Synthesis, thermal stability, crystal structure and optical properties of 1,1′-(1,n-alkanediyl)bis(4-methylpyridinium) bromobismuthates

Article abstract of DOI:10.1016/j.poly.2017.08.016

Four hybrid 1,1′-(1,n-alkanediyl)bis(4-methylpyridinium) bromobismuthates, namely (PiC₂)₂Bi₂Br₁₀ (1), PiC₄(H₅O₂)BiBr₆·2H₂O (2), (PiC₅)₂Bi₂Br₁₀ (3) and (PiC₆)₂(H₅O₂)Bi₂Br₁₁ (4), were prepared by a facile solution method. The crystal structures of 1 and 3 contain zero-dimensional Bi₂Br₁₀ anion units. A 2-D network structure consisting of {H₅O₂}[BiBr₆]·2H₂O interconnected by hydrogen bonds was found in 2 and a 1-D network structure consisting of {H₅O₂}[Bi₂Br₁₁] was observed in 4.

Full text of DOI:10.1016/j.poly.2017.08.016

Accepted Manuscript
Synthesis, Thermal Stability, Crystal Structure and Optical Properties of 1,1'-
(1,n-Alkanediyl)bis(4-methylpyridinium) Bromobismuthates
Vitalii Yu Kotov, Andrey B. Ilyukhin, Nikolai P. Simonenko, Sergey A.
Kozyukhin
PII:
S0277-5387(17)30547-8
DOI:
http://dx.doi.org/10.1016/j.poly.2017.08.016
POLY 12780
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
16 June 2017
9 August 2017
Please cite this article as: V.Y. Kotov, A.B. Ilyukhin, N.P. Simonenko, S.A. Kozyukhin, Synthesis, Thermal
Stability, Crystal Structure and Optical Properties of 1,1'-(1,n-Alkanediyl)bis(4-methylpyridinium)
Bromobismuthates, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.2017.08.016
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Synthesis, Thermal Stability, Crystal Structure and Optical Properties of
1,1'-(1,n-Alkanediyl)bis(4-methylpyridinium) Bromobismuthates
Vitalii Yu. Kotov*, Andrey B. Ilyukhin, Nikolai P. Simonenko, Sergey A. Kozyukhin
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
119991, Moscow, Russian Federation
Abstract
Four hybrid 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) bromobismuthates, namely
(PiC2)2Bi2Br10 (1), PiC4(H5O2)BiBr6·2H2O (2), (PiC5)2Bi2Br10 (3) and (PiC6)2(H5O2)Bi2Br11 (4),
were prepared by a facile solution method. The crystal structures of 1 and 3 contain zero-
dimensional Bi2Br10 anion units. A 2-D network structure consisting of {H5O2}[BiBr6]·2H2O
interconnected by hydrogen bonds was found in 2 and a 1-D network structure consisting of
{H5O2}[Bi2Br11] was observed in 4.
Keywords: Bismuth complexes, optical band gap, crystal structure, thermal stability
Introduction
In recent years, the chemistry of organic-inorganic hybrid halobismuthates has attracted growing
attention in advanced materials studies [1]. This interest was inspired by promising physical
properties characteristic for this class of compounds, for example, semiconductivity,
photochromism, luminescence, etc. Typically, the crystal structures of hybrid halobismuthates
are build up by isolated, corner-sharing or edge-sharing BiX6 octahedra, forming naturally
isolated ion units (0-D, eg. BiBr6 [2], Bi2Br11 [3], Bi2Br10 [4,5], Bi2Br9 [6,7]), infinite chains (1-
D, eg. (BiBr5)n [8] or (BiBr4)n [9]) or two dimensional networks (2-D). The inclusion of
hydroxonium ions into a structure is more likely to occur when hybrid halobismuthates are
isolated from an acid medium [10]. However, not all organic cations are stable in such media. In
particular, the recrystallization of 1,1'-(1,n-alkanediyl)bis(4-cyanopyridinium) halobismuthates
from acidic solutions can be complicated by the hydrolysis of the cationic nitrile groups [11]. In
this study we have focused on 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) bromobismuthates,
for which the cation has a structure close to that of 1,1'-(1,n-alkanediyl)bis(4-cyanopyridinium)
and no obstacles for the crystallization from acidic solutions are expected.

Results
The molecular structure of the title dications is presented in Scheme 1. The 1,1'-(1,n-
alkanediyl)bis(4-methylpyridinium) bromides (PiСnBr2), n = 2, 4-6 were synthesized from 4-
methylpyridine and α,ω-dibromalkanes in acetonitrile [12,13].
Scheme 1. The molecular structure of the 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) cations.
Synthesis of the bis(4-cyano-1-pyridino)propane halobismuthates
The interaction of 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) cations (n = 2, 4-6) with
bromobismuthate anions in concentrated HBr resulted in the formation of yellow solutions.
Upon standing in air at room temperature, beige or light yellow crystal solids (1-4) were formed
in the solutions (n = 2, 4-6):
-
2PiC22+ + 2Br- + 2BiBr4 = (PiC2)2Bi2Br10↓
(Compound 1)
(Compound 2)
(Compound 3)
(Compound 4)
PiC42+ + 2Br- + BiBr4 + H3O+ + 3H2O = PiC4(H5O2)BiBr6·2H2O↓
-
-
2PiC52+ + 2Br- + 2BiBr4 = (PiC5)2Bi2Br10↓
-
2PiC62+ + 3Br- + 2BiBr4 + H3O+ + H2O = (PiC6)2(H5O2)Bi2Br11↓
X-ray diffraction study.
The structure of 1 is formed from 1,1'-ethane-1,2-diylbis(4-methylpyridinium) cations and
centrosymmetric Bi2Br10 anions (Fig. 1). The Bi atom is located in an octahedral environment;
the Bi-Br bond lengths are different. The longest bonds were found for the bridging Br(3) atoms,
the shortest bonds were observed for Br atoms in trans positions to the bridge. The aliphatic
fragment has a gosh-conformation with a N(1)C(6)C(7)N(2) torsion angle equal to -57.6o. The
cationic and anionic “chains” (Fig. S1 in ESI) are staggered relative to each other. The short
contacts in the cationic chain, N(1)…N(1') 3.383, N(1)…C(1') 3.343, C(10)…C(10') 3.364 Å,
can be interpreted as stacking interactions.

Fig. 1. The crystal structure of 1. Atoms are represented at the 50% probability level. Selected
bond lengths and angles are given in Table. S1 in the ESI.
The structure of 2 is formed from dioxonium and 1,1'-butane-1,4-diylbis(4-methylpyridinium)
cations, BiBr6 anions and crystal water molecules (Fig. 2a). The H5O2 cations and BiBr6 anions
are situated in inversion centers. The C(6)-C(9) aliphatic chain has a gosh-trans-gosh (g-t-g)
conformation with torsion angles -62.3, 177.7, and 79.1o. Hydrogen bonds (HB) interconnect the
dioxonium cations, BiBr6 anions and crystal water molecules into layers (Fig. 2b, and Fig. S2 in
the ESI). Short C…C contacts between the cations exceed 3.6 Å. Short Bi-Br distances are
formed by Br atoms (2,4), which are involved in the HBs with the dioxonium ions.
a
b
Fig. 2. The crystal structure of 2 (a). Atoms are represented at the 50% probability level.
Selected lengths and angles are given in Table. S1, ESI. The 2D network structure of
{H5O2}[BiBr6] ·2H2O in 2 stabilized by hydrogen bonds (b).
The structure of 3 is similar to that of 1. This structure is formed by 1,1'-pentane-1,5-diylbis(4-
methylpyridinium) cations and centosymmetric Bi2Br10 anions (Fig. 3). The Bi atoms have an
octahedral environment. The Bi-Br bond lengths are different for different Br atoms. The
longest bonds were found for the bridging Br(2) atoms, the shortest bonds were observed for the
Br atoms in the trans-position to the bridge. The aliphatic N(1)...N(2) fragment has a g-t-t-g
conformation with torsion angles -52.3, -179.6, -166.6, and -64.1o. The cationic and anionic
“chains” (Fig. S3 in the ESI) are staggered relative to each other. The shortest contact in the
cationic C(2)…C(2') “chain” is 3.439 Å, The shortest contact distance in the anionic
Br(6)…Br(6') “chain” is 7.35 Å.
Fig. 3. The crystal structure of 3. Atoms are represented at the 50% probability level. Selected
bond lengths and angles are given in Table. S1 ESIǂ.

All the structure units in 4, namely the two crystallographically independent 1,1'-hexane-1,6-
diylbis(4-methylpyridinium) cations, dioxonium cation and Bi2Br11 anion, are located at
inversion centers (Fig. 4a). The difference in the Bi-Br bond lengths in the structure of 4 is
caused not only by the dimeric structure of the anion, but also by partial stereochemical activity
of the lone electron pairs of Bi atoms. Three Bi-Br bonds with Br atoms of one octahedral face
(Br(1), Br(3), Br(5)) are more than 0.2 Å shorter than the same bonds with the Br atoms of the
opposite face (Br(2), Br(4), Br(6)).
The conformations of the aliphatic chains of two independent cations are the same, namely g-
t-t-t-g (the torsion angles are 65.0, 179.4, 180.0, 179.4, 65.0 and 65.1, -178.2, 180.0, -178.2,
65.0o). The dioxonium cations unite the anions into 1D chains parallel to the c axis (Fig. 4b). In
the structure of 4, one can identify separate layers formed by organic cations and
{H5O2}[Bi2Br11] (Fig. S4 in the ESI).
a
b
Fig.4. The crystal structure of 4. Atoms are represented at the 50% probability level. Selected
bond lengths and angles are given in Table. S1, ESI. 1D network structure of the
{H5O2}[Bi2Br11] containing chain in 4 (b).
Thermal stability
According to the DSG-TGA results, decahalodibismuthates 1 and 3 are stable up to 230 oC (Fig.
S5 and Fig. S7 in the ESI†). For compounds 2 and 4 the first stage of mass loss occurs at 70-160
С (Fig. 5, Fig. S6 and Fig. S8 in the ESI†) and this corresponds to the loss of one HBr molecule
and 4 or 2 water molecules per formula unit:
2PiC4(H5O2)BiBr6·2H2O = (PiC4)2Bi2Br10 + 8H2O + 2HBr
(PiC6)2H5O2Bi2Br11 = (PiC6)2Bi2Br10 + 2H2O + HBr
DSG-TGA: exp. 15.17% for 2 (Fig. S5, ESI), calc. 15.24% for PiC4(H5O2)BiBr6·2H2O, exp.
6.30% for 4 (Fig. S7, ESI), calc. 6.27% for (PiC6)2H5O2Bi2Br11.
Fig. 5. TGA curve of 2.

After the loss of solvent molecules, the formed 1,1'-(1,n-alkanediyl)bis(4-methylpyridinium)
o
decabromodibismuthates are stable up to 190 C. Further heating of samples 2-4 results in their
o
o
o
melting: T = 242±1 C (2), 243±1 C (3), 194±1 C (4), ΔH= 5.96 cal/g (2), 5.60 cal/g (4). The
decomposition of the compounds starts at temperatures above 270±5 oC (1), 260±5 oC (2), 260±5
oC (3) and 250±5 oC (4) (Fig. S5-S8 in the ESI†).
Optical properties
The diffuse reflectance spectra (DRS) of 1, 2 and 4 are shown in Fig. S9 in the ESI† as the
Kubelka-Munk function vs light energy. The Kubelka-Munk equation is expressed as follows
[14]:
,
where Rd is the absolute reflectance of the sample layer. The optical band gap energies (Eg) were
estimated from extrapolation of the linear parts of the corresponding curves to F(Rd) = 0. The
optical band gap values are 2.86 eV (1), 2.92 eV (2), 2.91 eV (3) and 2.77 eV (4). These values
are typical for compounds containing bromobismuthate anions with a 0-D structure [2-4,7].

Table 1. Crystal data and structure refinement for 1-4.
Identification code
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
Crystal system
Space group
a, Å
b, Å
c, Å
α, °
β, °
1
2
3
4
C28H36Bi2Br10N4
1645.67
120(2)
0.71073
Monoclinic
P21/n
11.9860(6)
11.5401(6)
14.8312(7)
90
92.117(2)
90
2050.05(18)
2
2.666
C16H31BiBr6N2O4
1003.87
120(2)
0.71073
Triclinic
C34H48Bi2Br10N4
1729.82
150(2)
0.71073
Monoclinic
P21/n
12.5224(5)
11.8981(4)
16.3877(6)
90
90.3920(10)
90
2441.59(16)
2
2.353
C36H57Bi2Br11N4O2
1874.82
120(2)
0.71073
Triclinic
P-1
P-1
9.8287(7)
10.1037(7)
15.1922(12)
85.297(2)
71.244(2)
81.141(2)
1410.67(18)
2
10.4373(5)
10.6116(5)
14.3397(6)
107.1050(10)
95.5130(10)
114.9560(10)
1331.07(11)
1
γ, °
Volume, Å3
Z
D (calc), Mg/m3
µ, mm-1
2.363
14.769
2.339
14.890
18.343
15.408
F(000)
1496
932
1592
868
Crystal size, mm
θ range, °
Index ranges
0.32 x 0.28 x 0.08
2.146, 29.130
-16<=h<=16
-15<=k<=15
-20<=l<=20
25709
0.1 x 0.08 x 0.04
2.041, 26.732
-12<=h<=12
-12<=k<=11
-19<=l<=19
15233
0.36 x 0.24 x 0.18
2.361, 31.572
-18<=h<=18
-17<=k<=17
-23<=l<=23
35772
0.28 x 0.26 x 0.2
2.279, 27.483
-13<=h<=13
-13<=k<=13
-18<=l<=18
15409
Reflections collected
Independent reflections, Rint
Completeness to θ = 25.242°
Absorption correction
5522, 0.0723
100.0 %
5962, 0.0393
99.6 %
8124, 0.0684
99.9 %
6109, 0.0470
99.9 %
Semi-empirical
from equivalents
0.7462, 0.2838
Full-matrix
least-squares on F2
5522 / 0 / 199
1.028
Semi-empirical
from equivalents
0.0752, 0.0375
Full-matrix
least-squares on F2
5962 / 0 / 265
1.169
Semi-empirical
from equivalents
0.7462, 0.2558
Full-matrix
least-squares on F2
8124 / 0 / 226
0.971
Semi-empirical
from equivalents
0.5642, 0.2083
Full-matrix
least-squares on F2
6109 / 0 / 250
0.999
Max., min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit
R1, wR2 [I>2sigma(I)]
R1, wR2 (all data)
0.0347, 0.0896
0.0458, 0.0949
0.0423, 0.1017
0.0541, 0.1063
2.336, -1.746
0.0328, 0.0711
0.0535, 0.0784
1.925, -1.667
0.0300, 0.0740
0.0378, 0.0769
2.530, -2.087
Largest diff. peak and hole, e Å-3 2.270, -1.860

Conclusions
Two neutral
and
two
acid
hybrid
1,1'-(1,n-alkanediyl)bis(4-methylpyridinium)
bromobismuthates were prepared by a facile solution method and characterized by X-ray
diffraction, DRS and TGA. The later method demonstrated that for acid compounds 2 and 4 the
first stage of mass loss occurs at 70-160 С and corresponds to the loss of HBr and water
molecules with the formation of stable hybrid decabromodibismuthates.
Experimental
Materials
1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) bromides. A mixture containing 5 ml of α,ω-
dibromalkane (Aldrich, 97%) and 20 ml of 4-picoline(Aldrich, 98%) was slightly heated with
stirring on a magnetic stirrer for one day. The obtained precipitate, PiCnBr2, was successively
washed with acetonitrile (Komponent-Reactive, dry) and ethanol (Komponent-Reactive, 96%),
and then dried in air. In the case of 1,5-dibrompentane, the formed product was hygroscopic.
Therefore, after washing with dry acetonitrile, it was immediately dissolved in water or
concentrated HBr (Fluka, purum p.a. 48%), with the formation of a 2 M solution.
1,1'-(1,n-alkanediyl)bis(4-methylpyridinium) bromobismuthates. A 3 ml solution of 2 M
PiCnBr2 in concentrated HBr was added to 15 ml of 0.1 M BiBr3 (Lanhit, ultra dry, 99.999%)
solution in 15 ml of concentrated HBr. Crystalline substances precipitated from the light yellow
solutions in 1-2 days. The solids of 1-4 were separated from solution by decantation,
successively washed three times with dry acetonitrile and ethanol, and then dried in air.
Analytical methods
The reflectance spectra were measured with a Cary 5000 spectrophotometer in the frequency
range 10000-50000 cm-1 at room temperature.
The thermal behavior of the samples was studied by thermo gravimetric analysis (TGA) and
differential thermal analysis (DTA) using an SDT Q600 V8.3 Build 101 Module DSC-
o
TGA thermal analyzer instrument. The samples were heated at 10o/min from 25 to 300 C in air
atmosphere in an alumina open pan.
Single crystal X-ray diffraction data were collected on a Bruker SMART APEX2 instrument
[15] (Table 1). Absorptions were taken into account by a semi-empirical method based on
equivalents using SADABS [16]. The structures were determined using a combination of the
direct method and Fourier syntheses. The positions of hydrogen atoms in the organic cations
were calculated from geometrical considerations. The positions of the H atoms of H2O molecules

and H5O2 cations, (2, and 4) were partly localized from the difference Fourier syntheses and
partly calculated from geometric considerations. The structures were refined by the full-matrix
anisotropic least squares method. All calculations were carried out using SHELXS-2014,
SHELXS-2016, SHELXL-2014 and SHELXL-2016 software [17]. X-ray powder diffraction
analysis was carried out on a Bruker D8 ADVANCE X-ray diffractometer (CuKα, Ni-filter,
LYNXEYE detector, reflection geometry). Further experimental details for reflectance
spectroscopy and TGA-DTA can be found in the Electronic Supplementary Information.
Appendix A. Supplementary data
CCDC 1547684-1547687 contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
†Electronic supplementary information (ESI) available: CIF files of the structural data for
compounds 1-4, CCDC 1547684-1547687, additional figures, DRS and TGA TGA-DTA curves
for 1-4. For ESI and crystallographic data in CIF or other electronic format see DOI:
Acknowledgements
The authors are grateful to the centre for collective use of N.S. Kurnakov Institute of General
and Inorganic Chemistry for the opportunity to collect single crystal X-ray diffraction data, DRS,
TGA and DTA data.
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Fig.1

Fig.2.a

Fig.2.b

Fig.3

Fig.4.a

Fig.4.b

Fig.5

Two
neutral
and
two
acid
hybrid
1,1'-(1,n-alkanediyl)bis(4-methylpyridinium)
bromobismuthates were prepared by a facile solution method. For the acid compounds, the first
stage of mass loss corresponds to the loss of HBr and water molecules, with the formation of
stable hybrid decabromodibismuthates.