Methyl viologen iodobismuthates

Article abstract of DOI:10.1016/j.poly.2018.08.017

The interaction of iodobismuthate anions and methyl viologen [MV]²⁺ cations in aqueous solutions led to the formation of three compounds, two of which were identified as [MV][BiI₅] and [MV]₃[Bi₂I₁₁]I. Hybrid iodobismuthates [MV]₃[Bi₂I₁₁]I and [MV]₃[Bi₂I₉]₂(DMF)₃(H₂O) were isolated from dimethylformamide (DMF). The heating of the latter material (up to 200 ^oC) resulted in a mixture of products, one of which was identified as [MV][BiI₅]. A simple antisolvent precipitation method was proposed to create the [MV][BiI₅]/SiO₂ composite material.

Full text of DOI:10.1016/j.poly.2018.08.017

Accepted Manuscript
Methyl Viologen Iodobismuthates
Petr A. Buikin, Andrey B. Ilyukhin, Nikolai P. Simonenko, Veronika K.
Laurinavichyute, Vitalii Yu. Kotov
PII:
S0277-5387(18)30482-0
https://doi.org/10.1016/j.poly.2018.08.017
POLY 13340
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
23 May 2018
6 August 2018
7 August 2018
Please cite this article as: P.A. Buikin, A.B. Ilyukhin, N.P. Simonenko, V.K. Laurinavichyute, V.Y. Kotov, Methyl
Viologen Iodobismuthates, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.08.017
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Methyl Viologen Iodobismuthates
Petr A. Buikin,1,2 Andrey B. Ilyukhin,1 Nikolai P. Simonenko,1 Veronika K. Laurinavichyute,3
Vitalii Yu. Kotov1,2,4*
1N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
119991 Moscow, Russian Federation
2Higher Chemical College RAS, D. I. Mendeleev University of Chemical Technology of Russia,
125047 Moscow, Russian Federation
3Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow,
Russian Federation
4National Research University Higher School of Economics, 101000, Moscow, Russian
Federation
Highlights:
Two new methyl viologen iodobismuthates were synthesized.
The novel anion [Bi2I11]5- was found in two structures of hybrid iodobismuthates.
The deposition of [MV][BiI5] on a SiO2 substrate by the thermal decomposition of
[MV]3[Bi2I9]2(DMF)3(H2O) was proposed.
The interaction of iodobismuthate anions and methyl viologen [MV]2+ cations in aqueous
solutions led to the formation of three compounds, two of which were identified as [MV][BiI5]
and [MV]3[Bi2I11]I. Hybrid iodobismuthates [MV]3[Bi2I11]I and [MV]3[Bi2I9]2(DMF)3(H2O)
o
were isolated from dimethylformamide (DMF). The heating of the latter material (up to 200 C)
resulted in a mixture of products, one of which was identified as [MV][BiI5]. A simple
antisolvent precipitation method was proposed to create the [MV][BiI5]/SiO2 composite material.
Keywords: Bismuth complexes, optical band gap, crystal structure, thermal stability

1. Introduction
In recent years, the chemistry of organic-inorganic hybrid halobismuthates has attracted
growing attention in advanced materials studies. This interest was inspired by promising physical
properties inherent in this class of compounds, for example, semiconductivity, photochromism,
luminescence, etc. Alkyl viologen halobismuthates are ones of the most popular halobismuthates
[1-8]. Methyl viologen chlorobismuthates are remarkable for their photoinduced colour change,
due to outer-sphere charge transfers [1,2]. Methyl viologen iodobismuthate [MV][BiI5] [3], as
well as the mixed methyl viologen chloro-iodo-bismuthate [MV][BiCl2I3] [4] and methyl
viologen bromo-iodo-bismuthate [MV][BiBr3.8I1.2] [5] exhibit unusual spectral properties owing
to the appearance of low-energy exciton bands in their spectra. Their appearance is usually
associated with the presence of linear and quasilinear all trans-Bi-I-Bi-I chains in their crystal
structures with Bi-I-Bi and I-Bi-I angles about 180°. Our quantum-chemical calculations on the
electronic structure of 1,1'-(1,5-pentanediyl)bis(4-methylpyridinium) iodobismuthate [9]
demonstrated that the electronic transitions with the lowest energy in such compounds are 5py(I)
 6py(Bi). Most of the methyl viologen halobismuthates, including [MV][BiI5], were obtained
by solvothermal synthesis in a methanol solution. In the present work, we explored the
possibility of the synthesis of [MV][BiI5] in water solutions and its deposition on SiO2 substrates
for further studies of its photophysical properties.
2. Results
Scheme 1. The molecular structure of the methyl viologen cation ([C12H14N2]2+ or [MV]2+).
2.1.Synthesis and X-ray diffraction study
The interaction of aqueous solutions of [MV]I2 and potassium iodobismuthate (a mixed
solution of KI and Bi(NO3)3) in the molar ratio of 1:2 ([MV]2+:Bi3+) results in the fast formation
of a red precipitate (1). No colour change was observed for 1 in contact with the mother liquor
solution over 24 hours. Being separated from the reaction mixture, product 1 was found to be
stable for a long time. The experimental XRD pattern of 1 (Fig.S5) and the calculated XRD
pattern of [MV][BiI5] [3] are different.

Scheme 2. Synthesis of methyl viologen iodobismuthates
An increase in the [MV]2+ to Bi3+ molar ratio up to 1:1 results in the fast formation of the
red precipitate of 1 as well. However, in contact with the mother liquor solution the colour of the
precipitate changes to black within a few minutes. The obtained compound can be identified as
[MV][BiI5] [3] (Fig.S6 in the ESI). Details of the Rietveld refinement: space group P21, a =
6.4749(3) Å, b = 15.4048(7) Å, c = 11.2597(5) Å, β = 101.116(3) °, Rexp: 4.04%, Rwp: 6.64%,
Rp: 5.22%, GOF: 1.65. No colour change was observed for the black precipitate [MV][BiI5] in
contact with the mother liquor solution over 24 hours.
In the reaction mixture with a molar ratio of [MV]2+ to Bi3+ of 2:1 the initially formed red
precipitate 1 turns into the black precipitate [MV][BiI5] within a couple of minutes, and after
another 10 minutes it turns into a dark red precipitate [MV]3[Bi2I11]I (2). Further aging of 2 in
the reaction solution does not lead to any visible changes in the system. Details of the Rietveld
refinement for 2: space group P21, a = 16.103(1) Å, b = 32.246(2) Å, c = 11.5612(7) Å, β =
90.00(4) °, Rexp: 3.74%, Rwp: 11.78%, Rp: 8.84%, GOF: 3.15. (Fig. S7 in the ESI).
Recrystallization of 2 from DMF results in the formation of a crystalline product, however the
crystals were not suitable for single crystal X-ray analysis. Details of the Rietveld refinement:
space group P21, a = 16.102(1) Å, b = 32.267(1) Å, c = 11.5620(6) Å, β = 89.98(2) °, Rexp:
4.67%, Rwp: 11.82%, Rp: 8.58%, GOF: 2.53. According to the results of the X-ray powder
diffraction analysis, 1 and 2 are proved to be different phases (Fig.S5). However, the main
product of crystallization of 1 under the hydrothermal conditions (140 °C, 20 hours, aqueous
solution of 5.6 M KI) was identified as 2. Details of the Rietveld refinement: space group P21, a
= 16.092(1) Å, b = 32.252(1) Å, c = 11.5681(8) Å, β = 90.000(3) °, Rexp: 4.94%, Rwp: 11.35%,
Rp: 8.70%, GOF: 2.30. The crystals of 2 obtained by hydrothermal synthesis were found to be
suitable for single crystal X-ray analysis.
Our crystallization attempts of 1 or [MV][BiI5] from DMF led to the formation of a
coloured glass with inclusions of red crystals of [MV]3[Bi2I9]2(DMF)3(H2O) (3). The pure form
of this compound can be obtained by removing the solvent from a mixed solution of [MV]I2 and
BiI3 in DMF (with the molar ratio of [MV]I2:BiI3 of 3:4) in air. Details of the Rietveld
refinement (without sample grinding, Fig. S8 in the ESI): space group Cmc21, a = 17.0275(7) Å,
b = 34.723(1) Å, c = 14.8151(6) Å, Rexp: 1.20%, Rwp: 4.77%, Rp: 3.10% GOF: 3.98. The heating
of compound 3 up to 143 °C leads to its decomposition with the loss of three DMF molecules
and one H2O molecule (Fig. S1d in the ESI, the theoretical mass loss is 6.05%, the experimental
mass loss is 6.19%), and the formation of a black product. According to the X-ray powder

diffraction data, this product contains a mixture of 1 and [MV][BiI5] (Fig S9 in the ESI). It
should be note that compound 3 is subjected to a tribochemical reaction (similar to thermal
decomposition) during the grinding. According to X-ray powder diffraction analysis, the ground
crystals of 3 are contaminated by 1 and [MV][BiI5] (Fig S10 in the ESI). Details of the Rietveld
refinement: space group Cmc21, a = 17.0378(9) Å, b = 34.834(1) Å, c = 14.8900(6) Å, Rexp:
6.31%, Rwp: 12.56%, Rp: 9.37%, GOF: 1.99.
It is noteworthy that the сompound 2 contains [Bi2I11]5- anions, which has not been
described previously [10]. According to previous work [11], the Bi:halogen ratio in the anion can
be varied either by varying the reagent ratio in the reaction mixture or by adjusting the solution
acidity. In our work we observed the formation of 2 when changing the reagent ratio in the
reaction mixture from 1:1 to 2:1. The effect of acidity on the product composition can be
illustrated for 1,1'-(hexane-1,6-diyl)bis(2-aminopyridinium) (HBAP) halobismuthates. We
demonstrated for the iodobismuthate system that low acidity promotes crystallization of
[HBAP][BiI4]2∙2H2O (4), while high acidity (concentrated HI) facilitates the crystallization of
[HBAP]3(H3O)2[Bi2I11][BiI6]∙6H2O (5). One of the 1,1'-(hexane-1,6-diyl)bis(2-aminopyridinium)
bromobismuthates [12] contains the similar [Bi2Br11]5- anion.
NH2
N+
N+
NH2
Scheme 3. The molecular structure of the 1,1'-(hexane-1,6-diyl)bis(2-aminopyridinium)
cation ([C16H24N4]2+ or [HBAP]2+).
2.2. Single crystal X-ray analysis.
Crystal data for 2. The structure of 2 is formed by [MV]2+ cations, together with [Bi2I11]5- and I-
anions (Fig. 1a). The unit cell contains two crystallographically independent anions (both I-
anions are disordered over two positions) and six crystallographically independent cations. The
torsion angle between adjacent aromatic rings varies from 12.4o to 32.7o. Ionic associates
10-
[Bi2I11]2 are formed by short I(7)∙∙∙I(13') contacts (3.730 Å), while longer I(2)∙∙∙I(18) contacts
(3.925 Å) are responsible for the formation of a 1D-chain (Fig. 1b). If we approximate the chains
as rods, the latter will form a dense packing structure (Fig. S2a in the ESI). The shortest I∙∙∙I

contacts between the nearest chains are larger than 4.2 Å. [MV]2+ cations and I- anions are
located between the 1D-chains (Fig. S2 in the ESI).
a
b
Fig. 1. The asymmetric unit of the structure of 2 (thermal ellipsoids are shown at 50%
probability) (a) and the mutual arrangement of [Bi2I11]5- anions in the crystal structure of 2 (b).
Crystal data for 3. The crystal structure of 3 contains [MV]2+ cations, [Bi2I9]3- anions and
solvate molecules of DMF and H2O (Fig.2 a, b). Both the crystallographically independent
anions [Bi2I9]3- and cations, containing the N(1) and N(2) atoms, have crystallographic symmetry
m. Bridging I atoms in the anions lay in the plane m, where the plane m passes through the center
of the bridging C-C bond in the cation, containing the N(1) atom, and finally, the plane m is
perpendicular to the plane of the cation and passes through the atoms N(2,3) in the cation. Like
all the solvate molecules, the cation containing the N(4) atom is disordered about the plane m.
The shortest I∙∙∙I contact in the structure of 3 is 4.183 Å.
a
b
Fig. 2. Complex [Bi2Br9]3- anions (thermal ellipsoids are shown at 50% probability) (a); [MV]2+
cations and solvent molecules in the crystal structure of compound 3 (b).
Crystal data for 4. The structure of compound 4 is formed by [HBAP]2+ cations, 1D-chains of
[BiI4]nn- (parallel to the c-axis) and solvent H2O molecules (Fig. S4a in the ESI). The periodicity
of the chain is 7.82 Å and this coincides with the value of the parameter c. The HBAP aliphatic
fragment has the t-t-t-t-t-t conformation (the crystallographic symmetry of HBAP is -1). The
shortest I∙∙∙I contact is 4.256 Å. The aromatic fragment of the [HBAP]2+ cations take part in π-π
stacking interactions (the shortest N(1)∙∙∙C(3') contact is 3.518 Å, Fig. S4 b,c in the ESI).
Crystal data for 5. Both the [Bi2Br11]5- and [BiBr6]3- anions in the structure of 5 have
crystallographic symmetry -1 (Fig. 3a). One of two crystallographically independent [HBAP]2+

cations is located at the inversion center and the second cation occupies a common position. The
conformation of the aliphatic chain is the same (g-t-t-t-t-g) for both [HBAP]2+ cations. All eleven
crystallographically independent oxygen positions of the water molecules or oxonium ions are
partly populated (0.29-0.44). In addition, the structure of 5 contains channels filled with (H3O)+
cations and water molecules (Fig. S4 in the ESI). One of the oxygen positions, O(11) with a
population 0.29, is at a distance of 2.869 Å from the iodine atom I(7). Analogous interactions
between O and I atoms were found in two other iodine-containing compounds [13,14]: with
distances of 2.807 and 2.891 Å, respectively. Short I(5)∙∙∙I(8') contacts (3.786 Å) connect
adjacent [Bi2Br11]5- and [BiBr6]3- ions into a 1D-chain, as shown in Fig. 3b. The interchain I∙∙∙I
distances exceed 4.3 Å.
a
b
Fig. 3. Complex [Bi2Br11]5- and [BiBr6]3- anions (thermal ellipsoids are shown at 50%
probability) (a) and the anionic 1D-chain constructed by [Bi2Br11]5- and [BiBr6]3- anions in the
structure of 5 (b).

Table 1. Crystal data and structure refinement for 2-5.
Identification code
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
Crystal system
Space group
a, Å
b, Å
c, Å
α, °
β, °
2
3
4
5
C36H42Bi2I12N6
2499.51
150(2)
0.71073
Monoclinic
P21
15.9893(5)
32.1100(10)
11.4805(4)
90
90.030(10)
90
5894.3(3)
4
2.817
C45H65Bi4I18N9O4
3916.18
150(2)
0.71073
Orthorhombic
Cmc21
17.0347(4)
34.3159(8)
14.7712(3)
90
90
90
C16H28Bi2I8N4O2
1741.58
150(2)
0.71073
Monoclinic
P21/c
11.7592(7)
19.5474(11)
7.8227(5)
90
100.747(2)
90
1766.60(18)
2
3.274
C48H90Bi3I17N12O8
3747.55
150(2)
0.71073
Triclinic
P-1
11.7404(4)
13.7640(5)
14.8717(5)
94.7520(10)
93.0050(10)
103.8220(10)
2319.09(14)
1
γ, °
Volume, Å3
Z
8634.7(3)
4
3.012
D (calc), Mg/m3
2.683
11.380
µ, mm-1
12.278
14.602
16.957
F(000)
4408
6864
1516
1676
Crystal size, mm
θ range, °
Index ranges
0.2 x 0.18 x 0.18
2.181, 30.539
-22 ≤ h ≤ 22
-45 ≤ k ≤ 45
-16 ≤ l ≤ 16
72755
0.26 x 0.22 x 0.12
2.145, 29.127
-23 ≤ h ≤ 23
-46 ≤ k ≤ 46
-20 ≤ l ≤ 20
76082
0.16 x 0.08 x 0.02
2.730, 28.355
-15 ≤ h ≤ 15
-26 ≤ k ≤ 26
-10 ≤ l ≤ 10
43947
0.24 x 0.18 x 0.1
2.052, 31.546
-17 ≤ h ≤ 17
-20 ≤ k ≤ 19
-21 ≤ l ≤ 21
56695
Reflections collected
Independent reflections, Rint
Completeness to θ = 25.242°
Absorption correction
35317, 0.0321
99.9 %
11981, 0.0576
99.9 %
4411, 0.0691
99.9 %
14810, 0.0497
99.9 %
Semi-empirical
from equivalents
0.0511, 0.0192
Full-matrix
least-squares on F2
Semi-empirical
from equivalents
0.0237, 0.0031
Full-matrix
least-squares on F2
Semi-empirical
from equivalents
0.0479, 0.0151
Full-matrix
least-squares on F2
Semi-empirical
from equivalents
0.1015, 0.0354
Full-matrix
least-squares on F2
Max,. min. transmission
Refinement method

Data / restraints / parameters
Goodness-of-fit
35317 / 21 / 1042
0.800
11981 / 139 / 430
1.151
4411 / 0 / 145
0.970
14810 / 0 / 408
1.027
R1, wR2 [I>2sigma(I)]
R1, wR2 (all data)
0.0376, 0.0925
0.0459, 0.0988
0.0528, 0.1215
0.0684, 0.1293
-0.027(3)
0.0337, 0.0824
0.0521, 0.0931
0.0339, 0.0803
0.0466, 0.0852
Absolute structure parameter
Largest diff. peak and hole, e Å-3
1.691, -1.290
1.935, -2.583
2.137, -1.687
1.660, -1.839

2.3. Thermal stability, optical and electrochemical properties of the methyl viologen
iodobismuthates
Compounds 1, 2 and [MV][BiI5] were found to be stable when heated in air up to 275 °C
(Fig S1a-c in the ESI). The reflectance spectra of compounds 1, 2 and [MV][BiI5] are shown in
Fig. 4. The estimated optical band gap of [MV][BiI5] (Eg=1.57 eV) is somewhat lower than that
reported earlier (1.70 eV, [3]). The optical band gap value of 2 is 1.98 eV. The optical band gap
value of 3 is 2.06 eV (Fig S11 in the ESI).
Fig. 4. The reflectance spectra of 1 (A), [MV][BiI5] (B) and 2 (C).
Thus, all the obtained methyl viologen iodobismuthates have different optical properties
and their optical band gaps vary from 1.57 eV ([MV][BiI5]) to 2.06 eV (3). This difference
encouraged us to investigate the electrochemical behavior of the synthesized materials. A typical
cyclic voltammogram of 1,1′-(1,5-pentanediyl)bis(4-methylpyridinium) [PiC5]2+ iodobismuthate
[9] ([PiC5][BiI5]/carbon composite) deposited on FTO shows only two irreversible peaks
corresponding to the redox processes involving the [BiI5]2- anion: reduction of Bi(III) (process I,
Fig. 5) and oxidation of iodine (process II, Fig. 5). On changing 1,1′-(1,5-pentanediyl)bis(4-
methylpyridinium) to methyl viologen, two additional reduction peaks appear (III and IV),
corresponding to the redox transitions [MV]2+/[MV]+ and [MV]+/[MV] [15,16]. The relative
heights of these peaks increase with an increase of the MV content in the compounds: 1 <
[MV][BiI5] < 2. The electrochemical band gaps were determined as the difference between
the onsets of the oxidation (process II) and reduction (processes I or III) potentials. The onset
values were estimated by taking the intersection point between the baseline and the tangent line
drawn to the rising portion of the current. The resulting ΔE values are as follows: 0.90 V (1),
0.96 V ([MV][BiI5]), 0.92 (2), 1.03 V ([PiC5][BiI5]). These values are close to each other and
substantially smaller than the corresponding values of Eg.
Fig. 5. First cycles of cyclic voltammograms obtained in 0.1 M phosphate buffer solution (pH =
7.55) at FTO – supported films of 1/carbon (A), [MV][BiI5]/carbon (B), 2/carbon (C) and
[PiC5][BiI5]/carbon (D). The scan rate was 50 mV s-1.
9

2.4.Design of the [MV][BiI5]/SiO2 composite material
Due to the low Eg value, [MV][BiI5] can be considered as a promising light-harvesting
material for photovoltaics. [MV][BiI5] is fairly soluble in DMF and the corresponding solution
can be used for the deposition of [MV][BiI5] on an oxide surface. In this work we explored two
approaches to the formation of [MV][BiI5] coating on a SiO2 surface: 1) removing the solvent of
a [MV][BiI5] - DMF solution by heating and 2) antisolvent precipitation. Removing the solvent
of a [MV][BiI5] solution in DMF (on the surface of a SiO2 support at 200 °C) leads to the
formation of an orange-red spot. No [MV][BiI5] was detected by reflectance spectra. A similar
situation was observed after removing the solvent of the solution of 3 in DMF on the surface of a
SiO2 support. In the case of antisolvent precipitation (with crystallization of 3), a drop of a
saturated solution of 3 in DMF was placed on the SiO2 substrate (Silica gel/TLC-cards DC-
Alufolirn-Kieselgel, Fluka, thickness 0.2 mm). After 10 s, an excessive amount of an antisolvent
(namely acetonitrile, toluene or 95 % ethanol) was added to the spot, which was accompanied by
formation of microcrystals on the oxide surface. The sample was then heated up to 200 °C and
after ~20 sec of heating the spot became black. The product of the thermal decomposition has a
characteristic absorption band in the near-IR region. The maximum absorption value increases
with by varying of antisolvents in series: hexane  isopropanol  acetonitrile  toluene  95%
ethanol (Fig. 6).
Fig. 6. Reflectance spectra of the thermal decomposition products of 3 obtained on a SiO2
surface with different antisolvents (1 – hexane, 2 – isopropanol, 3 – acetonitrile, 4 – toluene, 5 -
95% ethanol).
The optical band gap estimated for the [MV][BiI5]/SiO2 composite material is about 0.1 eV
higher than for a pure sample or for the product of the thermal decomposition of 3 (Fig. S11b).
This difference can be ascribed to the small thickness of the colored layer.
Hybrid halobismuthates seem to be promising materials for applications in solar energy
conversion systems due to their low band gap values, good stability in humid air and low
toxicity. At the same time, we did not find any examples of effective solar cells with hybrid
halobismuthates in the literature. Perhaps the main reason for this gap is the difficulty of the non-
destructive deposition of the material onto oxide substrates. In this work we demonstrate the
10

possibility of [MV][BiI5] coating formation on SiO2 substrates, however a similar deposition on
TiO2 substrates is still under question. Nevertheless, our results indicate the prospects of the
antisolvent precipitation technique for the formation of [MV][BiI5] coatings on oxide substrates.
3. Conclusions
We have prepared and characterized four new hybrid iodobismuthates. Two of them,
namely methyl viologen iodobismuthate iodide and 1,1'-(hexane-1,6-diyl)bis(2-
aminopyridinium)-oxonium iodobismuthate hydrate, contain the novel [Bi2I11]5- anion in their
structures. The new methyl viologen iodobismuthate crystals have a red colour and their Eg
values are close to 2 eV. A slight difference in magnitudes of ΔE and a dramatic difference in the
values of Eg confirm the main role of the I(5py) → Bi(6py) electron transition in the optical
properties of hybrid halobismuthates with an all trans-1-D structure. Our results indicate the
prospects of using antisolvent precipitation to form [MV][BiI5] coatings on oxide substrates.
This technology can be use to produce composite materials on the base of [MV][BiI5] for further
study of their photophysical properties.
4. Experimental
4.1.Materials
Synthesis of 1. The reaction mixture of 1.10 g Bi(NO3)3·5H2O (Reachim, extra pure) and
3.00 g KI (Reachim, A.C.S.) in 15 ml of water was added to asolution of 0.500 g [MV]I2 and
1.50 g KI in 10 ml of water. The obtained red precipitate was filtered under vacuum, washed
with ethanol and dried in air. Yield: 0.92 g.
Synthesis of [MV][BiI5]. A solution of 0.550 g Bi(NO3)3·5H2O and 1.50 g KI in 15 ml of
H2O was added to the reaction mixture of 0.500 g [MV]I2 and 0.750 g KI in 10 ml of water. The
resulting red precipitate changed colour to black within several minutes. The obtained black
precipitate was filtered under vacuum, washed with ethanol and dried in air. Yield: 0.78 g (67%).
Synthesis of 2. A solution of 0.275 g Bi(NO3)3·5H2O and 0.750 g KI in 15 ml H2O was
added to a solution of 0.500 g [MV]I2 and 0.375 g KI in 10 ml of water. The resulting red
precipitate became black (in 1-2 minutes) and then dark red (in another 10 minutes). The
obtained dark red precipitate was filtered under vacuum, washed with ethanol and dried in air.
Yield: 0.46 g (64%). Crystalline [MV]3[Bi2I11]I was obtained in two ways. 1) In the first method,
0.5 g of 1 was added to 40 ml of a 5.6 M KI solution. The obtained mixture was placed into an
autoclave vessel and heating up to 140 °C for 20 hours. Crystals of 2, which precipitated upon
cooling, were decanted and washed with ethanol. Yield: 0.17 g.
11

2) In the second method, 0.5 g of powdered 2 were dissolved in 10 ml of DMF and left to
crystallize in the air at room temperature. After several days a glass with crystalline inclusions of
2 was formed. The crystals were separated from the glass manually. Yield: 0.12 g.
Synthesis of 3. A solution of 0.5 g BiI3 (Lanhit, extra dry, 99.998%) in 30 ml of DMF
was added to solution of 0.280 g [MV]I2 in 10 ml of DMF (Komponent-Reactiv, for
chromatography, 99.99%) and the resulting mixture was left in the air. Red crystals of 3
appeared after several days of storage. Yield: 0.76 g (91%).
Synthesis of 4. A solution of 14.07 g KI and 2.07 g Bi(NO3)3·5H2O in 15 ml H2O was
added to a solution of 0.890 g [HBAP]Br2 (see ESI) and 7.03 g KI in 20 ml H2O. The resulting
orange precipitate, [HBAP][BiI4]2∙2H2O (4), was filtered under vacuum, washed with ethanol
and dried in air. Yield: 3.06 g (85%).
Synthesis of 5. 5 ml of a 0.1 M BiI3 solution in concentrated HI was added to a solution of
0.204 g [HBAP]Br2 in 1 ml of concentrated HI (Sigma-Aldrich, 57 wt.% in H2O, 99.95%). After
24 hours, the resulting mixture was decanted, and the red precipitate (a mixture of crystals of 4
and 5) was washed with acetonitrile and dried in air. Crystals of 5 were separated manually.
4.2.Analytical methods
Reflectance spectra were measured on an Ocean Optics QE65000 spectrophotometer within the
frequency range 11,000-50,000 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-
TGA thermal analyzer instrument. The samples were heated in an alumina open pan at 10o/min
from 25 to 300 oC in air.
For the electrochemical measurements, an Autolab PGSTAT 30 potentiostat was used. The
counter electrode was platinized platinum foil (with a true surface of ~20 cm2) and the reference
electrode was an Ag/AgCl electrode (saturated KCl) connected to the working electrode
compartment via a Luggin capillary with a saturated KCl bridge. The working electrodes were
prepared as follows. A mixture of 30-40 mg of carbon black and 20 mg of compound 1, 2,
[MV][BiI5] or 1,1′-(1,5-pentanediyl)bis(4-methylpyridinium) iodobismuthate was ground with
silicon oil (AP 150 Wacker, Fluka). The resulting paste was smeared on the surface of the ITO
plate of ~ 0.5 cm2. Cyclic voltammograms were obtained at a scan rate of 50 mV/s.
X-ray powder diffraction analysis was carried out on a Bruker D8 ADVANCE X-Ray
diffractometer (CuKα, Ni-filter, LYNXEYE detector, reflection geometry). Full-profile X-ray
analysis of the patterns of the crystalline substances was made using TOPAS 4.2 software. [17]
12

The refinement was carried out using the structural models from [MV][BiI5] [3], 2 and 3. The
unit cell parameters and the scale factor were refined.
The X-ray data sets for 2-5 were collected on a Bruker SMART APEX II diffractometer
equipped with a CCD camera and a graphite monochromated MoKα radiation source [18]. Semi-
empirical absorption corrections were applied for all complexes [19]. The structures were solved
by direct methods using Fourier techniques and were refined by full-matrix least squares against
F2 with anisotropic thermal parameters for all non-hydrogen atoms. The positions of C-H
hydrogen atoms were calculated from geometrical considerations and localized from the Fourier
syntheses. The pseudo-rhombic structure 2 was refined in the P21 space group. Strong disorder
occurs when trying to refine 2 in the P212121 space group with an increase in symmetry. Pseudo-
metrohedral twinning and centrosymmetric twinning were taken into account in the refinement.
The ratio of the domains is 0.37:0.23:0.21:0.19. Our attempts to remove disorder in the structure
of 3 (taking twinning into account) lead to unrealistic geometric parameters for the [MV]2+
cations and the appearance of significant correlations, while disordering remains. All
calculations were carried out with the use of the SHELX program package [20]. The
crystallographic parameters and the refinement statistics are given in Table 1, the Bi-I bond
lengths are given in Table S1 in the ESI. Further experimental details for the reflectance
spectroscopy, XRD and TGA-DTA can be found in the Electronic Supplementary Information.
Acknowledgements
The authors are grateful to the center for collective use of N.S. Kurnakov Institute of General
and Inorganic Chemistry for the opportunity to collect single crystal X-ray diffraction, X-ray
powder diffraction, TGA and DTA data. The research was carried out within the State
Assignment on Fundamental Research to the N.S. Kurnakov Institute of General and Inorganic
Chemistry.
Appendix A. Supplementary data
CCDC 1843911-1843914 contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge 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.
5. References
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[18] SMART (Control) and SAINT (Integration) Software, Version 5.0, Bruker AXS Inc.,
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Heating [MV]3[Bi2I9]2(DMF)3(H2O), deposited by anti-solvent
precipitation on a SiO2 substrate, results in its decomposition and the formation of
a
[MV][BiI5] coating.
25