Infinite Polyiodide Chains in the Pyrroloperylene–Iodine Complex: Insights into the Starch–Iodine and Perylene–Iodine Complexes

Article abstract of DOI:10.1002/anie.201601585

We report the preparation and X-ray crystallographic characterization of the first crystalline homoatomic polymer chain, which is part of a semiconducting pyrroloperylene–iodine complex. The crystal structure contains infinite polyiodide I_∞^δ?. Interestingly, the structure of iodine within the insoluble, blue starch–iodine complex has long remained elusive, but has been speculated as having infinite chains of iodine. Close similarities in the low-wavenumber Raman spectra of the title compound and starch–iodine point to such infinite polyiodide chains in the latter as well.

Full text of DOI:10.1002/anie.201601585

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201601585
German Edition: DOI: 10.1002/ange.201601585
Structure Elucidation
Infinite Polyiodide Chains in the Pyrroloperylene–Iodine Complex:
Insights into the Starch–Iodine and Perylene–Iodine Complexes
Sheri Madhu, Hayden A. Evans, Vicky V. T. Doan-Nguyen, John G. Labram, Guang Wu,
Michael L. Chabinyc, Ram Seshadri,* and Fred Wudl*
ꢀ
Abstract: We report the preparation and X-ray crystallo-
graphic characterization of the first crystalline homoatomic
polymer chain, which is part of a semiconducting pyrroloper-
stability of short In moieties in the vacuum. These descrip-
tions of iodide chains, as well as numerous others, are better
described as oligomeric rather than polymeric chains of
iodine, with lengths typically shorter than 10 iodine units and
ylene–iodine complex. The crystal structure contains infinite
dꢀ
[9]
polyiodide I . Interestingly, the structure of iodine within the
usually containing molecular iodine within the chain.
1
insoluble, blue starch–iodine complex has long remained
elusive, but has been speculated as having infinite chains of
iodine. Close similarities in the low-wavenumber Raman
spectra of the title compound and starch–iodine point to such
infinite polyiodide chains in the latter as well.
Indeed, a seminal resonance Raman spectroscopic study of
starch iodine carried out in 1978 allowed the authors inferred
the presence predominantly I species.
5
ꢀ
[10]
A separate and highly relevant structural mystery involv-
ing iodine is that of one of the earliest organic electronic
[11]
conductors; the perylene–iodine charge-transfer complex,
[
1]
A
ccording to Saenger, the starch–iodine complex was
which to this day, has not been fully resolved. It is clear that
the hydrocarbon is partially oxidized and the iodine shows
discovered by Colin and de Claubry, over two hundred years
[
2]
[1]
[12]
ago. The complex is better described as amylose–iodine
hints of iodine and triiodide but the latter are disordered in
and has continuously, over the years, been considered as
a clathrate of polyiodide and carbohydrate. The nature of the
polyiodide in this complex still remains to be fully charac-
terized, and many of the references on iodine chain-contain-
ing compounds in the literature draw analogies with the
essentially, all examined cases.
Here we relate these stories and shed light on the science
of these functional organic materials. We have determined the
structure of a pyrroloperylene–iodine complex that comprises
helical, infinite iodine chains interspersed between p-stacks of
the pyrroloperylene. The electrical conductivity of this
compound is found to be close to 10 Scm at room
temperature, and a change in the temperature coefficient of
the conductivity at temperatures close to 150 K is suggested as
corresponding to a structural transition. Based on similarities
between the published low-frequency Raman spectroscopic
signatures of starch-iodine and the spectrum measured on the
title compound, it is suggested that starch–iodine must
similarly comprise infinite iodine chains.
Pyrroloperylene 3 was prepared in 80% to 85% yield by
a simple Cadogan reaction shown in Scheme 1.
preparation of the pyrroloperylene–iodide complex from
solution by slow cooling was straightforward, and employed
a benzene solution containing 15 mg (0.0566 mmol) of
pyrroloperylene 3 and 51 mg (0.198 mmol) of iodine, kept at
[
3]
elusive starch-iodine structure. For example, Kahr et al.
established the crystal structure of so-called herapathite:
ꢀ
2
ꢀ1
[4]
a quinine iodine complex with iodide trimers. Redel et al.
have reported a complex copper iodide with chains of up to 5
[
5]
iodine atoms. Lin et al. have reported bent anionic I chains
7
stabilized by complex multivalent organic ammonium cations.
[
6]
Schroder and co-workers have reviewed the rich structural
chemistry that emerges when macrocylic thioethers are
[
7]
employed to stabilize oligomeric iodine chains. Yin et al.
II
have reported a metal–organic framework based on Cu
cations and I5 and I7 chains. Kloo et al. have also
employed ab-initio techniques to study the structure and
ꢀ
ꢀ
[8]
[13]
The
[
*] Dr. S. Madhu, H. A. Evans, Dr. V. V. T. Doan-Nguyen,
Prof. Dr. R. Seshadri, Prof. Dr. F. Wudl
Materials Research Laboratory, University of California
Santa Barbara, CA 93106 (USA)
6
58C in a vial with a screw cap. The solution was allowed to
cool slowly from 658C to 308C over a period of five days in
a doubly insulated container. Shiny needles with a dark
yellow-green lustre were obtained at the bottom of the vial.
The crystals were found to be quite stable at room temper-
ature under STP conditions, but lost iodine at higher temper-
E-mail: seshadri@mrl.ucsb.edu
wudl@chem.ucsb.edu
H. A. Evans, Dr. G. Wu
Department of Chemistry and Biochemistry, University of California
Santa Barbara, CA 93106 (USA)
Dr. V. V. T. Doan-Nguyen, Dr. J. G. Labram
California NanoSystems Institute, University of California
Santa Barbara, CA 93106 (USA)
Prof. Dr. M. L. Chabinyc, Prof. Dr. R. Seshadri, Prof. Dr. F. Wudl
Materials Department, University of California
Santa Barbara, CA 93106 (USA)
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under http://dx.doi.org/10.
1002/anie.201601585.
Scheme 1. Synthetic route for pyrroloperylene 3.
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ature (see the thermogravimetric analysis in the Supporting
Information) The concentration most favorable for the
formation of large (> 1 mm) single crystals was 10 mg of
pyrroloperylene and 35 mg of iodine per 5 mL benzene
solution. The dimensions of these crystals varied in length
from 1 mm to 5 mm, the width from 100 mm to 200 mm, and
thickness from 10 mm to 50 mm.
The crystal structure of pyrroloperylene–iodine complex
solved at 100 K, refined to a composition of pyrrolloperylene-
I2.2 and is displayed in Figure 1. The structure is monoclinic,
space group C2/c (No. 15), solved with R1 = 5.91%. In the
crystal structure of the complex, pyrroloperylene exhibits
a nearly planar molecular conformation with an interplanar
found in the pyrroloperylene–iodine complex at 100 K and
room temperature is nearly linear.
We examined the electrical properties of four single
crystals of the complex and found some variation in their
electrical behavior attributable to mechanical defects and
cracking near the contacts during temperature changes (see
the Supporting Information). Because of their fragility, we did
not attempt four-probe measurements and our electrical data
includes effects due to injection at the contacts. A successful
measurement of the electrical behavior is shown in Figure 2a
displaying nonlinear I–V relationship over the range of
Figure 2. a) Current as a function of voltage applied along the length
of a single crystal of pyrroloperylene–iodine complex, measured at
various temperatures. b) Average differential conductivity between
ꢀ
2 V and ꢀ1.5 V and between 1.5 V and 2 V, acquired upon forward
Figure 1. Views of the crystal structure of pyrroloperylene–iodine com-
sweep, as a function of measurement temperature T. The inset
displays an optical microscope image of a single crystal on silica. At
the edge of the image the silver paste employed to contact the crystal
is visible. The crystal was assumed to be cylindrical with a length of
plex at 100 K, showing pyrroloperylene p-stacks separated by racemic
dꢀ
pairs of helical chains of I . In the top panel, the 99% probability
1
thermal ellipsoids of I in two of the chains are displayed.
1
.2 mm and a diameter of 50 mm. All measurements were carried out
ꢀ4
distance of 3.47 ꢀ. In the asymmetric unit, one of the
pyrroloperylene molecules exhibits disorder of the N over
two orientations related by the inversion center. The pyrro-
loperylene stacks are interspersed with polyiodide chains in
close proximity and parallel to each other. The 100 K crystal
structure showed the presence of nearly linear polyiodide
chains, with shallow helicity, and interatomic distances vary-
ing from 3.054 ꢀ to 3.174 ꢀ. Key interatomic distances for the
under vacuum (10 mbar). c) DSC heating and cooling traces sug-
gesting a highly reproducible incident near 150 K, corresponding to the
temperature at which the temperature-coefficient of conductivity
changes slope.
applied biases examined. The differential conductivity (dI/
dV) was extracted from the data and shows a ten-fold increase
in conductivity from 300 K to 150 K across the entire range of
applied bias, followed by a significant decrease [Figure 2b].
There is some asymmetry in the I–V data which we attribute
to imperfect contacts. We believe that the increase in differ-
ential conductivity is a materials property because poorly
injecting contacts would be expected to have the opposite
temperature dependence (injection would be worse at lower
temperature). Some hysteresis is observed between forward
and reverse measurements at higher voltages (see SI, Fig-
ure S5) and is hypothesized to be due to small structural
1
00 K and room temperature crystal structure are presented
in the SI. The interiodine distances in the chain both in the
1
3
00 K and room temperature structure are all greater than
.00 ꢀ, supporting the conclusion that no neutral I units
2
[14]
(
interatomic distance: 2.70 ꢀ) are part of the chains. This
implies that all the iodine atoms in the polyiodide chain carry
a partial negative charge. So far, with very few exceptions, the
5
ꢀ
7ꢀ
9ꢀ
geometry of polyiodide chains (I , I , and I ) reported in
[
11]
the literature is non-linear, whereas the polyiodide chain
2
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instabilities in the contact interface between the silver paste
and the pyrrolopyrelene–iodine crystal, or even perhaps some
electromigration. Overall the data is suggestive of metallic
behavior above 150 K. The decrease in differential conduc-
tivity near 150 K coincides with a phase transition with no
hysteresis observed using differential scanning calorimetry
[
Figure 2c] further suggesting that the electrical behavior is
representative of the crystal. Because the structure is one-
[15]
dimensional, it is possible that Peierls physics is involved.
Differential scanning calorimetry carried out on the complex
indeed suggests a reproducible solid-state phase transition at
approximately 150 K, as shown in Figure 2c, with no hyste-
resis. This led us to closely examine the structure of the
complex at room temperature, reported in detail in the
Supporting Information, which indeed suggests a slightly less
distorted polyiodide chain, consistent with the 150 K incident
corresponding to a structural distortion.
The Kubelka–Munk transformation of the diffuse reflec-
tivity of solid pyrroloperylene and the pyrroloperylene–
iodine complex, acquired in dispersion in BaSO is shown in
4
Figure 3a. The crystals of the pyrroloperylene–iodine com-
plex appear shiny and metallic and with an absorption
extending through visible range of the visible region into
the near-infrared. This, as well as the feature observed near
1
750 nm suggests the presence of free carriers, and is
[
16]
consistent with the electrical transport measurement.
Both spectra show identical overlapping bands in the region
of 450 nm, which is also seen in the solution spectrum of
pyrroloperylene (Figure S1a). Figure 3b compares the infra-
red spectra of pyrroloperylene and the pyrroloperylene–
iodine complex. The spectrum of the complex is dominated by
ꢀ1
free charge carriers, starting in the 500 cm extending all the
way to NIR region. The intramolecular vibrational peaks of
pyrroloperylene are very weak and are clearly masked by the
free charge carriers in the complex. The presence of these free
carriers also influences the lineshape of the room temperature
electron spin resonance (ESR) spectrum of the pyrroloper-
ylene–iodine complex, displayed in Figure 3c. The open-shell
complex displays an asymmetric signal centered at g = 2.0022,
with some complex features potentially arising from the
powder averaging of a crystalline material.
Figure 3. Solid state a) UV/Vis absorption (in BaSO ) and b) infrared
spectra of the pyrroloperylene and pyrroloperylene–iodine complex.
c) Solid-state ESR spectrum of the pyrroloperylene–iodine complex at
room temperature.
4
completely turned to brick red color. The reaction mixture was cooled
and transferred into 1 L of water. The solid was filtered, dried under
vacuum, and purified by column chromatography on silica gel with
hexane/toluene (75/25) as eluent to afford 2 as a brick-red crystal.
Finally, Figure 4 displays a Raman spectrum of the
pyrroloperylene–iodine complex, in the low-energy regions
associated with I-I modes. The strongest vibrational modes
1
Yield (1.77 g, 30%). H NMR (DMSO, 600 MHz): d = 8.56 (dd, 2H),
8.02–7.95 (m, 4H), 7.83 (d, J = 8.4 Hz, 1H), 7.77 (dd, 2H), 7.69 (t, J =
7.6 Hz, 1H), 7.59 ppm (t, J = 8.0 Hz, 1H). EI-MS, m (%), 297 (M ,
ꢀ
1
ꢀ1
+
are found to be at 106.8 cm and 150.1 cm . Previous reports
5
ꢀ
7ꢀ
9ꢀ
100%).
on compounds with finite chains of I , I , and I display
higher wave number signatures
[
4,6,9,17,18]
Synthesis of Pyrroloperylene or 6H-Phenanthro [1,10,9,8-
ie. varying from
[
13]
ꢀ
1
ꢀ1
c,d,e,f,g] carbazole (3):
A mixture of 0.50 g (1.7 mmol) of 1-
1
60 cm to 180 cm , which can also include signatures of I
2
Nitroperylene (2) and 5 mL of triethyl phosphite was heated at reflux
under argon for 2 h. Upon cooling the reaction mixture to room
temperature, the yellow brown amine 3 crystallized and crystals were
ꢀ1
[19]
at 215 cm in the solid.
This supports the assertion of
polymeric iodine speculated to be found in starch-iodine, as
[10]
1
reported in the spectrum from Teitelbaum et al.
collected by filtration. Yield (0.38 g, 85%). H NMR (DMSO,
6
8
00 MHz): d = 12.20 (s, 1H), 8.74 (d, J = 8.2 Hz, 2H), 8.19 (d, J =
.4 Hz, 2H), 7.99 (dd, 4H), 7.94 ppm (t, J = 7.4 Hz, 2H). C NMR
1
3
(
DMSO, 150 MHz): d = 131.1, 130.2, 128.8, 125.5, 125. 1, 124.7, 121.3,
+
Experimental Section
117.4, 116.0 ppm. EI-MS, m (%), 265 (M , 100%).
[
13]
Synthesis of 1-nitroperylene (2):
To a hot solution of perylene
For electrical transport measurements, a single crystal of the
pyrroloperylene-iodine complex was deposited onto a vitreous silica
substrate with a hypodermic needle. Using a stereo microscope,
a small volume of colloidal silver paste (Pelco) was deposited onto the
substrate at each end of the crystal, again using a hypodermic needle.
(5.0 g, 19.8 mmol) dissolved in 1,4-dioxane (200 mL) was added
a mixture of 5.0 mL of water and 4.5.0 mL of nitric acid (d = 1.5)
dropwise while stirring. The resulting solution was heated at 608C
with vigorous stirring for 30 minutes, and the initial yellow solution
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Angewandte
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All crystallographic representations were carried out with
[
22]
VESTA.
Acknowledgements
This work was supported by the U.S. Department of Energy,
Office of Science, Basic Energy Sciences under Award No.
DE-SC-0012541. V.D.N. is supported by the UC Presidentꢂs
Postdoctoral Fellowship and the Elings Prize Fellowship. The
use of shared experimental facilities of the Materials
Research Laboratory:
A National Science Foundation
MRSEC supported by grant number NSF DMR 1121053 is
gratefully acknowledged.
Keywords: conducting materials · perylenes · polyhalides ·
solid-state structures · X-ray diffraction
Figure 4. Comparative Raman spectra of pyrroloperylene–iodine com-
plex and starch iodine. The latter spectrum is digitized from Teitel-
baum et al.
[
[
[
1] W. Saenger, Naturwissenschaften 1984, 71, 31.
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[
10]
3
24, 1407.
The silver paste was allowed to dry at room temperature in air for 1 h
before the sample was transferred to a cryogenic probe station. The
[
[
4] E. Redel, C. Rçhr, C. Janiak, Chem. Commun. 2008, 2103 – 2105.
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ꢀ4
chamber was evacuated to a pressure of 1 ꢁ 10 mbar. The current
was then measured as a function of voltage applied across the length
of the crystal using a Keithley 2400 SourceMeter. The conductance
was extracted from the measured current–voltage characteristics
using 3-point differentiation and taking an average across all applied
voltages (ꢀ2 V to + 2 V). The conductivity was derived from the
conductance by approximating the crystal as a cylinder with a length
of 1.2 mm and a diameter of 50 mm, as determined by optical
microscopy. Raman spectroscopy was performed using a Horiba
Jobin–Yvon Lab ARAMIS instrument equipped with a 785 nm laser
and confocal microscope, equipped with a 10 ꢁ objective lens. The
single crystals were measured using a 400 mm aperture, 400 mm slit,
and 1200 gratings per mm, with exposure time of 1 s, averaged 20
times.
[
[
1
95 – 205.
7] Z. Yin, Q.-X. Wang, M.-H. Zeng, J. Am. Chem. Soc. 2012, 134,
857 – 4863.
4
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1203 – 1209.
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1978, 100, 3215 – 3217.
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[
12] R. C. Teitelbaum, S. L. Ruby, T. J. Marks, J. Am. Chem. Soc.
980, 102, 3215 – 3217.
1
[
13] a) J. I. G. Cadogan, M. Cameron-Wood, R. K. Mackie, R. J. G.
Searle, J. Chem. Soc. 1965, 4831 – 4837; b) J. J. Looker, J. Org.
Chem. 1972, 37, 3379 – 3381.
Single-crystal X-ray diffraction data acquisition was carried out
on a Bruker Kappa APEX II CCD diffractometer with graphite-
monochromatized (MoKa = 0.71073 ꢀ) radiation at a temperature of
T= 100(2) K. Data were collected with omega scan width of 0.58 at 3
different settings with exposure time of 15 s keeping the sample-to-
detector distance fixed at 60 mm. The X-ray data collection was
[
[
[
[
[
[
14] J. M. Reddy, K. Knox, M. B. Robin, J. Chem. Phys. 1964, 40,
1
082 – 1089.
15] P. W. Anderson, P. A. Lee, M. Saitoh, Solid State Commun. 1973,
3, 595 – 598.
1
[
20]
monitored by the APEX2 program. The data were corrected for
Lorentz, polarization and absorption effects using SAINT and
SADABS. SHELXTL was used for structure solution and full
16] J. B. Torrance, B. A. Scott, B. Welber, F. B. Kaufman, P. E.
Seiden, Phys. Rev. B 1979, 19, 730 – 741.
17] E. M. Nour, L. H. Chen, J. Laane, J. Phys. Chem. 1986, 90, 2841 –
[
21]
matrix least-squares refinement on F2.
All the H-atoms were
2
846.
18] F. W. Parrett, N. J. Taylor, J. Inorg. Nucl. Chem. 1970, 32, 2458 –
461.
19] A. G. Maki, R. Forneris, Spectrochim. Acta 1967, 23, 867 – 880.
placed in geometrically idealized position and constrained to ride on
their parent atoms. For the solution of the crystal structure of
pyrroloperylene–iodine complex, the details are as: Molecular
2
ꢀ
1
formula C130H70.5I14.5N6.5
0
,
M = 3563.48 gmol
,
plate, 0.25 ꢁ 0.05 ꢁ
[20] SMART Apex II, Version 2.1; Bruker AXS Inc.: Madison, WI,
3
.05 mm , monoclinic, space group C2/c, a = 37.939(7), b = 18.507(3),
c = 29.839(5) ꢀ, b = 101.376(10)8, V= 20540(6) ꢀ , Z = 8, T= 100-
2005.
3
[21] SHELXTL PC, Version 6.12; Bruker AXS Inc.: Madison, WI,
ꢀ3
(
4
2) K, 2qmax = 60.008,
D
calc = 2.305 gcm
,
F(000) = 13316, m =
2005.
ꢀ
1
.430 mm , 66320 reflections collected, 20967 unique reflections
[22] K. Momma, F. Izumi, Comm. Crystallogr. Comput. 2006, 7, 106 –
(
Rint = 0.509), 1635 observed [I > 2s(I)] reflections, multi-scan absorp-
tion correction, Tmin = 0.404, Tmax = 0.809, 633 refined parameters, S =
.684, R1 = 0.0591, wR2 = 0.0893 (all data R = 0.5242, wR2 = 0.1756),
maximum and minimum residual electron densities are D
119.
0
=
Received: February 15, 2016
Published online: && &&, &&&&
max
ꢀ
ꢀ3
ꢀ
ꢀ3
1
.061 e ꢀ and Dmin = ꢀ1.520 e ꢀ
.
4
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Angewandte
Communications
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Communications
Structure Elucidation
The crystal structure of the pyrrolopery-
lene–iodine complex (with a formula
close to pyrroloperylene–I ) has been
S. Madhu, H. A. Evans,
2
.2
V. V. T. Doan-Nguyen, J. G. Labram,
G. Wu, M. L. Chabinyc, R. Seshadri,*
solved, revealing infinite polyiodide
chains, the Raman spectrum of which
resembles that of the famous starch–
iodine complex, casting light on a histor-
ical puzzle (see picture). The complex
displays nearly metallic conductivity and
some signatures of a Peierls distortion of
the chains at 150 K.
F. Wudl*
&&&& — &&&&
Infinite Polyiodide Chains in the
Pyrroloperylene–Iodine Complex:
Insights into the Starch–Iodine and
Perylene–Iodine Complexes
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5
These are not the final page numbers!