Copper(i) ionic complexes based on imidazo[4,5-: F] [1,10]phenanthrolin diimine chelating ligands: Crystal structures, and photo- And electroluminescence properties

Article abstract of DOI:10.1039/c9nj05109k

Four new ionic diimine Cu(i) complexes with general formula [Cu(POP)(NN)]BF₄ have been synthesized by convenient methods from readily available starting materials. All the complexes were characterized by a range of spectroscopic, electrochemica

Full text of DOI:10.1039/c9nj05109k

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Copper(I) ionic complexes based on imidazo-
[4,5-f ][1,10]phenanthrolin diimine chelating
ligands: crystal structures, and photo- and
electroluminescence properties†
Cite this: New J. Chem., 2020,
44, 110
a
a
Anton V. Rozhkov, *a Svetlana N. Eliseeva,
Lev E. Zelenkov,
Sergey V. Baykov,
Dmitry O. Goriachiyb and Ilya V. Taydakov
a
b
Four new ionic diimine Cu(I) complexes with general formula [Cu(POP)(NN)]BF4 have been synthesized by
convenient methods from readily available starting materials. All the complexes were characterized by a
range of spectroscopic, electrochemical, and computational techniques and, in the cases of 1, 2, and 3, by
single crystal X-ray diffraction. The complexes are emissive in the solid state at ambient temperature and the
emission maxima are located in the orange range. Furthermore, the suitability of these complexes for
application in organic light-emitting diodes (OLEDs) has been demonstrated in a solution-processed device.
Received 10th October 2019,
Accepted 25th November 2019
DOI: 10.1039/c9nj05109k
rsc.li/njc
complexes have smaller SOC constants, which can result in an
increase in decay time and a decrease in triplet emission and can
Introduction
In recent times, luminescent Cu(I) complexes have been affect the OLED performance. Fortunately, copper complexes
the object of intense studies for application in organic light can show TADF with short radiative lifetimes at room temper-
emitting diodes (OLEDs).1–5 Cu(I) complexes possess significant ature.10–13 These TADF copper complex-based OLEDs present
advantages such as tunable phosphorescent emission bands, an internal quantum efficiency of 100% by harvesting both
long excited state lifetimes, abundance of the metal in nature singlet and triplet excitons. Copper(I) complexes with diimine
and easy mining, low cost, and environmental benignancy, ligands have been successfully used as TADF emitters.11,14,15
which make them a tempting alternative to the commonly used In particular, the imidazo[4,5-f][1,10]phenanthrolin derivatives
triplet phosphorescent iridium complexes in electroluminescent as ligands have been extensively utilized to prepare Cu(I)
device applications.6 Iridium and platinum complexes display complexes with attractive luminescence features.16–19
strong spin–orbital coupling (SOC) leading to effective intersystem
Herein, we describe the synthesis of a new series of cationic
crossing from the lowest excited singlet to the lowest triplet state, heteroleptic diimine–diphosphine copper(I) complexes with POP
which allows all injected excitons to be used for light generation (bis[2-(diphenylphosphino)phenyl]-ether) and 1,10-phenimidazole
in electroluminescent devices through the triplet harvesting (L1 = 2-(1H-imidazo[4,5-f ][1,10]phenanthrolin-2-yl)phenol, L2 =
effect.7 Yet another way to harvest excitons in OLEDs is to use 4-chloro-2-(1H-imidazo[4,5-f ][1,10]phenanthrolin-2-yl)phenol, L3 =
temperature activated delayed fluorescence (TADF) emitters.8,9 4-bromo-2-(1H-imidazo[4,5-f ][1,10]phenanthrolin-2-yl)phenol,
Due to the small energy separation DE(S1–T1) between the first L4
= 2-(1H-imidazo[4,5-f ][1,10]phenanthrolin-2-yl)-4-nitrophenol)
excited singlet state S1 and the triplet state T1, the S1 state can be ligands. These complexes demonstrated orange photolumines-
thermally populated from the energetically lower lying T1 state. In cence in the solid state at room temperature and were applied
an electroluminescent device, this mechanism allows utilizing all in solution-processed OLEDs using a host–guest system. We
injected excitons for light generation. Accordingly, the excitation have found that the color of electroemission can be fine-tuned
is harvested and emitted, essentially, via the singlet S1 state. by varying the dopant concentration.
As distinct from platinum and iridium complexes, copper(I)
a Institute of Chemistry, Saint Petersburg State University, Universitetskaya Nab. 7/9,
Results and discussion
Synthetic procedures
199034 Saint Petersburg, Russian Federation. E-mail: iomcrozhkov@gmail.com
b P. N. Lebedev Physical Institute of the Russian Academy of Science, Leninsky pr., 53,
119991 Moscow, Russian Federation
The diimine N^N ligands L1–L4 were prepared by condensation
of 1,10-phenanthroline-5,6-dione with an appropriate aldehyde
in the presence of ammonium acetate20–22 (Scheme 1).
† Electronic supplementary information (ESI) available. CCDC 1941884, 1941885
and 1953636. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c9nj05109k
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Scheme 1 The synthetic route to the N^N ligands L1–L4.
Scheme 2 The synthetic route to the Cu(I) complexes.
The synthetic route to the Cu(I) complexes is shown in Fig. 1 (complex 1), Fig. 2 (complex 2), and Fig. 3 (complex 3).
Scheme 2. Complexes 1–4 (X = H, Cl, Br, NO2) were prepared Selected bond lengths and bond angles are given in Table 1.
by the conventional reaction of [Cu(CH3CN)4]BF4 with 1 equiv.
of the POP ligand and 1 equiv. of the appropriate N^N ligand Complex 1 cocrystallized with one molecule of DMSO linked
in dichloromethane at room temperature.
All crystalized complexes display mononuclear structures.
via the O1Sꢀ ꢀ ꢀH3 hydrogen bond. Complex 2 cocrystallized with
The complexes were obtained in good yields as air stable, one molecule of dichloromethane. The Cl1Sꢀ ꢀ ꢀCl1 distance
yellow crystalline solids soluble in the majority of organic solvents, (3.36588(9) Å) is shorter than the corresponding sums of Bondi
including CHCl3, CH2Cl2, MeOH, MeCN, DMF, and DMSO. The vdW radii (3.5 Å),23 and the contact angle C1S–Cl1S–Cl1
formation of the desired Cu(I) complexes was confirmed by 1H, 13C, (154.2208(9)1) does not significantly deviate from 1601. Both
31P NMR and FTIR spectroscopy, as well as high-resolution mass facts allow us to assign the observed intermolecular interaction
spectrometry (see the Experimental section).
to halogen bonding (Fig. S1, ESI†).24 The Cu(I) center in all the
complexes has a distorted tetrahedral geometry formed by two
phosphorus atoms from the POP ligand and two nitrogen
atoms from the diimine ligand. The Cu–N and Cu–P bond
lengths are in the range of 2.05440(6)–2.081(2) Å) and
2.2059(9)–2.2988(9) Å, respectively, which are consistent with
the previously studied copper(I) complexes with the same or
similar ligands.16,18,25–27 The P–Cu–P bite angle is 112.93(3)1 in
Structure determination by single crystal X-ray diffraction
Single crystals suitable for X-ray determination were obtained
by slow evaporation of the solvent from a DMSO solution
(for complex 1) or by slow diffusion of pentane to a saturated
solution of the complex in CH2Cl2 at ambient temperature
(for complex 2). The structures obtained are presented in
Fig. 1 Crystal structure of 1ꢀDMSO with thermal ellipsoids shown at the 30% probability level. Most of the hydrogen atoms are omitted for clarity.
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Fig. 2 Crystal structure of 2ꢀCH2Cl2 with thermal ellipsoids shown at the 30% probability level. Most of the hydrogen atoms are omitted for clarity.
Fig. 3 Crystal structure of 3 with thermal ellipsoids shown at the 30% probability level. Most of the hydrogen atoms are omitted for clarity.
Table 1 Selected bond lengths (Å) and bond angles (1) in 1ꢀDMSO, 2ꢀ
CH2Cl2, and 3
nitrogen atom in all X-ray structures. It prevents the rotation of
the phenyl group around the C13–C14 bond and leads to
flattening of the diimine ligand and an increase in the degree
of its conjugation. The dihedral angles between the phenol ring
(C14–C19) and the mean plane of imidazo[4,5-f ][1,10]phenan-
throline are 2.98(11)1 in 1, 2.68540(8)1 in 2, and 0.30(11)1 in 3.
Also, N–Hꢀ ꢀ ꢀF hydrogen bonds are observed in 2 and 3 between
1ꢀDMSO
2ꢀCH2Cl2
3
Cu1–N1
Cu1–N2
Cu1–P1
Cu1–P2
N1–Cu1–N2
P1–Cu1–P2
N1–Cu1–P1
N1–Cu1–P2
N2–Cu1–P1
N2–Cu1–P2
2.059(2)
2.081(2)
2.074(3)
2.054(3)
2.2988(9)
2.2059(9)
81.18(9)
114.69(3)
98.33(7)
132.53(8)
101.57(7)
121.06(7)
2.068(2)
2.057(3)
2.2410(7)
2.2663(8)
80.92(8)
112.93(3)
118.12(7)
115.73(7)
118.13(6)
106.90(6)
2.2825(5)
2.2066(9)
81.10(9)
115.89(4)
106.13(7)
123.00(9)
100.10(8)
124.11(7)
ꢁ
the imidazole –NH group and the BF4 anion. In all obtained
crystals, each molecule interacts with a neighbouring molecule
through intermolecular pꢀ ꢀ ꢀp interactions (Fig. S2–S4, ESI†).
pꢀ ꢀ ꢀp Overlapping formed through the stacking of imidazo-
[4,5-f ][1,10]phenanthroline moieties with a pꢀ ꢀ ꢀp distance of
3.6118(17) Å in 1, 3.4092(16) Å in 2, and 3.6590(18) Å in 3.
1, 114.69(3)1 in 2, and 115.89(4)1 in 3. The angle between Cu–P1
and the mean plane of imidazo[4,5-f ][1,10]phenanthroline in 2
Thermal stability
(99.8875(12)1) is smaller than in 1 (128.27(4)1) due to the Thermogravimetric analysis (TGA) was performed on samples
intramolecular pꢀ ꢀ ꢀp interaction between the POP phenyl group of 1–4 powders under an argon atmosphere to investigate their
and the phenanthroline moiety of L2. The centroid distance is stability characteristics. The TGA traces are presented in Fig. 4.
3.33295(8) Å. Intramolecular O–Hꢀ ꢀ ꢀN hydrogen bonds are
As shown by the TGA results, these complexes are thermally
observed between the phenol –OH group and the other imidazole stable. The decomposition temperatures corresponding to a
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bands in the range of 270–380 nm are assigned to the spin-allowed
ligand centered (LC) transition (p - p*) of both the diimine ligand
and the POP ligand, as well as the ligand-to-ligand charge-transfer
(LLCT) transition. The weak low-energy bands in the range of
380 to 460 nm are attributed to the metal–ligand charge-transfer
(dp(Cu) - p*(N^N ligand) (MLCT) transition.16,17
Emission spectra. All the complexes show no obvious
emission in dichloromethane solution. The non-emissive behavior
of complexes 1–4 in dichloromethane solution is assumed to arise
from the active intramolecular motions (rotation and vibration).
Complexes 1–4 demonstrate intense luminescence in the solid
state at both 293 K and 77 K in air (Fig. 6 and Table 2).
At 293 K, the complexes show broad and structureless
intense emission bands with maxima at 577 nm (1), 578 nm
(2), 636 nm (3) and 594 nm (4), which could be assigned to the
metal to ligand charge transfer (MLCT) character.27,29 At 77 K,
complexes 1, 2, and 4 exhibit slightly lower energy emission
with the peaks at 602, 596, and 564 nm, respectively. The
Fig. 4 TGA curves of complexes 1–4.
5% loss of weight are 344 1C for 1, 193 1C for 2, 227 1C for 3, and considerable difference in emission between 293 K and 77 K
330 1C for 4.
indicates that the luminescence of these complexes in the solid
state might originate from two different excited states in
thermal equilibrium, that is, S1 and T1. Small energy separa-
tions DE(S1–T1) of about 0.12 eV were observed for 1, 2, and 4.
This behavior can be attributed to the TADF process.10 For
complex 3 we did not detect a shift in the luminescence
maxima upon a decrease in temperature to 77 K. The existence
of Br in 3 led to spin–orbit coupling due to the heavy atom
effect and we observed triplet emission at room temperature.
The luminescence quantum yields of 1–4 at room temperature
are in the range of 1.30–0.04% and the lifetimes are in the
range of 1.5–4.2 ms (Table 2), which are close to those of other
POP-based diimine copper complexes.16,27,30 It should be noted
that replacement of H with Br at position 4 of the phenyl moiety
in the N^N ligand leads to a decrease in the quantum yield
from 1.30 to 0.09% due to the heavy atom effect.31 Incorpora-
tion of an NO2 group leads to a decrease in the quantum yield,
too. Nitro group substituents that have acceptor properties may
withdraw the p-electron density from the aromatic ring, thus
increasing the ILCT and, accordingly, decreasing the MLCT
processes.
Photophysical properties
Absorption spectra. The absorption spectra of the complexes
in anhydrous dichloromethane are shown in Fig. 5 and the photo-
physical data are summarized in Table 2. The intense absorption
Electrochemical properties
The electrochemical properties of complexes 1, 2, 3, and 4 were
Fig. 5 Absorption spectra of complexes 1–4 in dichloromethane solution
at room temperature.
studied by cyclic voltammetry (Fig. 7).
Table 2 Photophysical data for the Cu(I) complexes
lem, nm
l
abs, nm (e ꢂ 10ꢁ5 l molꢁ1 cmꢁ1) (CH2Cl2)
293 K 77 K S1,a eV T1,b eV DES–T, eV
t
em, ms QY, % DEg,c eV HOMOd/LUMO,e eV
1
2
3
4
280 (1.20), 334 (0.37), 350 sh (0.27), 420 (0.07) 577
602 2.39
596 2.37
636 2.19
622 2.31
2.27
2.25
—
0.12
0.12
—
4.2
3.9
1.5
1.9
1.30
0.85
0.09
0.04
2.75
2.75
2.79
2.74
ꢁ5.53/ꢁ2.78
ꢁ5.55/ꢁ2.80
ꢁ5.55/ꢁ2.76
ꢁ5.67/ꢁ2.93
280 (0.57), 340 (0.24), 356 (0.21), 420 (0.06)
280 (1.04), 339 (0.36), 353 (0.32), 420 (0.09)
281 (1.01), 338 sh (0.31), 419 (0.08)
578
636
594
2.19
0.12
a
b
Estimated from the high-energy flank at 50% of the emission maximum intensity measured at 298 K. Estimated from the high-energy flank at
c
d
50% of the emission maximum intensity measured at 77 K. Calculated from the absorption edge. Estimated by cyclic voltammetry in DMF with
SCE (4.74 eV) as the reference.28 e Derived from the relation DE = HOMO–LUMO.
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Fig. 6 Normalized emission spectra of neat powders of complexes 1–4 at 293 K (a) and 77 K (b). lex = 450 nm.
DFT calculations
In order to obtain insight into the optical spectroscopic results,
TD-DFT (time-dependent DFT) calculations were performed.
The computational methodology is described in detail in the
Experimental section.
The frontier molecular orbitals (HOMO/LUMO) together
with simulated absorption spectra of complex 1 as a represen-
tative example are shown in Fig. 8.
A good match is observed between the experimental spec-
trum and calculated bars. As expected, the HOMO of the
complex is mainly localized over the metal center and phenyl
and imidazole moieties of the phenantroline-based ligand with
little contribution of the triphenylphosphine coligand. On the
other hand, the LUMO was mainly delocalized over the phe-
nanthroline moiety of the diimine ligand (Fig. 8a). The main
trends in the simulated spectra compare reasonably well with
the corresponding solution spectra (Fig. 8b). The calculated
lowest-energy absorption at 413 nm involves the HOMO -
LUMO transition, which can be assigned as the mixture of
metal to ligand (Cu - N^N) (MLCT), intra-ligand (ILCT), and
ligand to ligand (POP - N^N) (LLCT) charge transfer charac-
ters. At higher energies, i.e. 354, 323, 314, 302 and 289, MLCT
and ILCT are the main characters with minor contribution of
the LLCT character. At higher energies, i.e. 354, 323, 314, 302
and 289, IL, MLCT and ILCT are the main characters with
minor contribution of the LLCT character. The calculated
transitions with their assignments are summarized in Table 3.
Fig. S9–S12 (ESI†) depict the frontier molecular orbitals of
complexes 1–4.
Fig. 7 Cyclic voltammograms of complexes 1–4 in DMF solution.
In cyclic voltammetry (CV) studies in the potential range
from ꢁ0.2 to +1.0 V, complexes 1–4 show one oxidation peak at
0.72–0.86 V. Analysis of the CV dependence on the potential
range at a scan rate of 50 mV sꢁ1 shows that the peak potentials
stabilize at 0.72–0.86 V for oxidation of complexes 1–4, respec-
tively. The oxidation potential of complexes 1, 2, 3, and 4 in
DMF solution is 0.72, 0.74, 0.74 and 0.86 V, respectively. In the
CV of complex 4 we can see a wider oxidation peak at a higher
potential (0.86 V) compared with the other complexes. All the
Cu(I) complexes show an irreversible oxidation process, indicating
a rapid decomposition of the Cu(II) species. Nevertheless, based
on the start-of-oxidation potential, the highest occupied mole-
cular orbital (HOMO) energy levels of these Cu(I) complexes can
be calculated: ꢁ5.19 eV for 1, ꢁ5.21 eV for 2, ꢁ5.21 eV for 3 and
ꢁ5.33 eV for 4. The lowest unoccupied molecular orbitals
Electroluminescence properties
(LUMOs) were determined from EHOMO and the optical band Multilayer devices can be made by vacuum deposition, and
gap DEg values, which were obtained from the UV absorption commercial OLEDs are currently made using this process.
edge as reported elsewhere.32 The LUMOs (ꢁ2.64 eV for 1, However, vacuum thermal evaporation has the drawbacks of
ꢁ2.63 eV for 2, ꢁ2.62 eV for 3 and ꢁ2.59 eV for 4) of low material utilization rates, poor scalability, high capital cost,
these complexes were obtained using the equation ELUMO
=
and difficulty in patterning. Solution processing, in principle,
EHOMO ꢁ DEg. The corresponding data are summarized in provides a low-cost approach to fabricate OLEDs.33 To estimate
Table 2 along with the optical band gap.
the performance of the emitting compound upon electrical
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Fig. 8 Frontier orbitals (a) and simulated absorption spectra from TD-DFT calculations in dichloromethane (red bar) compared to solution absorption
spectra (black line) of complex 1 (b).
Table 3 Calculated absorption spectra of complexes 1–4
Model structure
l (nm)
Oscillator strength
Transitions
Assignment
1
413
354
323
314
0.1750
0.2353
0.4010
0.2038
HOMO - LUMO
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
MLCT/IL/LLCT
ILCT/LLCT
HOMOꢁ1 - LUMO+1
HOMO - LUMO+2
HOMOꢁ1 - LUMO+2
2
3
4
413
352
329
322
318
0.1811
0.3350
0.1537
0.2443
0.0706
HOMO - LUMO
MLCT/LLCT
MLCT/IL
LLCT
IL
ILCT
HOMOꢁ1 - LUMO+1
HOMO - LUMO+2
HOMOꢁ1 - LUMO+2
HOMOꢁ4 - LUMO
413
353
329
322
320
0.1796
0.3269
0.1659
0.1399
0.1374
HOMO - LUMO
MLCT/ILCT/LLCT
MLCT/ILCT/LLCT
IL/LLCT
IL/LLCT
ILCT
HOMOꢁ1 - LUMO+1
HOMO - LUMO+2
HOMOꢁ1 - LUMO+2
HOMOꢁ4 - LUMO
415
368
336
313
0.1561
0.0919
0.1261
0.4852
HOMO - LUMO+1
HOMOꢁ1 - LUMO
HOMOꢁ3 - LUMO
HOMOꢁ1 - LUMO+3
MLCT/LLCT
MLCT/ILCT
LLCT
IL
excitation, a solution-processed OLED test device was prepared observed a red shift of the complex emission maxima with
with the following architecture: ITO/PEDOT:PSS/complex:CBP/ increasing guest–host ratio (Fig. 10b). It is possibly due to
TPBI/LiF/Al (Fig. 9). Water-soluble PEDOT:PSS was used as increased stabilization of CT states as the concentration of
the hole-injection layer. A copper complex doped in the hole- highly polar dopant molecules increases. This behavior is very
transporting host (CBP (4,40-bis(N-carbazolyl)-1,10-biphenyl)) similar to the solvatochromic effect as a result of intermole-
was spin-coated in CHCl3 over PEDOT:PSS to form a light- cular solute–polar solvent interaction. The same phenomena
emitting layer. TPBI (2,20,200-(1,3,5-benzinetriyl)-tris(1-phenyl-1- were studied earlier for 2,3,5,6-tetrakis(3,6-diphenylcarbazol-9-
H-benzimidazole)) was vacuum deposited and used as the yl)-1,4-dicyanobenzene as a TADF dopant in a CBP:4CzTPN-Ph
electron-transporting and hole-blocking material.
blend as the emissive layer in OLEDs.34 Additionally, the
Complex 1 was used for a test device to optimize the guest similarity of the peak shifting in various solvents and with
concentration due to its higher quantum yield among the rest different concentrations suggests that our complex suspended
of the complexes. The EL spectra are presented in Fig. 10a.
in a solid matrix of CBP undergoes an energy shift due to self-
The EL spectra contain two types of emission bands: CBP polarization.35 When we increased the concentration of the
emission (from 340 to 450 nm) and complex emission (from 450 complex in non-polar CBP, the distance between nearest
to 800 nm). The CBP emission can be explained by incomplete complex molecules decreased, thereby increasing the local
energy transfer from host to guest molecules. In addition, we polarization field, which leads to the red shift. Furthermore,
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Fig. 9 Device architecture and molecular structures of the materials used in the OLEDs.
Fig. 10 EL spectra of the OLEDs (a) and EL emission maxima shift (b) at various doping concentrations of 1.
with increasing dopant concentration the Dexter-type triplet–
triplet energy transfer from the host to the dopant becomes
more efficient.36 The EL spectra of the host-free OLED
(100 wt%, Fig. 10a) are identical to the PL spectra at 77 K
(Fig. 6b), and the phosphorescence (triplet emission) process
was observed. The best performance was achieved at 15 wt%
of 1 and this concentration was used for all the complexes.
The EL spectra are shown in Fig. 11. The EL spectra and
luminance–voltage and current density–voltage characteristics
of the OLED for 1 at different host–guest ratios are shown
in Fig. S5 (ESI†).
Table 4 EL data for complexes 1–4
Complex Vturn-on (V) Lmax (cd mꢁ2) Zc (cd Aꢁ1) lem (nm)
CIE (x, y)
1
2
3
4
7
7
9
7
110
50
23
6
0.04 (10 V) 375, 386, 568 0.57, 0.39
0.02 (11 V) 375, 386, 568 0.57, 0.39
0.02 (10 V) 390, 595
0.60, 0.38
0.01 (7 V) 374, 387, 569 0.56, 0.39
Fig. 11 EL spectra of ITO/PEDOT:PSS/complex (15 wt%):CBP/TPBI/LiF/Al.
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The luminance–voltage and current density–voltage charac- consisting of a working electrode (glassy carbon 0.07 cm2), a
teristics of the OLED are shown in Fig. S6 and S7 (ESI†). The EL counter electrode (platinum wire) and a non-aqueous Ag/Ag+
data for complexes 1–4 are collected in Table 4.
reference electrode (Ag wire immersed in acetonitrile containing
0.1 M AgNO3). All potentials in the text are referenced vs. the non-
aqueous Ag/Ag+ electrode. The potential of the reference elec-
trode was +0.07 V vs. saturated calomel electrode (SCE). Cyclic
voltammetry measurements were performed at room tempera-
ture in argon purged anhydrous N,N-dimethylformamide
solutions containing 1 ꢂ 10ꢁ3 M of a complex and 0.1 M of
tetrabutylammonium tetrafluoroborate Bu4NBF4 (Aldrich) at a
scan rate of 50 mV sꢁ1. The three-electrode electrochemical cell
was sealed during the experiments. Before measurements, the
solutions were bubbled with dry argon for 20 minutes.
Conclusions
In summary, four mononuclear cationic Cu(I) orange emitting
complexes 1, 2, 3, and 4 bearing different substituents at
position 4 of the phenol ring in the 1,10-phenimidazole ligand
have been prepared and comprehensively characterized,
including spectroscopic, electrochemical, and computational
studies. The described complexes are suitable for applying
in solution-processed OLEDs. Their electroluminescence pro-
perties are strongly affected by the dopant concentration. The
optimal dopant concentration was estimated as 15 wt% for the
best performance. A maximum luminance of 110 cd mꢁ2 was
reached in the OLED based on complex 1. We believe that
further optimization of the ligand structure and device archi-
tecture would allow enhanced OLED performance.
Computational details
The DFT calculations were carried out with the B3LYP func-
tional with inclusion of the CH2Cl2 solvent model (PCM) for
studies of the electronic structures and the features of electronic
transitions of the present complexes using the Gaussian-09
program package.38 The starting structures for the geometry
optimization procedure were taken from the experimental
X-ray diffraction data and no symmetry restrictions were
applied. The calculations were performed using the LANL2DZ
effective core potentials and the appropriate contracted basis
sets for the copper atoms and the standard 6-31G* basis sets for
other atoms. Vibrational analysis at the same level was per-
formed to confirm that all the optimized structures do not have
imaginary frequencies.
Experimental
Measurement and characterization
1H, 13C, and 31P NMR spectra were measured on a Bruker
400 MHz WB Avance III spectrometer in DMSO-d6 at ambient
temperature; residual solvent signals were used as the internal
standard. The 31P chemical shifts are referenced to 85% H3PO4.
Melting points were measured on a Stuart SMP30 apparatus at a
heating rate of 2 1C minꢁ1 in capillaries and were not corrected.
Microanalyses (C, H, N) were carried out on a Euro EA3028-HT
analyzer. Electrospray ionization mass spectra were obtained
on a Bruker maXis spectrometer equipped with an electrospray
ionization (ESI) source. The instrument was operated in positive
ion mode using an m/z range of 50–3000. The capillary voltage of
the ion source was set at ꢃ70–150 V. The nebulizer gas pressure
was 0.4 bar, and the drying gas flow was 4.0 L minꢁ1. The most
intense peak is recorded in the isotopic pattern. Infrared spectra
(4000–400 cmꢁ1) were recorded on a Shimadzu IRPrestige-21
instrument in KBr pellets. Ultraviolet-visible (UV-vis) absorp-
tion spectra were measured with a Shimadzu UV-1800 spectro-
photometer. Emission spectra for solid-state samples at room
temperature and at 77 K were measured on a Fluorolog 3
(Horiba Jobin Yvon) spectrofluorimeter. The photolumines-
cence quantum yield was defined as the number of photons
emitted per photon absorbed by the system and was measured
with an integrating sphere by a reported method.37 TGA was
performed on ca. 2 mg samples of 1–4 by using a Netzsch TG
209 F1 Libra thermal analyzer. The samples were dried under
a vacuum at 50 1C before being heated from 40 to 600 1C at a
heating rate of 10 K minꢁ1. A flow rate of 10 mL minꢁ1 of dry
argon was used to purge the samples at all times.
OLED fabrication
1. Substrate preparation. ITO-coated glass substrates with
12 Ohm sqꢁ1 resistance were purchased from Lumtec Taiwan.
The substrates were cleaned by sequential ultrasonication
in alcohol 15% KOH solution, double distilled water, and iso-
propanol for 15 minutes each, followed by drying with a nitrogen
flow. The substrates were additionally treated by UV/ozone in a
UV-cleaning chamber (Ossila, UK) just before use.
2. Film deposition. In order to obtain films of PEDOT-PSS
and complex:CBP we used a KW-4A spin coater from Chemat
Technology (USA) operating in air. To form the PEDOT-PSS film
(Lumtec LT-PS001), 200 mL of an aqueous solution was poured
onto a resting ITO-substrate, then the rotation at 2000 rpm for
1 min was started. The 50 nm PEDOT-PSS films thus obtained
were annealed at 100 1C for 30 min in an N2 atmosphere.
Complex:CBP films were obtained by spin-coating on
ITO/PEDOT-PSS from a 5 g lꢁ1 solution in chloroform by
applying 100 mL of the solution onto a rotating substrate at
1500 rpm rotation for 1 min.
A 15 nm TPBi (Lumtec LT-E302) film was thermally deposited
in a vacuum less than 103 Pa from a quartz cuvette heated with a
tantalum coil. Then 1 nm of LiF (Lumtec LT-E001) at a rate of
0.1 A sꢁ1 and 40 nm of aluminium at a rate of 0.2 nm sꢁ1 were
thermally deposited through a mask to form four 12 mm2 pixels.
3. Measurements. The electroluminescence spectra were
Cyclic voltammetry
Electrochemical measurements were carried out with an Autolab obtained with an Ocean Optics Maya 2000 Pro CCD spectrometer
PGSTAT30 (Eco Chemie, Netherlands) in a three-electrode cell sensitive within 200–1100 nm. The current–voltage characteristics
New J. Chem., 2020, 44, 110--120 | 117
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were obtained using two DT 838 digital multimeters. The lumi- 130.6, 129.3 (t, JCP = 4.4 Hz), 127.0, 125.7, 123.6 (t, JCP = 14.6 Hz),
nance of the OLED samples was measured by a TKA-PKM 121.1, 120.0, 117.8, 113.3. 31P NMR (162 MHz, DMSO-d6)
luminance meter produced by TKA Scientific Instruments. The d: ꢁ11.64 (s). HRMS (ESI+, MeOH): calcd for C55H40CuN4O2P2 [M]+
deposition rate was measured in situ by a Leybold Inficon IC-6000 913.1917; found 913.1915. IR (KBr, selected bands, cmꢁ1): 3538,
deposition controller calibrated using a NT-MDT atomic force 3228, 3054, 1710, 1586, 1574, 1564, 1480, 1462, 1436, 1407,
microscope of the Integra family.
1359, 1258, 1213, 1186, 1096, 1070, 732, 694.
Complex 2 was crystallized from CH2Cl2/pentane to yield the
product as yellow crystals (82%).
Materials and reagents
[Cu(CH3CN)4]BF4,39 1,10,-phenanthro-5,6-dione,40 2-(1H-imidazo-
1H NMR (400 MHz, DMSO-d6) d: 14.23 (s, 1H), 12.45 (s, 1H),
[4,5-f][1,10]phenanthrolin-2-yl)phenol (L1),21 4-chloro-2-(1H- 9.14 (d, J = 8.3 Hz, 2H), 8.87 (d, J = 4.7 Hz, 2H), 8.27 (d, J =
imidazo[4,5-f ][1,10]phenanthrolin-2-yl)phenol (L2),20 and 2.4 Hz, 1H), 8.01–7.89 (m, 2H), 7.48–7.43 (m, 3H), 7.31 (d, J =
4-bromo-2-(1H-imidazo[4,5-f ][1,10]phenanthrolin-2-yl)phenol (L3)22 7.4 Hz, 4H), 7.24–7.16 (m, 10H), 7.12 (m, 3H), 6.99 (m, 8H),
were prepared according to the procedures reported in the 6.70–6.66 (m, 2H). 13C NMR (101 MHz, DMSO-d6) d: 158.4
literature. Bis[(2-diphenylphosphino)phenyl]ether (POP), poly- (t, JCP = 5.9 Hz), 156.3, 150.5, 148.4, 141.3, 134.3, 133.2
(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS), (t, JCP = 8.0 Hz), 132.8, 132.0, 131.8, 131.0 (t, JCP = 16.9 Hz),
4,40-bis(N-carbazolyl)-1,10-biphenyl (CBP), and 2,20,200-(1,3,5- 130.6, 129.3 (t, JCP = 4.5 Hz), 125.7, 123.6 (dd, JCP = 16.1 Hz,
benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI) were obtained 13.0 Hz), 121.1, 119.7, 114.8, 55.4. 31P NMR (162 MHz, DMSO-d6)
from commercial sources and used without further purification. d: ꢁ11.63 (s). HRMS (ESI+, MeOH): calcd for C55H39ClCuN4O2P2
All experiments with air and moisture sensitive intermediates and [M]+ 947.1527; found 947.1517. IR (KBr, selected bands, cmꢁ1):
compounds were carried out under an inert atmosphere of dry 3538, 3228, 3054, 1710, 1586, 1574, 1564, 1480, 1462, 1436, 1407,
argon using standard Schlenk techniques. The solvents were 1359, 1258, 1213, 1186, 1096, 1070, 732, 694.
purified and dried by conventional methods.
Complex 3 was crystallized from CHCl3/pentane to yield the
Synthesis of 2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-4- product as orange crystals (78%).
nitrophenol (L4). 1,10-Phenanthro-5,6-dione (0.50 g, 2.38 mmol), 2-
1H NMR (400 MHz, DMSO-d6) d: 13.43 (br s, 2H), 9.05 (d, J =
hydroxy-5-nitrobenzaldehyde (0.40 g, 2.38 mmol), and ammonium 8.1 Hz, 2H), 8.77 (d, J = 4.6 Hz, 2H), 8.42 (s, 1H), 7.83 (m, 2H),
acetate (3.66 g, 47.57 mmol) were dissolved in glacial acetic acid 7.44 (m, 3H), 7.30 (t, J = 7.3 Hz, 4H), 7.24–7.16 (m, 10H), 7.09
(25 mL). The mixture was refluxed for 5 h with vigorous stirring (t, J = 7.5 Hz, 2H), 7.02–6.95 (m, 9H), 6.69–6.63 (m, 2H).
using a magnetic stirrer. After the reaction mixture was cooled 13C NMR (101 MHz, DMSO-d6) d: 158.4 (t, JCP = 6.2 Hz), 156.9,
to room temperature, the solution was poured into cold water 147.2, 140.8, 134.3, 133.2 (t, JCP = 8.1 Hz), 132.8, 131.6, 131.2
(200 mL) and cautiously neutralized with NH3ꢀH2O until (t, JCP = 16.7 Hz), 130.5, 129.2 (t, JCP = 4.5 Hz), 128.8, 125.6,
neutral. The precipitate was filtered off, washed with water 125.2, 123.7 (t, JCP = 14.4 Hz), 121.1, 119.6, 110.5, 79.8, 79.6,
and then acetone and vacuum dried at 50 1C to give the product 79.4, 79.1. 31P NMR (162 MHz, DMSO-d6) d: ꢁ11.88 (s). HRMS
as an orange solid (0.72 g, 85%). Mp: 4300 1C.
(ESI+, MeOH): calcd for C55H39BrCuN4O2P2 [M]+ 991.1022;
1H NMR (400 MHz, DMSO-d6) d: 13.98 (br s, 2H), 8.99–8.93 found 991.1022. IR (KBr, selected bands, cmꢁ1): 3540, 3070,
(m, 3H), 8.70 (dd, J = 8.1, 1.5 Hz, 2H), 8.08 (dd, J = 9.1, 2.8 Hz, 3055, 1587, 1574, 1479, 1462, 1435, 1398, 1257, 1211, 1161,
1H), 7.72 (dd, J = 8.1, 4.3 Hz, 2H), 6.98 (d, J = 9.1 Hz, 1H). 1094, 1055, 1000, 988, 873.
13C NMR (101 MHz, DMSO-d6) d: 163.3, 148.8, 148.6, 144.2,
Complex 4 was crystallized from CH2Cl2/pentane to yield the
140.0, 130.0, 126.7, 123.6, 120.9, 122.5, 118.4, 113.4. HRMS (ESI+, product as orange crystals (81%).
MeOH): calcd for C19H11N5O3 [M + H]+ 358.0935; found
1H NMR (400 MHz, DMSO-d6) d: 14.02 (br s, 1H), 9.15 (s, 3H),
358.0936. IR (KBr, selected bands, cmꢁ1): 3068, 1594, 1481, 8.89 (s, 2H), 8.23 (s, 1H), 7.95 (s, 2H), 7.46 (t, J = 7.9 Hz, 3H),
1411, 1342, 1301, 1126, 803, 738, 639.
General procedure for the synthesis of complexes 1–4. A (m, 8H), 6.69 (m, 2H). 13C NMR (101 MHz, DMSO-d6) d: 158.4
mixture of [Cu(CH3CN)4]BF4 (0.24 g, 0.76 mmol) and POP (t, JC–P = 5.8 Hz), 148.5, 141.4, 140.4, 134.3, 133.2 (t, JC–P
7.31 (m, 4H), 7.25–7.16 (m, 8H), 7.11 (t, J = 7.5 Hz, 3H), 7.00
=
(0.41 g, 0.76 mmol) in CH2Cl2 (15 mL) was stirred for 1 h at 8.1 Hz), 132.9, 131.0 (t, JC–P = 16.9 Hz), 130.6, 129.3, 125.7, 123.6
room temperature. Then an N^N ligand (L1–L4) (0.76 mmol) (t, JC–P = 14.6 Hz), 121.1, 55.4. 31P NMR (162 MHz, DMSO-d6)
was added and the mixture was stirred for 8 h. After solvent d: ꢁ11.63 (s). HRMS (ESI+, MeOH): calcd for C55H39CuN5O4P2 [M]+
removal, the crude product was purified by crystallization.
958.1768; found 958.1791. IR (KBr, selected bands, cmꢁ1): 3490,
Complex 1 was crystallized from CH2Cl2/pentane to yield the 3255, 3055, 1710, 1607, 1589, 1506, 1480, 1463, 1435, 1340, 1300,
product as yellow crystals (0.66 g, 87%).
1260, 1216, 1127, 1095, 1075, 1028, 998, 974.
1H NMR (400 MHz, DMSO-d6) d: 14.20 (s, 1H), 12.37 (s, 1H),
9.16 (d, J = 7.5 Hz, 2H), 8.87 (d, J = 4.3 Hz, 2H), 8.22 (d, J =
X-Ray crystallography
7.4 Hz, 1H), 7.94 (s, 2H), 7.47–7.42 (td, J = 7.9, 1.8 Hz, 3H), 7.30 The XRD experiments for complex 1 and 3 were performed on a
(t, J = 7.4 Hz, 4H), 7.25–7.18 (m, 10H), 7.14–7.08 (m, 4H), 7.05– SuperNova (Agilent Technologies/Oxford Diffraction) diffracto-
6.96 (m, 8H), 6.68 (m, 2H). 13C NMR (101 MHz, DMSO-d6) meter, equipped with a dual microfocus Cu/Mo X-ray source and
d: 158.4 (t, JCP = 6.1 Hz), 157.6, 152.0, 148.3, 141.2, 134.3, 133.2 Atlas CCD detector, using monochromated Cu Ka (l = 1.54184 Å)
(t, JCP = 8.1 Hz), 132.8, 132.4, 132.0, 131.0 (t, JCP = 16.9 Hz), radiation. The XRD experiment for the 2 single crystal was
118 | New J. Chem., 2020, 44, 110--120
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NJC
14 F. Zhang, Y. Guan, X. Chen, S. Wang, D. Liang, Y. Feng,
S. Chen, S. Li, Z. Li, F. Zhang, C. Lu, G. Cao and B. Zhai,
Inorg. Chem., 2017, 56, 3742–3753.
performed on an Xcalibur (Agilent Technologies/Oxford Diffrac-
tion) diffractometer using monochromated Mo Ka (l = 0.71073 Å)
radiation. The temperature was kept at 100 K for 2 and 3, and
130 K for 1 because of possible crystal destruction at 100 K. The
structures were solved by direct methods by means of the SHELX
program41 incorporated in the OLEX2 program package.42 An
empirical absorption correction was applied in the CrysAlisPro43
software package using spherical harmonics implemented in the
SCALE3 ABSPACK scaling algorithm. Supplementary crystallo-
graphic data for this paper have been deposited at the Cambridge
Crystallographic Data Centre (CCDC numbers 1941884, 1941885,
and 1953636).†
´
15 F. Brunner, A. Babaei, A. Pertegas, J. M. Junquera-
´
Hernandez, A. Prescimone, E. C. Constable, H. J. Bolink,
´
M. Sessolo, E. Ortı and C. E. Housecroft, Dalton Trans., 2019,
48, 446–460.
16 R. Liu, M.-M. Huang, X.-X. Yao, H.-H. Li, F.-L. Yang and
X.-L. Li, Inorg. Chim. Acta, 2015, 434, 172–180.
17 M.-M. Huang, Y.-M. Guo, Y. Shi, L. Zhao, Y.-W. Niu, Y. Shi
and X.-L. Li, Inorg. Chim. Acta, 2017, 457, 107–115.
18 X. Liu, R. Li, L. Ma, X. Feng and Y. Ding, New J. Chem., 2016,
40, 619–625.
19 C. Yi, S. Xu, J. Wang, F. Zhao, H. Xia and Y. Wang, Eur.
J. Inorg. Chem., 2016, 4885–4890.
Conflicts of interest
20 N. M. Gabra, B. Mustafa, Y. P. Kumar, C. Shobha Devi,
M. Shilpa, K. L. Reddy and S. Satyanarayana, Med. Chem.
Res., 2014, 23, 224–235.
There are no conflicts to declare.
21 Z.-B. Cai, L.-F. Liu, Y.-Q. Hong and M. Zhou, J. Coord. Chem.,
2013, 66, 2388–2397.
22 M. Gomleksiz, B. Erdem and C. Alkan, S. Afr. J. Chem., 2013,
66, 107–112.
23 A. Bondi, J. Phys. Chem., 1966, 70, 3006–3007.
24 G. Cavallo, P. Metrangolo, R. Milani, T. Pilati, A. Priimagi,
G. Resnati and G. Terraneo, Chem. Rev., 2016, 116, 2478–2601.
25 Y. Shi, X. Liu, Y. Shan, X. Zhang, W. Kong, Y. Lu, Z. Tan and
X.-L. Li, Dalton Trans., 2019, 48, 2430–2441.
Acknowledgements
This work was supported by RSF (17-73-10078). Physicochemical
studies were performed at the Centre for Magnetic Resonance,
Centre for X-ray Diffraction Studies, Thermogravimetric and Calori-
metric Research Centre, Centre for Optical and Laser Materials
Research, and Centre for Chemical Analysis and Materials Research
(all belong to Saint Petersburg State University).
26 X. Liu, Y. Shan, J. Xu, X. Zhang, S. Shang and X.-L. Li,
Polyhedron, 2019, 164, 152–158.
References
27 L. Shi and B. Li, Eur. J. Inorg. Chem., 2009, 2294–2302.
28 C. Q. Ma, L. Q. Zhang, J. H. Zhou, X. S. Wang, B. W. Zhang,
Y. Cao, P. Bugnon, M. Schaer, F. Nu¨esch, D. Q. Zhang and
Y. Qiu, J. Mater. Chem., 2002, 12, 3481–3486.
29 D. G. Cuttell, S.-M. Kuang, P. E. Fanwick, D. R. McMillin and
R. A. Walton, J. Am. Chem. Soc., 2002, 124, 6–7.
30 S.-X. Xu, J.-L. Wang, F. Zhao, H.-Y. Xia and Y.-B. Wang,
Transition Met. Chem., 2015, 40, 723–732.
1 F. Dumur, Org. Electron., 2015, 21, 27–39.
2 C. Bizzarri, E. Spuling, D. M. Knoll, D. Volz and S. Brase,
Coord. Chem. Rev., 2018, 373, 49–82.
3 R. Hamze, J. L. Peltier, D. Sylvinson, M. Jung, J. Cardenas,
R. Haiges, M. Soleilhavoup, R. Jazzar, P. I. Djurovich,
G. Bertrand and M. E. Thompson, Science, 2019, 363, 601.
4 M. Xie, C. Han, Q. Liang, J. Zhang, G. Xie and H. Xu, Sci.
Adv., 2019, 5, eaav9857.
¨
31 K. N. Solov’ev and E. A. Borisevich, Phys.-Usp., 2005, 48,
231–253.
5 M. W. Mara, K. A. Fransted and L. X. Chen, Coord. Chem.
Rev., 2015, 282–283, 2–18.
32 J. Chen, T. Teng, J.-Y. Wang, L. Kang, X.-L. Chen, L.-J. Xu,
R. Yu and C.-Z. Lu, Eur. J. Inorg. Chem., 2016, 3036–3041.
33 P.-A. Will and S. Reineke, in Handbook of Organic Materials
for Electronic and Photonic Devices, ed. O. Ostroverkhova,
Woodhead Publishing, 2nd edn, 2019, pp. 695–726.
34 Y. R. Cho, S. J. Cha and M. C. Suh, Synth. Met., 2015, 209,
47–54.
´
6 D. Volz, M. Wallesch, C. Flechon, M. Danz, A. Verma,
¨
J. M. Navarro, D. M. Zink, S. Brase and T. Baumann, Green
Chem., 2015, 17, 1988–2011.
7 H. Yersin, A. F. Rausch, R. Czerwieniec, T. Hofbeck and
T. Fischer, Coord. Chem. Rev., 2011, 255, 2622–2652.
8 H. Yersin, R. Czerwieniec, M. Z. Shafikov and A. F. Suleymanova,
ChemPhysChem, 2017, 18, 3508–3535.
´
35 V. Bulovic, A. Shoustikov, M. A. Baldo, E. Bose, V. G. Kozlov,
9 Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao, J. Xu, Z. Chi
and M. P. Aldred, Chem. Soc. Rev., 2017, 46, 915–1016.
10 R. Czerwieniec, M. J. Leitl, H. H. H. Homeier and H. Yersin,
Coord. Chem. Rev., 2016, 325, 2–28.
M. E. Thompson and S. R. Forrest, Chem. Phys. Lett., 1998,
287, 455–460.
36 W. S. Jeon, T. J. Park, S. Y. Kim, R. Pode, J. Jang and
J. H. Kwon, Org. Electron., 2009, 10, 240–246.
¨
11 Y. Zhang, M. Schulz, M. Wachtler, M. Karnahl and
37 C. Wu¨rth, M. Grabolle, J. Pauli, M. Spieles and U. Resch-
Genger, Nat. Protoc., 2013, 8, 1535.
B. Dietzek, Coord. Chem. Rev., 2018, 356, 127–146.
¨
12 C. Bizzarri, F. Hundemer, J. Busch and S. Brase, Polyhedron,
38 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
2018, 140, 51–66.
13 L. Bergmann, G. J. Hedley, T. Baumann, S. Brase and
¨
I. D. W. Samuel, Sci. Adv., 2016, 2, e1500889.
New J. Chem., 2020, 44, 110--120 | 119
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020

View Article Online
NJC
Paper
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. B. Foresman, J. V. Ortiz and D. J. Fox, Gaussian 09,
Revision C.01, Gaussian, Inc., Wallingford, CT, 2009.
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, 39 N. Busschaert, C. Caltagirone, W. Van Rossom and
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, P. A. Gale, Chem. Rev., 2015, 115, 8038–8155.
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, 40 J. R. Hickson, S. J. Horsewill, C. Bamforth, J. McGuire,
V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
C. Wilson, S. Sproules and J. H. Farnaby, Dalton Trans.,
2018, 47, 10692–10701.
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, 41 G. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015, 71,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, 3–8.
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, 42 O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard
R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, and H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339–341.
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, 43 CrysAlisPro, Version 1.171.136.120, Agilent Technologies
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, Ltd, release 127-106-2012.
120 | New J. Chem., 2020, 44, 110--120
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