Pairing heterocyclic cations with closo-dodecafluorododecaborate (2-): Synthesis of binary heterocyclium(1+) salts and a Ag4(heterocycle) 84+ salt of B12F122-

Article abstract of DOI:10.1016/j.jfluchem.2011.07.009

Eight binary salts that pair triazolium(1+), imidazolium(1+), pyrimidinium(1+), or purinium(1+) cations with the icosahedral closo-dodecafluorododecaborate(2-) anion (B₁₂F₁₂ ^2-) were synthesized using open-air benchtop metathesis reactions in water or acetonitrile. The scale of the reactions varied from just milligrams to nearly one gram of the K₂B₁₂F₁₂ starting material. Other reaction conditions, the scope of the reaction, and the solubilities for the new salts are discussed. Five [heterocyclium] ₂[B₁₂F₁₂] salts, which were obtained in yields ranging from 84% to 99%, displayed significantly higher densities than the corresponding previously reported analogous [heterocyclium]₂[B ₁₂H₁₂] and [heterocyclium][CB₁₁H₁₂] salts. A ninth high-density salt consisted of B₁₂F₁₂ ^2- paired with a complex Ag₄(triazole)₈ ⁴⁺ cation. The structures of eight of the nine new compounds were determined by single-crystal X-ray diffraction analysis. The density of five [heterocyclium]₂[B₁₂F₁₂] salts was found to increase approximately linearly as the distance between the five-membered-ring heterocyclium(1+) cation centroids decreased. This work demonstrates additional flexibility for the rational design of ionic structures with predictable properties, which will ultimately permit the tailoring of ingredient-response behavior.

Full text of DOI:10.1016/j.jfluchem.2011.07.009

Journal of Fluorine Chemistry 132 (2011) 925–936
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Pairing heterocyclic cations with closo-dodecafluorododecaborate (2ꢀ)
4+
Synthesis of binary heterocyclium(1+) salts and a Ag4(heterocycle)8
salt of B12F12
2ꢀ
c
John L. Belletire a, Stefan Schneider b, Scott A. Shackelford b, , Dmitry V. Peryshkov ,
Steven H. Strauss
*
c,**
a ERC Inc., AFRL/RZSP, 10 East Saturn Blvd., Edwards AFB, CA 93524-7680, United States
b Air Force Research Laboratory, AFRL/RZSP, 10 East Saturn Blvd., Edwards AFB, CA 92524-7680, United States
c Department of Chemistry, Colorado State University, Ft. Collins, CO 80523, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
Eight binary salts that pair triazolium(1+), imidazolium(1+), pyrimidinium(1+), or purinium(1+) cations
with the icosahedral closo-dodecafluorododecaborate(2ꢀ) anion (B12F122ꢀ) were synthesized using
open-air benchtop metathesis reactions in water or acetonitrile. The scale of the reactions varied from
just milligrams to nearly one gram of the K2B12F12 starting material. Other reaction conditions, the scope
of the reaction, and the solubilities for the new salts are discussed. Five [heterocyclium]2[B12F12] salts,
which were obtained in yields ranging from 84% to 99%, displayed significantly higher densities than the
Received 21 April 2011
Received in revised form 9 July 2011
Accepted 11 July 2011
Available online 20 July 2011
Keywords:
corresponding previously reported analogous [heterocyclium]2[B12H12] and [heterocyclium][CB11H12
]
Heterocyclium
salts. A ninth high-density salt consisted of B12F122ꢀ paired with a complex Ag4(triazole)84+ cation. The
structures of eight of the nine new compounds were determined by single-crystal X-ray diffraction
analysis. The density of five [heterocyclium]2[B12F12] salts was found to increase approximately linearly
as the distance between the five-membered-ring heterocyclium(1+) cation centroids decreased. This
work demonstrates additional flexibility for the rational design of ionic structures with predictable
properties, which will ultimately permit the tailoring of ingredient-response behavior.
Published by Elsevier B.V.
Dodecafluorododecaborate
Perfluoroborane
Icosahedral borane
Icosahedral carborane
Metathesis
1. Introduction
clustering of 12 B atoms into an icosahedral cage provides a
polycenter of delocalized boron orbital bonding, which, like
Eight new binary salts that pair the icosahedral closo-
dodecafluorododecaborate(2ꢀ) anion (B12F122ꢀ) with heterocy-
aromatic hydrocarbon rings, is very stable to chemical attack [5].
The 12 B–H vertexes of B12H122ꢀ, like the C–H vertexes in benzene,
can undergo a wide variety of aromatic substitution reactions [2–4].
2ꢀ
clium(1+) cations and one new salt of B12F12 with a tetrameric
4+
2ꢀ
Ag4(triazole)8 cation were synthesized and characterized. All
This characteristic permitted the synthesis of the B12F12 dianion
nine salts were prepared using open-air metathesis reactions in
which stoichiometric amounts of a heterocyclium(1+) halide and
K2B12F12 were mixed in either water or acetonitrile.
by electrophilic attack of supercritical HF in 1992 (it was isolated as
Cs2(H2O)B12F12 in 38% yield) [6]. Since then, the structures of nine
other salts of B12F122ꢀ have been reported. The first of the nine was
the structure of [CPh3]2[B12F12] (also reported was an improved
synthesis of K2B12F12 in 72% yield) [7]. The next three were salts
contained bridged heterocyclium(2+) dications, where the func-
tional unsaturated sites, centered in the alkyl-based bridge
structure, have a heterocyclium(1+) moiety tethered at each alkyl
bridge terminus [8]. More recent examples include a detailed X-ray
crystal structure of K2B12F12 [9], the reactant used in the metathesis
reactions described herein, and in the synthesis of the hetero-
cyclium(2+) salts [8]. Finally, the structures of K2(H2O)2B12F12 [10],
K2(H2O)2B12F12 [10], K3(AsF6)B12F12 [11], and Cs3(AsF6)B12F12 [11]
have just been reported (the latter two are rare examples of salts
containing fluoroanions with different shapes and charges).
2ꢀ
The B12F122ꢀ dianion is analogous to the isostructural B12H12
dianion that was first reported by Pitochelli and Hawthorne [1]. The
2ꢀ
B12H12
anion has been called a ‘‘super-aromatic’’ polyhedral-
shaped structure, with 26 delocalized valence electrons in its
bonded framework, and is conceptually similar to the delocalized
s
-
p-
systemsofplanararomatichydrocarbonssuchasbenzene[2–4]. The
* Corresponding author. Tel.: +1 661 718 2665.
** Corresponding author. Tel.: +1 970 491 5104; fax: +1 970 491 1801.
E-mail addresses: scott.shack@roadrunner.com (S.A. Shackelford),
steven.strauss@colostate.edu (S.H. Strauss).
0022-1139/$ – see front matter. Published by Elsevier B.V.
doi:10.1016/j.jfluchem.2011.07.009

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J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
in H2O and others were quite soluble. Therefore, they were isolated
and purified by procedures parallel to those discussed above. Salts
2, 5, and 6 could be synthesized using either H2O or CH3CN as the
solvent.
The new salts exhibit significantly higher densities than those
of the aforementioned analogous heterocyclium(1+) salts of
2ꢀ
ꢀ
B12H12 and CB11H12 [12]. Reaction conditions, product yields,
density values, certain salt melting/decomposition behaviors, and
the general scope of the synthesis of binary heterocyclium salts of
2ꢀ
B
12F12 are addressed in this paper.
2. Results and discussion
2.1. General comments
A long sought-after goal of synthetic chemistry has been the
ability to rationally design chemical structures which will exhibit
predictable chemical and physical properties for attaining
desired chemical or physical behavioral responses [12,13,17].
Heterocyclic salts offer three different types of flexibility for
achieving this goal. The cation ring structure or its pendant
groups can be altered ((e.g., 1-NH2-3-H-1,2,3-triazolium(1+) vs.
4-NH2-1-H-1,2,4-triazolium(1+) or 1-NH2-3-H-1,2,3-triazo-
lium(1+) vs. 1-NH2-3-Me-1,2,3-triazolium(1+)) when paired
with a common anion [12,13]. The chemical structure of the
anion can also be changed ((e.g., a polyhedral borane(2ꢀ) anion
vs. a carborane(1ꢀ) anion)) when paired with an identical cation
[12,13]. Furthermore, a cation with a different composition (with
an identical anion), or an entirely different anion (with a common
cation), can be substituted in a given salt ((e.g., imidazolium(1+)
vs. triazolium(1+) cation [12], or nitrate(1ꢀ) vs. a polyhedral
borane(2ꢀ) anion)) [17].
2ꢀ
2ꢀ
(top), B12H12
Fig. 1. Examples of binary heterocyclium(1+) salts of B12F12
(middle), and CB11H12ꢀ (bottom). Each vertex of the icosahedral anions bears an F
atom (top) or a H atom (middle and bottom). The black sphere in the drawing of the
CB11H12ꢀ anion is the C–H vertex. The anion drawings also show the numbering of
the vertexes.
Tailoring the thermochemical initiation response of two
bridged heterocyclium salts of borane(2ꢀ) anions, and of bridged
heterocyclium(2+) nitrate(1ꢀ) salts, to rapid self-sustained com-
bustions in air by altering the cation chemical structure, or by
substitution of the anion, has been demonstrated experimentally
[17] and was explained by an updated high-energy-material
The binary [heterocyclium]2[B12F12
] salts containing two
heterocyclium(1+) cations reported in this work represent a
new type of B12F122ꢀ salt. These salts, and all previously reported
[heterocyclium]2[B12H12] [12,13] and [heterocyclium][CB11H12
salts [12–16], have a unique common characteristic. For each type,
a planar aromatic -electron-delocalized heterocyclium(1+) cat-
ion is stoichiometrically paired with a polyhedral (icosahedral or
pseudo-icosahedral) aromatic -electron-delocalized dianion in
initiation-sensitivity concept [18]. Like the previously reported
2ꢀ
]
bridged heterocyclium(2+) salts of B12F12
[8], the binary
heterocyclium(1+) salts of B12F122ꢀ described in this paper provide
additional examples in the flexibility of the heterocyclium(n+)
system for rational structural design, predicable property modifi-
cation, and the resultant tailoring of the chemical/physical
behavior of this important class of salts.
p
s
the same lattice [12,13]. Examples of each of the three types of salt
we have studied are shown in Fig. 1.
The previously reported biꢀnary heterocyclium(1+) salts con-
2.2. Synthesis of new salts
2ꢀ
taining B12H12 and CB11H12 can be divided into two general
types based on their solubilities. Some are only sparingly soluble in
H2O and precipitated from the aqueous metathesis-reaction
medium during the open-air benchtop synthesis [12]. Others
were very soluble in H2O and could be isolated in pure form only by
repeated extraction of the crude solid reaction product from the
two solid reactant salts using hot CH3CN, followed by subsequent
removal of the solvent [13].
The nine salts shown in Fig.
2 were synthesized using
metathesis reactions similar to the example shown in Scheme 1
for the synthesis of salt 2. Most of the metatheses were carried out
on a small scale initially (e.g., 44–101 mg K2B2F12) using H2O as the
solvent. As with the previously reported binary [heterocy-
clium]2[B12H12] [12,13] or [heterocyclium][CB11H12] salts [12–
16], the solubility of the particular B12F122ꢀ salt dictated whether
H2O or CH3CN could be used as the solvent for a high-yield
metathesis reaction [12,13]. It was found that salts 2, 5, and 6 could
The new [heterocyclium]2[B12F12] salts, which are shown in
Fig. 2, were of the same two types: some were essentially insoluble
Scheme 1.

J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
927
Fig. 2. The compositions of salts 1–9 studied in this work. The positive charge in salt 8 is delocalized over the entire fused-ring system. The positive charges in salt 9 are
delocalized to some extent over the eight triazole molecules, which are coordinated to the Ag+ cations.
be prepared in good yield in either solvent. In contrast, salts 1 and 3
were best prepared using CH3CN (even small-scale reactions in this
solvent gave good yields). Finally, salts 4 and 7–9 were best
prepared using H2O as the solvent. The metathesis reaction
solvent, reaction scale, yield, and melting/decomposition behavior
of binary salts 1–4 and 6 are listed in Table 1.
The improved synthesis of K2B12F12 reported in 2009 [19] made
this reactant salt available in significantly larger quantities than if
the original synthesis reported in 2003 had been used [7]. The
larger-scale and shorter-reaction-time synthetic method was
achieved by perfluorination of 10 g of K2B12H12 to K2B12F12 in
74% yield and 99.5+% purity by continuously bubbling 20/80 F2/N2
through a CH3CN solution of commercially available K2B12H12
using ordinary glassware [19]. The enhanced availability of
K2B12F12 permitted relatively large-scale metathesis reactions to
be conducted in this work using 0.453–0.902 g quantities of
K2B12F12. This allowed salts 2, 4, and 6 to be prepared in quantities
exceeding 1 g in this work, as was also the case in the work
reported in Ref. [8].
Accomplishing these large-scale syntheses permitted reliable
isolated product yields and spectroscopic characterization data to
be obtained for salts 2, 4, and 6. Additionally, a direct comparison
between two identical metathesis reactions was made using the
same amount of K2B12F12 and either H2O or CH3CN as the solvent to
prepare salt 2 (see Table 1). A lower yield of salt 2 was isolated from
the H2O solvent (i.e., 84% vs. 99% when CH3CN was the solvent).
Salt 4 was prepared by reacting a stoichiometric amount of [4-
NH2-1-Me-1,2,4-triazolium][I] with 0.902 g K2B12F12. The digested
solid was filtered and dried and afforded 1.03 g of a fine white
powder of 4 (90.0% yield). Single-crystal X-ray diffraction analysis
of this sample of salt 4 were consistent with the single-crystal X-
ray determined structure of 4 using crystals prepared with a small-
scale metathesis reaction. Salt 6 was prepared by reacting a
stoichiometric amount of [1-NH2-3-Me-1,2,3-triazolium][I] with
Table 1
Metathesis reaction solvent, scale, yield, and melting/decomposition behavior for 1–4 and 6.a
Salt
Solvent
Rxn. scale (g K2B12F12
)
Yield
Melting/decomposition behavior
1
2
2
3
4
6
CH3CN
CH3CN
H2O
0.100
0.454
0.453
0.101
0.436
0.436
90%
99%
84%
93%
90%
92%
Not determined
Slowly converted to a dark-brown solid with some liquification and gas evolution up to 398 8C
Slowly converted to a dark-brown solid with some liquification and gas evolution up to 398 8C
Not determined
CH3CN
H2O
Sintered at 190.1–191.2 8C; liquified at 191.3–193.2 8C
Sintered at 201.3–202.2 8C; liquified at 202.3–204.2 8C
H2O
a
The five salts listed in this table are as follows: 1, [1-Et-3-Me-imidazolium]2[B12F12]; 2, [1-H-3-Me-imidazolium]2[B12F12]; 3, [H(imidazolium)]2[B12F12]; 4, [4-NH2-1-Me-
1,2,4-triazolium]2-[B12F12]; 6, [1-NH2-3-Me-1,2,3-triazolium]2[B12F12]. Drawings of the cations in these salts are shown in Fig. 2.

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J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
0.901 g K2B12F12 under the same conditions just described to
prepare salt 4. This afforded, after filtering and drying, 1.06 g of 6 as
an off-white solid (92.3% yield). Proton and 13C NMR and FTIR
spectroscopic data for this sample of 6 were consistent with the
single-crystal X-ray structure of 6 determined from crystals
prepared using a small-scale milligram (87.2 mg) metathesis
reaction. The spectroscopic data between the large-scale and
small-scale prepared samples of salt 6 also matched.
To minimize the presence of residual KX byproduct in these
larger scale reactions (X = Cl, Br) [8], the aqueous metatheses were
conducted by dropwise addition of an aqueous solution of K2B12F12
to a refluxing aqueous solution of the heterocyclium(1+) halide.
After refluxing for 5–8 min, during which precipitation of the
desired [heterocyclium]2[B12F12] perfluoroborane salt product 2, 4,
or 6 occurred, the reaction suspension was cooled to room
temperature prior to final isolation by filtration and subsequent
vacuum drying. Samples of salt 2 prepared using either H2O or
CH3CN as the metathesis solvent were analyzed for the presence of
Clꢀ by ion chromatography. In both cases the mass% of Clꢀ was
only 0.01%, demonstrating the level of purity that is possible using
the metathesis reactions shown in Scheme 1.
Fig. 3. Heterocyclium(1+) cations with no alkyl substituents did not readily form
binary [heterocyclium]2[B12F12] salts using the metathesis reactions shown in
Scheme 1.
The attempted synthesis of [4-NH2-1-H-1,2,4-triazolium]2
[B12F12] instead produced [4-NH2-1-H-1,2,4-triazolium]2[B12F12].
4-NH2-1,2,4-triazole (5). The inclusion of the neutral 4-NH2-1,2,4-
triazole molecule in salt 5 was first thought to result from an
equilibrium between the reagent [4-NH2-1-H-1,2,4-triazo-
lium][Cl] and the free-base triazole in H2O. However, when the
same reaction was carried out in CH3CN, the product was also salt
5. Both of these perplexing but reproducible results were
confirmed by single crystal X-ray analysis. One might expect a
higher density for salt 5 were it devoid of this neutral triazole
molecule.
The previously reported CH3CN-trituration procedure [13],
successfully used for water-soluble binary heterocyclium(1+) salts
of B12H122ꢀ and CB11H12ꢀ, also was attempted, but without success.
A different metathesis reaction was also tried in order to prepare the
elusive binary salt [1-NH2-3-H-1,2,3-triazolium]2[B12F12
] (i.e.,
[13]2[B12F12]) by driving the metathesis reaction to completion
through aqueous AgCl precipitation [13]. This metathesis reaction
between [13][Cl] and [Ag(CH3CN)2]2[B12F12] in H2O led not to the
desired product but instead to the isolation of crystalline [Ag4(1-
NH2-1,2,3-triazole)8][B12F12] (9) with a tetrameric tetracation,
which was characterized by single-crystal X-ray diffraction.
Apparently the equilibrium shown in Rxn. (1) lies far to the left,
precluding the precipitation of AgCl (tz = 1-NH2-1,2,3-triazole):
Small-scale aqueous metathesis reactions were used to prepare
salts 7 and 8, which crystallized with three or two H2O molecules
per formula unit in their respective lattices (see Fig. 2). The
presence of H2O molecules in the lattices of these salts precludes a
detailed comparison of the packing of the B12F122ꢀ anions and the
six-membered-ring pyrimidinium(1+) cations in 7ꢁ3H2O or the
bicyclic purinium(1+) cations in 8ꢁ2H2O with the five-membered-
ring heterocyclium(1+) cation salts 1–4 and 6. In this regard the
lattice H2O molecules in 7ꢁ3H2O and 8ꢁ2H2O are acting like the
Ag4ðtzÞ84þ þ 4 HClÐ 4 AgCl # þ 4HðtzÞþ þ 4tz
(1)
The new salts 2, 4, and 6, prepared with the large-scale
metathesis reactions, were characterized by 1H and 13C NMR and
FTIR spectroscopy. In one case, salt 6 prepared using a small-scale
reaction had spectra that matched those recorded for a sample of 6
which was synthesized using a significantly larger-scale metathe-
sis reaction. Samples of salt 2 prepared using either solvent were
analyzed for the presence of Clꢀ by ion chromatography. In both
cases the mass% of Clꢀ was only 0.01%, demonstrating the level of
purity that is possible using the metathesis reactions shown in
Scheme 1. Most of the new salts prepared using small-scale
metathesis reactions were also compositionally characterized by
single-crystal X-ray diffraction analysis (see below). The single-
crystal X-ray structure of salt 7 was not of sufficient quality for
publication, but analysis of a low-quality data set confirmed the
trihydrate composition shown in Fig. 2.
‘‘extra’’ 1-NH2-1,2,3-triazole molecule in 5, taking up what is
2ꢀ
presumably empty space in the lattice of B12F12
protonated heterocyclium(1+) cations.
anions and
Although the expected binary salts 1–4 and 6 and the hydrated
salts 7 and 8 could be readily formed using the metathesis
reactions in Scheme 1, we were not able to isolate binary [hetero-
cyclium]2[B12F12] salts using halide salts of the protonated non-
alkylated heterocyclium(1+) cations 10+–13+, shown in Fig. 3, as
metathesis reagents. For cations 10+–12+, it appears that the
putative [heterocyclium]2[B12F12] salts are more soluble in H2O
than K2B12F12. For cation 13+, only the mixed-cation crystalline
‘‘half-salt’’ product [K][13][B12F12]ꢁ2H2O, which was characterized
by a preliminary X-ray structure (not shown), was obtained using
H2O as the solvent. This apparently resulted from the
[13][K][B12F12] ‘‘half salt’’ product being less soluble in H2O
reaction solvent than were either the K2B12F12 reactant salt or the
2.3. X-ray structures of the new salts
Crystallographic data and structure refinement parameters for
2ꢀ
desired [13]2[B12F12] salt product (note that a similar ‘‘half-salt’’
new B12F12 hetero-cyclium(1+) salts 1–6, 8, and 9 are listed in
2ꢀ
product with the B12H12
anion, [K][4-NH2-1-H-1,2,4-triazo-
Table 2. Thermal ellipsoid plots of all eight formula units are shown
in Supplementary data. Portions of the structures of salts 1–6 that
are relevant to the discussion below are shown in Figs. 4 and 5.
These figures depict all atoms as spheres of arbitrary size for
clarity. In addition, Figs. 4 and 5 depict the centroid of each
lium][B12H12], was recently reported [13].) While the four different
protonated, non-alkylated heterocyclium(1+) cations 10+, 11+, 13+,
and [4-H-1H-1,2,4-triazolium]+ each formed previously reported
binary [heterocyclium]2[B12H12
] and [heterocyclium][CB11H12]
2ꢀ
salts [12,13], only the [4-NH2-1H-1,2,4-triazolium]2[B12F12]ꢁ4-
NH2-1,2,4-triazole salt 5, with an occluded neutral triazole
molecule, was isolated.
B12F12 anion (i.e., the B12 centroid, for which the symbol ꢂ is
used) as a small sphere connected by dashed lines to other B12
centroids in order to show the idealized rhombs formed by eight

J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
929
Table 2
Crystallographic data and structure refinement parameters for B12F12 salts 1–6, 8, and 9.a
2ꢀ
1
2
3
4
5
6
8
9
Molecular formula C12H22B12F12N4 C8H14B12F12N4 C6H10B12F12N4 C6H14B12F12N8 C6H14B12F12N12 C6H14B12F12N8 C10H18B12F12N12O2 C8H16Ag2B12F12N16
Formula weight
Crystal system
Space group
Z
580.06
Monoclinic
P21/c
523.95
Monoclinic
P21/c
495.90
Monoclinic
C2/m
555.97
Monoclinic
P21/c
612.01
Orthorhombic
P212121
4
555.97
Monoclinic
C2/c
606.08
Monoclinic
C2/c
909.83
Monoclinic
P21/n
4
2
4
2
4
4
4
Color of crystal
Unit cell dimens.
White
White
White
White
White
White
White
White
˚
a, A
15.6537(6)
9.0441(3)
17.2734(6)
90
7.5255(2)
17.0776(4)
7.9652(2)
90
14.245(2)
14.556(2)
10.025(1)
90
7.6121(9)
17.941(2)
8.494(1)
90
10.882(1)
13.047(1)
16.194(2)
90
19.065(2)
9.2222(8)
14.806(2)
90
25.148(1)
11.7631(5)
9.0568(4)
90
8.9933(5)
11.7111(6)
28.124(1)
90
˚
b, A
˚
c, A
a,8
b
,8
90.980(2)
90
102.234(1)
90
119.971(9)
90
113.247(2)
90
90
120.639(4)
90
104.634(2)
90
97.807(2)
90
g,8
90
3
˚
Unit cell vol., A
2445.1(2)
100(2)
1000.42(4)
173(2)
1800.7(5)
100(2)
1065.9(2)
173(2)
2299.1(4)
173(2)
R1 = 0.032
wR2 = 0.085
1.069
2239.7(4)
173(2)
2592.2(2)
173(2)
2934.6(3)
296(2)
Temperature, K
Final R indices
R1 = 0.046
wR2 = 0.144
1.048
R1 = 0.039
wR2 = 0.100
1.124
R1 = 0.086
wR2 = 0.217
1.101
R1 = 0.034
wR2 = 0.097
1.089
R1 = 0.069
wR2 = 0.196
1.086
R1 = 0.037
wR2 = 0.103
1.064
R1 = 0.038
wR2 = 0.105
1.030
[I > 2s(I)]
GOF on F2
a
The eight salts listed in this table are as follows: 1, [1-Et-3-Me-imidazolium]2[B12F12]; 2, [1-H-3-Me-imidazolium]2[B12F12]; 3, [H(imidazolium)]2[B12F12]; 4, [4-NH2-1-
Me-1,2,4-triazolium]2[B12F12]; 5, [4-NH2-1-H-1,2,4-triazolium]2[B12F12].4-NH2-1,2,4-triazole; 6, [1-NH2-3-Me-1,2,3-triazolium]2[B12F12]; 8, [2,6-(NH2)2-1-H-puri-
nium]2[B12F12].2H2O; 9, [Ag4(1-NH2-1,2,3-triazole)8][B12F12]. Drawings of the cations in these salts are shown in Fig. 2.
2ꢀ
B12F12
anions in salts 1–6. Selected solid-state structure
The recently published structures of [K2(H2O)2][B12F12] and
[K2(H2O)4][B12F12] revealed a structural motif for B12F12 salts
consisting of a rhomb of anions containing a pair of hydrated K+
cations. The ꢂꢁ ꢁ ꢁ ꢂ distances in those rhombs ranged from 6.915 to
2ꢀ
2ꢀ
2ꢀ
parameters for B12F12 salts 1–6 and for related B12H12 salts
with the same cations, including the ꢂꢁ ꢁ ꢁ ꢂ distances that define
the anion rhombs, are listed in Table 3.
Fig. 4. The packing of pairs of heterocyclium(1+) cations inside rhombs of eight B12F122ꢀ anions in the structures of [1-Et-1-Me-imidazolium]2[B12F12] (1, top), [1-H-3-Me-
imidazolium]2[B12F12] (2, bottom left), and [H(imidazolium)]2[B12F12] (3, bottom right). The gray spheres are N atoms. The eight corners of the rhombs are composed of B12
centroids. Each rhomb contains two complete cations or, in the case of 1, parts of four cations that yield two complete cations. Structural drawings of these cations in salts 1–3
are seen in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

930
J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
Fig. 5. The packing of pairs of heterocyclium(1+) cations inside rhombs of eight B12F122ꢀ anions in the structures of [4-NH2-1-Me-1,2,4-triazolium]2[B12F12] (4, top), [4-
NH2-1-H-1,2,4-triazolium]2[B12F12].4-NH2-1,2,4-triazole (5, middle), and [1-NH2-3-Me-1,2,3-triazolium]2-[B12F12] (6, bottom). The gray spheres are N atoms. The
eight corners of the rhombs are composed of B12 centroids. Each rhomb contains two complete cations in 4 and 6. In 5, each rhomb contains parts of four triazolium
cations and two triazole molecules that yield two complete cations and one complete triazole molecule (each five-membered ring is nearly centered on each of the six
faces of the anion rhomb). Structural drawings of these cations in salts 4–6 are seen in Fig. 2. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of the article.)
Table 3
Solid-state parameters for B12F12 and B12H12 salts of heterocyclium(1+) cations.a
2ꢀ
2ꢀ
3
d
Ref.b
Formula unit vol., A
Densityc, g cmꢀ3
ꢂꢁ ꢁ ꢁ ꢂ, A
Cationꢁ ꢁ ꢁcation, A
˚
˚
˚
Compound
[1-Et-3-Me-imidazolium]2[B12F12] (1)
tw
611.3(1)
549.4(2)
500.21(2)
461.9(4)
450.2(1)
533.0(1)
454.3(1)
574.8(1)
559.9(1)
620.1(1)
1.576
1.101e
1.739
1.107f
1.829
1.732
1.243g
1.768
1.649
1.19i,j
9.003, 9.044, 10.675
8.268, 8.673, 8.846
7.525, 7.965, 9.422
7.535, 8.167, 9.348
7.122, 7.278, 8.938
7.612, 8.891, 9.925
7.036, 8.140, 8.140
8.100, 8.480, 8.712
7.609, 9.222, 10.692
8.689, 8.959, 10.324
5.708
4.119
4.585
4.113
3.589
4.647
4.124
5.445h
5.287
3.785
[1-Et-3-Me-imidazolium]2[B12H12
]
[12]
tw
[1-H-3-Me-imidazolium]2[B12F12] (2)
[1-H-3-Me-imidazolium]2[B12H12
]
[12]
tw
[H(imidazolium)]2[B12F12] (3)
[4-NH2-1-Me-1,2,4-triazolium]2[B12F12] (4)
[4-NH2-1-Me-1,2,4-triazolium]2[B12H12
tw
]
[12]
tw
[4-NH2-1-H-1,2,4-triazolium]2[B12F12].4-NH2-1,2,4-triazole (5)
[1-NH2-3-Me-1,2,3-triazolium]2[B12F12] (6)
tw
[1-NH2-3-Me-1,2,3-triazolium]2[B12H12
]
[12]
a
See also Table 2.
b
tw = this work.
c
X-ray diffraction-derived densities at 173(2) or 100(2) K.
d
e
f
The shortest distance between the centroids of the five-membered rings of the heterocyclium(1+) cations.
The density of [1-Et-3-Me-imidazolium][CB11H12] at 173 K is 1.03 g cmꢀ3
.
The density of [1-H-3-Me-imidazolium][CB11H12] at 173 K is 1.11 g cmꢀ3 [12].
The density of [4-NH2-1-Me-1,2,4-triazolium][CB11H12] at 173 K is 1.12 g cmꢀ3 [12].
g
h
This is the shortest distance between cation centroids. The shortest distance between a cation centroid and the five-membered ring centroid of the neutral molecule of 4-
˚
NH2-1,2,4-triazole is 4.936 A.
i
The density of [1-NH2-3-Me-1,2,3-triazolium][CB11H12] at 173 K is 1.10 g cmꢀ3 [12].
j
The density reported here for [1-NH2-3-Me-1,2,3-triazolium]2[B12H12] was determined at 25 8C by pycnometry on a vacuum-dried sample because crystals
of this compound contained two molecules of CH3CN per formula unit [12]. The X-ray density of [1-NH2-3-Me-1,2,3-triazolium]2[B12H12].2CH2CN is 1.132 g cmꢀ3 [12].

J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
931
2ꢀ
ꢀ
˚
8.598 A, which is comparable to the range of ꢂ ꢁ ꢁ ꢁ ꢂ distances for
heterocyclium(1+) B12H12 and CB11H12 salts (for example, the
densities of benzene and hexafluorobenzene are 0.877 and 1.61 g
cmꢀ3, respectively, and the densities of n-hexane and perfluoro-n-
hexaneare0.655and 1.67 g cmꢀ3, respectively). A comparison ofthe
structures of [1-H-3-Me-imidazolium]2[B12F12] (2) and [1-H-3-Me-
imidazolium]2[B12H12] [12] is especially appropriate. Interestingly,
the anion rhombs are very similar in the two salts: the ꢂꢁ ꢁ ꢁ ꢂ
+
˚
salts 1–6, 7.122–10.675 A. In addition, the distance between the K
cations within the rhombs in [K2(H2O)2][B12F12
˚
]
and
[K2(H2O)4][B12F12] are ca. 4.3 A, which is the middle of the range
˚
of cationꢁ ꢁ ꢁcation distances in salts 1–6, 3.589–5.708 A (these
distances, also listed in Table 3, are the shortest distances between
the centroids of the five-membered rings of the heterocyclium(1+)
cations in salts 1–6 and will hereinafter be referred to as catꢁ ꢁ ꢁcat
distances).
˚
distances are ca. 7.5, 8.0, and 9.4 A in both salts, and the acute
ꢂꢁ ꢁ ꢁ ꢂ ꢁ ꢁ ꢁ ꢂ angles are 65.0, 77.8, and 84.98 in 2 and 63.9, 66.1, and
89.78intheB12H122ꢀ salt,demonstratingthattherelativesizesofthe
2.3.1. Imidazolium(1+) salts 1, 2, and 3
B
12F122ꢀ and B12H122ꢀ anions are quite similar (typical B–F and B–H
˚
2ꢀ
A drawing of the rhombs of B12F12 centroids (ꢂ) and their
distances in these anions are ca. 1.38 and 1.12 A and typical ꢂ ꢁ ꢁ ꢁ F
˚
pairs of heterocyclium(1+) cations for each of these three salts is
shown in Fig. 4. The rhomb for salt 1 contains parts of four 1-Et-3-
Me-imidazolium(1+) cations that add up to two complete cations;
the rhombs for salts 2 and 3 contain two complete 1-H-3-Me-
imidazolium(1+) or H(imidazolium)(1+) cations, respectively, in
the middle of their rhombs. The data in Table 3 demonstrate that as
the imidazolium(1+) substituents change from Et/Me to H/Me to
H/H the formula unit volumes and the ꢂꢁ ꢁ ꢁ ꢂ and catꢁ ꢁ ꢁcat
distances all decrease and the density increases. The increase in
density for the hypothetical transformation 1 ! 2 ! 3 is from
1.576 to 1.739 to 1.829 g cmꢀ3, respectively (Table 3).
and ꢂ ꢁ ꢁ ꢁ H distances are ca. 3.08 and 2.80 A, respectively). In
addition, the catꢁ ꢁ ꢁcat distances are also similar (they only differ by
11%), 4.585 A in 2 and 4.113 A in the B12H122ꢀ salt. Nevertheless, the
densities differ by a factor of 1.571 (1.739 vs. 1.107 g cmꢀ3), mostly
becausethemolarmassoftheB12F122ꢀ andB12H122ꢀ anionsdifferby
a factor of 2.52 (357.72 vs. 141.84 g molꢀ1).
˚
˚
Comparison of imidazolium(1+) salts 1–3 and 1,2,4-triazo-
lium(1+) salts 4 and 5 reveals that the salt density is higher when
the cation is a protonated heterocyclium(1+) cation instead of an
alkylated heterocyclium(1+) cation. In fact, there is a nearly linear
relationship between the salt density and the shortest catꢁ ꢁ ꢁcat
2ꢀ
Unlike the cation orientations in the structure of 1, the five-
membered rings of the two cations within the anion rhombs in 2
and 3 are nearly parallel: the dihedral angles of their least-squares
planes with respect to one another are 3.6 and 2.58, respectively.
Furthermore, the perpendicular distances of the atoms of one five-
membered cation ring to the least-squares plane of the other are
distance for these five B12F12
salts, as shown in Fig. 6.
2ꢀ
Interestingly, there is no such correlation for the B12H12 salts:
the data in Table 3 show that the densities, and the shortest catꢁ ꢁ ꢁcat
distances, are nearly the same for [1-Et-3-Me-imidazolium][B12H12
]
ꢀ3
˚
(1.101 g cm and 4.119 A) and [1-H-3-Me-imidazo-lium][B12H12
]
ꢀ3
(1.107 g cmꢀ3 and 4.113 A), despite the fact that the 1.576 g cm
˚
˚
3.3–3.5 A in both cases, producing a graphite-like separation of
density of [1-Et-3-Me-imida-zolium][B12F12] (1) is more than 10%
lower than the 1.739 g cmꢀ3 density of [1-H-3-Me-imidazo-
lium][[B12F12] (2).
the two cations despite the repulsion of the positive charges on
each ring.
2.3.2. Aminotriazolium(1+) salts 4, 5, and 6
2.3.3. Salt 8
2ꢀ
A drawing of the rhombs of B12F12 centroids (ꢂ) and their
The packing of 2,6-(NH2)2-1-H-purinium(1+) cations and H2O
molecules inside the rhomb of eight B12F12
structure of [2,6-(NH2)2-1-H-purinium]2[B12F12].2H2O (8) is
shown in Fig. 7. The planes of the two purinium(1+) cations are
nearly parallel (dihedral angle of only 0.28) and the C and N atoms
2ꢀ
heterocyclium(1+) cations for each of these three salts is shown in
Fig. 5. The structures of salts 4 and 6, like those of salts 2 and 3,
contain two complete heterocyclium(1+) cations within the
anions in the
˚
˚
rhombs, catꢁ ꢁ ꢁcat distances of 4.647 A in 4 and 5.287 A in 6.
However, unlike the nearly parallel orientations of the cation five-
membered rings in salts 2 and 3, the dihedral angles between the
˚
of the fused-ring system of one cation are ca. 3.4 A from the least-
squares plane of the C and N atoms that make up the fused-ring
least-squares cation rings in
4 and 6 are 56.7 and 52.78,
respectively. The density for salts 4 and 6 are 1.739 g cmꢀ3 and
1.649 g cmꢀ3, respectively (Table 3).
The composition of salt 5, and its solid-state structure, are
different than those of salts 1–4 and 6. In addition to the two 4-NH2-
2ꢀ
1-H-1,2,4-triazolium(1+) cations paired with each B12F12 anion,
there is a molecule of neutral 4-NH2-1,2,4-triazole in the formula
unit. There is a five-membered ring approximately centered on each
of the six faces of the anion rhomb, four 4-NH2-1-H-1,2,4-
triazolium(1+) cations and two 4-NH2-1,2,4-triazoles (only two
cations and one neutral triazole are shown in Fig. 5 for clarity). Not
surprisingly, the shortest catꢁ ꢁ ꢁcat distance in salt 5, which is
˚
5.445 A, is longer than the shortest distance between a cation
centroid and the five-membered ring centroid of the neutral triazole
˚
molecule, which is 4.936 A. Also not surprisingly, the interactions
between the triazolium(1+) cations and the neutral triazole
˚
molecule in salt 5 are N–Hꢁ ꢁ ꢁN hydrogen bonds ((N)Hꢁ ꢁ ꢁN = 1.911 A,
˚
˚
˚
A, N–Hꢁ ꢁ ꢁN = 166.58, Nꢁ ꢁ ꢁN = 2.747 A; (N)Hꢁ ꢁ ꢁN = 2.025 A, N–
˚
Hꢁ ꢁ ꢁN = 168.58, Nꢁ ꢁ ꢁN = 3.001 A; neither of these hydrogen bonds
involve NH2 groups). The density of salt 5 is 1.768 g cmꢀ3 (Table 3).
The density of each of the [heterocyclium]2[B12F12] salts 1, 2, 4,
and 6 can be compared to the density of the corresponding
[heterocyclium]2[B12H12] salt (see Table 3). As with perfluorocarbon
versus analogous hydrocarbon organic compounds, the hetero-
2ꢀ
Fig. 6. Plot of salt density and the shortest catꢁ ꢁ ꢁcat distance for the five B12F12
2ꢀ
cyclium(1+) B12F12 salts are more dense than the corresponding
salts 1–4 and 6. The line is a linear least-squares fit to the five points.

932
J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
2ꢀ
Fig. 7. The packing of 2,6-(NH2)2-1-H-purinium(1+) cations and H2O molecules inside the rhomb of eight B12F12
anions in the structure of [2,6-(NH2)2-1-H-
purinium]2[B12F12]ꢁ2H2O (8) and the packing of H(imidazolium)(1+) cations inside the rhomb of B12F122ꢀ anions in the structure of [H(imidazolium)]2[B12F12] (3) (the corners
of the rhombs are composed of B12 centroids). The unlabeled gray spheres are N atoms while significant labeled O, B, and F atom distances and hydrogen bonding interactions
2ꢀ
are illustrated in the figure, respectively. These drawings emphasize the dovetail-like packing of the B12F12 anions. The ꢂꢁ ꢁ ꢁ ꢂ distances for the two anions shown are
˚
˚
7.423 A for 8 and 7.122 A for 3. The angles between the two highlighted F–B–B–F planes in each drawing are 78.78 for 8 and 908 for 3. The Fꢁ ꢁ ꢁF distances shown are 2.779,
˚
˚
3.193, 3.689, and 3.796 A in 8 and 2.908 (2ꢃ) and 3.108 A (2ꢃ) in 3. Structural drawings of these cations in salts 3 and 8 are seen in Fig. 2. (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of the article.)
2ꢀ
system of the other cation, once again a graphite-like interaction of
of the B12F12 anions. The ꢂꢁ ꢁ ꢁ ꢂ distances for the two anions
˚
˚
the two cations. The H2O molecules form (N)Hꢁ ꢁ ꢁO hydrogen bonds
shown are 7.423 A for 8 and 7.122 A for 3. The angles between the
two highlighted F–B–B–F planes in each drawing are 78.78 for 8
and 908 for 3. The Fꢁ ꢁ ꢁF distances shown are 2.779, 3.193, 3.689,
˚
with an Hꢁ ꢁ ꢁO distances of 1.78 A and N–Hꢁ ꢁ ꢁO angles of 1548 and
two (O)Hꢁ ꢁ ꢁF hydrogen bonds with Hꢁ ꢁ ꢁF distance of 2.12 and
˚
˚
˚
2.21 A. The ꢂꢁ ꢁ ꢁ ꢂ distances in the structure of 8 are 7.423 (2ꢃ) and
and 3.796 A in 8 and 2.908 (2ꢃ) and 3.108 A (2ꢃ) in 3 (note that
˚
˚
12.241 A.
twice the van der Walls radius of an F atom is ca. 3.0 A). This
Fig. 7 also shows a drawing of the structure of salt 3 for
comparison. These drawings emphasize the dovetail-like packing
dovetail-like packing was also observed in the structures of
[K(H2O)n]2[B12F12] (n = 1, 2) [10] and in heterocyclium(1+) salts of
Fig. 8. The centrosymmetric Ag4(1-NH2-1,2,3-triazole)84+ tetracation in the structure of [Ag4(1-NH2-1,2,3-triazole)8][B12F12] (9). The smaller gray spheres are N atoms, and
the larger gray spheres represent the four Ag+ cations. The four Ag+ ions are rigorously coplanar with Agꢁ ꢁ ꢁAg distances of 3.764(2) and 3.858(2) A and Agꢁ ꢁ ꢁAgꢁ ꢁ ꢁAg angles of
˚
65.8(1) and 114.2(1)8. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)

J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
933
Table 4
Structural results for tetrameric silver(I) triazole compounds.a
Parameter
[Ag4(tz-1)8][B12F12
This work
]
2
[Ag4(tz-2)7][ClO4]4
[20]
[Ag4(tz-3)6][NO3]4ꢁ4H2O
Reference
[21]
˚
˚
Ag1–N
2.211(3), 2.238(3), 2.322(4) A
2.179(4), 2.200(4), 2.314(5) A
2.230(3), 2.247(3), 2.317(3)
˚
Ag1–F
2.960(3) A
˚
˚
Ag2–N
2.255(3), 2.263(3), 2.404(3), 2.492(4) A
2.283(4), 2.283(4), 2.326(5), 2.369(4)
2.253(3), 2.255(3), 2.311(3) A
˚
Ag2–F
2.806(3) A
Ag1 bond-valence sum
Ag2 bond-valence sum
Ag1ꢁ ꢁ ꢁAg2
1.05
1.13
1.09
1.14
0.98
0.96
˚
˚
˚
3.764(2) A
3.156(1) A
3.714(2) A
Ag1ꢁ ꢁ ꢁAg20
3.858(2) A
3.632(1) A
3.905(2) A
˚
˚
˚
Ag2ꢁ ꢁ ꢁAg1ꢁ ꢁ ꢁAg2
Ag1ꢁ ꢁ ꢁAg2ꢁ ꢁ ꢁAg1
114.2(1)8
65.8(1)8
156.418(3)
132.688(3)
92.8(1)8
87.2(1)8
a
tz-1 =1-NH2-1,2,3-triazole; tz-2 = 4-NH2-1,2,4-triazole; tz-3 = 4-(3-C6H4OH)-1,2,4-triaz.
the B12H122ꢀ and CB11H12ꢀ anions [12,13]. The density of salt 8 is
scope of the reaction for binary [heterocyclium]2[B12F12]
1.784 g cmꢀ3 at 173 (2) K.
icosahedral perfluoroborane salts was found to be more limited.
One binary dialkylated [heterocyclium]2[B12F12] product salt 1
was synthesized. Three binary [heterocyclium]2[B12F12] per-
fluoroborane salt products (2, 4, 6) were isolated that contained
three different methylated heterocyclium(1+) cations using
either H2O or CH3CN solvent. All four alkylated product salts
2.3.4. Salt 9
The packing of the discrete Ag4(1-NH2-1,2,3-triazole)84+ cations
2ꢀ
and B12F12 anions in the structure of [Ag4(1-NH2-1,2,3-triazo-
le)8][B12F12]2 (9) is complicated and will not be discussed here.
Instead, we describe the structure of the tetrameric tetracation,
shown in Fig. 8, and compare it to two similar Ag4(triazole)n
tetracations [20,21]. Relevant structural parameters are listed in
Table 4. The four Ag+ ions in each tetracation in 9 are rigorously
1, 2, 4, and
6
have corresponding binary [heterocy-
4+
clium]2[B12H12] and [heterocyclium][CB11H12] product analogs
that have been reported.
Only one protonated, non-alkylated binary [imidazo-
lium]2[B12F12] salt 3 was prepared although a number of similar
˚
coplanar, with Agꢁ ꢁ ꢁAg distances of 3.764(2) and 3.858(2) A and
Agꢁ ꢁ ꢁAgꢁ ꢁ ꢁAg angles of 65.8(1) and 114.2(1)8. These are similar to
the corresponding parameters in the structures of [Ag4(4-NH2-
1,2,4-triazole)7][ClO4] [20] and [Ag4(4-(3-C6H4OH)-1,2,4-triazo-
le)6][NO3]4.4H2O [21].
binary protonated triazolium [heterocyclium]2[B12H12] and
[heterocyclium][CB11H12] salts are reported. This reduction in
reaction scope resulted from the lower solubility of K2B12F12
relative to several putative [heterocyclium]2[B12F12] product salts
that could not be isolated, and in these cases, the unreacted
K2B12F12 reactant salt was usually the solid recovered from the
metathesis reaction. In one case the cation 13+ formed the mixed
cation [13][K][B12F12] perfluoroborane ‘‘half salt’’ which was
isolated instead of the expected [13]2[B12F12] salt product. One
An interesting feature of the structure of the tetrameric Ag4(1-
4+
NH2-1,2,3-triazole)8 cation in 9 is that the Ag1 cations are only
bonded to the more basic N3 atoms of three
m-(1-NH2-1,2,3-
triazole)- N2: N3 ligands, with Ag1–N3 distances of 2.211(3),
k
k
˚
2.238(3), and 2.322(4) A. The Ag2 cations, on the other hand, are
bonded to the less basic N2 atoms of the three bridging triazole
ligands, with Ag2–N2 distances of 2.263(3), 2.404(3), and
[heterocyclium][K][B12H12
appeared in the literature.
] ‘‘half salt’’ product recently has
˚
2.492(4) A. Probably because of the weaker bonding between
Larger protonated heterocyclic cations, a six-membered pyr-
imidinium and a fused bicyclic purinium species, gave new
sparingly soluble [heterocyclium]2[B12F12] salts 7 and 8, respec-
tively. These two product salts each were isolated from an aqueous
metathesis reaction mixture, although both contained solvent
molecules (H2O) in the crystalline salts.
Ag2 and the three bridging triazole ligands, each Ag2 cation is also
coordinated to a terminal 1-NH2-1,2,3-triazole ligand through N3,
with a Ag2–N3 distance of 2.255(3) A. If not for this terminal
triazole ligand, the sum of bond-valences [22] for Ag2 would be
significantly less than 1.0 (an Ag–N distance of 2.255 A corre-
˚
˚
sponds to a bond valence of 0.335 [22]). The density of salt 9 is
There were two anomalous observations made with binary
product salts that were synthesized during this work. First, when
attempting to synthesize [4-NH2-1-H-1,2,4-triazolium]2[B12F12] in
either H2O or CH3CN as the solvent, the neutral triazole molecule [4-
NH2-1,2,4-triazole] was incorporated into the product salt structure
(i.e., the composition was [4-NH2-1-H-1,2,4-triazolium]2[4-NH2-
1,2,4-triazole][B12F12] (5)). Second, an attempt was made to drive
an aqueous metathesis reaction to completion with AgCl precipita-
tion. Reacting the [1-NH2-3H-1,2,3-triazolium][Cl] salt with
2.059 g cmꢀ3 at room temperature.
3. Conclusions
Five new binary [heterocyclium]2[B12F12] salts 1–4 and 6
were synthesized in 84–99% isolated yield. In addition, three
salts 5, 7, and 8 that also contained neutral molecules, either a
triazole molecule or H2O, were also prepared. These are the first
salts that contain two single heterocyclium(1+) cations paired
2ꢀ
[Ag(CH3CN)2]2[B12F12] as the source of the B12F12 anion in place
with the icosahedral B12F12
perfluorododecaborate dianion.
of K2B12F12, resulted in the Ag+ ions coordinating to the N atoms of
neutral triazole molecules to give a complex tetracation that formed
a unique high density salt [Ag4(1-NH2-1,2,3-triazole)8][B12F12]2 (9).
The density of individual [heterocyclium]2[B12F12] perfluoro-
dodecaborane salts were significantly higher than are the recently
2ꢀ
Open-air benchtop double-displacement (metathesis) reactions
using common laboratory glassware were employed, in which a
stoichiometric amount of heterocyclium(1+) halide salt was
treated with K2B12F12 in either H2O or CH3CN solvent.
Depending on the particular salt, the synthesis was carried
out at a temperature that ranged from room temperature to
100 8C and on a scale that ranged from 44 mg of K2B12F12 to
nearly 1 g of this salt.
published analogous [heterocyclium]2[B12H12
clium][CB11H12] salts (Table 3). Additionally, protonated [hetero-
cyclium]2[B12F12 salts displayed higher density that did
] and [heterocy-
]
a
analogous alkylated [heterocyclium]2[B12F12] salts. In fact, an
interesting linear correlation between salt density and catꢁ ꢁ ꢁcat
separation was discovered for a set of five B12F122ꢀ salts 1–4, and 6
Compared with previously reported analogous binary hetero-
2ꢀ
cycliumꢀcation(1+) salts of the icosahedral B12H12 borane and
2ꢀ
CB11H12 anions that were synthesized in a similar manner, the
that does not appear to be followed for B12H12 salts.

934
J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
4. Experimental
4.1. General comments
washed with anhydrous CHCl3, and dried under vacuum. The
preparation of [1-Et-3-Me-imidazolium][Br] for the synthesis of
salt 1 was achieved by reacting EtBr (23.1 mmol) and 1-Me-
imidazole (11.2 mmol) in refluxing anhydrous benzene (20 mL) for
2 h. Filtering the cooled reaction mixture, washing the white
crystalline product, and drying under vacuum afforded [1-Et-3-
Caution! While no special protective equipment or handling
procedures were used with salts (1–9), these are high energy
materials, and the analogous binary heterocyclium salts of B12H12
and CB11H12ꢀ can be initiated to rapid energy-releasingphenomena.
2ꢀ
Me-imidazolium][Br] in 64% yield. The salt [Ag(CH3CN)2]2[B12F12
was prepared as previously described [24].
]
Thermalinitiationcan occur ona hot platesurface(>275 8C)to rapid
combustion with protonated binary heterocyclium(1+) salts [17]
4.2. Spectroscopy, X-ray crystallography, ion chromatography, and
melting points
2ꢀ
and bridged heterocyclium(2+) salts of B12H12
[17]. Recent
standard impact, friction, and electrostatic discharge (ESD) hazards
testing conducted on the binary salt [1-NH2-3-Me-1,2,3-triazo-
lium]2[B12H12], the analogue of the new salt [1-NH2-3-Me-1,2,3-
triazolium]2[B12F12], gave a 100% impact non-initiation (‘‘no-go’’)
response at 156 kg cm, a 21.6 kg cm friction minimum non-
initiation response, but initiated electrostatically at 0.040 J on an
ESD test [13]. These two 100% ‘‘No-Go’’ impact initiation values
compare with known explosives for which the following more
sensitive 50% initiation kg cmvaluesare available:CL-20 at33; PETN
at 67; HMX at 115; and RDX at 117 kg cm. One bridged
A Bruker Avance 400 Digital NMR instrument was used to
obtain both 1H and 13C spectra. FTIR spectra were taken as powder
samples in air using a Nicolet 6700 Spectrometer equipped with an
HATR optical system. Only the significant peaks that were
observed are listed below. The FTIR spectrum of K2B12F12 salt
exhibits only two strong peaks at 1221 cmꢀ1
(
n
(BF)) and 719 cmꢀ1
2ꢀ
(
n
(BB)) [19]. The presence of B12F12 was confirmed in [hetero-
cyclium]2[B12F12] salts 2, 4, and 6 by the presence of two strong
peaks at ca. 1220 and ca. 720 cmꢀ1 in their respective FTIR spectra.
Single-crystal X-ray diffraction data for salts 2, 4–6, 8, and 9 were
2ꢀ
heterocyclium(2+) salt of B12F122ꢀ, the only salt of B12F12 tested
to date, gave a minimum non-initiation impact at 147 kg cm (100%
‘‘no-go’’ non-initiation value), a minimum non-initiation friction
response at 21.6 kg cm, but initiated at 0.090 J in the ESD test [13].
All water used was deionized water obtained from a Millipore
collected at Edwards AFB using
diffractometer equipped with a SMART APEX 2 detector with the
-axis fixed at 54.748 using Mo K or Cu K radiation from a fine-
focus tube. The goniometer head, equipped with a Nylon Cryoloop
and magnetic base, was used to mount the crystals using
perfluoropolyether oil. Diffraction data for salts 1 and 3 were
collected at Colorado State University using a Bruker Kappa APEX II
a Bruker 3-circle-platform
x
a
a
MILL-Q Reagent Grade Water System at the 18 M
V cm level of
purity. All organic solvents were commercially available as either
Reagent Grade or HPLC purity and were used as received.
With one exception, the neutral heterocyclic compounds used
to synthesize B12F122ꢀ salts 1–9 were commercially available and
were used as received. The exception is the compound 1-NH2-
1,2,3-triazole, which was prepared using a published procedure
[23]. Conversion of each neutral heterocycle to the corresponding
hydrochloride or N-methylated iodide salt was carried out as
previously described (see Supplemental Information in Ref. [12]).
Two detailed examples are included in this paper in the following
two paragraphs. The heterocyclium(1+) hydrochloride salts were
obtained from the commercial free bases via treatment with
concentrated aqueous HCl in ethanol at 25 8C, followed by removal
of all volatiles by rotary evaporation and drying under vacuum
(ꢄ0.1 mTorr). The remaining solids were recrystallized from a
minimum amount of hot 2-propanol. In some cases the addition of
diethyl ether after the onset of crystallization resulted in a slightly
higher yield. The microcrystalline products were filtered, washed
with diethyl ether, and dried under vacuum.
CCD diffractometer at 110(2) K employing Mo Ka radiation
(graphite monochromator). Unit cell parameters were obtained
from least-squares fits to the angular coordinates of all reflections,
and intensities were integrated from a series of frames (
v and w
rotation) covering more than a hemisphere of reciprocal space.
Absorption and other corrections were applied using SADABS [25].
The structures were solved using direct methods and refined (on F2
using all data) by a full-matrix, weighted least-squares process.
Standard Bruker control and integration software (APEX II) was
employed [26], and Bruker SHELXTL software was used for structure
solution, refinement, and molecular graphics [27]. Crystal data and
refinement details for salts 1–6, 8, and 9 are listed in Table 2.
For ion chromatography Clꢀ analyses, each sample was
weighed to 0.01 mg and diluted to 25 mL in a class B centrifuge
tube with 18 M
V cm deionized water. The samples that were not
readily soluble were heated to 80 8C with a reflux cap. All solution
transfers and injections were accomplished with sterile syringes
An alternative method is possible for the synthesis of the
hydrochloride of 4-NH2-1,2,4-triazole. This salt can also be
synthesized in a 250 mL round-bottom flask by adding 2.50 g
(29.7 mmol) of 4-NH2-1,2,4-triazole and 2.50 mL (29.9 mmol) of
37% aqueous HCl to 50 mL MeOH and letting the mixture stand at
room temperature for two days. High vacuum removal of the
solvent under vacuum afforded 3.53 g of a thick syrup that was
recrystallized from hot MeOH and Et2O. Filtration, rinsing with a
small portion of Et2O, and vacuum drying afforded 2.24 g of
microcrystalline [4-NH2-1-H-1,2,4-triazolium][Cl] (62.6% yield).
The methylated heterocyclium(1+) iodide salts were obtained by
reaction of the neutral free-base heterocycle with excess CH3I in
EtOH at room temperature for at least 12 h followed by removal of
all volatiles by rotary evaporation (the reaction vessel was
wrapped with foil to protect the reaction mixture from direct
light). If necessary, some of these salts were recrystallized from
MeOH. The preparation of [H(imidazolium)][Cl] for the synthesis of
salt 3 was achieved by bubbling dry HCl gas (10–15 mL/min flow
rate) through an anhydrous CHCl3 solution of imidazole for 30 min.
The white needle-shaped crystals that formed were filtered,
and syringe filters (IC Millex LG filter unit 0.2
linear calibration curve was generated using a blank deionized
water solution, followed by a 0.1, 1, and 5 ppm (
g gꢀ1) NIST
mm). A four-point
m
traceable Clꢀ standard where the peak area was determined for
each chloride standard solution. Lower detection limits (LDL) and
lower quantitation limits (LQL) were determined using seven
individually prepared blanks consisting only of deionized H2O
(LDL = 3 times and LQL = 5 times the standard deviation of the
seven blank runs). Concentrations were calculated by comparing
peak area response versus the linear calibration graph and are
corrected for dilution.
Melting points were determined using a Stanford Research
Systems OptiMelt MPA100-Automated Melting Point Apparatus
equipped with digital image video playback software.
4.3. Small-scale CH3CN solvent synthesis procedure
The heterocyclium halide salt was dissolved in CH3CN and
mixed with a CH3CN solution of K2B12F12 at room temperature to
form a white KX precipitate (X = Cl, Br). The solution was filtered

J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
935
and dried to give the desired binary [heterocyclium]2[B12F12] salt,
which was subsequently recrystallized from CH3CN.
in 5 mL H2O and heated to 95 8C for 15 min. The solvent was
removed under vacuum (ca. 18 mTorr) for 12 h and the resultant
solid was redissolved in 1 mL H2O and placed in a refrigerator
(3.5 8C) overnight. This afforded crystals of 5 suitable for single-
crystal X-ray diffraction analysis which revealed that one neutral
4-NH2-1,2,4-triazole molecule occupied the formula unit.
4.3.1. [1-Et-3-Me-imidazolium]2[B12F12] (1)
Solutions of [1-Et-3-Me-imidazolium][Br] (0.088 g, 0.45 mmol)
in 2 mL CH3CN and K2B12F12 (0.10 mg, 0.22 mmol) in 2 mL CH3CN
were mixed at room temperature, affording 0.13 g of salt 1 (90%
yield). Single-crystal X-ray diffraction analysis confirmed the
composition of this salt.
4.4.3. [2,4,6-(NH2)3-1-H-pyrimidinium]2[B12F12] (7)
The compounds [2,4,6-(NH2)3-1-H-pyrimidinium][Cl] (64.6 mg,
0.400 mmol) and K2B12F12 (87.2 mg, 0.200 mmol) were dissolved in
3 mL H2O, brought to a boil, and cooled. The cooled solution
deposited crystals of 7.3H2O that were used for a preliminary X-ray
diffraction study.
4.3.2. [H(imidazolium)]2[B12F12] (3)
Solutions of [H(imidazolium)][Cl] (0.048 g, 45 mmol) in 2 mL
CH3CN and K2B12F12 (0.10 mg, 0.22 mmol) in 2 mL CH3CN were
mixed at room temperature, affording 0.10 g of salt 3 (93% yield).
Single-crystal X-ray diffraction analysis confirmed the composi-
tion of this salt.
4.4.4. [2,6-diamino-1-H-purininium]2[B12F12] (8)
The compounds [2,6-(NH2)2-1-H-purinium][Cl] (74.6 mg,
0.400 mmol) and K2B12F12 (87.2 mg, 0.200 mmol) were dissolved
in 3 mL H2O and brought to a boil. When cooled, this solution
deposited crystals of 8.2H2O suitable for single crystal X-ray
diffraction analysis.
4.3.3. [4-NH2-1-H-1,2,4-triazolium]2[4-NH2-1,2,4-triazole][CI] (5)
The compounds [4-NH2-1-H-1,2,4-triazolium][Cl] (20.1 mg,
0.167 mmol) and K2B12F12 (36.4 mg, 0.0835 mmol) mixed together
were triturated with 5ꢃ 8 mL of boiling CH3CN. The solution was
cooled and the solvent was removed under vacuum to yield 48.9 mg
(95.7%) yield) of off-white solid (95.7%). The solid was dissolved in a
mixtureof1 mLCH3CNand40 mLEt2O, andafterstandingovernight
in a dessicator this solution deposited crystals of 5 suitable for single
crystal X-ray diffraction analysis which revealed that one neutral 4-
NH2-1-H-1,2,4-triazole molecule occupied the formula unit.
4.4.5. [Ag4(1-NH2-1,2,3-triazole)8][B12F12]2 (9)
The compounds [1-NH2-3-H-1,2,3-triazolium][Cl] (24.1 mg,
0.280 mmol) and [Ag(CH3CN)2]2[B12F12] (73.7 mg, 0.0999 mmol)
were dissolved in 7 mL water and filtered through Celite. Solvent
removal under high vacuum gave 42.4 mg (38.8% yield) of a solid
which was dissolved in EtOH, filtered, and recrystallized from EtOH
to give crystals of 9 suitable for single-crystal X-ray diffraction
analysis.
4.3.4. [1-NH2-3-Me-1,2,3-triazolium]2[4-NH2-1,2,4-triazole][CI] (6)
The compounds [1-NH2-3-Me-1,2,3-triazolium][I] (0.0904 g,
0.400 mmol) and K2B12F12 (87.2 mg, 0.200 mmol) were each
dissolved in a minimum amount of CH3CN at room temperature.
The two solutions were mixed and the solvent was removed under
vacuum to yield 0.179 g of a solid containing some KI byproduct. The
crude solid, dissolved in a sufficient amount of H2O, was refluxed,
and cooled, to produce crystals of 6 used for single crystal X-ray
4.5. Large-scale CH3CN solvent synthesis of [1-Me-3-H-
imidazolium]2[B12F12] (2)
In a reaction flask containing a Teflon-coated magnetic stirring
bar, [H(MeIm)][Cl] (0.254 g, 2.15 mmol) was dissolved in 5 mL
CH3CN at room temperature. K2B12F12 (0.454 g, 1.04 mmol) was
dissolved in 4 mL CH3CN at room temperature in a second glass
vessel. The K2B12F12 solution was added during 4 min to the stirred
reaction flask solution using a disposable pipette, forming a
precipitate. The second glass vessel was rinsed with 2ꢃ 0.5 mL
portions CH3CN, each of which was added to the stirred reaction
flask during 1 min for a total addition time of 6 min. The
suspension was stirred at room temperature for 17 h, then was
filtered using Celite to remove the white solid KCl byproduct. The
CH3CN solvent filtrate was removed by rotary evaporation and
gave an off-white solid. Removal of the volatiles under high
vacuum at 65 8C (24 h) in an Electrothermal ChemDry1 apparatus
gave 0.540 g (98.9% yield) of a light tan solid. 1H NMR (400 MHz;
diffraction analysis. 1H NMR (400 MHz, DMSO-d6
(dovlap., 2H); 8.60 (dovlap., 2H); 8.28 (s, 4H); 4.21 (s, 6H). 13C NMR
(100 MHz, DMSO-d6 ( 39.51)): 131.54, 126.84, 39.64 (shoulder on
DMSO-d6 peak 39.64) and CD3CN ( 1.39): 132.22, 129.58, 118.41
(d 2.50)): d 8.74
d
d
d
d
d
(CD3CN), 41.12. HATR-FTIR: 3375, 3309, 3185, 3166, 1624, 1534,
1434, 1394, 1222 (B12F122ꢀ), 1091, 1029, 948, 798, 725 (B12F122ꢀ),
667, 631 cmꢀ1. These spectroscopic data essentially are identical to
those listed for salt 6 in Section 4.6.3.
4.4. Small-scale H2O solvent synthesis procedure
The [heterocyclium][halide] salt and K2[B12F12] were mixed as
solids into one flask. The mixture was dissolved in a minimum
amount of H2O and warmed if necessary, usually below the boiling
point. The solution was cooled to room temperature and placed
into a refrigerator (3.5 8C) overnight or until crystals formed. This
generally produced crystals suitable for single-crystal X-ray
diffraction analysis. Otherwise suitable crystals were obtained
with solvent removal followed by recrystallization.
DMSO-d6
2H); 7.66 (m, 2H); 3.86 (s, 6H). 13C NMR (100 MHz; DMSO-d6
39.51)): 135.82, 123.16, 119.78, 35.42. HATR-FTIR: 3397, 3355,
(d 2.50)): d 14.17 (bd s, 2H); 9.03 (s, 2H); 7.69–7.68 (m,
(
d
d
3178, 3122, 3087, 1640, 1585, 1552, 1443, 1329, 1306, 1218
(B12F122ꢀ), 1142, 1104, 1082, 1008, 874, 844, 763, 723 (B12F122ꢀ),
697, 616 cmꢀ1. An aqueous synthesis of this salt 2 conducted on
the same scale is described in Section 4.6.1.
4.4.1. [4-NH2-1-Me-1,2,4-triazolium]2[B12F12] (4)
4.6. Large-scale H2O solvent synthesis procedure
The compounds [4-NH2-1-Me-1,2,4-triazolium][I] (42.5 mg,
0.329 mmol) and K2B12F12 (43.6 mg, 0.100 mmol) were dissolved
in 0.54 mL H2O and heated. Cooling gave crystals of 4 suitable for
single-crystal X-ray diffraction analysis.
The [heterocyclium][halide] salt was dissolved in a minimum
volume of H2O in a 25 mL 14/20 single-necked recovery flask
reaction vessel containing a Teflon-coated stirring bar. The flask
was connected to a water-cooled reflux condenser and the
solution was stirred and heated to reflux in a 107–108 8C oil bath
for 5 min. At this time, an aqueous solution of K2B12F12 that had
been prepared in a minimum amount of warm H2O in a 15 mL
single-necked pear-shaped flask was added dropwise to the
4.4.2. [4-NH2-1H-1,2,4-triazolium]2[4-NH2-1,2,4-triazole][B12F12
]
(5)
The compounds [4-NH2-1-H-1,2,4-triazolium][Cl] (17.2 mg,
0.143 mmol) and K2B12F12 (43.6 mg, 0.100 mmol) were dissolved

936
J.L. Belletire et al. / Journal of Fluorine Chemistry 132 (2011) 925–936
reaction flask, during 5–7 min, through the center of the reflux
condenser using a disposable pipette, at which point a precipitate
was observed. The pear-shaped flask that previously contained
the K2B12F12 solution was rinsed with 2ꢃ 1 mL portions of H2O,
each of which was added dropwise to the refluxing reaction
mixture. After an additional 5 min, the cloudy reaction mixture
was cooled to room temperature and placed in a 3.5 8C refrigerator
overnight. Vacuum filtration, rinsing the solid cake with 2ꢃ 1 mL
of 3.5 8C H2O and air-drying in the Bu¨ chner funnel at room
temperature for ca. 1 h gave a semi-dry solid. The solid was placed
into a 4 dram bottle and dried at 65 8C under vacuum (ca.
10ꢀ4 Torr) in a Electrothermal ChemDry1 apparatus for 18–55 h
to yield the desired anhydrous salt.
629 cmꢀ1. These spectroscopic data essentially are identical to
those listed for salt 6 in Section 4.3.4.
Acknowledgments
The authors thank the AFRL Space and Missiles Division (AFRL/
RZS), Edwards AFB, CA, and ERC, Inc., Huntsville, AL, for funding
support, Dr. Jerry A. Boatz (AFRL/RZSP) and Prof. Herman L. Ammon
(Department of Chemistry and Biochemistry, University of Mary-
land) for helpful technical discussions, and Mr. Brett A. Wight (AFRL/
RZSP) for the Clꢀ ion chromatography analyses of samples of salt 2.
Appendix A. Supplementary data
4.6.1. [1-Me-3-H-imidazolium]2[B12F12] (2)
[H(MeIm)][Cl] (0.254 g, 2.14 mmol) was dissolved in 1 mL
H2O, and K2B12F12 (0.453 g, 1.04 mmol) dissolved in 4 mL H2O
was added dropwise over 7 min, resultant suspension was then
cooled 24 h in the refrigerator, filtered, and vacuum dried 24 h.
Yield: 0.460 g (84.4%) of a slightly off-white solid. 1H NMR
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jfluchem.2011.07.009.
References
(400 MHz, DMSO-d6
7.68 (m, 2H); 7.66 (m, 2H); 3.86 (s, 6H). 13C NMR (100 MHz,
DMSO-d6 ( 39.51)): 135.81, 123.15, 119.77, 35.42. HATR-FTIR:
(d 2.50)): d 14.15 (bd. s, 2H); 9.03 (s, 2H),
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4.6.2. [4-NH2-1-Me-1,2,4-triazolium]2[B12F12] (4)
[4-NH2-1-Me-1,2,4-triazolium][I] (0.964 g, 4.27 mmol) was
dissolved in 2 mL H2O, and K2B12F12 (0.902 g, 2.07 mmol) dissolved
in 8 mL H2O was added dropwise over 5 min., resultant suspension
was then cooled 21.5 h in the refrigerator, filtered, and vacuum
dried 18.5 h. Yield: 1.03 g (90.0%) of a slightly off-white solid. 1H
NMR (400 MHz, DMSO-d6
6.95 (s, 4H); 4.02 (s, 6H) and CD3CN (
2H); 5.85 (s, 4H); 4.02 (s, 6H). 13C NMR (100 MHz, DMSO-d6
39.51)): 145.04, 142.95, unknown (3rd peak masked by DMSO)
and CD3CN ( 1.39): 146.13, 143.95, 118.41 (CD3CN), 40.24.
(
d
2.50)):
d
10.06 (s, 2H); 9.16 (s, 2H);
d
1.95): 9.22 (s, 2H); 8.54 (s,
d
(
d
d
d
d
HATR-FTIR: 3386, 3317, 3159, 3120, 1620, 1582, 1567, 1434, 1407,
1220 (B12F122ꢀ), 1170, 1072, 993, 980, 942, 891, 722 (B12F122ꢀ),
659, 621 cmꢀ1
.
4.6.3. [1-NH2-3-Me-1,2,3-triazolium]2[B12F12] (6)
[1-NH2-3-Me-1,2,3-triazolium][I] (0.964 g, 4.26 mmol) was
dissolved in 2 mL H2O, and K2B12F12 (0.901 g, 2.07 mmol)
dissolved in 7 mL H2O was added dropwise over 5 min, resultant
suspension was then cooled 18.5 h in the refrigerator, filtered, and
vacuum dried for 54.5 h. Yield: 1.06 g (92.3%) of a light tan solid.
1H NMR (400 MHz, DMSO-d6
(dovlap., 2H); 8.28 (s, 4H); 4.21 (s, 6H). 13C NMR (100 MHz, DMSO-
d6 39.51)): 131.52, 126.83, unknown (3rd peak masked by
DMSO) and CD3CN ( 1.39): 132.23, 129.59, 41.13. HATR-FTIR:
(d 2.50)); d 8.74 (dovlap., 2H); 8.60
(
d
d
d
d
3374, 3309, 3185, 3166, 1622, 1533, 1434, 1400, 1329, 1218
(B12F122ꢀ), 1090, 1049, 1028, 947, 798, 722 (B12F122ꢀ), 663,