Dual-Emissive Platinum(II) Metallacycles with Thiophene-Containing Bisacetylide Ligands

Article abstract of DOI:10.1021/acs.inorgchem.6b01464

Three cis-diphosphino Pt(II) metallacycles with thiophene-containing bisacetylide ligands were synthesized and their absorption and emission properties examined. These properties are explained by DFT and TD-DFT analysis of ground-state as well as singlet-

Full text of DOI:10.1021/acs.inorgchem.6b01464

Article
pubs.acs.org/IC
Dual-Emissive Platinum(II) Metallacycles with Thiophene-Containing
Bisacetylide Ligands
Yang Cao, Michael O. Wolf,* and Brian O. Patrick
Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
S
* Supporting Information
ABSTRACT: Three cis-diphosphino Pt(II) metallacycles with
thiophene-containing bisacetylide ligands were synthesized
and their absorption and emission properties examined. These
properties are explained by DFT and TD-DFT analysis of
ground-state as well as singlet- and triplet-state energies and
geometries. Two of the metallacycles show room-temperature
dual emission (fluorescence and phosphorescence) with
different intensity ratios. Replacing the phenylene or
ethynylene groups with thiophene rings in the bisacetylide
ligand of the metallacycles results in modulation of the S1 and T1 states to show stronger fluorescence and weaker
phosphorescence. More rigid and planar metallacycles suffer less from energy loss due to smaller degrees of structural
reorganization and thermal deactivation. These are important factors to consider when designing single-component dual-emissive
materials for applications such as white-emitting OLEDs, self-referencing oxygen sensors, and hypoxia contrast agents.
is also crucial for these applications since such decay often
results in degraded performance and device overheating.
Oligomers and polymers containing trans-substituted Pt(II)
bisacetylide centers have broad applications in nonlinear optical
materials, OLEDs, polymer solar cells, and other molecular
electronics applications.6 They typically exhibit high triplet
yields and long-lived ligand-localized triplet excited states.2a,7 In
molecules containing [trans-Pt(PR3)2(−CC−Ar−CC−)]
units (Scheme 1, left), replacing the phenylene aryl groups in
INTRODUCTION
■
Heavy atom-induced spin−orbit coupling (SOC) has been
widely used to encourage intersystem crossing (ISC) in organic
molecules from singlet excited states to triplet manifolds. For
instance, iridium-containing dyes allow highly efficient ISC and
emission from both the triplet and the singlet excited states,
resulting in up to 100% internal efficiency in organic light-
emitting devices (OLEDs) using these materials. This is
significantly higher than the 25% efficiency limit of most
fluorescent compounds that only emit from their singlet excited
states.1
Scheme 1
In molecules, SOC leads to the mixing of singlet and triplet
wave functions with a coupling coefficient λ that is proportional
to the spin−orbit coupling energy ESO and inversely propor-
tional to the corresponding singlet−triplet energy gap (ES−ET)
λ = ESO/(ES − ET)
As a result of stronger SOC, the “spin flip” of the electron in
molecules with heavier atoms becomes more favorable due to
involvement of atomic orbitals with higher angular momentum.
ISC is also much faster when corresponding frontier MOs of
singlet and triplet states have a stronger contribution from
heavy atoms.2 Therefore, in molecules with heavy metal centers
such as platinum(II), it is possible to attenuate ISC by varying
the relative contribution of the metal atom in relevant MOs.
Additionally, by tuning the singlet−triplet (ES−ET) energy gap,
S1 and T1 states may both be populated upon excitation of the
molecules. This also allows control over fluorescence/
phosphorescence (FL/PH) ratios which is potentially useful
for various important applications such as white-emitting
OLEDs,3 ratiometric oxygen sensors,4 and hypoxia imaging in
A1 with thiophene rings results in lower T1 states in molecule
A2 with a relatively unchanged energy gap between S1 and T1
states. Similar effects were observed in both monomeric and
polymeric materials, except that the ES−ET gap is smaller in the
latter.2a
Received: June 17, 2016
biological systems.5 Limiting the nonradiative decay rates (kNR
)
© XXXX American Chemical Society
A
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In polymers B1, B2, and B3, relatively stronger fluorescence
and weaker phosphorescence are observed when the ligand is
extended in conjugation length from thiophene to bithiophene
to terthiophene (Scheme 1, right). From B1 to B3, the
increasing number of thiophene rings reduces the influence of
the heavy metal center that is mainly responsible for the
intersystem crossing, making the T1 state less accessible while
the energy gap between S1 and T1 remains relatively constant.8
Additionally, a longer conjugated system gives rise to a lower
energy T1 state, which makes ISC less efficient from higher
singlet excited states (Sn). Therefore, S1 states are relatively
more efficiently populated than T1 via fast internal conversion
(IC) processes, resulting in stronger fluorescence.8 These
observations provide guidance to use similar strategies in
platinum compounds to encourage stronger fluorescence,
allowing room-temperature dual fluorescence (FL) and
phosphorescence (PH) to be simultaneously observed with
various FL/PH ratios.
Scheme 3
RESULTS AND DISCUSSION
■
Synthesis. Metallacycles 1, 2, and 3 were synthesized using
a modification of Hagihara’s method12 using TMS-protected
bidentate proligands L1, L2, and L3, respectively, as shown in
Scheme 4. Alkynes were deprotected in situ and reacted with
Metallacycles containing cis-Pt bisacetylide metal centers
were first reported almost two decades ago (Scheme 2);9,10
Scheme 2. Metallacycles C1,9 C2,10 and C310 with Cis-
Substituted Pt(II) Bisacetylide Metal Centers
Scheme 4. Synthesis of Metallacycles 1, 2, and 3
they were found to give rise to very efficient ISC and thus have
been considered good candidates as triplet sensitizers and for
nonlinear optical applications.11 Castellano et al. showed that
such metallacycles show enhanced light absorption compared
to their noncyclic analogues.11b,c Additionally, the more rigid
cyclic structure gives rise to suppressed thermal deactivation
and thus higher emission quantum efficiency. Therefore, cis-Pt
bisacetylide metallacycles with higher stability and room-
temperature tunable dual emission would be interesting for
the applications discussed above and remain unknown to date.
In this article, three new cis-Pt(II) bisacetylide metallacycles
1, 2, and 3 are discussed and compared with complex 411c
previously reported by Castellano et al. (Scheme 3). Complex 4
provides an excellent starting point for these studies since it
only shows green ligand-based phosphorescence at 497 nm in
deaerated solutions. The effect of introducing thiophene rings
at different positions in the ligand system while maintaining the
cyclic structure is systematically explored by first replacing the
two phenyl rings in 4 with thiophene rings to give complex 1.
Similarly, by introducing one additional thiophene ring to 1,
metallacycle 2 is formed. Finally, by changing the bridging
acetylene in 4 to a thiophene ring, 3 is obtained. Complex 2 is
found to fluoresce, while 1 and 3 show dual emission with
varying FL/PH ratios.
Pt(dppp)Cl2 to incorporate the metal center with phosphine
ancillary ligands. Pro-ligand L2 was previously reported by our
group,13 and L1 and L3 were conveniently synthesized via
Sonogashira reactions between trimethylsilylacetylene and the
corresponding dibromo precursors in reasonable yields
(Scheme 5).
Solid-State Structures. Crystal structures of 1, 2, and 3
were obtained (Figures 1 and 2). As shown in Figure 2,
complex 3 has two crystallographically distinct structures (A
and B) in the unit cell each with different ligand conformations
with multiple hydrogen bonds between them (Figure S1a). The
metal centers in both structures A and B have almost identical
C−Pt−C bond angles, unaffected by conformational differences
in the relatively remote bisacetylide ligands. All metallacycles
have square-planar geometries at the platinum centers, in line
with other similar cis-substituted platinum bisacetylides in the
literature.9,10,14
Compared with 2 and 3, complex 1 has a smaller C−Pt−C
bond angle of 84.8°, which indicates some degree of ring strain
in this structure. While the bisacetylide ligands in 1 and 2 are
only slightly twisted (S1−C4−C7−S2 torsion angle of 14.8° in
1, dihedral angles between adjacent rings of 9.9° and 4.9° in 2),
the central thiophene ring in 3 is significantly out of the plane
(dihedral angles between adjacent rings of 35.2° and 30.6° in
B
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Scheme 5. Synthesis of Proligands
Figure 3. (a) UV−vis spectra of ligands L1, L2, and L3 in CH2Cl2 (1.0
× 10−5 M), and excitation and emission spectra of L1 (b), L2 (c), and
L3 (d) in CH2Cl2 (1.0 × 10−5 M).
attributed to the relatively smaller HOMO−LUMO gap of the
π−π* transition on the more conjugated terthiophene moiety.
The excitation spectra of L1, L2, and L3 are shown in Figure
3b−d. All emission spectra show some vibrational fine
structure. Emission maxima are at 392, 475, and 412 nm for
L1, L2, and L3, respectively. L1 has the smallest Stokes shift,
indicating a smaller degree of geometrical relaxation in the
excited state.
The absorption spectra of metallacycles 1, 2, and 3 in
CH2Cl2 are shown in Figure 4. All complexes absorb strongly
below 350 nm, attributed to high-energy localized π−π*
transitions of the acetylene moieties. Complex 1 shows a lowest
energy peak at 398 nm that is however red shifted
Figure 1. Perspective views of metallacycles (a) 1 and (b) 2 showing
CH2Cl2 solvent molecules hydrogen bonding with each metallacycle.
Thermal ellipsoids are shown at the 50% probability level; hydrogens
on the metallacycles are omitted for clarity.
Figure 2. Perspective views of the two crystallographically distinct
structures of complex 3: (a) structure A and (b) structure B. Thermal
ellipsoids are shown at the 50% probability level; hydrogens are
omitted for clarity.
structure A; 26.0°and 25.5° in structure B). The crystals of 1, 2,
and 3 all have CH2Cl2 solvent molecules in the crystal lattice.
The CH2Cl2 molecules form hydrogen bonds with only one
side of the ligand in 1, while in 2 they bond to both sides of the
ligand as well as with the sulfur atom on the central thiophene
ring (with H44A). The CH2Cl2 molecules interact with 3 in a
similar fashion to how they do with 2; however, two protons
are involved in this case (Figure S1b).
Electronic Absorption and Emission Spectra. The
absorption spectra of L1, L2, and L3 are shown in Figure 3a.
The lowest energy absorption maxima of L1 and L3 are at 380
and 343 nm, respectively, in CH2Cl2. L2 absorbs at higher
wavelengths into the visible region, showing a maximum at 405
nm and a shoulder at ∼430 nm. The resulting yellow color is
Figure 4. UV−vis spectra of metallacycles (a) 1, (b) 2, and (c) 3 in
CH2Cl2 (1.0 × 10−5 M); (d) excitation spectrum of 1 with argon
purging (emission @ 600 nm), and emission spectra under argon and
air (excitation @ 390 nm).
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approximately 20 nm relative to the absorption features of L1.
The low-energy absorption shoulder of 2 is shifted to 500 nm,
from 430 nm in L2, and 3 shows only a very weak feature
tailing to 460 nm without a clear maximum, indicating the low
oscillator strength between the S0 and the S1 states. In all cases,
the metallacycle absorption is somewhat red shifted from the
absorption of the proligands. This can be rationalized by
restricted rotation and planarization of the structure upon
formation of a bidentate chelate, resulting in more π
conjugation which reduces the HOMO−LUMO gap.
The excitation and emission spectra of metallacycle 1 in
CH2Cl2 are shown in Figure 4d. Compared with the purely
phosphorescent analogue 4,11c which emits at 497 nm,
metallacycle 1 with two thiophene rings in the ligand instead
of two o-phenylene groups shows significantly red-shifted
phosphorescence at 610 nm and additionally a broad weak
band between 400 and 550 nm. This relatively higher energy
emission is considered to be fluorescence as assessed by its
sensitivity to the presence of oxygen. This is suggestive of kISC
to T1 occurring on the same timescale as kFL, slow enough so
that both S1 and T1 states are effectively populated and
emitting.
Figure 6. (a) Emission spectra of 3 under argon show two bands (500
and 620 nm), while excitation spectra of the two bands diverge at
higher energy. (b) Emission of 3 in air, and dual emission under argon
(excitation @ 400 nm).
energy light, these states are populated giving rise to faster ISC
to T1 and thus stronger phosphorescence. Similar effects are
known in some platinum-containing conjugated polymers.16
Emission of both 1 and 3 is sensitive to oxygen, yet some
phosphorescence remains in air-equilibrated solutions (Figures
4d and 6b). The phosphorescence is only completely quenched
under pure O2, which is beneficial for applications in high-
concentration ratiometric O2 sensing using unaffected
fluorescence as a reference. Moreover, 1 and 3 have similar
T1−S0 energy gaps as they phosphoresce at similar wavelengths.
However, 3 fluoresces at a higher wavelength than 1 at 490 nm,
indicating a lower-lying first singlet excited (S1) state in 3.
Electronic absorption and emission data including emission
lifetimes (τem) and quantum yields (Φem) of the three
metallacycles are collected in Table 1. All complexes show
By contrast, metallacycle 2 containing three thiophene rings
shows no phosphorescence (even at lower temperatures, Figure
5a), but instead bright yellow fluorescence is observed in
Table 1. Electronic Absorption and Emission Data of
Metallacycles in CH2Cl2 Solution
λabs
λFL
(nm)
τFL
(ns)
λPH
(nm)
τPH
(μs)
entry (nm)
ΦFL
ΦPH
Figure 5. (a) Variable-temperature fluorescence spectra of 2 in a
MeOH/EtOH medium, and (b) excitation and emission spectra of
metallacycle 2 in air-equilibrated solution (1.0 × 10−5 M in CH2Cl2,
excitation @ 460 nm and emission @ 540 nm).
1
2
3
398
405
536
490
0.011
0.15
0.70
0.45
0.61
610
620
0.053
2.23
1.97
500
∼400
0.0062
0.0054
short fluorescence lifetimes of less than 1 ns, while 1 and 3
show relatively long phosphorescence with lifetimes of ∼2 μs,
indicating that kPH is 3 orders of magnitude slower than kFL.
The fluorescence quantum efficiency of 2 is moderate, while 1
shows much weaker dual emission with a FL/PH ratio around
0.2. The FL/PH ratio of 3 is approximately 0.9 higher than that
of 1; however, the overall emission quantum efficiency is barely
1%.
By comparing 1 with 4 and 2 with 3 (Scheme 3), it is noted
that replacing phenyl groups with thiophene rings in metalla-
cycles can enhance fluorescence without adding extra
conjugation. The difference between 1 and 2 demonstrates
that adding conjugation length to the ligand leads to drastically
increased fluorescence; however, the phosphorescence is
diminished. It should be pointed out that although complexes
1 and 3 show many similarities, they are not directly
comparable in an empirical way in the sense that only one
type of group (C−C triple bond, benzene or thiophene ring) is
replaced with another.
solution (Figure 5b). Some terthiophene-containing structures
are known to have low-lying nonemissive triplet states.8,13 The
nonradiative decay rate of triplet excited states increases
exponentially as the triplet energy (T1−S0 gap) decreases,
while nonradiative decay of S1 is relatively energetically
insensitive.7a,15 Therefore, the absence of phosphorescence of
2 may be explained by the presence of a terthiophene-centered
T1 excited state that is very low in energy and only decays
rapidly through nonradiative pathways.
In metallacycle 3 a single thiophene ring is introduced by
replacing the central acetylene bridge in complex 4, in
anticipation of lowering the ligand-based triplet state and
allowing both phosphorescence and fluorescence. Complex 3
can also be considered as an analog of 2 but with two phenyl
rings replacing the outer thiophene rings. This change indeed
gives rise to dual emission with a higher FL/PH ratio close to 1
(Figure 6). Interestingly, the phosphorescence of 3 is stronger
with shorter excitation wavelengths compared to the
fluorescence. After ruling out the possibility of contamination
by trace amounts of residual emissive ligand, the possibility that
higher singlet excited states (Sn) of 3 have stronger coupling
with the T1 state may be considered. When excited with higher
DFT and TD-DFT Simulations. DFT and TD-DFT
calculations were carried out to help understand the photo-
physics of the metallacycles and simulate their ground- and
excited-state properties. Optimized ground-state (S0) geo-
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metries of 1, 2, and 3 are shown in Table 2 (left column).
Structure B was used for complex 3 due to its lower energy
compared to structure A.
with δ = 7.61 ppm in the proligand L2, both in CDCl3),
indicate the presence of “ring current” in the metallacycle.
At the S1 and T1 excited states, however, all metallacycles
have almost perfectly planar ligand structures. This indicates
that 3 undergoes significant planarization going from the GS to
the S1 or T1 excited states, resulting in poor overlap between
GS and excited-state MOs. It is also consistent with the very
weak low-energy absorption features of this complex and may
lead to the very low fluorescence and phosphorescence
quantum efficiencies of 3 since nonradiative processes with
low energy barriers become more favorable. Additionally, all
metallacycles in the excited state show “quinoid-like” structure
with reversed bond lengths for the single and double bonds
relative to the GS geometry especially in T1 (Table S1). It is
also clear that the metallacycles 2 and 3 have much more in
common between the excited states S1 and T1 than between GS
and T1/S1 in terms of bond lengths and the geometry of the π-
conjugated bisacetylide ligands.
Table 2. DFT- and TD-DFT-Calculated Geometries of 1, 2,
and 3 for S0, S1, and T1 Electronic States
The frontier orbitals of the ground-state metallacycles are
presented in Table 3. All three complexes have π character
localized on the ligand in the HOMO and π* character in the
LUMO. The HOMO and LUMO of 1 are uniformly
distributed with some contributions from 5dxz and 5dyz orbitals
on platinum yet are mostly comprised of π or π* orbitals from
the bisacetylide ligand. In metallacycles 2 and 3, however, the
LUMOs are strongly metal centered with contributions from
empty 6pz orbitals on platinum while the HOMOs are
delocalized. This is indicative of the presence of ligand-to-
metal charge transfer (LMCT) states in complexes 2 and 3,
which have previously been observed in conjugated Pt
polymers with electron-rich ligands.16,17
The relative energies of metallacycles 1, 2, and 3 in T1 and S0
electronic states with T1/S0 geometries are summarized in
Table S2. Metallacycle 2 has the lowest calculated T1 state. The
T1−S0 transition energies of 1.54 (0−0) and 1.17 eV (vertical)
correspond to phosphorescence in the IR region (808 and 1060
nm), where fast thermal deactivation may render the T1 state
nonemissive at room temperature. Similarly, metallacycles 1
and 3 are calculated to exhibit phosphorescence with 0−0
transition energies of 1.89 and 2.06 eV, respectively, close to
the experimental values at maximum intensity (2.02 and 1.99
eV). The relative energies of metallacycles 1, 2, and 3 in the S1
and S0 electronic states with S1/S0 geometries are summarized
in Table S3. Vertical transition energies and oscillator strengths
have also been calculated and are summarized in Table 4.
All structures show no symmetry (C1) despite the presence
of symmetric bisacetylide ligands. Complexes 1 and 2 show
almost completely planar ligand geometries; however, the
central thiophene ring in 3 still lies out of the plane by 44.5°.
DFT-calculated geometry optimization of the lowest triplet
state (T1) of the metallacycles in CH2Cl2 solutions is shown in
Table 2 (right column). TD-DFT-calculated optimized geo-
metries of the first singlet excited state (S1) of the metallacycles
in CH2Cl2 solutions are presented in Table 2 (central column).
All three metallacycles exhibit highly planar T1 and S1 excited-
state structures.
Selected bond lengths in the optimized geometries of 1, 2,
and 3 in different electronic states are shown in Table S1. In the
ground state, all metallacycles show bond averaging between
single and double bonds in the innermost ring. In 1 and 2, the
thiophene double bond is notably longer (1.40 Å) in the inner
ring compared to the bonds in the outer ring (1.36 Å). These
observations along with a downfield shift of the proton signal
on the central thiophene ring of 2 (δ = 6.72 ppm compared
a
Table 3. Frontier Orbitals of Ground-State Metallacycles
a
Only the HOMO and LUMO are involved in the lowest energy S0 → S1 electronic transitions for all three complexes.
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calculated emission assuming decay from a relaxed S1 state to
relaxed GS (i.e., 0−0 relaxation) agrees very well with the
experimental values. Indeed, the vibronic fine structure in the
fluorescence spectra of 2 at both room temperature and lower
temperatures in Figure 5 shows that the first peak is always
strongest in intensity. Therefore, the fluorescence maxima of 1,
2, and 3 are considered to be 0−0 emission instead of vertical
transitions.
Table 4. Vertical Excitation Energies of S1 and T1 States
vertical transition
energy (eV)
oscillator
strength
entry states
major transition
1
2
3
S1
T1
S1
T1
S1
T1
HOMO−LUMO
HOMO−LUMO
HOMO−LUMO
HOMO−LUMO
HOMO−LUMO
HOMO−LUMO
3.10
2.25
2.44
1.92
3.22
2.80
0.169
0.100
0.001
EXPERIMENTAL SECTION
■
General. 1H NMR, 13C{1H} NMR, and 31P{1H} NMR spectra
were recorded on a Bruker Avance 400 (400 MHz) spectrometer. 31P
NMR chemical shifts are referenced to external 85% H3PO4, and other
chemical shifts are referenced to the residual solvent signals. ESI mass
spectra were measured in house using a Waters LC-MS ESI mass
spectrometer. Infrared spectroscopy (IR) was performed on an
attenuated total reflection (ATR) crystal using a PerkinElmer Frontier
FTIR spectrometer. Absorption spectra were obtained on a Varian
Cary 5000 UV-vis-NIR spectrophotometer, and emission measure-
ments were performed on a PTI QuantaMaster 50 fluorimeter.
Quantum yields were measured using a Labsphere general purpose
integrating sphere. Phosphorescence lifetimes were recorded on a
Horiba Jobin Yvon Fluorocube instrument equipped with a 370 nm
nanosecond LED light source using time-correlated single-photon
counting (TCSPC) collection. Fluorescence lifetimes were measured
using a transient absorption and fluorescence lifetime measurement
system with a Hamamatsu streak camera detector, a pulsed xenon cell
light source, and a Pi-Acton spectrometer (200−900 nm spectral
range) with a temporal range of 2 ns.
These energies are used to construct energy diagrams of
electronic states of metallacycles 1, 2, and 3 in Figure 7. From 1
Synthesis. All syntheses were carried out under a dry N2
atmosphere using standard Schlenk techniques. Dry toluene and
tetrahydrofuran (THF) were purchased from Aldrich and purified by
passing through towers containing activated alumina and molecular
sieves under nitrogen. All other chemicals were purchased from
commercial sources and used without further purification. Proligand
L2 (3,3″-bis(trimethylsilylethynyl)-2,2′:5′,2″-terthiophene,
Figure 7. Summarized energy diagrams showing electronic transitions
of metallacycles (a) 1, (b) 2, and (c) 3. Energies shown in the above
diagrams are in electron volts (eV) (Ev = vertical transition energy, E00
= 0−0 transition energy).
to 3, the decreasing oscillator strength of the vertical S0−S1
excitation is in line with the incrementally weaker molar
extinction coefficients of the lowest energy absorption bands
(Figure 4a−c). The T1 state in 3 has a much higher vertical
excitation energy but suffers more energy loss during relaxation
to its lowest vibronic state: 0.74 eV is lost vs 0.36 eV in 1 and
0.38 eV in 2. This may be related to the rotation of the
thiophene ring between the ground state and the excited states.
Calculated absorption and emission wavelengths are
summarized in Table 5. Calculated absorption and triplet
12
TMS2A2T3)13 and Pt(dppp)Cl2 were synthesized using reported
methods. L1 and L3 were conveniently synthesized from L4 and L5
via Sonogashira reactions. L418 and L519 were synthesized using
methods different from those in the literature (Scheme 5).
WARNING: Flammable and explosive gas forms when calcium carbide
becomes wet. Calcium carbide should be kept in a cool, dry, and well-
ventilated place and away from heat and sources of ignition and handled
carefully according to its Material Safety Data Sheet (MSDS).
L4 (Br2TET), 1,2-Bis(3-bromothiophen-2-yl)ethyne. CaC2 (3.85 g,
60 mmol), Pd(PPh3)4 (1.16 g, 1.0 mmol), and CuI (380 mg, 2.0
mmol) were added to a round-bottom flask with a side arm under N2.
N2-sparged CH3CN (60 mL) was then added to the flask, followed by
triethylamine (8.4 mL, 60 mmol) and 3-bromo-2-iodothiophene (3.70
g, 12.8 mmol). H2O (1.1 mL, 60 mmol) was added slowly with stirring
over 30 min, while the reaction temperature was maintained below 50
°C. The mixture was then kept at 50 °C using an oil bath and stirred
overnight. Black insoluble solids were filtered off, and the solvent was
removed from the filtrate under vacuum to obtain a brown-yellowish
crude product. The pure product was obtained using flash column
chromatography on silica (hexanes) as a white solid. Yield 1.70 g, 76%.
Table 5. Calculated Absorption and Emission Properties
absorption wavelength (nm)
emission wavelength (nm)
S0 → S1
S1 → S0
S1 → S0
0−0
T1 → S0
0−0
entry
vertical
vertical
a
1
2
3
400 (398)
508 (500)
459
639
544
428 (410)
557 (536)
471(485)
655 (610)
1
385 (∼400)
329 (355)
602 (620)
497 (497)
The H NMR and mass spectra matched with literature values.
b
4
L5 (Br2BTB), 2,5-Bis(2-bromophenyl)thiophene. Pd(PPh3)4 (462
mg, 0.4 mmol), 2-bromophenylboronic acid (1.69 g, 8.4 mmol), 2,5-
diiodothiophene (1.34 g, 4.0 mmol), and K2CO3 (2.32 g, 16.8 mmol)
were added to a round-bottom flask with a stir bar under N2. A N2-
sparged solvent mixture consisting of 20 mL of THF and 20 mL of
deionized water was added to the flask with stirring. The mixture was
slowly warmed to 70 °C and stirred for 18 h. The mixture was
concentrated in vacuo to remove THF and extracted with diethyl ether
(3 × 20 mL). The organic phases were combined, washed with water
and brine, and dried over magnesium sulfate. The crude product was
obtained after filtration and removal of the solvent under vacuum. The
pure product was obtained using flash column chromatography on
a
b
Experimental values given in parentheses. Data for 4 from the
literature.11c
emission (phosphorescence) energies are in good agreement
with the experimental values. Singlet emission energies were
calculated using nonequilibrium solvation of the excited states,
assuming vertical emission from relaxed S1 states decaying with
frozen geometry (i.e., vertical relaxation), yet large discrep-
ancies with experimental data were observed. Interestingly the
F
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1
silica (hexanes) as an off-white solid. Yield 1.08 g, 68%. H NMR
(CDCl3, 400 MHz): δ 7.20 (td, J1 = 10.4 Hz, J2 = 2.2 Hz, 2H, 2 CH),
7.33−7.39 (m, 4H, 4 CH), 7.59 (dd, J1 = 10.3 Hz, J2 = 2.2 Hz, 2H, 2
CH), 7.72 (dd, J1 = 10.6 Hz, J2 = 1.3 Hz, 2H, CH). 13C{1H} NMR
(CDCl3, 100 MHz): δ 122.6 (C4, C−Br), 127.6 (CH, thienyl), 127.8
(CH, phenyl), 129.1 (CH, phenyl), 131.9 (CH, phenyl), 133.9 (CH,
phenyl), 135.0 (CH, phenyl), 142.4 (CH, thienyl). Positive HRMS
(APCI/ESI): m/z = 392.8944, [M + H]+.
400 MHz): δ 2.02−2.17 (m, 2H, CH2), 2.52 (br, 4H, 2CH2), 6.23 (dd,
J1= 7.7 Hz, J2= 0.9 Hz, 2H, 2 CH), 6.78 (td, J1= 7.6 Hz, J2= 1.2 Hz,
2H, 2 CH), 6.98 (s, 2H, 2CH), 7.00 (td, J1= 7.6 Hz, J2= 1.2 Hz, 2H, 2
CH), 7.35−7.42 (m, 14H, 14 CH), 7.70−7.72 (m, 8H, 8 CH).
31P{1H} NMR (CDCl3, 162 MHz): δ −5.58 (JPt−P = 2183 Hz).
Positive ESI-TOF: m/z = 889.1721, [C47H37SP2194Pt + H]+. FTIR
(ATR) = 2105 cm−1 (νCC).
X-ray Crystallography. Crystals of 1, 2, and 3 suitable for single-
crystal X-ray diffraction were obtained by diffusion of pentane into
solutions of the complexes in CH2Cl2 or CH2Cl2/CH3CN mixed
solvent. X-ray diffraction data were collected with a Bruker X8 APEX
II diffractometer with graphite-monochromated Mo Kα radiation.
Data were collected and integrated using the Bruker SAINT20 software
package. Data were corrected for absorption effects using the
multiscan technique (SADABS).21 The data were corrected for
Lorentz and polarization effects. The structures were solved by direct
methods.22 All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were placed in calculated positions. Selected bond
lengths and bond angles are summarized for 1 and 2 (Table S4) and
two crystallographically independent structures of 3 (Table S5).
1·CH2Cl2 crystallizes with one disordered CH2Cl2 solvent molecule
in the asymmetric unit. The structure is in the P21/n space group, with
a primitive monoclinic unit cell containing four molecules of 1. 2·
1.2[CH2Cl2]·0.8CH3CN crystallizes with one complete CH2Cl2
molecule as well as one site that is partially occupied by CH2Cl2
and also by CH3CN (∼1:4) in the asymmetric unit. The structure is in
the P-1 space group, with a primitive triclinic unit cell containing two 2
molecules. 3·CH2Cl2 crystallizes with two crystallographically
independent molecules in the asymmetric unit. Additionally, there
are two molecules of CH2Cl2 in the asymmetric unit. The structure is
in the P21/n space group with a primitive monoclinic unit cell
containing eight molecules of 3.
DFT Stimulations. Density functional theory (DFT) calculations
were carried out using the Gaussian 09 Rev.D01 suite of programs.23
The PBE0 hybrid functional24 with 6-31G* basis set (for C, H, S, and
P atoms) and the LANL2DZ effective-core pseudopotential25 (for Pt)
was employed to simulate the ground-state (S0) and T1 structure of all
three metallacycles. Triplet states are treated using unrestricted
formalism. Structural coordinates from X-ray crystallography were
used as starting points of geometry optimizations. Optimized
structures were confirmed to be the minimum on the potential energy
surface by vibrational frequency calculations. Time-dependent DFT
(TD-DFT) calculations were also performed to understand S1 excited-
state electronics and the absorption and emission behaviors of these
complexes. For all simulations, a solvation effect of CH2Cl2 (ε = 8.93)
was implemented using the polarizable continuum model26 (PCM) in
Gaussian 09.
Frequency calculations on 1, 2, and 3 in their optimized geometries
confirmed that they are on the global minimum on the potential
energy surface. Frequency calculations also give some insight into their
IR absorptions. They are predicted to show symmetric and
antisymmetric stretching modes where vibrations of the two CC
bonds are in phase or out of phase, respectively. The antisymmetric
mode is calculated to have a much weaker IR absorption than the
symmetric mode. Experimentally, only one peak is observed in 1, 2,
and 3. The same goes for compound 4 in the literature.11c This may be
due to the constrained geometry in cyclic structures as similar acyclic
cis-Pt(II) bisacetylides show two peaks.27 After applying an empirical
scaling factor of 0.95 (for the PBE0 hybrid functional and 6-31G*
basis set),28 the predicted IR frequencies are reasonably close to
experimental values (Table S6). Small discrepancies may be attributed
to the PCM solvation assumptions used in DFT calculations, while IR
spectra were recorded in the solid state using powder samples.
L1 (TMS2A2TET), 1,2-Bis(3-(trimethylsilylethynyl)thiophen-2-yl)-
ethyne. CuI (80 mg, 0.4 mmol), Pd(PPh3)4 (280 mg, 0.4 mmol),
and L4 (696 mg, 2.0 mmol) were added to a round-bottom flask with
a stir bar under N2. A N2-sparged solvent mixture consisting of 15 mL
of diisopropylamine and 30 mL of toluene was added to the flask with
stirring, followed by trimethylsilylacetylene (471.5 mg, 4.8 mmol). The
mixture was slowly warmed to 75 °C and stirred for 12 h. The reaction
mixture was added to 30 mL of saturated NH4Cl solution and
extracted with ethyl acetate (4 × 20 mL). The organic phases were
combined, washed with water and brine, and dried over magnesium
sulfate. The brown crude product was obtained after filtration and
removal of the solvent under vacuum. The pure product was obtained
using flash column chromatography on silica (hexanes) as a light-
yellow solid. Yield 580 mg, 76%. 1H NMR (CDCl3, 400 MHz): δ 0.28
(s, 18H, 6 CH3), 7.03 (d, J = 5.3 Hz, 2H, CH), 7.19 (d, J = 5.2 Hz, 2H,
CH). 13C{1H} NMR (CDCl3, 100 MHz): δ 0.1 (CH3), 89.8 (C4, C
C), 98.8(C4, CC), 99.7 (C4, CC), 126.7 (CH, thienyl), 127.0
(C4, thienyl), 127.1 (C4, thienyl), 129.8 (CH, thienyl). Positive
HRMS (APCI/ESI): m/z = 383.0774, [M + H]+. FTIR (ATR) = 2152
cm−1 (νCC).
L3 (TMS2A2BTB), 2,5-Bis(2-(trimethylsilylethynyl)phenyl)-
thiophene. The same reaction conditions, workup procedure, and
purification method were used for L1 except that L5 was used as the
starting material instead of L4. A pale-yellow solid was obtained after
column purification in 52% yield. 1H NMR (CDCl3, 400 MHz): δ 0.29
(s, 18H, 6 CH3), 7.23 (td, J1 = 7.6 Hz, J2 = 1.2 Hz, 2H, CH), 7.35 (td,
J1 = 7.6 Hz, J2 = 1.4 Hz, 2H, CH), 7.59−7.64 (m, 4H, 2 CH), 7.79 (s,
2H, CH). 13C{1H} NMR (CDCl3, 100 MHz): δ −0.1 (CH3), 99.7
(C4, CC), 105.2 (C4, CC), 120.2 (C4, phenyl), 127.0 (CH,
phenyl), 127.4 (CH, phenyl), 128.6 (CH, phenyl), 129.0 (CH,
phenyl), 134.6 (CH, thienyl), 135.9 (C4, phenyl), 142.2 (C4, thienyl).
Positive HRMS (APCI/ESI): m/z = 429.1522, [M + H]+. FTIR
(ATR) = 2150 cm−1 (νCC).
Complex 1, Pt(dppp)A2TET. Proligand L1 (193 mg, 0.505 mmol),
Pt(dppp)Cl2 (339 mg, 0.500 mmol), and CuI (10 mg, 0.05 mmol)
were added to a round-bottom flask with a stir bar under N2. Then 30
mL of a N2-sparged solvent mixture consisting of 15 mL of
diisopropylamine and 15 mL of CH2Cl2 was added to the flask with
stirring. A solution of 1.0 M tetrabutylammonium fluoride (TBAF, 2.1
mL, 2.1 mmol) in THF was slowly added to the mixture over 30 min,
and the resulting solution was stirred for 18 h. Solvents were removed
under vacuum to give the crude mixture, which was then purified using
flash column chromatography on silica (20% CHCl3 in hexanes, v/v)
1
to give the pure product as a yellow powder. Yield 282 mg, 67%. H
NMR (CD2Cl2, 400 MHz): δ 2.00−2.11 (m, 2H, CH2), 2.62 (br, 4H,
2CH2), 6.51 (d, J = 5.2 Hz, 2H, 2 CH), 7.10 (d, J = 5.2 Hz, 2H, 2
CH), 7.39−7.44 (m, 12H, 12 CH), 7.77−7.82 (m, 8H, 8 CH).
31P{1H} NMR (CD2Cl2, 162 MHz): δ −6.92 (JPt−P = 2215 Hz).
Positive ESI-TOF: m/z = 843.0982, [C41H31S2P2194Pt + H]+. FTIR
(ATR) = 2095 cm−1 (νCC).
Complex 2, Pt(dppp)A2T3. The same procedure used for 1 was
employed except proligand L2 was used instead. An orange powder
was obtained as the pure product. Yield 288 mg, 64%. 1H NMR
(CD2Cl2, 400 MHz): δ 1.93−2.06 (m, 2H, CH2), 2.56−2.60 (m, 4H,
2CH2), 5.95 (d, J = 5.2 Hz, 2H, 2 CH), 6.72 (s, 2H, 2 CH), 6.74 (d, J
= 5.2 Hz, 2H, 2 CH), 7.41−7.44 (m, 12H, 12 CH), 7.67−7.72 (m, 8H,
8 CH). 31P{1H} NMR (CD2Cl2, 162 MHz): δ −5.99 (JPt−P = 2177
Hz). Positive ESI-TOF: m/z = 923.0652, [C43H32S3P2194Pt + Na]+.
FTIR (ATR) = 2098 cm−1 (νCC).
CONCLUSIONS
■
In summary, we prepared and characterized three different
thiophene-containing Pt metallacycles 1, 2, and 3 with dppp
ancillary ligands. Crystal structures show that they all possess
square-planar metal centers with similar metallacycle ring size.
Complex 3, Pt(dppp)A2BTB. The same procedure used for 1 was
employed except proligand L3 was used instead. A yellow powder was
1
obtained as the pure product. Yield 249 mg, 56%. H NMR (CDCl3,
G
DOI: 10.1021/acs.inorgchem.6b01464
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
9591. (c) Han, M.; Tian, Y.; Yuan, Z.; Zhu, L.; Ma, B. Angew. Chem.,
Int. Ed. 2014, 53, 10908.
(4) (a) Xiang, H.; Zhou, L.; Feng, Y.; Cheng, J.; Wu, D.; Zhou, X.
Inorg. Chem. 2012, 51, 5208. (b) Lin, C. J.; Chen, C. Y.; Kundu, S. K.;
Yang, J. S. Inorg. Chem. 2014, 53, 737. (c) Liu, Y.; Guo, H.; Zhao, J.
Chem. Commun. 2011, 47, 11471.
(5) (a) Zhang, G.; Palmer, G. M.; Dewhirst, M. W.; Fraser, C. L. Nat.
Mater. 2009, 8, 747. (b) Zhang, S.; Hosaka, M.; Yoshihara, T.; Negishi,
K.; Iida, Y.; Tobita, S.; Takeuchi, T. Cancer Res. 2010, 70, 4490.
(c) Zhao, Q.; Zhou, X. B.; Cao, T. Y.; Zhang, K. Y.; Yang, L. J.; Liu, S.
J.; Liang, H.; Yang, H. R.; Li, F. Y.; Huang, W. Chem. Sci. 2015, 6,
1825. (d) Zheng, X.; Wang, X.; Mao, H.; Wu, W.; Liu, B.; Jiang, X.
Nat. Commun. 2015, 6, 5834.
(6) Delor, M.; Keane, T.; Scattergood, P. A.; Sazanovich, I. V.;
Greetham, G. M.; Towrie, M.; Meijer, A. J. H. M.; Weinstein, J. A. Nat.
Chem. 2015, 7, 689.
(7) (a) Wilson, J. S.; Chawdhury, N.; Al-Mandhary, M. R.; Younus,
M.; Khan, M. S.; Raithby, P. R.; Kohler, A.; Friend, R. H. J. Am. Chem.
Soc. 2001, 123, 9412. (b) Liu, Y.; Jiang, S.; Glusac, K.; Powell, D. H.;
Anderson, D. F.; Schanze, K. S. J. Am. Chem. Soc. 2002, 124, 12412.
(8) Chawdhury, N.; Kohler, A.; Friend, R. H.; Wong, W. Y.; Lewis, J.;
Younus, M.; Raithby, P. R.; Corcoran, T. C.; Al-Mandhary, M. R. A.;
Khan, M. S. J. Chem. Phys. 1999, 110, 4963.
In solution, both phosphorescence and fluorescence are
attributed to ligand-based excited states. It is confirmed that
replacing phenyl groups with thiophene rings in metallacycles
can induce or enhance fluorescence without adding extra
conjugation to the ligand, thus obtaining room-temperature
dual emission with different FL/PH ratios. It is also revealed
that adding thiophene rings to extend the conjugation length in
metallacycles (from 1 to 2) will likely shut down phosphor-
escence due to ligand-based low-lying nonemissive T1 states.
DFT and TD-DFT calculations show that upon excitation
from S0 to S1, 2 and 3 undergo charge transfer from the ligand
to the empty 6pz orbital of the Pt atom while 1 shows only
π−π* transitions. It is also revealed that all three metallacycles
show very planar quinoid-like structure in the S1 and T1 excited
state with contracted single bonds and lengthened double/
triple bonds in the ligand. Complex 3 undergoes significant
planarization going from the GS to the S1 or T1 excited states,
resulting in weaker absorbance and much larger energy loss in
vibrational relaxation processes compared to 1 and 2. Both
fluorescence and phosphorescence maxima of these metalla-
cycles are attributed to 0−0 relaxation from corresponding
relaxed S1 and T1 excited states and match up with calculated
values. We anticipate the above findings may be useful for
future applications of these types of complexes in single-
component white-emitting OLEDs, self-referencing oxygen
sensors, and hypoxia contrast agents.
(9) Bradshaw, J. D.; Guo, L.; Tessier, C. A.; Youngs, W. J.
Organometallics 1996, 15, 2582.
(10) Alqaisi, S. M.; Galat, K. J.; Chai, M.; Ray, D. G.; Rinaldi, P. L.;
Tessier, C. A.; Youngs, W. J. J. Am. Chem. Soc. 1998, 120, 12149.
(11) (a) Fan, Y.; Zhao, D. ACS Appl. Mater. Interfaces 2015, 7, 6162.
(b) Hua, F.; Kinayyigit, S.; Cable, J. R.; Castellano, F. N. Inorg. Chem.
2006, 45, 4304. (c) Hua, F.; Kinayyigit, S.; Rachford, A. A.; Shikhova,
E. A.; Goeb, S.; Cable, J. R.; Adams, C. J.; Kirschbaum, K.; Pinkerton,
A. A.; Castellano, F. N. Inorg. Chem. 2007, 46, 8771.
(12) Sonogashira, K.; Yatake, T.; Tohda, Y.; Takahashi, S.; Hagihara,
N. J. Chem. Soc., Chem. Commun. 1977, 291.
(13) Kuchison, A. M.; Wolf, M. O.; Patrick, B. O. Inorg. Chem. 2010,
49, 8802.
(14) Johnson, C. A.; Haley, M. M.; Rather, E.; Han, F.; Weakley, T. J.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01464.
Supplementary crystallographic and DFT/TD-DFT data
(PDF)
X-ray crystallographic data for metallacycle 1 (CIF)
X-ray crystallographic data for metallacycle 2 (CIF)
X-ray crystallographic data for metallacycle 3 (CIF)
R. Organometallics 2005, 24, 1161.
(15) (a) Kuchison, A. M.; Wolf, M. O.; Patrick, B. O. Dalton Trans.
2011, 40, 6912. (b) Cao, Y.; Wolf, M. O.; Patrick, B. O. Inorg. Chem.
2013, 52, 5636.
(16) Sheng, C. X.; Singh, S.; Gambetta, A.; Drori, T.; Tong, M.;
Tretiak, S.; Vardeny, Z. V. Sci. Rep. 2013, 3, 2653.
(17) Minaev, B.; Jansson, E.; Lindgren, M. J. Chem. Phys. 2006, 125,
094306.
(18) Boudreault, P.-L. T.; Hennek, J. W.; Loser, S.; Ortiz, R. P.;
Eckstein, B. J.; Facchetti, A.; Marks, T. J. Chem. Mater. 2012, 24, 2929.
(19) Hung, T. Q.; Dang, T. T.; Villinger, A.; Sung, T. V.; Langer, P.
Org. Biomol. Chem. 2012, 10, 9041.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mwolf@chem.ubc.ca.
Notes
■
The authors declare no competing financial interest.
(20) SAINT, Version 8.34A; Bruker AXS Inc.: Madison, WI, 1997−
ACKNOWLEDGMENTS
We thank the Natural Sciences and Engineering Research
Council of Canada for funding this research.
■
2013.
(21) Krause, L.; Herbst-Irmer, R.; Sheldrick, G. M.; Stalke, D. J. Appl.
Crystallogr. 2015, 48, 3.
(22) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71,
3.
REFERENCES
■
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.; Brothers, E. N.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.;
Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.;
Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
(1) (a) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J.
Appl. Phys. 2001, 90, 5048. (b) Lamansky, S.; Djurovich, P.; Murphy,
D.; Abdel-Razzaq, F.; Lee, H. E.; Adachi, C.; Burrows, P. E.; Forrest, S.
R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304. (c) Sun, Y.;
Giebink, N. C.; Kanno, H.; Ma, B.; Thompson, M. E.; Forrest, S. R.
Nature 2006, 440, 908.
(2) (a) Kohler, A.; Beljonne, D. Adv. Funct. Mater. 2004, 14, 11.
̈
(b) Samonina-Kosicka, J.; DeRosa, C. A.; Morris, W. A.; Fan, Z.;
Fraser, C. L. Macromolecules 2014, 47, 3736. (c) Kozhevnikov, D. N.;
Kozhevnikov, V. N.; Shafikov, M. Z.; Prokhorov, A. M.; Bruce, D. W.;
Gareth Williams, J. A. Inorg. Chem. 2011, 50, 3804.
(3) (a) Glazer, E. C.; Magde, D.; Tor, Y. J. Am. Chem. Soc. 2005, 127,
4190. (b) Zhou, C.; Tian, Y.; Yuan, Z.; Han, M.; Wang, J.; Zhu, L.;
Tameh, M. S.; Huang, C.; Ma, B. Angew. Chem., Int. Ed. 2015, 54,
H
DOI: 10.1021/acs.inorgchem.6b01464
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
̈
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, Revision D.01; Gaussian, Inc.: Wallingford, CT, 2009.
(24) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996,
77, 3865. (b) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.
1996, 77, 3865; Phys. Rev. Lett. 1997, 78, 1396.
(25) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
̌
(26) Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 1981, 55, 117.
(27) Adams, C. J.; Fey, N.; Harrison, Z. A.; Sazanovich, I. V.; Towrie,
M.; Weinstein, J. A. Inorg. Chem. 2008, 47, 8242.
(28) Merrick, J. P.; Moran, D.; Radom, L. J. Phys. Chem. A 2007, 111,
11683.
I
DOI: 10.1021/acs.inorgchem.6b01464
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