M.A. Bondarenko, P.A. Abramov, P.E. Plyusnin et al.
Polyhedron 202 (2021) 115217
Hereby we present three new bromoantimonates which were iso-
lated in presence of bis(pyridinium)ethane (PyC2), -propane (PyC3)
and –butane (PyC4, respectively) salts – (PyC2){[SbBr6](Br3)} (1),
(PyC3)2[Sb2Br9][SbBr6] (2) and (PyC4){[SbBr6](Br3)} (3); features of
non-covalent interactions in their crystal structures, as well as
thermal stabilities, are discussed.
3. Results and discussion
Complexes 1 and 3 belong to the same structural type (one of
the most common among the products of reactions between bro-
moantimonates(III) and Br2). In both crystal structures, there are
mononuclear [SbVBr6]ꢀ anions (the Sb-Br bond lengths are similar
to those found [27] in other related compounds (2.544–2.565 and
2.546–2.566 Å, respectively)) accompanied by symmetric tribro-
mides (Br-Br = 2.539 and 2.547 Å, respectively). These units build
infinite linear supramolecular chains (Fig. 1) due to the presence
of Brꢁ ꢁ ꢁBr non-covalent interactions (3.467 and 3.394 Å, respec-
tively, which are less than the sum of Bondi’s van der Waals radii
for two Br atoms (3.66 Å, [33,34] viz. 95% and 93% from the
vdWsum). These short Brꢁ ꢁ ꢁBr contacts between [SbVBr6]ꢀ and tri-
bromides units are particularly interesting as they are anion-anion
contacts and should be destabilized by repulsion between same-
2. Experimental part
2.1. General remarks
Bromides of PyC2, PyC3 and PyC4 were obtained by reactions of
pyridine and corresponding 1,x-dibromoalkanes (2.05:1) in ace-
tonitrile (reflux, overnight) with nearly quantitative yields; their
purity was confirmed by 1H NMR and element analysis data. All
reagents were obtained from commercial sources and used as pur-
chased. In all cases, concentrated HBr was used. Caution: for work
with Br2-containing solutions, safety measures must be taken
(obligatory use of fume hood, skin and eye protection).
sign ions, but crystal-packing effects and
interactions (Fig. 2) are strong enough for stabilization of such
supramolecular associates in the solid state.
r-hole-like non-covalent
The Sb-Brterm-BrBr3 and Brterm-Brbr3-BrBr3 angles are 158.5 and
164.1° in 1 and 158.6 and 150.0° in 3, respectively. Applying the
classification of halogenꢁ ꢁ ꢁhalogen contacts which was proposed
by Desiraju et al. [36] and is widely exploited now [37], those must
be regarded as Type I interactions. Interestingly, the contacts
between bromide ligands of neighboring [SbBr6]ꢀ are absent in 1
and 3, despite those were encountered in other Sb(V) bromide
complexes [27]. In both these structures, there are numerous short
Hꢁ ꢁ ꢁBr contacts which are common for halometalates with organic
cations.
2.2. Synthesis of 1–3
1: 8.4 mg (0.029 mmol) of Sb2O3 were dissolved in 7 ml of con-
centrated HBr, followed by addition of 1 ml of 1 M Br2 solution in
HBr and solution of 20 mg (0.058 mg) of PyC2Br2 in 5 ml of HBr. The
mixture was kept at 6 °C for 18 h, resulting in dark cherry-red crys-
tals of 1. Yield 79%. For C12H14Br9N2Sb calcd, %: C, 14.2; H, 1.4; N,
2.8; found, %: C, 14.4; H, 1.4; H, 2.8.
2: the procedure was similar to 1, using 18 mg (0.063 mmol) of
Sb2O3 in 5 ml of HBr, 1 ml of HBr/Br2 solution and 15 mg
(0.042 mmol) of PyC3Br2 in 4 ml of HBr. Crystals of 2 form within
wo days. Yield 81%. For C26H32Br15N4Sb3 calcd, %: C, 16.0; H, 1.7;
N, 2.9; found, %: C, 16.1; H, 1.7; N, 3.0.
3: the procedure was similar to 1, using 10 mg (0.035 mmol) of
Sb2O3 in 10 ml of HBr, 1 ml of HBr/Br2 and 26 mg (0.07 mmol) of
PyC4Br2 in 2 ml of HBr. The crystals of 3 form within 18 h. Yield
70%. For C14H18Br9N2Sb calcd, %: C, 16.1; H, 1.7; N, 2.7; found, %:
C, 16.3; H, 1.8; N, 2.7.
Complex 2 represents a very rare case of mixed-valence bro-
moantimonate (among the whole palette of products of ‘‘[SbIIIBr6]3-
ꢀ
+ Br2 + CatBrx” reactions, only one such case was described yet;
under such conditions Sb(III) is typically oxidized to Sb(V)). There
are two types of anions in the crystal structure. First, there are bin-
uclear [Sb2Br9]3ꢀ anions built of two face-sharing {SbBr6} octahe-
dra (this is
a very common structural type for group 15
halometalates [38–40]); the Sb-Br distances match well with the
ranges found in other relevant structures (Sb-Brterm = 2.643–
2.681 Å, Sb-l2-Br = 2.935–3.045 Å). Second, there are mononuclear
[SbVBr6]ꢀ which show prominent disordering. Only two trans-Br
positions are ordered (Sb-Br = 2.547 Å), while each of four bromide
ligands is disordered over four positions with different occupancies
(Figs. 3a and b). The system of non-covalent interactions in this
structure is more sophisticated then in 1 and 3. It is very likely that
there are contacts between Brterm in neighboring [SbBr6]ꢀ, but their
lengths cannot be estimated in a straightforward manner. Addi-
tionally, there are interactions between non-disordered Brterm of
2.3. X-ray diffractometry
Crystallographic data and refinement details for 1–3 are given
in Table 1. Diffraction data were collected on a New Xcalibur (Agi-
[SbBr6]ꢀ and 2-Br of [Sb2Br9]3ꢀ (3.353 Å).
l
lent Technologies) diffractometer with MoK
a
radiation
In order to estimate the energies of Brꢁ ꢁ ꢁBr energies in the crys-
tals of 1 and 3, we followed the protocol which was used by us for
investigation of supramolecular features in structures of other
related halometalates [27], as well as in other complexes [41–45]
(DFT calculations for non-optimized structures and QTAIM analysis
[46] of electronic density distribution). Results are shown in Table 2
and presented on Figs. 3a and b. The energy values (2.1–2.5 kcal/-
mol) agree well with those found in other polybromide-bromoan-
timonate(V) associates [27]. Applying relevant criteria, we can
state that these interactions are: a) attractive [47] and b) purely
supramolecular (covalent contribution is absent [48]). Unfortu-
nately, we had to exclude structure 2 from consideration due to
disordering which makes application of abovementioned approach
impossible.
(k = 0.71073) by doing u scans of narrow (0.5°) frames at 130 K.
Absorption correction was done empirically using SCALE3
ABSPACK
(CrysAlisPro,
Agilent
Technologies,
Version
1.171.37.35). Structures were solved with SHELXT [30] method
and refined by full-matrix least-squares treatment against |F|2 in
anisotropic approximation with SHELX 2014/7 [31] in ShelXle
[32] program. Hydrogen atoms were refined in geometrically cal-
culated positions (1 and 3) and some H-atoms were located
directly from experiment in the case of 2. The crystallographic data
have been deposed in the Cambridge Crystallographic Data Centre
under the deposition codes CCDC 2,058,211 (1), 2,058,212 (2) and
2,058,213 (3).
Thermogravimetric analyses (TGA) were carried out on a TG
209 F1 Iris thermobalance (NETZSCH, Germany). The measure-
ments were made in a helium flow using the heating rate of 10 °-
C minꢀ1, the gas flow rate of 60 ml minꢀ1 and open Al crucibles.
Details of DFT calculations and PXRD are given in SI.
According to PXRD (SI), 1–3 can be isolated as single phases,
allowing their further characterization. The TGA curves for 1 and
3 are shown on Fig. 4. It can be seen that those are very similar;
2
Bondarenko, Mikhail A.
