Formation of Hetero-binuclear Pt(II)-M(II) Complexes Based on (2-(1 H-Tetrazol-5-yl)phenyl)diphenylphosphine Oxide for Superior Phosphorescence of Monomers

Article abstract of DOI:10.1021/acs.inorgchem.8b03326

Novel hetero-binuclear platinum complexes (HBC-Pt(II)-M(II), M = Ca(II), Mg(II), Zn(II), and Cd(II)) have been synthesized by the reaction of the corresponding precursors [Pt(ppy)(μ-Cl)]₂ with (2-(1H-tetrazol-5-yl)phenyl)diphenylphosphine oxide

Full text of DOI:10.1021/acs.inorgchem.8b03326

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Formation of Hetero-binuclear Pt(II)-M(II) Complexes Based on (2-
(1H‑Tetrazol-5-yl)phenyl)diphenylphosphine Oxide for Superior
Phosphorescence of Monomers
Juan Huang,† Zhuo Liu,† Hui Chen,‡ Hailing Zhang,† Han Zhang,† Chunmei Liu,† Qin Gao,†
Chenxia Du,*,† and Bin Zhang*,†
†College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China
‡Institute of Chemistry, Henan Academy of Sciences, Zhengzhou 450002, China
S
* Supporting Information
ABSTRACT: Novel hetero-binuclear platinum complexes
(HBC-Pt(II)-M(II), M = Ca(II), Mg(II), Zn(II), and Cd(II))
have been synthesized by the reaction of the corresponding
precursors [Pt(ppy)(μ-Cl)]2 with (2-(1H-tetrazol-5-yl)-
phenyl)diphenylphosphine oxide (TTPPO). The X-ray
structures of the complexes show that two ancillary ligands
TTPPO in the square-planar Pt(II) moiety act as a
quadridentate chelating agent for the other metal center,
eventually forming a distorted octahedral configuration. There
are no significant π−π interactions and Pt−M metallophilic interactions in the crystal lattice, due to the steric hindrances
associated with the rigid octahedral structure together with the bulky TTPPO. Consequently, HBC-Pt-M complexes show
monomer emission characteristics with quantum yields up to 59% in powder, suggesting their great potential for practical
applications. DFT and TD-DFT calculations on HBC-Pt-Zn reveal that the phosphorescence can be ascribed to intraligand
charge transfer (3ILCT) combined with some metal-to-ligand charge transfer (3MLCT) in the Pt(ppy) moiety, which is
consistent with the observations from the photophysical investigations.
efficient Pt(II) phosphor is becoming one of the most
challenging issues.
INTRODUCTION
■
The platinum can induce strong spin−orbit coupling (SOC)
and promote an effective intersystem crossing (ISC), which
results in a near unity internal electronic-optical conversion
efficiency in electro-photonic devices.1,2 Luminescent cyclo-
metalated platinum(II) complexes are thus a hot research topic
in organic light-emitting diodes (OLEDs) and light-emitting
electrochemical cells (LEECs).3−7 Meanwhile, phosphorescent
Pt(II) complexes also find widespread applications in
bioimaging applications and luminescent chemosensing.8−11
However, the square-planar coordination geometry of d8 Pt(II)
favors structural distortion and intermolecular interactions,
resulting in reduction of color purity, luminescent efficiency
decrease, and poor stability of the emitters in the device.12−17
Recently, studies have uncovered that it is an efficient way to
promote the phosphorescence property of platinum(II)
complexes by introducing steric hindrance into the struc-
ture.18−25 In 2015, Cheng et al. demonstrated a novel type of
Pt(II) dendrimers with bidentate ligands, and realized distinct
optoelectronic properties.26 In 2016, Spokoyny et al. showed a
Pt(II) complex based on 1,10-bis(o-carborane) effectively
shuts down undesired intermolecular interactions in the solid
state.27 In our previous work,28 the Pt(II) complex based on 2-
(diphenylphosphino) benzoic acid also exhibited phosphor-
escence of monomers with a higher quantum yield. In fact,
developing new ligands with steric hindrance for highly
Notably, it is well-known that the octahedral geometry could
also hinder the intermolecular interactions well, such as six-
coordinate Ir(III) complexes.29 Zhu et al. demonstrated that
the heterobimetallic platinum-iridium complex could effec-
tively prevent the aggregation formation in neat film.30 Thus,
the introduction of octahedral metal ions in the Pt(II)
complexes would pave a more simple way for efficient
phosphorescence of monomers. However, to the best of our
knowledge, the reported phosphorescent Pt(II)-M hetero-
metallic complexes until now have been mainly focus on the
d8−d10 metallophilic interaction in the complexes.31−35
Moreover, the additional Pt-M intermetallic usually changes
the structured emission spectrum into a broad one, which is
detrimental to the color purity.36−38
Aiming at exploring new types of phosphorescent platinum
complexes with monomers character, in this context, a series of
heterometallic binuclear Pt(II) complexes (HBC-Pt-M, M =
Mg(II), Ca(II), Zn(II), and Cd(II)) are designed based on 2-
phenylpyridine (ppy) with (2-(1H-tetrazol-5-yl)phenyl)-
diphenylphosphine oxide (TTPPO) as a bridging ligand.
Doerrer has demonstrated that the metal−metal interactions
Received: November 29, 2018
© XXXX American Chemical Society
A
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Scheme 1. Synthetic Pathway for the Synthesis of the Ligand TTPPO
Scheme 2. Synthetic Pathway for the Synthesis of the HBC-Pt-M Complexes
Figure 1. Molecular structure (a) and crystal packing (b) of the HBC-Pt-Zn. The ground-state structure of HBC-Pt-Zn (c). Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.
between Pt(II) and Zn(II), Mg(II), or Ca(II) are very weak,
especially for Ca(II) and Mg(II).39 Thus, the design strategy in
this paper takes advantage of rigid octahedral structures
without significant metal−metal bond affects. Meanwhile,
additional steric hindrance by the bulky TTPPO is also
favorable for hindering the intermolecular interactions. Finally,
the use of environmentally friendly and low-cost Zn(II),
Mg(II), or Ca(II) is advantageous for potential applications.
The solid-state structures of HBC-Pt-M complexes have been
elucidated by X-ray diffraction analysis. The photophysical
properties of the complexes have been systematically
investigated and corroborated by theoretical calculations.
[Pt(ppy)Cl]2 with TTPPO in the presence of corresponded
metal salt together with sodium carbonate as base (Scheme 2).
The molecular structures of all the HBC-Pt-M complexes are
determined by NMR spectroscopy and single crystal X-ray
structure analysis.
Crystal Structure. The crystals of HBC-Pt-M complexes
suitable for X-ray diffraction analysis are obtained by
evaporation of the solvent at room temperature. The
crystallographic details are summarized in Tables S1 and S2.
The selected bond lengths and angles of the complexes are
given in Table S3 in the Supporting Information (SI). As
shown in Figure 1a and Figures S1a, S2a, and S3a in the SI, the
heterometallic binuclear Pt(II)-M(II) complexes show similar
molecular structures containing a slightly deformed square-
planar geometry around the Pt(II) and a distorted octahedral
environment for the other metal center. Notably, the Pt(II)−
M(II) distances are all longer than the sum of atom radii,
ruling out the presence of Pt(II)−M(II) interactions (Table
1). As the different metal ions (M2+) having no significant
impact on the molecular structure, the structure of the HBC-
Pt-Zn complex is briefly described as a representative.
The structure depicted in Figure 1a reveals that the
platinum(II) center adopts a minimally distorted square-planar
coordination geometry with the C1−Pt1−N7trans angle of
RESULTS AND DISCUSSION
■
Synthesis of the Complexes. The synthetic procedures
for (2-(1H-tetrazol-5-yl)phenyl)diphenylphosphine oxide
(TTPPO) is shown in Scheme 1. The triarylphosphine oxide
(TAPO) is directly synthesized from 2-bromobenzonitrile and
Ph2HP(O) by a reported method.40 The TTPPO is then
accomplished by the reaction of TAPO with sodium azide in
the presence of ammonium chloride in DMF. The chemical
structure of TTPPO is confirmed by 1H and 31P NMR
spectroscopy. The HBC-Pt-M complexes are prepared by a
debridging reaction of the chloride-bridged dimer precursor
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indicate that the different ions do not significantly influence
the molecular accumulation. More importantly, the rigid
octahedral structures together with the bulky TTPPO
effectively hinder the intermolecular interactions, which is
one of the most essential features for realizing efficient
phosphorescence of monomers.
DFT calculations in a solution of CH2Cl2 for the HBC-Pt-M
have been carried out to predict the energy minimized
structure. As shown in Figure 1c, Figure S5, Table S4, and
Table S5, calculated bond distances and angles for the
optimized geometry in the ground state are well-correlated
with the crystallographic values, ensuring the accuracy of DFT
optimization studies at the B3LYP level.
Absorption Properties. UV−vis absorption spectra for
these HBC-Pt(II)-M(II) complexes are investigated in CH2Cl2
solution with a concentration of 1.0 × 10−5 mol L−1 at room
temperature. The pertinent data are summarized in Table S6.
It is notable that the spectral patterns of these complexes are
almost identical (Figure 2a), which can be due to the lack of
significant changes in structure among the complexes. Clearly,
this phenomenon also confirms that there is no obvious
metal−metal interactions between the additional M(II) ions
and Pt(II) ion. In particular, strong UV−vis absorption peaks
of the complexes in the solid state are observed at ca. 400 nm
(Figure S6 in the SI), which is in line with the low-lying
absorption band of the complexes in CH2Cl2, demonstrating
the intermolecular interactions of HBC-Pt-M are very weak.
Obviously, strong absorption at λ < 320 nm (ε > 1 × 104 L
mol−1 cm−1) in CH2Cl2 is observed, normally attributed to
intraligand charge transfer (ILCT) transitions. To gain further
insights into the origins of the electronic transitions for the
low-lying absorption band in CH2Cl2, locating in the range of
340−420 nm, time-dependent density functional theory (TD-
DFT) calculation has been carried out at the B3LYP level on
the optimized geometries of HBC-Pt-M.47 Only HBC-Pt-Zn is
considered here, because the influence of the additional M(II)
ions on the low-lying absorption band is identical (Figures 2a
and 3, Tables S7 and S8). The positions of the first 15 singlet−
singlet transitions are obtained and used to generate the
simulated absorption curves (Figure 2b). Clearly, the fit
between calculated and observed lowest energy bands is
acceptable.
Table 1. Intramolecular Pt···M Distances
experimental
distance (Å)
sum of covalent
sum of atomic
a
compound
radii (Å)39,41
radii (Å)42
HBC-Pt-Mg
HBC-Pt-Ca
HBC-Pt-Zn
HBC-Pt-Cd
3.796 (Pt2+−Mg2+)
3.779 (Pt2+−Ca2+)
3.763 (Pt2+−Zn2+)
3.770 (Pt2+−Cd2+)
2.77
3.12
2.58
2.80
3.22
3.71
3.19
3.38
a
http://periodictable.com/Properties/A/VanDerWaalsRadius.v.html.
178.50(18)° and N1−Pt1−N3trans angle of 175.21(16)°. The
bond lengths of the Pt1−C1 (ppy) (2.008(5) Å), Pt1−N1
(ppy) (2.021(4) Å), Pt−N3 (tetrazol) (2.014(4) Å), and Pt−
N7 (tetrazol) (2.104(4) Å) are similar to those of previously
studied mononuclear cyclometalated Pt(II) complexes.43,44
Additionally, there are large dihedral angles (53.053°, 65.326°)
between the tetrazol groups of the ancillary ligands (TTPPO)
and Pt(ppy), taking advantage to prevent the π−π interactions
between adjacent molecules. More importantly, the Zn2+ ion
adopts a typical octahedral coordination environment, which is
furnished by the Pt(ppy)(TTPPO)2 and another TTPPO. In
other words, the Pt(ppy)(TTPPO)2 moiety acts as a
quadridentate chelating agent for Zn(II); the overall structure
of the complex HBC-Pt-Zn can be described as a octahedral
configuration, which is favorable for reducing intermolecular
stacking interactions.
Indeed, the crystal packing of HBC-Pt-Zn (Figure 1b) shows
that the shortest distance between the centers of the aryl rings
is 3.95 Å. Additionally, the dihedral angles of the
corresponding aromatic rings are about 26°. Sander and
Hunter have suggested that the van der Waals interactions are
strongest between the overlapped aromatic rings when the
interplanar separations is more than 3.4 Å.45,46 As a result, the
complex rules out any significant π−π interactions. The
shortest Pt···Pt separation distance amounts to 9.90 Å,
precluding any noticeable Pt···Pt interactions in the crystal
lattice of HBC-Pt-Zn. Projection of the crystal structure of
HBC-Pt-Zn along the (ac) plane shows no apparent layering,
and the intermolecular interactions along the b-axis are also
negligible (Figure S4). As shown in Figure S3, the view along
the b-axis of the HBC-Pt-Cd is identical to that of HBC-Pt-Zn.
Additionally, when viewed along the b-axis, the projections of
the crystal structures of HBC-Pt-Mg and HBC-Pt-Ca are the
same (Figures S1 and S2), which are also similar to that of the
HBC-Pt-Zn. These nearly identical crystal packing modes
The simulated UV−vis absorption results have shown that
the moderately intense absorption band at the 328 nm region
is mainly attributed to the H-2 → L transition. According to
Figure 2. UV/vis absorption spectra of the HBC-Pt-M complexes in CH2Cl2 solution (a). Comparisons between the simulated and experimental
absorption spectra of HBC-Pt-Zn in the low-energy region (b).
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to those of the Pt(ppy) analogues.48−50 Thus, the lumines-
cence from HBC-Pt-M complexes tentatively originates from
Pt(ppy) centered triplet radiative transitions (3(ILCT/
MLCT)). Notably, the HBC-Pt-M complexes show high
emission quantum yields (Φ) of up to 31% (HBC-Pt-Ca). The
phosphorescence lifetimes of complexes in CH2Cl2 at 298 K
require a double exponential fit (Figure S7), dominated by the
short lifetime component τ1 (around 3 μs). This phenomenon
can be due to the presence of weakly coordinating solvent
CH2Cl2, which results in an increasing freedom for the
structural change in the excited state for the most molecules.
Meanwhile, along with the slight decrease in molecular rigidity,
the nonradiative decay rates (knr) of the complexes in CH2Cl2
are more than 24 × 104 s−1, and the emission peak wavelengths
of the complexes in CH2Cl2 are even a little longer than that of
the HBC-Pt-M (except for HBC-Pt-Cd) in powder. The time-
resolved emission spectra of the complexes in CH2Cl2 at 298 K
are measured and presented in Figure S8. The shapes of the
spectra remain unvaried except in their amplitudes, which
corresponded to delay times before or after the two decay
components (τ1 and τ2).
Considering that the similarities of results may be ascribed
to monometallic Pt(II) species left after dissociation of M2+
ions, HBC-Pt-Mg and HBC-Pt-Cd in CH3OH are further
characterized by mass spectrometry (MS). For both com-
plexes, the MS responses of HBC-Pt-M are the most abundant
peaks (Figures S9 and S10), indicating that the reference
complexes are relatively stable in CH3OH. It is well-known
that the coordination ability of CH3OH is higher than that of
CH2Cl2 for the Pt(II) and the relevant M(II) ions;51 the HBC-
Pt-M complexes are obviously more stable in CH2Cl2 and the
properties being thus due to heterometallic binuclear Pt(II)
complexes.
Figure 3. Calculated low-energy transitions for HBC-Pt-Zn (f
(oscillator strengths)) together with the energy levels of the LUMO
(L), HOMO (H), H-1, and H-2 and contribution of Pt and ppy
moieties (the contributions of zinc ion for these frontier molecular
orbits are nearly zero).
the molecular orbital (MO) calculations (Figure 3), the H-2
for the HBC-Pt-Zn is mainly constructed from the platinum
center (34%) and cyclometalated ppy ligand (37%), while the
LUMO for the complex is mainly situated on the ppy (88%).
Thus, this absorption band is tentatively attributed to
combinations of intraligand π−π* transitions (ILCT) and
metal-to-ligand (MLCT) charge transfer. The absorption
bands located at ∼343 nm are probably due to H-1 → L
transition. The platinum(II) gives a substantial contribution to
the H-1 (89%). Therefore, MLCT transition should be
responsible for this absorption. The lowest energy transition
at 371−391 nm mainly corresponds to the H → L excitation.
The HOMO refers to the π orbital localized on the ppy unit
mixed with the dπ(Pt) orbital. Consequently, this low-lying
absorption band can be described by an admixture of ILCT
and MLCT transitions.
On the other hand, if the emission properties of
monometallic Pt species left after decoordination of M2+ ion
are different from those of the HBC-Pt-M complexes, it will
further confirm that the photoluminescent properties of the
HBC-Pt-M in CH2Cl2 ascribe to heterometallic binuclear
Pt(II) complexes. HBC-Pt-Mg is chosen as a representative. In
order to remove Mg2+ cation from HBC-Pt-Mg, a mixture of
HBC-Pt-Mg and EDTA-2Na (1:1, mol/mol) in DMSO-d6/
D2O (5:1, V/V) is treated by an ultrasonic reflux reactor at 50
Photoluminescence Properties. The photoluminescent
(PL) properties of the complexes in dichloromethane solution
at 298 K are obtained with excitation at 391 nm (Figure 4,
Table 2). Notably, the akin spectroscopic profiles, peaking at
482 and ca. 516 nm with a shoulder at ca. 546 nm, are similar
1
°C for 15 min. A H NMR spectrum of the mixture is carried
out at room temperature. As can be seen in Figure S11, the
aromatic region is a set of multiplets within the range 8.10−
6.80 ppm (ca. 59H), as well as resonances for the protons of
EDTA-2Na at 3.12 ppm (8H) and 2.60 ppm (4H). Obviously,
1
the H NMR features of the mixture are clearly different from
those of HBC-Pt-Mg and EDTA-2Na, confirming Mg2+ cation
could be removed from the HBC-Pt-Mg molecular framework
by using the chelating ligand EDTA. The photoluminescent
property of HBC-Pt-Mg in DMSO/H2O (5:1, V/V) in the
presence of different amounts of EDTA-2Na is investigated.
When excited at 345 nm, the shapes of emission spectra of the
solutions hardly changed by addition of EDTA-2Na (Figure
S12), proving that the luminescence probably originates from
the Pt(ppy) moiety. However, in the presence of 1 equiv of
EDTA-2Na, the luminescent intensity is reduced to 77% of
that of the solution without EDTA-2Na. These observations
not only indicate that the adjacent M(II) cation has
considerable influence on the luminescent properties of
HBC-Pt-M in solution but also infer that HBC-Pt-M is stable
in common solvent except for the presence of a chelate ligand
Figure 4. Normalized emission spectra of HBC-Pt-M complexes in
CH2Cl2 solution (λex = 391 nm).
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Table 2. Photophysical Data for the HBC-Pt-M Complexes in CH2Cl2 at 298 K
a
b
c
d
complexes
λmax (nm)
τobs (μs)
Φ (%)
kr (104 s−1
)
knr (104 s−1
)
HBC-Pt-Mg
HBC-Pt-Ca
HBC-Pt-Zn
HBC-Pt-Cd
482, 516, 545 sh
482, 515, 547 sh
482, 516, 546 sh
2.29
2.77
2.65
3.04
22
31
27
25
9.6
11.2
10.2
8.2
34.1
24.9
27.5
24.7
482, 516, 547 sh
a
b
2
2
Average emission lifetimes τobs = (A1τ1 + A2τ2 )/(A1τ1 + A2τ2). The Φ was measured in CH2Cl2 solutions relative to fac-[Ir(ppy)3] (Φ =
40%).52 Radiative decay rate kr = Φ/τ. Nonradiative decay rate knr = (1 − Φ)/τ.
c
d
(EDTA-2Na). Thus, the intense emissions of HBC-Pt-M in
CH2Cl2 could be due to heterometallic binuclear Pt(II)
complexes.
As expected, the emission profiles of the complexes in neat
powder show no obviously red shift, indicating that the
emissions of HBC-Pt-M mainly originate from the monomer
(Figure 5 and Table 3). More importantly, under the condition
HBC-Pt-Cd are close to each due to their identical crystal
packing modes.
Low temperature emission spectra for the HBC-Pt-M
complexes in powder at 77 K are investigated. As shown in
Figure 6 and Table 4, the Pt(II)-M(II) complexes show
Figure 6. Normalized emission spectra of HBC-Pt-M complexes in
powder at 77 K (λex = 400 nm).
Figure 5. Normalized emission spectra of HBC-Pt-M complexes in
powder at 298 K (λex = 400 nm).
Table 4. Photophysical Data for the HBC-Pt-M Complexes
at 77 K (λex = 400 nm)
compounds
λmax (nm)
of without solvent, the radiative and nonradiative decay rates
became slower (less than 4 × 104 s−1), especially for knr.
Consequently, the photoluminescent quantum yields (Φ) of
these complexes are up to 59% in powder, which are even
higher than that of Ir(ppy)3.29,53 These unique properties
confirm that the intermolecular interactions of the HBC-Pt-M
complexes in the concentrated phases are effectively hindered,
which is coincident well with the crystal-packing characteristics
of the complex discussed above. Additionally, the short decay
lifetimes of the complexes (Table 3 and Figure S13) in powder
(<19 μs) suggest the heterometallic platinum complexes
promote an effective intersystem crossing (ISC). Notably,
although the emission properties of HBC-Pt-M mainly
originate from the monomer in the solid state, the emission
shapes are slightly affected by aggregation. As the projection of
the crystal structures of HBC-Pt-Mg and HBC-Pt-Ca along the
(ac) plane are identical, the spectroscopic profiles are very
similar. Meanwhile, the spectral shapes of the HBC-Pt-Zn and
HBC-Pt-Mg
HBC-Pt-Ca
HBC-Pt-Zn
HBC-Pt-Cd
491, 520 sh, 528, 561
472, 481, 490, 496, 508, 525, 536
471, 490, 518 sh, 528, 560 sh
472, 483, 495, 518, 535 sh, 551
remarkably well-resolved vibrational satellite peaks without
distinctly rigidochromic shift than that at 298 K. These unique
PL properties further confirmed that the emissions mainly arise
from the ligand-centered triplet state.54−56 Interesting, the
emission spectra of HBC-Pt-Mg and HBC-Pt-Zn are very
similar. Che et al. have found that the solid-state emission of
some Pt(II) complexes in low temperature could be provi-
sionally taken as monomeric emission,57 implying that the
intermolecular interactions are reduced at 77 K. Meanwhile,
the bond lengths of the Pt1−C1 (ppy) and Pt1−N1 (ppy) as
well as the C1−Pt1−N1 angle for HBC-Pt-Mg are more
similar to those for HBC-Pt-Zn (Table S3). Thus, the
Table 3. Photophysical Data for the HBC-Pt-M Complexes in Powder at 298 K (λex = 400 nm)
a
b
c
complexes
λmax (nm)
τobs (μs)
Φ (%)
kr (104 s−1
)
knr (104 s−1
)
HBC-Pt-Mg
HBC-Pt-Ca
HBC-Pt-Zn
HBC-Pt-Cd
477, 501, 512, 531 sh
477, 501, 512, 531 sh
479 sh, 494, 513
18.73
18.14
16.45
18.13
59
43
55
42
3.2
2.4
3.3
2.3
2.2
3.1
2.7
3.2
489, 516, 550 sh
a
b
c
The Φ of the powder was measured using an integrating sphere. Radiative decay rate kr = Φ/τ. Nonradiative decay rate knr = (1 − Φ)/τ.
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luminescences from HBC-Pt-Zn and HBC-Pt-Mg complexes,
tentatively originating from Pt(ppy), are nearly identical with
each other.
chemical calculations indicate the phosphorescence is pre-
dominantly a 3ILCT (ppy) transition, with mixing of a 3MLCT
[dπ(Pt) → π*(ppy)] character. Remarkably, this design
strategy allows the platinum complexes to show monomer
emission characteristics with quantum yields up to 59% in
powder. The present work affords a feasible approach to settle
some defects of the luminescent cyclometalated platinum(II)
complexes, including the low emission quantum yield and poor
color purity in high concentration.
Since the HBC-Pt-M complexes show similar PL properties,
the influence of the additional M(II) ions on the photophysical
properties is semblable. In order to elucidate the PL behaviors
of the studied complexes, the triplet state structure of HBC-Pt-
Zn in CH2Cl2 solution is selected to be optimized. Although
the singlet ground state and the lowest triplet states are
geometrically similar to each other (Figure 1c, Figure S14,
Tables S5 and S10), a little reduction of the Pt−ppy bond
length can be observed, indicating the MLCT transition
process induces the phosphorescence emission. The S0 → T1
wavelength (589 nm) for HBC-Pt-Zn, determined by using the
time-dependent density functional theory (TD-DFT), is a little
longer than the corresponding experimental emission wave-
length, which have been widely observed for the simulation of
phosphorescence.58,59 Additionally, the lowest triplet states T1
of HBC-Pt-Zn mainly arise from the HOMO → LUMO
transition (89%). As shown in Figure 7, the analysis of the
EXPERIMENTAL SECTION
■
Materials and Methods. All commercial chemicals of analytical
grade were used without further purification, unless otherwise stated.
All air and moisture sensitive reactions were carried out under an
argon atmosphere. 2-Diphenylphosphoryl-benzonitrile (TAPO) was
prepared according to the reported procedures.40 The platinum(II)
chlorobridged dimer [Pt(ppy)Cl]2 was also synthesized following
literature methods.60 The HBC-Pt-M complexes were grinded into
powder and dried at 329 K under vacuum for measurements (except
for single crystal X-ray diffraction analysis). 1H and 31P NMR spectra
of the compounds were recorded on a Bruker DPX-400 MHz
spectrometer at room temperature. C, H, and N analyses were carried
out by employing a Carlo-Erba1106 Elemental Analyzer. Mass spectra
of HBC-Pt-Mg and HBC-Pt-Cd in CH3OH were recorded with a Q-
TOF Micro MS spectrometer. UV−vis absorption spectra of the
complexes were carried out on a Cary 5000 UV−vis−NIR
spectrophotometer. Steady-state Phosphorescence spectra, lumines-
cence lifetime, time-resolved emission spectra, and photolumines-
cence quantum yields were obtained by an Edinburgh Instruments
Ltd. (FLS980). Additionally, the Φ of the complexes in solution was
calculated by a comparison of the emission intensities (integrated
areas) of a standard sample (Ir(ppy)3, Φ = 40%).52 The Φ of the
complexes in powder was obtained through an absolute method by
employing an integrating sphere.
Synthesis of 5-[2-(Diphenylphosphoryl)phenyl]-1H-tetra-
zole (TTPPO). A mixture of the TAPO (1.82g, 6 mmol), sodium
azide (0.78 g, 12 mmol), and ammonium chloride (0.64 g, 12 mmol)
were added in a flame-dried, argon flushed three-neck flask.
Anhydrous DMF (20 mL) was injected through a syringe, and the
reaction contents were stirred at 130 °C until TLC (thin-layer
chromatography) showed complete consumption of TAPO (ca. 5 h).
After cooling to room temperature, the solvent was poured into water.
A solution of HCl (2 mol L−1) was added to adjust the pH = 3, and
then the whole was extracted with CH2Cl2. The combined organic
extract was dried with anhydrous sodium sulfate and concentrated in
vacuo. The residue was purified by column chromatography on silica
gel (eluent: EtOAc/CH2Cl2) to give 1.25 g of TTPPO as a white
powder in 60% yield. 1H NMR (400 MHz, CDCl3) δ 8.63−8.59 (m,
1H), 7.78 (tt, J = 7.8, 1.5 Hz, 1H), 7.62−7.52 (m, 6H), 7.52−7.44
(m, 5H), 7.21−7.15 (m, 1H). 31P NMR (162 MHz, CDCl3) δ 38.79.
Elemental analysis calcd (%) for C19H15N4OP: C 65.89, H 4.37, N
16.18. Found: C 65.81, H 4.39, N 16.16.
Figure 7. Calculated S0 → T1 transition for HBC-Pt-Zn in the triplet
state and contribution of Pt, Zn, and ppy moieties.
frontier molecular orbitals reveals that the Zn(II) ion makes
negligible contribution to the HOMO and LUMO (∼0%).
The HOMO orbital is mainly located on the Pt(II) center and
ppy skeleton (32% and 65%, respectively), while the ppy
moiety makes the predominate contribution to the LUMO
(88%). Consequently, the 3ILCT-dominated transition togeth-
er with some 3MLCT features should account for the emission,
which agrees well with its PL properties.
General Syntheses of Complexes (HBC-Pt-M). The complexes
were synthesized according to similar procedures. A slurry of the
crude chloro-bridged Pt(II) dimer (0.39 g, 0.5 mmol), TTPPO (0.70
g, 2 mmol), and 10 equiv of Na2CO3 (1.10 g, 10 mmol) in the
presence of corresponding metal salt (MgCl2 (0.11 g, 1.1 mmol),
CaCl2 (0.12 g, 1.1 mmol), ZnCl2 (0.15 g, 1.1 mmol), and CdCl2 (0.20
g, 1.1 mmol)) was stirred in 2-ethoxyethanol (15 mL) under an argon
atmosphere at 110 °C for 20 h. After the mixture was cooled to RT,
the reaction mixture was concentrated under reduced pressure. An
excess of water was added gradually to give a precipitate of crude
product. The precipitate was filtered and purified by silica gel column
chromatography using a mixture of CH3OH/CH2Cl2 as eluent to give
the HBC-Pt-M complexes. Yellow-green crystals were grown from the
slow evaporation of a saturated 2-ethoxyethanol solution.
CONCLUSION
■
A series of hetero-binuclear platinum complexes (HBC-Pt-M)
are successfully prepared. The rigid octahedral structures
together with the bulky TTPPO ligand effectively rule out any
significant π−π interactions and metallophilic interactions in
the crystal lattice. Indeed, comparing with the emission spectra
of the complexes in CH2Cl2 solutions, the emission spectra in
powder showed no obvious red shift. The distinct vibronic fine
structure of the luminescence suggests that the photoemission
of these complexes is dominated by cyclometalating ligand
(ppy) centered 3ILCT transition. This delineation is
coincident with the negligibly rigidochromic shift of the low
temperature emission spectra. Furthermore, the quantum
1
HBC-Pt-Mg. Yield 35%. H NMR (400 MHz, DMSO-d6) δ 8.36−
8.15 (m, 2H), 8.11−7.93 (m, 4H), 7.93−7.50 (m, 16H), 7.49−7.24
(m, 12H), 7.24−7.00 (m, 7H), 6.99−6.85 (m, 2H), 6.83−6.67 (m,
F
DOI: 10.1021/acs.inorgchem.8b03326
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
4H), 6.58−6.43 (m, 1H), 6.12−5.94 (m, 2H). 31P NMR (162 MHz,
DMSO-d6) δ 33.88, 33.67, 31.83. Anal. Calcd (%) for C68H50N13O3-
P3PtMg: C 57.94, H 3.58, N 12.92. Found: C 57.85, H 3.55, N 12.90.
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
HBC-Pt-Ca. Yield 30%. H NMR (400 MHz, DMSO-d6) δ 8.34−
AUTHOR INFORMATION
Corresponding Authors
*E-mail: dcx@zzu.edu.cn (C.D.).
*E-mail: bz@zzu.edu.cn (B.Z.).
■
8.17 (m, 2H), 8.10−7.94 (m, 4H), 7.93−7.47 (m, 17H), 7.47−7.24
(m, 11H), 7.24−7.06 (m, 6H), 7.04−6.84 (m, 3H), 6.83−6.67 (m,
4H), 6.58−6.43 (m, 1H), 6.12−5.93 (m, 2H). 31P NMR (162 MHz,
DMSO-d6) δ 33.87, 33.67, 31.83. Anal. Calcd (%) for C68H50N13O3-
P3PtCa: C 57.30, H 3.54, N 12.78. Found: C 57.35, H 3.52, N 12.71.
ORCID
1
HBC-Pt-Zn. Yield 45%. H NMR (400 MHz, DMSO-d6) δ 8.34−
Bin Zhang: 0000-0001-8600-0850
Notes
The authors declare no competing financial interest.
8.16 (m, 2H), 8.12−7.93 (m, 4H), 7.93−7.50 (m, 15H), 7.50−7.24
(m, 13H), 7.23−7.07 (m, 6H), 7.06−6.85 (m, 3H), 6.85−6.65 (m,
4H), 6.57−6.42 (m, 1H), 6.14−5.93 (m, 2H). 31P NMR (162 MHz,
DMSO-d6) δ 38.62, 38.42, 36.57. Anal. Calcd (%) for C68H50N13O3-
P3PtZn: C 56.30, H 3.47, N 12.55. Found: C 56.40, H 3.45, N 12.61.
ACKNOWLEDGMENTS
1
■
HBC-Pt-Cd. Yield 49%. H NMR (400 MHz, DMSO-d6) δ 8.36−
8.21 (m, 1H), 8.20−7.99 (m, 4H), 7.99−7.48 (m, 19H), 7.48−7.20
(m, 12H), 7.19−7.07 (m, 4H), 7.07−6.99 (m, 3H), 6.98−6.80 (m,
5H), 6.38−6.27 (m, 1H), 6.15−6.03 (m, 1H). 31P NMR (162 MHz,
DMSO-d6) δ 34.74, 33.68, 30.59. Anal. Calcd (%) for C68H50N13O3-
P3PtCd: C 54.54, H 3.37, N 12.16. Found: C 54.45, H 3.35, N 12.14.
X-ray Crystallography. X-ray data for complexes HBC-Pt-M
were collected by an Oxford Diffraction Xcalibur CCD diffractometer
(Mo-Kα radiation (λ = 0.71073 Å) for HBC-Pt-Ca, HBC-Pt-Zn and
HBC-Pt-Cd, Cu-Kα radiation (λ = 1.54184 Å) for HBC-Pt-Mg). The
diffraction frames were integrated and corrected from absorption by
the program suite CrysAlisPro.61 Using Olex2,62 the crystal structures
of the HBC-Pt-M complexes were solved by direct methods using
SHELXS63 and refined anisotropically by full-matrix least-squares
method on F2 with SHELXL.64 All hydrogen atoms were included in
calculated positions and refined in a riding model along with attached
atoms. CCDC 1879296 for HBC-Pt-Mg, 1879294 for HBC-Pt-Ca,
1879297 for HBC-Pt-Zn, and 1879295 for HBC-Pt-Cd contain the
supplementary crystallographic data for this paper, which can be
obtained free of charge from The Cambridge Crystallographic Data
Centre.
This work was supported by the National Natural Science
Foundation of China (NSFC) (Nos. 21601156, 21502045,
21371154).
REFERENCES
■
(1) Penfold, T. J.; Gindensperger, E.; Daniel, C.; Marian, C. M. Spin-
Vibronic Mechanism for Intersystem Crossing. Chem. Rev. 2018, 118,
6975−7025.
(2) Im, Y.; Byun, S. Y.; Kim, J. H.; Lee, D. R.; Oh, C. S.; Yook, K. S.;
Lee, J. Y. Recent Progress in High-Efficiency Blue-Light-Emitting
Materials for Organic Light-Emitting Diodes. Adv. Funct. Mater. 2017,
27, 1603007.
(3) Zhu, Z.-Q.; Klimes, K.; Holloway, S.; Li, J. Efficient
Cyclometalated Platinum(II) Complex with Superior Operational
Stability. Adv. Mater. 2017, 29, 1605002.
(4) Strassner, T. Phosphorescent Platinum(II) Complexes with
C∧C* Cyclometalated NHC Ligands. Acc. Chem. Res. 2016, 49,
2680−2689.
(5) O’Brien, C.; Wong, M. Y.; Cordes, D. B.; Slawin, A. M. Z.;
Zysman-Colman, E. Cationic Platinum(II) Complexes Bearing Aryl-
BIAN Ligands: Synthesis and Structural and Optoelectronic
Characterization. Organometallics 2015, 34, 13−22.
(6) Huo, S.; Carroll, J.; Vezzu, D. A. K. Design, Synthesis, and
Applications of Highly Phosphorescent Cyclometalated Platinum
Complexes. Asian J. Org. Chem. 2015, 4, 1210−1245.
(7) Ogawa, T.; Sameera, W. M. C.; Saito, D.; Yoshida, M.;
Kobayashi, A.; Kato, M. Phosphorescence Properties of Discrete
Platinum(II) Complex Anions Bearing N-Heterocyclic Carbenes in
the Solid State. Inorg. Chem. 2018, 57, 14086−14096.
(8) Li, K.; Ming Tong, G. S.; Wan, Q.; Cheng, G.; Tong, W.-Y.; Ang,
W.-H.; Kwong, W.-L.; Che, C.-M. Highly Phosphorescent Platinum-
(II) Emitters: Photophysics, Materials and Biological Applications.
Chem. Sci. 2016, 7, 1653−1673.
(9) Dorazco-Gonzalez, A. Chemosensing of Chloride Based on a
Luminescent Platinum(II) NCN Pincer Complex in Aqueous Media.
Organometallics 2014, 33, 868−875.
(10) Ma, D.-L.; He, H.-Z.; Leung, K.-H.; Chan, D. S.-H.; Leung, C.-
H. Bioactive Luminescent Transition-Metal Complexes for Bio-
medical Applications. Angew. Chem., Int. Ed. 2013, 52, 7666−7682.
(11) Yang, X.; Huang, Z.; Dang, J.; Ho, C.-L.; Zhou, G.; Wong, W.-
Y. Effective Phosphorescence Quenching in Borylated PtII ppy-type
Phosphors and Their Application as I− Ion Sensors in Aqueous
Medium. Chem. Commun. 2013, 49, 4406−4408.
(12) Lam, W. H.; Lam, E. S.-H.; Yam, V. W.-W. Computational
Studies on the Excited States of Luminescent Platinum(II) Alkynyl
Systems of Tridentate Pincer Ligands in Radiative and Nonradiative
Processes. J. Am. Chem. Soc. 2013, 135, 15135−15143.
Computational Methodology. All the calculations are imple-
mented by the Gaussian 09 program package.65 The initial
coordinates of models were derived from the crystal structure of
HBC-Pt-Zn. The geometries in ground state and triplet state were
optimized via using restricted and unrestricted density functional
theory DFT (RDFT and UDFT) with the B3LYP hybrid exchange-
correlation functional, respectively.66,67 The absorption and phos-
phorescence properties of the investigated complex were explored by
using the time-dependent density functional theory (TD-DFT).68−70
Since the spectroscopic properties of HBC-Pt-Zn were obtained in
CH2Cl2 solution, all the calculations were performed in CH2Cl2
solvent with the polarized continuum model (PCM).71,72 Throughout
the calculation, the “double-ζ” quality basis set (LANL2DZ) was
employed for heavy metal atoms (Pt, Zn, and Cd) and the 6-
31G(d,p) basis set was applied to the light atoms (C, H, N, O, P, Mg,
and Ca).73−75 Visualization of the optimized structures and frontier
molecular orbitals was performed by GaussView. The Multiwfn 3.3.7
was used for analyzing the simulated absorption spectrum.76
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03326.
Additional experimental data, including tables and
figures (PDF)
(13) Hudson, Z. M.; Sun, C.; Helander, M. G.; Chang, Y.-L.; Lu, Z.-
H.; Wang, S. Highly Efficient Blue Phosphorescence from
Triarylboron-Functionalized Platinum(II) Complexes of N-Hetero-
cyclic Carbenes. J. Am. Chem. Soc. 2012, 134, 13930−13933.
(14) Shafikov, M. Z.; Suleymanova, A. F.; Kozhevnikov, D. N.;
Accession Codes
CCDC 1879294−1879297 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
̈
Konig, B. Tuning the Excimer Emission of Amphiphilic Platinum(II)
G
DOI: 10.1021/acs.inorgchem.8b03326
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Complexes Mediated by Phospholipid Vesicles. Inorg. Chem. 2017,
56, 4885−4897.
of a heterobimetallic Pt(II)-Ir(III) complex used as a single-
component emitter in white PLEDs. Dalton Trans. 2012, 41, 2972−
2978.
(31) Arnal, L.; Fuertes, S.; Martin, A.; Sicilia, V. The Use of
Cyclometalated NHCs and Pyrazoles for the Development of Fully
Efficient Blue PtII Emitters and Pt/Ag Clusters. Chem. - Eur. J. 2018,
24, 9377−9384.
(32) Zhang, L.-Y.; Xu, L.-J.; Wang, J.-Y.; Zeng, X.-C.; Chen, Z.-N.
Photoluminescence and electroluminescence of cationic PtAu2
heterotrinuclear complexes with aromatic acetylides. Dalton Trans.
2017, 46, 865−874.
(15) Cho, Y.-J.; Kim, S.-Y.; Son, H.-J.; Cho, D. W.; Kang, S. O. Steric
Effect on Excimer Formation in Planar Pt(II) Complexes. Phys. Chem.
Chem. Phys. 2017, 19, 5486−5494.
(16) Xiong, W.; Meng, F.; Tan, H.; Wang, Y.; Wang, P.; Zhang, Y.;
Tao, Q.; Su, S.; Zhu, W. Dinuclear platinum complexes containing
aryl-isoquinoline and oxadiazole-thiol with an efficiency of over 8.8%:
in-depth investigation of the relationship between their molecular
structure and near-infrared electroluminescent properties in PLEDs. J.
Mater. Chem. C 2016, 4, 6007−6015.
(17) Rausch, A. F.; Monkowius, U. V.; Zabel, M.; Yersin, H. Bright
Sky-Blue Phosphorescence of [n-Bu4N][Pt(4,6-dFppy)(CN)2]: Syn-
thesis, Crystal Structure, and Detailed Photophysical Studies. Inorg.
Chem. 2010, 49, 7818−7825.
(33) Li, Y.-P.; Fan, X.-X.; Wu, Y.; Zeng, X.-C.; Wang, J.-Y.; Wei, Q.-
H.; Chen, Z.-N. High-efficiency organic light-emitting diodes of
phosphorescent PtAg2 heterotrinuclear acetylide complexes supported
by triphosphine. J. Mater. Chem. C 2017, 5, 3072−3078.
(34) Zeng, X.-C.; Wang, J.-Y.; Xu, L.-J.; Wen, H.-M.; Chen, Z.-N.
Solution-processed OLEDs based on phosphorescent PtAu2 com-
plexes with phenothiazine-functionalized acetylides. J. Mater. Chem. C
2016, 4, 6096−6103.
(35) Zhang, L.-Y.; Xu, L.-J.; Zhang, X.; Wang, J.-Y.; Li, J.; Chen, Z.-
N. Spectroscopic and Phosphorescent Modulation in Triphosphine-
Supported PtAg2 Heterotrinuclear Alkynyl Complexes. Inorg. Chem.
2013, 52, 5167−5175.
(36) Horiuchi, S.; Moon, S.; Sakuda, E.; Ito, A.; Arikawa, Y.;
Umakoshi, K. U- to Z-shape isomerization in a Pt2Ag2 framework
containing pyridyl-NHC ligands. Dalton Trans. 2018, 47, 7113−7117.
(37) Fuertes, S.; Woodall, C. H.; Raithby, P. R.; Sicilia, V.
Heteropolynuclear Pt(II)−M(I) Clusters with a C∧N∧C Biscyclome-
talated Ligand. Organometallics 2012, 31, 4228−4240.
(18) Leopold, H.; Heinemeyer, U.; Wagenblast, G.; Munster, I.;
̈
Strassner, T. Changing the Emission Properties of Phosphorescent
C∧C*-Cyclometalated Thiazol-2-ylidene Platinum(II) Complexes by
Variation of the β-Diketonate Ligands. Chem. - Eur. J. 2017, 23,
1118−1128.
(19) Kong, F. K.-W.; Tang, M.-C.; Wong, Y.-C.; Chan, M.-Y.; Yam,
V. W.-W. Design Strategy for High-Performance Dendritic Carbazole-
Containing Alkynylplatinum(II) Complexes and Their Application in
Solution-Processable Organic Light-Emitting Devices. J. Am. Chem.
Soc. 2016, 138, 6281−6291.
(20) Wang, B.; Liang, F.; Hu, H.; Liu, Y.; Kang, Z.; Liao, L.-S.; Fan,
J. Strongly phosphorescent platinum(II) complexes supported by
tetradentate benzazole-containing ligands. J. Mater. Chem. C 2015, 3,
8212−8218.
(21) Ko, S.-B.; Park, H.-J.; Gong, S.; Wang, X.; Lu, Z.-H.; Wang, S.
Blue phosphorescent N-heterocyclic carbene chelated Pt(II) com-
plexes with an α-duryl-β-diketonato ancillary ligand. Dalton Trans.
2015, 44, 8433−8443.
(22) Li, H.; Li, J.; Ding, J.; Yuan, W.; Zhang, Z.; Zou, L.; Wang, X.;
Zhan, H.; Xie, Z.; Cheng, Y.; Wang, L. Design, Synthesis, and
Optoelectronic Properties of Dendrimeric Pt(II) Complexes and
Their Ability to Inhibit Intermolecular Interaction. Inorg. Chem. 2014,
53, 810−821.
(23) Ohba, T.; Kobayashi, A.; Chang, H.-C.; Kouyama, T.; Kato, T.;
Kato, M. Hysteretic vapour response of a heterodinuclear platinum-
(ii)−copper(ii) complex derived from the dimer-of-dimer motif and
the guest-absorbing site. Dalton Trans. 2014, 43, 7514−7521.
(38) Fornies, J.; Fuertes, S.; Martin, A.; Sicilia, V.; Gil, B.; Lalinde, E.
Extended structures containing Pt(II)-Tl(I) bonds. Effect of these
interactions on the luminescence of cyclometalated Pt(II) com-
pounds. Dalton Trans. 2009, 2224−2234.
(39) Baddour, F. G.; Hyre, A. S.; Guillet, J. L.; Pascual, D.; Lopez-
de-Luzuriaga, J. M.; Alam, T. M.; Bacon, J. W.; Doerrer, L. H. Pt−Mg,
Pt−Ca, and Pt−Zn Lantern Complexes and Metal-Only Donor−
Acceptor Interactions. Inorg. Chem. 2017, 56, 452−469.
(40) Zhao, Y.-L.; Wu, G.-J.; Li, Y.; Gao, L.-X.; Han, F.-S.
[NiCl2(dppp)]-Catalyzed Cross-Coupling of Aryl Halides with
Dialkyl Phosphite, Diphenylphosphine Oxide, and Diphenylphos-
phine. Chem. - Eur. J. 2012, 18, 9622−9627.
́
́
(41) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.;
́
́
́
(24) Berenguer, J. R.; Fernandez, J.; Gil, B.; Lalinde, E.; Sanchez, S.
Reversible Binding of Solvent to Naked PbII Centers in Unusual
Homoleptic Alkynyl-Based Pt2Pb2 Clusters. Chem. - Eur. J. 2014, 20,
2574−2584.
Echeverría, J.; Cremades, E.; Barragan, F.; Alvarez, S. Covalent radii
revisited. Dalton Trans. 2008, 2832−2838.
(42) Bondi, A. van der Waals Volumes and Radii. J. Phys. Chem.
1964, 68, 441−451.
́
́
(25) Fornies, J.; Fuertes, S.; Lopez, J. A.; Martín, A.; Sicilia, V. New
Water Soluble and Luminescent Platinum(II) Compounds, Vapo-
chromic Behavior of [K(H2O)][Pt(bzq)(CN)2], New Examples of
the Influence of the Counterion on the Photophysical Properties of d8
Square-Planar Complexes. Inorg. Chem. 2008, 47, 7166−7176.
(26) Li, H.; Yuan, W.; Wang, X.; Zhan, H.; Xie, Z.; Cheng, Y.
Enhancement of luminescence performance from the alteration of
stacking patterns of Pt(II) dendrimers. J. Mater. Chem. C 2015, 3,
2744−2750.
(43) Chen, J.-L.; Tan, X.-Z.; Chen, X.-X.; Wang, J.-Y.; Cao, X.-F.;
He, L.-H.; Hua, J.-Y.; Wen, H.-R. Luminescent mononuclear Pt(II)
chloride complexes with C-linked 2,2′-bipyridyl tetrazole terdentate
chelating ligands. Inorg. Chem. Commun. 2013, 30, 120−123.
(44) Santoro, A.; Whitwood, A. C.; Williams, J. A. G.; Kozhevnikov,
V. N.; Bruce, D. W. Synthesis, Mesomorphism, and Luminescent
Properties of Calamitic 2-Phenylpyridines and Their Complexes with
Platinum(II). Chem. Mater. 2009, 21, 3871−3882.
(45) Clegg, W.; Elsegood, M. R. J.; Errington, R. J.; Fisher, G. A.;
Norman, N. C. Structure of BiBr2Ph: a solid-state architecture
involving secondary bonding and π-π interactions. J. Mater. Chem.
1994, 4, 891−893.
(46) Hunter, C. A.; Sanders, J. K. M. The nature of π−π interactions.
J. Am. Chem. Soc. 1990, 112, 5525−5534.
(47) Zhang, F.; Xu, Y.; Zhang, W.; Shen, W.; Li, M.; He, R.
Theoretical Studies of Photodeactivation Pathways of NHC−Chelate
Pt(II) Compounds with Different Numbers of Triarylboron Units:
Radiative and Nonradiative Decay Processes. J. Phys. Chem. A 2017,
121, 690−698.
(48) Rajendra Kumar, G.; Thilagar, P. Tuning the Phosphorescence
and Solid State Luminescence of Triarylborane-Functionalized
Acetylacetonato Platinum Complexes. Inorg. Chem. 2016, 55,
12220−12229.
(27) Kirlikovali, K. O.; Axtell, J. C.; Gonzalez, A.; Phung, A. C.;
Khan, S. I.; Spokoyny, A. M. Luminescent metal complexes featuring
photophysically innocent boron cluster ligands. Chem. Sci. 2016, 7,
5132−5138.
(28) Zhang, B.; Zhang, L.; Liu, C.; Zhu, Y.; Tang, M.; Du, C.; Song,
M.
A
platinum(II) complex bearing deprotonated 2-
(diphenylphosphino)benzoic acid for superior phosphorescence of
monomers. Dalton Trans. 2014, 43, 7704−7707.
(29) Takayasu, S.; Suzuki, T.; Shinozaki, K. Intermolecular
Interactions and Aggregation of fac-Tris(2-phenylpyridinato-C2,N)-
iridium(III) in Nonpolar Solvents. J. Phys. Chem. B 2013, 117, 9449−
9456.
(30) Li, X.; Liu, Y.; Luo, J.; Zhang, Z.; Shi, D.; Chen, Q.; Wang, Y.;
He, J.; Li, J.; Lei, G.; Zhu, W. Synthesis and optoelectronic properties
H
DOI: 10.1021/acs.inorgchem.8b03326
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(49) Bossi, A.; Rausch, A. F.; Leitl, M. J.; Czerwieniec, R.; Whited,
M. T.; Djurovich, P. I.; Yersin, H.; Thompson, M. E. Photophysical
Properties of Cyclometalated Pt(II) Complexes: Counterintuitive
Blue Shift in Emission with an Expanded Ligand π System. Inorg.
Chem. 2013, 52, 12403−12415.
(50) Begantsova, Y. E.; Bochkarev, L. N.; Ketkov, S. Y.; Baranov, E.
V.; Bochkarev, M. N.; Yakhvarov, D. G. Synthesis, characterization
and photophysical properties of new cyclometallated platinum(II)
complexes with pyrazolonate ancillary ligand. J. Organomet. Chem.
2013, 733, 1−8.
(51) Lincoln, S.; Pisaniello, D.; Spotswood, T.; Tkaczuk, M. A
phosphorus-31 nuclear magnetic resonance study of triphenylphos-
phine oxide exchange on magnesium(II) and zinc(II). Aust. J. Chem.
1981, 34, 283−289.
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.;
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. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Revision C.01; Gaussian, Inc.:
Wallingford, CT, 2011.
(66) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-
Salvetti correlation-energy formula into a functional of the electron
density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(67) Becke, A. D. Density-functional thermochemistry. III. The role
of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652.
(68) Bauernschmitt, R.; Ahlrichs, R. Treatment of electronic
excitations within the adiabatic approximation of time dependent
density functional theory. Chem. Phys. Lett. 1996, 256, 454−464.
(69) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R.
Molecular excitation energies to high-lying bound states from time-
dependent density-functional response theory: Characterization and
correction of the time-dependent local density approximation
ionization threshold. J. Chem. Phys. 1998, 108, 4439−4449.
(70) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. An efficient
implementation of time-dependent density-functional theory for the
calculation of excitation energies of large molecules. J. Chem. Phys.
1998, 109, 8218−8224.
(71) Barone, V.; Cossi, M.; Tomasi, J. A new definition of cavities
for the computation of solvation free energies by the polarizable
continuum model. J. Chem. Phys. 1997, 107, 3210−3221.
(72) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. New
developments in the polarizable continuum model for quantum
mechanical and classical calculations on molecules in solution. J.
Chem. Phys. 2002, 117, 43−54.
(73) Chiodo, S.; Russo, N.; Sicilia, E. LANL2DZ basis sets
recontracted in the framework of density functional theory. J. Chem.
Phys. 2006, 125, 104107.
(74) Del Bene, J. E.; Person, W. B.; Szczepaniak, K. Properties of
Hydrogen-Bonded Complexes Obtained from the B3LYP Functional
with 6-31G(d,p) and 6-31+G(d,p) Basis Sets: Comparison with
MP2/6-31+G(d,p) Results and Experimental Data. J. Phys. Chem.
1995, 99, 10705−10707.
(75) Hay, P. J.; Wadt, W. R. Ab initio effective core potentials for
molecular calculations. Potentials for the transition metal atoms Sc to
Hg. J. Chem. Phys. 1985, 82, 270−283.
(76) Lu, T.; Chen, F. Multiwfn: A multifunctional wavefunction
analyzer. J. Comput. Chem. 2012, 33, 580−592.
(52) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.;
Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. Synthesis and
Characterization of Facial and Meridional Tris-cyclometalated
Iridium(III) Complexes. J. Am. Chem. Soc. 2003, 125, 7377−7387.
(53) Kawamura, Y.; Goushi, K.; Brooks, J.; Brown, J. J.; Sasabe, H.;
Adachi, C. 100% phosphorescence quantum efficiency of Ir(III)
complexes in organic semiconductor films. Appl. Phys. Lett. 2005, 86,
071104−3.
(54) Axtell, J. C.; Kirlikovali, K. O.; Djurovich, P. I.; Jung, D.;
Nguyen, V. T.; Munekiyo, B.; Royappa, A. T.; Rheingold, A. L.;
Spokoyny, A. M. Blue Phosphorescent Zwitterionic Iridium(III)
Complexes Featuring Weakly Coordinating nido-Carborane-Based
Ligands. J. Am. Chem. Soc. 2016, 138, 15758−15765.
(55) Lai, P.-N.; Brysacz, C. H.; Alam, M. K.; Ayoub, N. A.; Gray, T.
G.; Bao, J.; Teets, T. S. Highly Efficient Red-Emitting Bis-
Cyclometalated Iridium Complexes. J. Am. Chem. Soc. 2018, 140,
10198−10207.
́
́
(56) Julia, F.; García-Legaz, M.-D.; Bautista, D.; Gonzalez-Herrero,
P. Influence of Ancillary Ligands and Isomerism on the Luminescence
of Bis-cyclometalated Platinum(IV) Complexes. Inorg. Chem. 2016,
55, 7647−7660.
(57) Li, K.; Cheng, G.; Ma, C.; Guan, X.; Kwok, W.-M.; Chen, Y.;
Lu, W.; Che, C.-M. Light-emitting platinum(ii) complexes supported
by tetradentate dianionic bis(N-heterocyclic carbene) ligands:
towards robust blue electrophosphors. Chem. Sci. 2013, 4, 2630−
2644.
(58) Zhang, W.; Wang, J.; Xu, Y.; Li, W.; Shen, W. Fine tuning
phosphorescent properties of platinum complexes via different N-
heterocyclic-based C∧N∧N ligands. J. Organomet. Chem. 2017, 836−
837, 26−33.
(59) Solomatina, A. I.; Aleksandrova, I. O.; Karttunen, A. J.; Tunik,
S. P.; Koshevoy, I. O. Dibenzothiophene-platinated complexes:
probing the effect of ancillary ligands on the photophysical
performance. Dalton Trans. 2017, 46, 3895−3905.
(60) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba,
I.; Bau, R.; Thompson, M. E. Synthesis and Characterization of
Phosphorescent Cyclometalated Platinum Complexes. Inorg. Chem.
2002, 41, 3055−3066.
(61) CrysAlisPro, Version 1.171.36.28; Agilent Technologies: Santa
Clara, CA, 2013.
(62) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. OLEX2: a complete structure solution, refinement
and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341.
(63) Sheldrick, G. A short history of SHELX. Acta Crystallogr., Sect.
A: Found. Crystallogr. 2008, 64, 112−122.
(64) Sheldrick, G. Crystal structure refinement with SHELXL. Acta
Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8.
(65) 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.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.;
I
DOI: 10.1021/acs.inorgchem.8b03326
Inorg. Chem. XXXX, XXX, XXX−XXX