24N60) was
successfully synthesized, in which the
isolated cyclopentazolate anions and
sodium ions constructed a zeolitic
architecture through strong metal
coordination bonds.
Wenquan Zhang, Kangcai Wang,
Juecheng Li, Zhien Lin, Siwei Song,
Shiliang Huang, Yu Liu, Fude Nie, and
Qinghua Zhang*
Page 1 – Page 4
Stabilization of the Pentazolate Anion
in a Zeolitic Architecture with Na20N60
and Na24N60 Nanocages
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