Platinum(II) Complexes of Tridentate N∧N- ∧N -Coordinating Ligands Based on Imides, Amides, and Hydrazides: Synthesis and Luminescence Properties

Article abstract of DOI:10.1002/ejic.202000879

Five Pt(II) complexes are described in which the metal ion is bound to anionic (Formula presented.) -coordinating ligands. The central, deprotonated N atom is derived from an imide Ar?C(=O)?NH?C(=O)?Ar {PtL^1–2Cl; Ar=pyridine or pyrimidine}, an amide py?C(=O)?NH?CH₂?py {PtL³Cl}, or a hydrazide py?C(=O)?NH?N=CH?py {PtL⁴Cl}. The imide complexes PtL^1–2Cl show no significant emission in solution but are modestly bright green/yellow phosphors in the solid state. PtL³Cl is weakly phosphorescent. PtL⁴Cl is formed as a mixture of isomers, bound through either the amido or imino nitrogen, the latter converting to the former upon absorption of light. Remarkably, the imino form displays fluorescence in solution, λ^0,0=535 nm, whereas the amido shows phosphorescence, λ^0,0=624 nm, τ=440 ns. It is highly unusual for two isomeric compounds to display emission from states of different spin multiplicity. The amido-bound PtL⁴Cl can act as a bidentate (Formula presented.) -coordinating ligand, demonstrated by the formation of bimetallic complexes with iridium(III) or ruthenium(II).

Full text of DOI:10.1002/ejic.202000879

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^
À ^
Platinum(II) Complexes of Tridentate N N N -Coordinating
Ligands Based on Imides, Amides, and Hydrazides:
Synthesis and Luminescence Properties
[a]
[b]
[c]
[a]
Emma V. Puttock, Jiri Sturala, Jos C. M. Kistemaker, and J. A. Gareth Williams*
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Five Pt(II) complexes are described in which the metal ion is
bound through either the amido or imino nitrogen, the latter
converting to the former upon absorption of light. Remarkably,
the imino form displays fluorescence in solution, λ =535 nm,
^
^
bound to anionic N N N-coordinating ligands. The central,
0,0
deprotonated N atom is derived from an imide ArÀ C(=O)À NHÀ C
1–2
0,0
(
(
(
=O)À Ar {PtL Cl; Ar=pyridine or pyrimidine}, an amide pyÀ C
whereas the amido shows phosphorescence, λ =624 nm, τ=
3
=O)À NHÀ CH À py
{PtL Cl},
or
a
hydrazide
pyÀ C
440 ns. It is highly unusual for two isomeric compounds to
display emission from states of different spin multiplicity. The
2
4
1–2
=O)À NHÀ N=CHÀ py {PtL Cl}. The imide complexes PtL Cl show
4
^
no significant emission in solution but are modestly bright
amido-bound PtL Cl can act as a bidentate O N-coordinating
ligand, demonstrated by the formation of bimetallic complexes
with iridium(III) or ruthenium(II).
3
green/yellow phosphors in the solid state. PtL Cl is weakly
phosphorescent. PtL Cl is formed as a mixture of isomers,
4
Introduction
M(ECE) unit, coupled with the lability of the MÀ X bond for some
metals like Ni(II) and Pd(II), underpins much of the success of
[3]
Metal complexes of pincer ligands occupy a prominent position
pincer complexes in homogeneous catalysis.
In the field of inorganic photochemistry and photophysics,
square-planar platinum(II) complexes continue to offer much
interest to researchers. The high spin-orbit coupling constant
of Pt can greatly facilitate formally forbidden triplet phosphor-
escence in complexes with aromatic ligands. Over the past
15 years, a number of very brightly phosphorescent complexes
of Pt(II) have been reported. Some have opened up new
avenues of research in bio-imaging and sensing whilst others
have attracted interest as potential phosphors for OLEDs.
Unlike related complexes of d metal ions such as Ir(III), the
propensity of these flat Pt(II) molecules to undergo face-to-face
interactions can lead to the generation of excimers and/or
aggregates that may emit at lower energy, leading to further
scope in accessing deep red/NIR emitters and/or generation of
[1]
in modern organometallic chemistry. The term ‘pincer’ is used
to describe monoanionic tridentate ligand platforms that
feature a central anionic site bound to the metal, flanked by
two charge-neutral ligating units such as amines, imines,
pyridines, phosphines or sulfides. In many instances, the central
anionic unit is formally a deprotonated benzene ring – i.e., a
cyclometallated aromatic unit – giving E C E coordination (e.g.,
E=N, P, S). The strongly σ-donating cyclometallated ring in
combination with, for example, lateral π-accepting pyridines
[4]
[5]
^
^
[4]
[6]
[7]
[
8]
[
2]
6
(
Figure 1a) leads to strong ligand fields. Thus, in the resulting
8
complexes with d metal ions such as Ni(II), Pd(II), Pt(II), Ir(I) and
Au(III), a square-planar coordination geometry typically arises,
with the fourth site occupied by a relatively weakly bound
monodentate ligand X, such as a halide. The robustness of the
[9]
white light using a single OLED dopant.
Key to the design of luminescent platinum(II) complexes is
to build into the molecule a high degree of rigidity, in order to
ensure that potentially competitive non-radiative decay path-
ways are minimised. Certain pincer-type complexes of Pt(II)
offer such rigidity and are luminescent under ambient con-
ditions. For example, Pt(II) complexes of 1,3-di(2-pyridyl)
benzene (dpybH) and its derivatives, such as Pt(dpyb)Cl (Fig-
ure 1b), are intensely luminescent in solution at room
temperature. They are readily amenable to colour tuning and
form strongly emissive excimers: they have shown promise as
OLED emitters in the visible and NIR, and as long-lived probes
for bioimaging. Despite this promise, there are some draw-
backs to systems based on such N C N-coordinating ligands.
[a] Dr. E. V. Puttock, Prof. Dr. J. A. G. Williams
Department of Chemistry
Durham University
DH1 3LE, U.K. Durham
[10]
E-mail: j.a.g.williams@durham.ac.uk
www.dur.ac.uk/chemistry/staff/profile/?id=205
b] Dr. J. Sturala
[
Department of Inorganic Chemistry
University of Chemistry and Technology Prague
Technicka 5, 166 28 Prague 6, Czech Republic
c] Dr. J. C. M. Kistemaker
[11]
[
Centre for Organic Photonics and Electronics, The School of Chemistry and
Molecular Biosciences
[12]
University of Queensland
[13]
4072 Queensland, Australia
^
^
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202000879
These ligands are synthesised most readily from palladium-
catalysed cross-coupling reactions.
relatively costly precursors – either pyridyl stannanes (which are
toxic) in the case of Stille reactions or benzene diboronic acids
©
2020 The Authors. European Journal of Inorganic Chemistry published by
[14]
They require use of
Wiley-VCH GmbH. This is an open access article under the terms of the
Creative Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly cited.
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Figure 1. (a) Generic structure of a metal coordinated to a pincer ligand featuring flanking pyridyl rings, where Z is typically a carbon or nitrogen atom. (b)
Previous examples of related pincer Pt(II) complexes: Pt(dpyb)Cl (i.e., Z=C); Pt(bpi)Cl and Pt(bqa)Cl (Z=N). Phenanthridinyl analogues of Pt(bqa)Cl are
represented by the dashed lines. (c) Structures of the complexes PtL ClÀ PtL Cl investigated in this work.
1
4
in the case of the alternative Suzuki strategy. Their reliance on
Pd catalysts can also lead to trace palladium contamination in
final products, undesirable in the photonic industry.
previously been reported. One of the complexes has the
potential to bind a second metal ion as an N O-bidentate
ligand, as evidenced by the formation of two heterometallic
dinuclear compounds with Ru(II) and Ir(III) units.
^
We, and others, have been interested in using deprotonated
À
azole units in place of cyclometallated rings; i.e., N donors in
À [15,16]
place of C .
For example, 2-pyridylbenzimidazole proves to
be an attractive alternative to phenylpyridine in bidentate Ir(III) Results and Discussion
[15a]
complexes,
whilst Chi and co-workers have pioneered the
use of a variety of bidentate ligands incorporating triazoles that
Synthesis
[16]
bind through deprotonation. Nevertheless, few pincer com-
plexes of Pt(II) with a central anionic nitrogen have been
investigated for luminescence. The most notable examples are
Pt(bpi)Cl and a limited number of its derivatives {bpi=1,3-bis(2-
pyridylimino)isoindoline, Figure 1b}, and very recent work on
bis(8-quinolyl)amine and bis(4-phenanthridinyl)amine com-
plexes {e.g. Pt(bqa)Cl, Figure 1b}. They show weak, deep-red
The target mononuclear complexes are shown in Figure 1c.
1
3
PtL Cl and PtL Cl have been isolated previously by others, the
latter inadvertently as an unexpected product involving quite
[20]
different chemistry. The synthetic pathways to the requisite
ligands and their complexes are summarised in Scheme 1.
1
The ligand HL , known as bis(2-pyridylcarbonyl)amide or
[17,18,19]
luminescence under ambient conditions.
In this contribution, we have sought to examine Pt(II)
bca, has been studied for many years in the context of metal
complexes for single-molecule magnets, catalysis of CO2
het
À
het
[21,22]
complexes of other pincer ligands of the type N À N À N
reduction, and coordination polymers.
It was originally
het
(N
=an N-heterocycle such as pyridine), aiming to identify
obtained as an unexpected product of metal-catalysed hydrol-
[21]
whether they may offer scope in providing access to new
phosphorescent molecular materials. We describe the synthesis
of four such ligands and their Pt(II) complexes, together with
their luminescence properties. Analogous Pd(II) complexes have
ysis of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tpyt). That reaction
lends itself well to the synthesis of gram quantities of the
ligand; the procedure was employed here using copper nitrate
followed by treatment with EDTA to remove the metal
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Scheme 1. Synthesis of the proligands and their corresponding Pt(II) complexes.
2
3
(
Scheme 1a). A similar procedure allows access to HL from
simple ether wash. Ligand HL , N-(2-picolyl)-picolinamide, is
2
,4,6-tris(2-pyrimidyl)-1,3,5-triazine (tpymt). The precursor tpymt
accessible in one simple step to form the amide bond, by
reaction of ethyl 2-picolinate with 2-picolylamine under micro-
wave irradiation for 1 h (Scheme 1b). Meanwhile, HL – an
acylhydrazone or hydrazide – was prepared in two steps by the
initial formation of 2-picolylhydrazine from ethyl 2-picolinate
was obtained by cyclotrimerisation of 2-cyanopyrimidine at
[23]
4
1
50°C. Contrary to previous reports in which arduous purifica-
[21]
tion was required, we found that this reaction gave tpymt in
8
0% yield, in sufficient purity for subsequent use, by using a
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and hydrazine, followed by condensation with pyridyl-2-carbox-
aldehyde to form the imine bond and thus introduce the
second pyridine ring (Scheme 1b). As previously discussed by
Hecht and co-workers for a range of other acylhydrazones, we
and b-PtL Cl correspond to the amido and imino-bound forms
respectively, as labelled in Scheme 1.
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Further support for the assignment is provided by DFT
calculations, which were carried out on the two Pt(II) isomers
using one of three functionals (CAM-B3LYP, BMK, or ωB97X-D),
with Def2-TZVP as the basis set and with the dichloromethane
solvent taken into account using the conductor-like polarised
continuum model (C-PCM). Details are given in the Experimen-
tal Section, and atomic coordinates of the optimised ground-
state structures are listed in Section 5 of the Supporting
Information. The calculations reveal that the imino b-PtL Cl
isomer is unequivocally less stable than the amido a-PtL Cl by
around 52 kJmol (values of 52.4, 51.4 and 52.8 kJmol were
obtained using the three functionals listed above, respectively),
consistent with the experimentally observed b!a interconver-
sion.
4
1
observed exclusive formation of the E-isomer of HL by H NMR
[
24]
spectroscopy, with no evidence of the Z form being present.
4
Clearly, if HL is to coordinate in a tridentate fashion to a single
metal ion, then isomerisation to the Z form will need to occur.
1
3
The complexes PtL Cl and PtL Cl were readily prepared by
1
3
reaction of the respective ligands HL and HL with Pt(COD)Cl
2
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4
in acetonitrile solution, in the presence of triethylamine as a
base to facilitate deprotonation of the central NÀ H. They are
both bright yellow solids. The same procedure did not lend
4
À 1
À 1
2
itself well to the preparation of PtL Cl, owing to poor solubility.
2
This complex was prepared instead by reaction of HL with
K PtCl in DMF. The resulting complex was only poorly soluble,
2
4
and it was separated from traces of residual ligand by
crystallisation from hot DMSO, again giving yellow crystals.
4
The reaction of HL with Pt(COD)Cl in the presence of NEt
Bimetallic complexes
2
3
1
led to a dark purple solid, which was found by H NMR to
consist of a mixture of primarily two Pt(II) complexes. The two
complexes could be successfully separated by column chroma-
tography on silica. The first complex to elute is burnt orange in
colour and is appreciably soluble in chlorinated solvents,
whereas the second complex is dark purple, having more
limited solubility. The two complexes have identical masses by
mass spectrometry, both corresponding to the expected
st
Dipyridylcarbonyl complexes of 1 row transition metals have
previously been used in the construction of multinuclear
systems and coordination polymers: the deprotonated C(=
À
O)À NÀ C(=O) unit resembles acac (Hacac=2,4-pentanedione,
commonly known as acetylacetone) and may thus be able to
^
[19]
bind to a metal in a bidentate O O-chelating manner. Given
[
26]
the recent interest in dinuclear PtÀ Ir complexes, coupled with
the ubiquity of bis-cyclometallated iridium chemistry in the field
of luminescence, we reasoned that it could be of interest to
4
composition PtL Cl, suggesting that they are isomeric; they will
4
4
be referred to henceforth as a-PtL Cl and b-PtL Cl respectively.
We noted that, in solution, the b form gradually converted to
1
examine the PtL Cl unit as a bidentate ligand to iridium(III) in an
1
^
^
the a form under ambient room lighting, as monitored by H
Ir(N C) (L L) complex. The standard iridium precursor [Ir
2
1
NMR spectroscopy.
(ppy) (μ-Cl)] was treated with PtL Cl (2 equiv.) under conditions
2
2
^
^
Nakajima and co-workers have previously explored the
typically used to prepare [Ir(N C) (O O-acac)] complexes,
2
4
coordination chemistry of the same ligand HL with
namely the use of a mixed DCM/MeOH solvent system at a
temperature of 65°C. However, there was no clear spectro-
scopic evidence for the formation of the desired product, even
after prolonged reaction times. It may be noted that, although
the biscarbonylamide ligand is deprotonated, the combination
with Pt in oxidation state +2 and the monodentate chloride
[25]
palladium. They were able to isolate three products, depend-
ing on the conditions, each identified crystallographically: a
^
4
complex of the form Pd(N N-HL )Cl featuring the non-deproto-
2
4
^
nated ligand HL bound to the metal in an N N manner through
the pyridylimine unit; and a pair of isomeric complexes of
^
4
1
composition Pd(N NN-L )Cl, featuring the deprotonated ligand
bound in a tridentate fashion. These two isomers differ
according to which is the central nitrogen atom: either the
leads to a net charge on the PtL Cl unit of zero, as opposed to
^
À 1 on acac in Ir(III) complexes with acac as an O O ligand. The
1
charge neutrality probably makes the PtL Cl unit a poor ligand
4
amido nitrogen (as in form a of PtL Cl in Scheme 1c) or the
for Ir(III). The known examples in which charge-neutral M(bca)2
complexes act as ligands are in combination with “harder”,
imino nitrogen (form b). The latter palladium complex con-
2
+
3+ [19]
verted to the former in solution in the presence of light, whilst
more oxophilic metal ions such as Mn and Fe
.
^
^
4
4
Pd(N N N-HL )Cl also converted to the tridentate amido form
The complex PtL Cl also has the potential to bind to a
2
^
thermally, indicating that the amido form is the thermodynami-
cally favoured product. We were not able to obtain crystals of
the Pt(II) complexes of sufficient quality for structural confirma-
second metal ion, in this case as a charge-neutral O N-chelating
ligand. Indeed, Nakajima and co-workers previously prepared a
4
dinuclear PdÀ Ru complex starting from a ligand similar to L ,
1
tion by X-ray diffraction. However, the H NMR spectra of our a
but with a 2-quinolyl as opposed to 2-pyridyl pendant on the
[27]
4
and b Pt(II) isomers closely match those of the crystallo-
graphically confirmed amido and imino Pd(II) complexes
respectively: the four spectra are reproduced collectively for
comparison in Figure S1 in the Supporting Information. Based
on these observations, together with the light-activated b!a
imine. We found that treatment of a-PtL Cl with [Ir(ppy) (μ-
2
Cl)] (2:1 ratio) in DCM/MeOH at 65°C successfully gave the
2
4
desired heterodinuclear complex [PtCl(μ-L )Ir(ppy) ]PF as a dark
2
6
green solid after anion exchange in aqueous KPF (Scheme 2).
6
To allow a direct comparison with the palladium work of
4
4
conversion, there can be little doubt that the isomers a-PtL Cl
Nakajima, a-PtL Cl was also treated with RuCl (PPh ) to form
2
3 2
4
the charge-neutral Pt(II)À Ru(II) complex [PtCl(μ-L )RuCl (PPh ) ].
2
3 2
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Scheme 2. Synthesis of the dimetallic compounds from the mononuclear Pt(II) complexes.
Complexation to Ru(II) was accompanied by a large up-field
shift of the imine proton in the H NMR spectrum, fully
free ligands. The somewhat weaker bands at longer wave-
1
lengths have no counterpart in the free ligands and are thus
likely to be due to charge-transfer (CT) transitions involving the
metal. Based on the structural similarity of the complexes to Pt
(dpyb)Cl and on the experimental and theoretical studies on
such complexes,
[
27]
consistent with the PdÀ Ru complex.
both PtL Cl and PtL Cl are charge-neutral, rather than anionic.
As potential ligands,
4
1
4
^
The fact that PtL Cl can successfully act as an O N bidentate
ligand to Ir(III), whereas there is no evidence of O O binding of
PtL Cl to Ir(III), may be a reflection of the “softer” character of
^
[11,12]
the lowest-energy CT transitions are likely
1
to involve charge-transfer from filled orbitals spanning the Pt
iridium, favouring binding of more polarisable nitrogen donors
over harder, exclusively oxygen donors.
centre, the chloride and probably also the central N atom, to π*
orbitals based on the heterocycles. TD-DFT calculations on
1
PtL Cl in the S state confirm this expected localisation of the
0
frontier orbitals (Figure S2 in the Supporting Information).
Such an interpretation readily accounts for the observed
trend in energies amongst the three complexes PtL Cl. Thus,
Photophysical properties of the mononuclear complexes
PtL Cl
1
–4
1–3
the red-shift in the lowest-energy absorption band on going
1
2
(i) Absorption
from PtL Cl to PtL Cl will arise as a result of the lower-energy of
3
π* orbitals on pyrimidine compared to pyridine rings. In PtL Cl
(which lacks the C2v symmetry of PtL Cl), the lowest-energy π*
1
–3
1–2
The imide-based complexes PtL Cl are very poorly soluble in
all common organic solvents. Their UV-visible absorption
spectra in dilute dichloromethane solution at ambient temper-
ature are shown in Figure 2 (numerical values are included
amongst the characterisation data for each complex in the
Experimental Section). The complexes show very strong
absorption bands at λ<300 nm, which may be attributed to
πÀ π* transitions within the aromatic rings of the ligands: bands
of comparable intensity are observed in the same region for the
orbitals would be expected to be those based on the pyÀ C=O
1
(i.e., as in PtL Cl) as opposed to the pyÀ CH ring, due to the
2
electron-withdrawing nature of the carbonyl unit. The red-shift
compared to PtL Cl, therefore, likely arises not from a significant
difference in the LUMO energy but rather from the platinum-
based HOMO being displaced to somewhat higher energies,
owing to the Pt being coordinated by a more electron-rich
pyÀ CH2 unit. The interpretation is supported by absorption
1
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9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
1–3
Figure 2. UV-Vis absorption spectra of PtL Cl in CH
2
Cl
2
at 295�3 K.
spectra modelled using the lowest-energy series of excited
states of the three complexes obtained by DFT using the
aforementioned functionals. The simulated spectra show the
same trend of decreasing energy of the first spin-allowed
absorption band in the order PtL Cl>PtL Cl>PtL Cl (Figur-
es S5–S7 in the Supporting Information).
The absorption spectra of the two isolated forms of the
hydrazide complex, a/b-PtL Cl, are shown in Figure 3. To the
eye, these compounds are more strongly coloured than those
of PtL Cl and indeed the spectra of both forms reveal a more
intense band further into the visible than the lowest-energy
band of the other complexes, centred around 470 nm. Similarly
intense and well-defined bands were observed by Nakajima
and co-workers for palladium complexes a/b-PdL Cl, albeit at
4
slightly shorter wavelength (450 nm), assigned to transitions of
1
2
3
[27]
predominantly πÀ π* character within the hydrazide unit. The
transition must be influenced by the metal too, given that the
change from Pd to Pt lowers the energy of the band by around
4
À 1
1000 cm . The molar absorptivities of the a form are signifi-
cantly lower than those of the b isomer across almost all
wavelengths, and by a factor of about 2 for the longest
wavelength λmax values (Figure 3). The theoretical spectra
1
–3
4
Figure 3. UV-Vis absorption spectra of the two isomers of PtL Cl in CH
2
Cl
2
at 295�3 K.
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calculated with various DFT functionals closely match the
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
experimental ones (Figures S8 and S9). Moreover, the higher
molar aborptivity of the b isomer is consistent with the higher
calculated oscillator strengths f of most of the transitions (e.g.,
for the lowest-energy transition, f=0.25 and 0.40 for the a and
b isomers respectively; Table S1 and Table S2 in the Supporting
Information).
(ii) Emission
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
1
2
Solid samples of the imide complexes PtL Cl and PtL Cl appear
bright green and yellow/orange, respectively, when viewed
under long-wavelength UV irradiation. Spectra and quantum
yields were recorded on powdered samples using an integrat-
ing sphere: the emission spectra are shown in Figure 4. The
2
emission maximum of the pyrimidinyl complex PtL Cl is
1
displaced towards the red compared to PtL Cl, mirroring the
trend in absorption, and likely associated with the lower energy
π* orbitals of pyrimidine compared to pyridine rings as
described earlier. The quantum yields are are 1.6 and 1.4 % for
3
Figure 5. Emission spectrum of PtL Cl in CH
(*=Raman CÀ H band of solvent).
2
Cl
2
at 295�3 K, λex =430 nm
1
2
PtL Cl and PtL Cl respectively, with lifetimes of 770 and 1000 ns
respectively. Lifetimes in the microsecond range are quite
typical of phosphorescent Pt(II) complexes {e.g., as in the
ligands, where the term “enhanced phosphorescence emission
in the solid state”, or EPESS, has started to be used as a
Such a situation can, of course, arise in any
molecule in which there is significant excited-state distortion
that is inhibited by the more rigid environment within the solid
^
^
structurally related, N C N-coordinated Pt(dpyb)Cl derivatives},
where the formally forbidden T !S process is facilitated
[28]
descriptor.
1
0
3
through the SOC effect of the Pt centre. The emission of PtL Cl
was too weak in the solid state to record a convincing
spectrum.
3
compared to solution. The amide complex PtL Cl, on the other
In deoxygenated solution at room temperature, the imide
hand, does show weak luminescence in the red region of the
spectrum in solution at room temperature (Figure 5 and
Table 1). Nevertheless, the low quantum yield and short lifetime
are indicative of fast non-radiative decay processes competing
efficiently to deactivate the triplet excited state and render the
phosphorescence weak. This complex shows no significant
1
–2
complexes PtL Cl are essentially non-luminescent, presumably
due to efficient non-radiative decay processes being opened up
in solution compared to the more rigid environment in the solid
state. Such a trend has been described in some detail for Ir(III)
complexes containing bidentate carbonyl- or imine-based
1
2
Figure 4. Normalised emission spectra of PtL Cl and PtL Cl in the solid state at 295�3 K, λex =420 nm.
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1
–4
Table 1. Luminescence data for PtL Cl in solution at room temperature and in a glass at 77 K.
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
[a]
[b]
Complex
Emission at 295�3 [K]
Emission at 77 [K]
[c]
[d]
λ
max [nm]
τ/ns
Φ/%
λmax [nm]
τ/[ns]
1
[e]
[e]
[e]
[e]
PtL Cl
–
–
–
–
474, 503, 539, 580
486, 519, 555
8300
5300
100
2
[e]
[e]
PtL Cl
–
–
3
PtL Cl
622
48
0.2
0.7
0.2
563, 599, 643
[
39]
440
220]
4
a-PtL Cl
624, 683, 745
535, 567, 605
627, 687, 738
503, 540, 580
900
[
4
[f]
[f]
b-PtL Cl
–
–
1
3
4
[
a] In deoxygenated CH
2
Cl
2
solution. [b] In diethyl ether/isopentane/ethanol (2:2:1 v/v) for PtL ClÀ PtL Cl, and in butyronitrile for a/b-PtL Cl. [c] Corresponding
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
values in air-equilibrated solution are shown in parenthesis. [d] Quantum yields of luminescence determined using Ru(bpy)
3
Cl in water as the standard. [e]
2
No significant emission was detectable from these complexes in solution at room temperature. For values in the solid state at room temperature, see
4
Figure 4. [f] The lifetime of b-PtL Cl was too short for determination using the available equipment, the intensity being too weak to reliably deconvolve the
decay from the instrument response function.
1
–2
4
emission in the solid state, in contrast to PtL Cl, presumably
due to deactivation pathways that involve intermolecular
interactions. In dilute glassy solution at 77 K, all three com-
The pair of isomeric hydrazide complexes a/b-PtL Cl are
both weakly luminescent in solution at room temperature
(Figure 6 and Table 1). The isomer a-PtL Cl displays a vibration-
4
1
–3
plexes PtL Cl are weakly emissive, with some vibrational
structure evident in the spectra (Figure S11 and Table 1).
We note that PdL Cl, the palladium analogue of PtL Cl, has
previously been prepared and structurally characterised, but no
emission properties were reported for that material. In most
cases, Pd(II) complexes do not show significant phosphores-
cence at room temperature where their Pt(II) analogues may do
so. The superiority of Pt(II) in this respect has two origins. Firstly,
the stronger ligand field associated with platinum may help
raise potentially deactivating d–d states to thermally less
accessible energies, reducing their ability to act as a quenching
pathway for the emissive excited states. Secondly, the higher
spin-orbit coupling of Pt compared to Pd facilitates the formally
ally structured spectrum. Such structured spectra, when
observed under ambient conditions, tend to be associated with
excited states of predominantly πÀ π* character, as opposed to
CT. The component band of highest intensity is the 0,0 band,
indicative of little distortion between the emissive excited state
and the ground state and hence a highly rigid chromophoric
unit. In line with this interpretation, the corresponding spec-
trum at 77 K is very similar to that at room temperature, with
no significant shift of the vibrational band maxima. The
luminescence lifetime is 440 ns in deoxygenated solution, which
is again consistent with formally forbidden phosphorescence
from the triplet excited state facilitated by the Pt(II) centre. The
lifetime falls to 220 ns under air-equilibrated conditions, from
1
1
[29]
[2]
forbidden T !S transition.
which the bimolecular rate constant for quenching by O may
1
0
2
4
4
Figure 6. Normalised emission spectra of a-PtL Cl and b-PtL Cl in CH
7 K in EPA (dashed lines).
2
Cl
2
at 295�3 K (solid orange and green lines respectively), and corresponding spectra at
7
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9
À 1 À 1
be estimated to be 1.0×10 M s , a value quite typical of
phosphorescent metal complexes with molecular weights
and Figure S4 and Table S1) and energies, based on their similar
lowest-energy absorption bands (Figure 3), but their triplet
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
À 1
[11d]
4
around 500 gmol , such as those based on Pt(dpyb)Cl.
state energies differ. The large S À T energy gap for b-PtL Cl
1
1
4
The complex b-PtL Cl emits at much shorter wavelengths
than its isomer. Based on the wavelengths of the 0,0 bands (624
and 535 nm for a and b respectively), the difference in energy
between the emissive excited states of the two complexes is
estimated to be 2700 cm . The vibrational structure in the
room temperature spectrum of the b form is less well-resolved
than the a isomer and, unlike the a isomer, it shows a modest
(Figure S10) probably serves to diminish the rate of S !T
1
1
intersystem crossing (inversely proportional to the energy
[5]
gap ) such that S fluorescence is observed for this isomer. It is
1
also likely that there is less metal character in the singlet excited
state of the b isomer compared to the a (Figure S3 and
Figure S4) which would further contribute to limiting the rate of
intersystem crossing.
À 1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
À 1
shift to the blue on going to 77 K, of around 1200 cm . Both
No phosphorescence was reported for the related Pd(II)
[25]
observations suggest a higher degree of excited state distortion
for the b isomer and thus perhaps to an excited state of
different character. For this isomer, the lifetime proved too
short for detection with the available equipment, probably
complexes previously reported,
in contrast to our newly
4
prepared Pt(II) complexes of ligand L . As noted earlier,
potentially emissive ligand-centred or charge-transfer excited
states in Pd(II) complexes are normally subject to more efficient
non-radiative decay processes, owing to low-lying d-d states
arising from the weaker ligand field associated with Pd(II), whilst
the spin-orbit coupling effect of Pd is also weaker.
<
1 ns, and indeed the emission in solution was not detectably
quenched upon aeration, an observation that also points to the
lifetime being short. Finally, it may be noted that the Stokes’
shift of this complex is particularly small: its absorption
spectrum tails to around 530 nm, a value remarkably similar to
the 0,0 band of the emission spectrum. Taken together, these
Photophysical properties of the dinuclear complexes
observations strongly suggest that the observed emission of b-
4
4
PtL Cl is due to fluorescence from the S state as opposed to the
The conversion of PtL Cl to the bimetallic PtÀ Ru complex PtCl
1
4
4
T phosphorescence observed for a-PtL Cl.
(μ-L )RuCl (PPh ) is accompanied by the appearance of a
relatively intense absorption band at long wavelength, λmax =
677 nm (Figure 7). The band is most likely due to an MLCT
transition from the Ru(II) centre to the bridging L ligand. A low-
1
2
3 2
To provide further insight into this remarkable and
unexpected difference, the S !S fluorescence and T !S
1
0
1
0
4
phosphorescence spectra of the two isomeric complexes were
calculated at the CAM-B3LYP/Def2-TZVP level of theory (Fig-
energy band was also observed by Nakajima and co-workers in
4
ure S10). The calculated phosphorescence spectrum of a-PtL Cl
their corresponding PdÀ Ru complex, albeit at somewhat longer
[27]
closely matches (in energy) the experimentally observed
emission, whereas for the b isomer, the observed emission falls
in the calculated fluorescence region. Thus, it appears that the
lowest-energy singlet states of the two isomers have similar
wavelength beyond 700 nm. The well-defined band present
4
at 473 nm in a-PtL Cl is slightly blue-shifted (455 nm) in the
4
PtÀ Ru complex, suggesting that the d(Pt)!π*(L ) transition is
somewhat raised in energy upon coordination of Ru(II),
1
character (hydrazide-localised πÀ π* state, vide supra, Figure S3
probably owing to a small destabilisation of the π* orbitals on
4
4
Figure 7. Absorption spectra of [PtCl(μ-L )RuCl
2
(PPh
3
)
2
] (red line) and [PtCl(μ-L )Ir(ppy)
2
]PF
6
(blue line) in CH
2
Cl
2
at 298�3 K, together with the spectrum of a-
4
PtL Cl for comparison (dashed green line)
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4
4
L . The dinuclear complex [PtCl(μ-L )Ir(ppy) ]PF also has bands
sents a highly unusual case of isomerism determining the
singlet versus triplet nature of emission in a metal complex.
Whilst the luminescence performance of these first exam-
2
6
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
in the 400–500 nm region that can reasonably be attributed to
those typically observed in this region for Ir(ppy) derivatives,
2
^
^
superimposed on the visible absorption band associated with
the Pt unit. In addition, a weak, low-energy, broad band centred
around 600 nm is apparent.
Neither of these bimetallic complexes shows detectable
luminescence at room temperature. For the RuÀ Pt complex, this
observation is in line with other studies where low-energy
absorbing RuL X units efficiently quench the excited states of
covalently linked higher-energy emitters.
ppy) (L X)-based complexes are brightly emissive, those with
ancillary L X ligands having low-energy excited states associ-
ples of N N N-bound Pt(II) complexes are inferior to the
cyclometallated systems, it may be anticipated that modifica-
tions to these core structures may lead to significant improve-
ments. For example, from the well-known precedent of [Pt(tpy)
+
Cl] and Pt(phbpy)Cl and their derivatives (tpy=terpyridine,
phbpy=6-phenylbipyridine), the metathesis of the chloride
ligand to strong-field ligands such as acetylides may help to
increase the metal character in the excited state, particularly for
4
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
[30]
Whilst many Ir
^
4
(
the complexes of PtL Cl, and thus promote the radiative decay
2
^
[32]
rate. Similarly, the appendage of an additional ligating unit,
ated with them are often not so. A well-known example is that
such as a phenolate, into the structures to generate a
^
of Ir(ppy) (O O-dbm) (dbm=dibenzoylmethane), where the
tetradentate ligand may confer the additional rigidity necessary
2
[33]
lack of emission is attributed to vibrational quenching in the
to limit non-radiative decay pathways.
The presence of
^
[31]
low-frequency region of the conjugated O O ligand. It seems
likely that a similar effect may be at work in the present
instance.
additional, potentially bidentate ligating units in the resulting
complexes renders them of potential interest in the generation
of multimetallic structures, as exemplified here by the formation
4
of two heterodinuclear complexes incorporating the a-PtL Cl
unit bound to Ru(II) or Ir(III).
Concluding Remarks
This work demonstrates that platinum(II) complexes of pincer Experimental Section
À
ligands featuring N central ligating atoms – formed by
deprotonation of imide, amide or hydrazide units – can be
prepared readily from corresponding proligands. The proligands
1
13
H and C NMR spectra were recorded on Varian or Bruker
instruments at the frequencies indicated. Chemical shifts (δ) are in
ppm, referenced relative to residual protio-solvent resonances, and
coupling constants (J) are in hertz. All solvents used in the
preparative work were of at least analytical reagent grade, and
water was purified using the Purite system. Solvents used for
3
4
HL and HL are available via simple condensation reactions
from a standard organic compound – ethylpicolinate – whilst
1
HL is likewise prepared easily by hydrolysis of low-cost
1
–4
optical spectroscopy were HPLC grade. Proligands HL
prepared broadly following procedures described elsewhere.
The platinum precursor Pt(COD)Cl was prepared by a standard
were
tripyridyltriazine. The ease of synthesis and lack of requirement
for expensive organometallic reagents or palladium catalysts
contrasts with routes typically used to prepare related cyclo-
metallating pincer ligands – featuring a central carbon in place
of nitrogen – such as 1,3-dipyridylbenzene (dpyb) and its
[18,23,24]
2
[34]
procedure.
1
PtL Cl
[14]
derivatives.
The resulting Pt(II) complexes featuring the ligands bound
in a tridentate manner – with a monodentate chloride ligand
completing the coordination sphere – do show luminescence,
albeit much weaker than that displayed by Pt(dpyb)Cl. The
imide complexes display green or green-yellow phosphores-
cence in the solid-state, but the emission is largely quenched in
solution at ambient temperature, due to efficient non-radiative
Pt(COD)Cl (83 mg, 0.22 mmol) and NEt (22 mg, 0.22 mmol) were
2 3
1
added to a solution of HL (50 mg, 0.22 mmol) in MeCN (2 mL) and
the mixture was stirred at 60°C under argon for 18 h. The resulting
yellow suspension was filtered and the solid was washed with
MeCN (5×5 mL) and dried under vacuum to yield the title
1
compound as a bright yellow solid (65 mg, 64%). The H NMR and
MS data were consistent with those previously reported by Miguel
[20]
et al.
UV/Vis (CH Cl ): λ (ɛ)=262sh (14000), 328 (5710), 389
2
2
max
À 1
À 1
3
(2760), 408sh nm (2520 M cm ). Elemental analysis calcd (%) for
C H N O ClPt (rigorously dried material): C 31.6, H 1.8, N 9.2; found
decay processes being introduced. In contrast, PtL Cl – the
1
12
8
3
2
amide analogue of imide PtL Cl featuring only one C=O unit –
C 31.3, H 2.2, N 8.9.
shows weak red phosphorescence in solution, with the shift to
lower energy likely due to a destabilisation of the highest
2
4
PtL Cl
occupied orbitals. PtL Cl can exist as two isomers, both of which
are luminescent in solution with modest quantum yields. The
2
A mixture of HL (150 mg, 0.65 mmol) and K PtCl (272 mg,
2
4
“
amide-N-bound” a form is red-shifted compared to the “imine-
0.65 mmol) in DMF (10 mL) was stirred at 60°C under argon for
24 h. The resulting orange suspension was filtered. Water (10 mL)
was added to the filtrate, which was then extracted into DCM (3×
N-bound” b isomer and it emerges that the emission has an
unexpectedly different origin in the two cases. The ‘a form’
displays phosphorescence from the triplet state, whereas the
origin of the ‘b form’ emission is fluorescence, as supported
both by DFT calculations and by the short emission lifetime and
insensitivity of the emission to dissolved oxygen. This repre-
2
0 mL). The solvent was removed under reduced pressure to give a
dark orange solid, which was recrystallized from DMSO to yield the
product as a yellow solid (10 mg, 3%). H NMR (700 MHz, DMSO-d ):
1
6
195
1
4
6
δ=9.32 (d, J=5.0, J( PtÀ H)=38, 4H; H and H ), 7.96 ppm (t, J=
5
13
5.0, 2H; H ). The material was not sufficiently soluble to obtain a
C
NMR spectrum. IR (solid, ATR): ν=3593 (w), 1742 (s), 1654 (m), 1582
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+
+
(
(
(
m), 1368 (w), 1341 (s), 1305 (w), 1274 (w), 1190 (w), 1033 (w), 696
[M+H] ; HRMS (ASAP+): m/z 455.0175 [M] ; calculated for
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
À 1
194
+
s), 676 (m), 666 (m), 506 (w) cm ; UV/Vis (CH Cl ): λ (ɛ)=270sh
[C H N O PtCl] 455.0170.
12 10 4
2
2
max
À 1
À 1
9240), 334 (4310), 401 (1920), 432sh nm (1480 M cm ). MS (ES+):
+
194
2
+
m/z: 459 [M+H] ; HRMS (ES+): m/z calcd for [C H N O PtCl] :
457.9915 [M+H] ; found: 457.9919. Elemental analysis calcd (%) for
1
0
7
5
+
4
[a-PtCl(μ-L )Ir(ppy) ]PF
2 6
C H N O ClPt.(CH ) SO: C 26.9, H 2.3, N 13.1; found C 27.4, H 2.5,
N 12.7.
1
0
6
5
2
3 2
4
[
Ir(ppy) (μ-Cl)]
(12 mg, 0.011 mmol) and a-PtL Cl (10 mg,
2
2
0.022 mmol) were heated in a MeOH/DCM mixture (6:5 v/v, 2.2 mL)
at 65°C for 2 h, after which the solvent was removed under
vacuum. The residue was dissolved the minimum volume of MeCN/
3
PtL Cl
H O (1:1 v/v) and the resulting solution was added dropwise to a
2
Pt(COD)Cl (53 mg, 0.14 mmol) and NEt (14 mg, 0.14 mmol) were
saturated aqueous solution of KPF (5 mL). The resulting precipitate
was separated by centrifugation and washed with water (3×5 mL)
to give the dimetallic product as a green solid (20 mg, 82%). H
NMR ((CD ) CO, 600 MHz): 10.17 (dd, J=8.0 and 1.5; 1H), 9.54 (ddd,
J=6.0, 1.5 and 0.5; 1H), 8.80 (ddd, J=6.0, 1.5 and 1.0; 1H), 8.67
(ddd, J=6.0, 1.5 and 1.0; 1H), 8.39 (td, J=8.0 and 1.5, 1H), 8.29 (td,
J=8.0 and 1.5, 1H), 8.27–8.25 (m, 2H), 8.22 (dd, J=8.0 and 1.5, 1H),
8.07–8.04 (m, 2H), 8.01 (ddd, J=8.0, 6.0 and 1.5, 1H), 7.85 (td, J=8.0
and 1.0, 2H), 7.73 (ddd, J=7.5, 6.0 and 1.5, 1H), 7.48 (dd, J=8.0 and
1.5, 1H), 7.39 (ddd, J=7.0, 6.0 and 1.5, 1H), 7.34 (ddd, J=7.5, 6.0
and 1.5, 1H), 7.30 (s, 1H), 7.01 (td, J=7.5 and 1.0, 1H), 6.97 (td, J=
7.5 and 1.0, 1H), 6.87 (td, J=7.5 and 1.0, 1H), 6.83 (td, J=7.5 and
1.0, 1H), 6.32 (dd, J=8.0 and 1.0, 1H), 6.18 ppm (dd, J=7.5 and 1.0,
2
3
6
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
3
added to a solution of HL (30 mg, 0.14 mmol) in MeCN (2 mL) and
the mixture was stirred at 60 C under argon for 18 h. The resulting
yellow slurry was filtered and the solid was washed with MeCN (5×
1
°
3 2
5
mL) and dried under vacuum to yield the title compound as a
1
bright yellow solid (24 mg, 41%). H NMR (700 MHz, CDCl ): δ=9.13
d, J=5.5, 1H; H ), 9.02 (d, J=5.5, 1H; H ), 8.02 (td, J=8.0 and 1.5,
H; H ), 7.94 (td, J=8.0 and 1.5, 1H; H ), 7.81 (d, J=8.0, 1H; H ), 7.48
3
6’
6
(
1
(
5
5’
3
4
3
’
ddd, J=8.0, 5.5 and 2.0, 1H; H ), 7.42 (d, J=8.0, 1H; H ), 7.30 (t, J=
4’ CH2
7.0, 1H; H ), 5.07 ppm (s, 2H; H ). Primed resonances indicate the
13
pyÀ CH=N ring; non-primed the pyÀ CO ring. C NMR (176 MHz,
2
’
C=O
2
6’
6
CDCl ): δ=169.5 (C ), 168.4 (C ), 157.9 (C ), 150.0 (C ), 149.5 (C ),
3
5
5’
4
3
9’
3’
1
5
39.9 (C ), 138.7 (C ), 127.2 (C ), 125.7 (C ), 123.7 (C ), 122.3 (C ),
5.0 ppm (C ). The IR data are consistent with those previously
CH2
13
1H). C NMR ((CD ) CO, 151 MHz): 167.8, 166.9, 158.3, 153.4, 150.9,
3
2
[20]
reported by Miguel et al. UV/Vis (CH Cl ): λ (ɛ)=266 (9430), 324
150.2, 149.3, 147.9, 147.6, 144.9, 144.0, 142.3, 140.9, 139.8, 139.2,
139.0, 133.0, 132.4, 131.7, 130.3, 130.1, 129.5, 128.0, 127.8, 124.9,
124.4, 123.5, 122.7, 122.5, 119.9, 119.6 ppm. IR (solid): 1605 (w),
1570 (w), 1481 (m), 1374 (w), 1300 (w), 833 (s), 798 (m), 764 (m), 753
(s), 764 (m), 753 (s), 733 (m), 680 (w), 670 (w), 556 (s), 467 (w), 419
w) cm . UV/Vis (CH Cl ): λ (ɛ)=335sh (5100), 387 (4720), 415
2
2
max
À 1
À 1
+
(
5200), 415 nm (1640 M cm ). MS(ES+): m/z 443 [M+H] ; HRMS
194 + +
(ES+): m/z calcd for [C H N O PtCl] : 442.0217 [M+H] ; found:
12
11
3
442.0227. Elemental analysis calcd (%) for C12H N OClPt (rigorously
10 3
dried material): C 32.6, H 2.3, N 9.5; found C 32.2, H 2.5, N 9.2.
À 1
(
(
2
2
max
À 1
À 1
3920), 467 (3410), 498 (2700), 600 nm (323 M cm ). MS (ES+): m/
z 956 [M] ; HRMS (ES+): m/z 955.1071 [M] ; calculated for
4
+
+
PtL Cl
194 +
[
C H N OCl PtIr] 955.1033.
4
34 25 6
A
solution of HL (91 mg, 0.40 mmol), Pt(COD)Cl2 (150 mg,
0.4 mmol) and NEt3 (41 mg, 0.40 mmol) in MeCN (6 mL) was
refluxed under argon for 48 h, after which a purple solid was
isolated by filtration of the reaction mixture. The solid material was
loaded onto silica gel in DCM and purified by column chromatog-
raphy (5% MeOH/DCM) to give, after removal of solvent from the
4
a-PtCl(μ-L )RuCl (PPh )
2
3 2
4
A mixture of a-PtL Cl (20 mg, 0.04 mmol) and RuCl (PPh ) (42 mg,
2 3 3
0.04 mmol) in DCM (7 mL) was stirred for 4 h. The resulting solution
was reduced to approximately 2.5 mL by evaporation of solvent
under reduced pressure, and hexane (9 mL) added leading to
precipitation. The suspension was filtered to yield the product as a
dark green solid (41 mg, 75%). H NMR (CDCl , 600 MHz): 10.06 (d,
J=6.5, 1H), 9.41 (d, J=6.0, 1H), 7.92 (td, J=8.0 and 1.0, 1H), 7.85 (d,
J=3.0, 1H), 7.71 (td, J=7.5 and 1.0, 1H), 7.67–7.64 (m, 6H), 7.55 (d,
J=8.0, 1H), 7.49 (ddd, J=7.5, 5.5 and 1.0, 1H), 7.47–7.43 (m, 6H),
.25–7.22 (m, 6H), 7.20 (ddd, J=7.0, 6.0 and 1.5, 1H), 7.16–7.13 (m,
H), 7.06–7.02 (m, 6H), 6.13 ppm (d, 1H, J=8.0). IR/cm : 1607 m,
4
respective fractions, a-PtL Cl as a burnt-orange solid (51 mg, 28%)
4
and b-PtL Cl as a dark purple solid (27 mg, 15%).
2
2
1
Data for a-PtL Cl: R
(
=0.3. H NMR (600 MHz, DMSO-d
): δ=10.0
1
f
6
6’
195
3
d, J=6, 1H,; H , no Pt satellites observed in this solvent), 9.39 (d,
6
4
4
’
J=6.0, 1H; H ), 8.29–8.26 (m, H and H , 2H), 7.98 (dd, J=8.0 and
3
3’
1
.0, 1H; H ), 7.89 (dd, J=8.0 and 1.0, 1H; H ), 7.81 (ddd, J=7.5, 6.0
5 imine
and 1.5, 1H; H ), 7.73 (s, 1H; H ), 7.55 ppm (ddd, J=7.0, 6.0 and
7
6
1
6
5’
13
C=O
1
.5, 1H; H ). C NMR (DMSO-d , 151 MHz): δ=170.3 (C ), 151.9
À 1
6
6’
2’
6
4’
4
4’
4
(C ), 149.4 (C ), 149.3 (C ), 141.7 (C or C ), 140.1 (C or C ), 136.7
583 w, 1569 w, 1482 m, 1431 m, 1384 m, 1298 m, 1090 m, 753 m,
93 s, 672 m, 535 s, 522 vs, 500 s, 464 m, 426 m, 412 m. UV/Vis
(CH Cl ): λ (ɛ)=332(8920), 380sh (4830), 455 (6940), 677 nm
2
imine
3’
5
3
5’
(
C ), 136.7 (C ), 129.6 (C ), 129.1 (C ), 126.3 (C ), 124.9 ppm (C ).
IR (solid): 1682 (m), 1605 (w), 1484 (w), 1316 (m), 1303 (m), 1284 (s),
2
2
max
À 1
1
168 (w), 1154 (m), 1124 (w), 1105 (w), 765 (s), 757 (m), 731 (m), 676
À 1
+
(2570 M cm ). MS (ES+): m/z 1117 [M(À Cl)+H] ; HRMS (ES+):
À 1
(s), 580 (m), 521 (w), 470 (w), 440 (m) cm . UV/Vis (CH Cl ): λ (ɛ)
+
99
194
+
2
2
max
m/z 1112.0632 [MÀ Cl] ; calculated for [C H N OP Cl Ru Pt]
À 1
+ +
À 1
4
8
39
4
2
2
=
260 (11700), 316 (7440), 473 nm (6040 M cm ). MS (ES+): m/z
1
112.0662. Elemental analysis calcd (%) for C H N OP Cl RuPt:
48 39 4 2 3
457 [M+H] . HRMS (ES+): m/z 455.0211 [M] ; calculated for
[C12
C 49.21; H 3.42; N 5.12; found: C 50.03, H 3.41, N 4.86.
194
+
H
N
O
4
PtCl] 455.0170.
10
22
1
Data for b-PtL Cl: R =0.2. H NMR (CDCl , 400 MHz): δ =9.97 (dd,
f
3
H
195
1
6’
195
Photophysical measurements
J=6.0 and 1.5, J( Pt– H)=39, 1H; H ), 9.39 (d, J=6.0, J( Pt)=
39.0, 1H; H ), 9.04 (dd, J=8.5 and 2, 1H; H ), 8.36 (s, 1H; H ), 8.10
6
3
imine
Absorption spectra in solution were measured on a Biotek Instru-
ments XS spectrometer, using quartz cuvettes of 1 cm path length.
Samples for emission measurements were contained within quartz
cuvettes of 1 cm path length modified to allow connection to a
high-vacuum line. Degassing was achieved via a minimum of three
freeze-pump-thaw cycles whilst connected to the vacuum manifold;
4
4’
4
(
dt, J=8.0 and 2.0, 1H; H or H ), 7.90 (dt, J=8.0 and 1.5, 1H; H or
4
’
5
3
’
H ), 7.50–7.44 (m, 2H; H and H ), 7.32 ppm (ddd, J=8.0, 6.0 and
5’
13
1
.5, 1H; H ). The material was not sufficiently soluble to obtain a
C
NMR spectrum. IR (solid): 1572 (w), 1553 (m), 1498 (s), 1435 (w),
1
373 (s), 1319 (m), 1188 (w), 1162 (m), 764 (m), 755 (s), 669 (m), 614
À 1
(w) cm . UV/Vis (CH Cl ): λ (ɛ)=264 (9810), 291 (13900), 320
(10100), 379 (9660), 468 nm (10500 M cm ). MS (ES+): m/z 457
À 2
2
2
max
final vapour pressure at 77 K was <5×10 mbar, as monitored
using a Pirani gauge. Spectra were recorded on a Jobin Yvon
À 1
À 1
Eur. J. Inorg. Chem. 2021, 335–347
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345
© 2020 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH

Full Papers
doi.org/10.1002/ejic.202000879
Fluoromax-2 spectrofluorimeter with an R928 PMT detector and Acknowledgements
corrected for the wavelength dependence of the monochromator
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
and detector. Luminescence quantum yields were determined
We thank EPSRC and Durham University for support. Computa-
tional resources were supplied by the project “e-Infrastruktura CZ”
e-INFRA LM2018140) provided within the program “Projects of
using [Ru(bpy) ]Cl in aqueous solution as the standard (Φ=
3
2
[35]
0.040). The luminescence lifetimes of the complexes (both in
solution and solid state) were measured by time-correlated single
photon counting (TCSPC), following excitation at 404 nm with a
pulsed diode laser. The emitted light was detected at 90° geometry
using a Peltier-cooled R928 PMT after passage through a mono-
chromator. The estimated uncertainty in the quoted lifetimes is
�10% or better. Spectra at 77 K were recorded in a glass of EPA
(
Large Research, Development and Innovations Infrastructures.”
Conflict of Interest
(
diethyl ether/isopentane/ethanol, 2:2:1 v/v) or butyronitrile. The
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
The authors declare no conflict of interest.
spectra and quantum yields of solid state samples were recorded
using a Jobin Yvon Quanta-Φ integrating sphere operated in
conjunction with a Fluorolog spectrometer.
Keywords: Platinum · Luminescence · Coordination modes ·
Hydrazones · Photochemistry
DFT Calculations
[36]
The studied molecules were optimized in Gaussian 16 to the
corresponding minimum (S or S state), which was confirmed by
0
1
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[37]
B3LYP functional was used for the optimization together with the
Def2-TZVP basis set and C-PCM model for dichloromethane solvent.
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listed in Section 4 of the Supporting Information.
Absorption, fluorescence, and phosphorescence spectra were
[
38]
calculated using the Dalton program. For this purpose, the S0
geometry (for absorption and phosphorescence spectra) and S1
geometry (for fluorescence spectra) derived from previous calcu-
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first 20 excited states were considered. For fluorescence spectra,
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B3LYP functional, ANO-DK3 basis set (6s 4p 3d 1f) for platinum, and
cc-pVTZ-DK for all other elements.
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À 1
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1
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and high-resolution mass spectra of complexes; representative
1–4
frontier orbital plots; simulated absorption spectra of PtL Cl and
emission spectra of a/b-PtL Cl calculated by TD-DFT; additional
4
spectra at 77 K, calculated xyz atomic coordinates of the energy-
minimised structures.
Eur. J. Inorg. Chem. 2021, 335–347
www.eurjic.org
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© 2020 The Authors. European Journal of Inorganic Chemistry published
by Wiley-VCH GmbH

Full Papers
doi.org/10.1002/ejic.202000879
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