Synthesis and luminescence properties of [Pt{4-(o-MeC6H 4)-pzbipy}Cl]SbF6 [pzbipy = 6-2″-pyrazinyl-2, 2′-bipyridine]

Article abstract of DOI:10.1515/znb-2007-0319

The synthesis and characterisation of the 4-(o-R-C₆H ₄)pzbipy [R = H, CH₃ or CF₃; pzbipy = 6-(2″-pyrazinyl)-2,2′-bipyridyl] ligands are described. Reaction of the 4-(o-MeC₆H₄)pzbipy ligand with [Pt(PhCN) ₂Cl₂] in the presence of AgSbF₆ affords [Pt(4-(o-MeC₆H₄)pzbipy}Cl]SbF₆ as a marooncoloured microcrystalline solid. The [Pt{4-(o-MeC₆H ₄)pzbipy)Cl]⁺ cation exhibits low intensity photoluminescence in dichloromethane that maximises at 543 nm and which is assigned to a ³MLCT excited state (τ = 20 ns). The emission spectrum of the cation was also recorded in a frozen DME (1:5:5 (v/v) DMF / MeOH / EtOH} glass; a highly structured band is observed with vibrational spacings of ca. 1400 cm^-1, indicating emission from an intraligand ³π-πz.ast; state (τ = 11 μs). Variable temperature solid emission spectra show maxima that occur at significantly lower energies than is observed in fluid solution and that shift to the red when the temperature is lowered; specifically, λ(em)_max is 674 nm at 280 K (τ = 80 ns) and 723 nm at 80 K (τ = 1.3 μs). Emission behaviour of this type is typical of emission from a metal-metal-ligand charge transfer (MMLCT) excited state that has its origins in d_z2 (Pt)-d_z(Pt) orbital interactions in the crystal.

Full text of DOI:10.1515/znb-2007-0319

Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)-
pzbipy}Cl]SbF6 [pzbipy = 6-2ꢀꢀ-pyrazinyl)-2,2ꢀ-bipyridine]
John S. Fielda, Jan-Andre´ Gertenbacha, Raymond J. Hainesa, Orde Q. Munroa, and
David R. McMillinb
a School of Chemistry, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg, 3201,
South Africa
b Department of Chemistry, Purdue University, West Lafayette, Indiana, 47907-1393, USA
Reprint requests to Prof. J. S. Field. E-mail: fieldj@ukzn.ac.za
Z. Naturforsch. 2007, 62b, 447 – 452; received November 14, 2006
This paper is dedicated to our good friend and colleague, Helgard G. Raubenheimer,
on the occasion of his 65th birthday
The synthesis and characterisation of the 4-(o-R-C6H4)pzbipy [R = H, CH3 or CF3; pzbipy = 6-(2ꢀꢀ-
pyrazinyl)-2,2ꢀ-bipyridyl] ligands are described. Reaction of the 4-(o-MeC6H4)pzbipy ligand with
[Pt(PhCN)2Cl2] in the presence of AgSbF6 affords [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6 as a maroon-
coloured microcrystalline solid. The [Pt{4-(o-MeC6H4)pzbipy}Cl]+ cation exhibits low intensity
photoluminescence in dichloromethane that maximises at 543 nm and which is assigned to a 3MLCT
excited state (τ = 20 ns). The emission spectrum of the cation was also recorded in a frozen DME
{1 : 5:5 (v/v) DMF / MeOH / EtOH} glass; a highly structured band is observed with vibrational
spacings of ca. 1400 cm−1, indicating emission from an intraligand 3π-π∗ state (τ = 11 µs). Variable
temperature solid emission spectra show maxima that occur at significantly lower energies than is
observed in fluid solution and that shift to the red when the temperature is lowered; specifically,
λ(em)max is 674 nm at 280 K (τ = 80 ns) and 723 nm at 80 K (τ = 1.3 µs). Emission behaviour
of this type is typical of emission from a metal-metal-ligand charge transfer (MMLCT) excited state
that has its origins in dz2 (Pt)-dz2 (Pt) orbital interactions in the crystal.
Key words: Pyrazinylbipyridyl Ligand, Platinum Complex, Luminescence
Introduction
relevance is their synthesis of the 4-p-tolyl-2,6-di(2-
pyrazinyl)pyridylligand, where both the outer pyridine
rings of the 2,2ꢀ : 6ꢀ,2ꢀꢀ-terpyridyl moiety have been re-
placed by a pyrazine ring [23]. Here we report the
synthesis of the closely related 4-(2ꢀꢀꢀ-R-phenyl)-6-(2ꢀꢀ-
pyrazinyl)bipyridyl [4-(o-R-C6H4)pzbipy with R = H,
CH3, or CF3] ligands, where just one of the outer
pyridine rings in 2,2ꢀ : 6ꢀ,2ꢀꢀ-terpyridine has been re-
placed by a pyrazine ring. As will be shown, this sim-
ple change has a marked effect on the solid state emis-
sion properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
as compared to that previously reported for [Pt{4ꢀ-(o-
MeC6H4)trpy}Cl]SbF6 [13].
Polypyridine ligands, especially 2,2ꢀ-bipyridine
(bipy) and 2,2ꢀ : 6ꢀ,2ꢀꢀ-terpyridine (trpy), have been ex-
tensively used to confer desirable photophysical prop-
erties on complexes of ruthenium(II) [1] and plat-
inum(II) [2 – 18]. Their attraction derives from the
presence of a delocalised π-system that allows for
facile electron transfer from the metal to the ligand,
thus giving rise to easily accessible metal-to-ligand
charge-transfer (MLCT) excited states. Less studied
are polypyridine ligands that incorporate a pyrazine
ring, this despite the fact that it has been shown that
substituting pyrazine for pyridine can have a dramatic
effect on the photophysical properties of a complex
[19, 20]. Pyrazine is a poorer σ-donor and better π-
acceptor ligand than pyridine [19, 21]. It is also dis-
tinguished from pyridine by the presence of two ni-
trogen donor atoms, a property that has been used to
advantage by Lever and coworkers [22]. Of particular
Results and Discussion
The synthesis of the 4-(o-R-C6H4)pzbipy ligands
followed the Kro¨hnke method [24] and is illustrated
in Scheme 1. The pyrazine ring was introduced via the
enolate with the synthesis of N-{1-pyrazinyl-1-oxo-2-
0932–0776 / 07 / 0300–0447 $ 06.00 © 2007 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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448
J. S. Field et al. · Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
Scheme 1.
ethyl}pyridinium iodide (PZPI) by adaptation of the
method for the assembly of the well known N-{1-(2ꢀ-
pyridyl)-1-oxo-2-ethyl}pyridinium iodide [24]. Reac-
tion of the enones [1-(2ꢀ-pyridyl)-3-(2ꢀꢀ-R-phenyl)-
prop-2-en-1-one (R = H, CH3, or CF3)] with PZPI
in refluxing ethanolic ammonium acetate, affords a
product that is isolated as a pale-yellow crystalline
material in yields of 21 – 43 %. A similar approach
was used by Drew and coworkers for the synthesis
of the closely related 6ꢀ-pyrazin-2-yl-4ꢀ-(4-heptyloxy-
phenyl)-2,2ꢀ-bipyridine ligand, the only difference be-
ing that the pyrazinyl moiety was incorporated via the
enone rather than the enolate [25]. Details of the spec-
troscopic characterisation of the new ligands are given
in the Experimental Section.
In order to synthesise [Pt{4-(o-MeC6H4)pzbipy}Cl]
SbF6, the same approach was used as that previ-
ously employed for the synthesis of the trpy ana-
logue [13]. Thus [Pt(PhCN)2Cl2] was first reacted
with AgSbF6 in refluxing acetonitrile, the AgCl that
formed filtered-off, and the 4-(o-MeC6H4)pzbipy lig-
and added to the reaction mixture, finally affording
the product as a maroon-coloured microcrystalline
solid in a yield of 50 %. Characterisation of [Pt{4-(o-
MeC6H4)pzbipy}Cl]SbF6 was by means of elemen-
tal analysis for C, H and N, as well as by infrared
and 1H NMR spectroscopy. Unfortunately, despite re-
peated attempts, it was not possible to grow single
crystals suitable for an X-ray diffraction study.
Fig. 1. Absorption spectrum of [Pt{4-(o-MeC6H4)pzbipy}
Cl]SbF6 in acetonitrile solution.
pyridyl ligand complexes of platinum(II) [4 – 18]. Of
particular interest is the effect on the positions of the
MLCT absorption bands of replacing an outer pyri-
dine of the trpy ligand with a pyrazine ring. In this re-
gard we note that the corresponding MLCT absorption
bands recorded in acetonitrile for [Pt{4-(o-MeC6H4)
trpy}Cl]SbF6 occur at 380 and 399 nm [13] i. e., at a
slightly higher energy than for the pyrazinylbipyridyl
ligand complex. This is consistent with the stronger π-
acceptor ability of the 4-(o-MeC6H4)pzbipy ligand as
compared to the 4ꢀ-(o-MeC6H4)trpy ligand [19, 21].
The [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6 complex
exhibits low intensity photoluminescence in dichloro-
methane but not in acetonitrile. As shown in Fig. 2, the
spectrum comprises a broad band centred at 543 nm
with a barely discernible shoulder at 565 nm. Charge-
transfer emission from platinum(II) terpyridines is
characterised by an envelope of vibronic structure that
shows a monotonically decreasing intensity with an
increase in wavelength i. e., the highest energy tran-
sition in the progression is the most intense and is
attributable to the zero-zero band [4, 10, 18]. Though
the band in Fig. 2 is poorly resolved, in this respect
it does appear to show features typical of 3MLCT
Photophysical properties of [Pt{4-(o-MeC6H4)-
pzbipy}Cl]SbF6
The electronic absorption spectrum of [Pt{4-(o- emission. Also, consistent with an 3MLCT assign-
MeC6H4)pzbipy}Cl]SbF6 measured in acetonitrile is ment is the absence of any emission signal in acetoni-
shown in Fig. 1. The intense high energy peak at trile, since emissions from planar complexes of plat-
285 nm and the vibrationally structured band in the inum(II) tend to be quenched in a coordinating solvent,
290 – 375 nm region are assigned to π-π∗ absorptions like acetonitrile [12]. The emission spectrum of the
localised on the conjugated ligand. At longer wave- trpy analogue of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
lengths weaker absorptions are observed that com- has not been measured in fluid solution. However,
prise a shoulder at 387 nm and a broad peak cen- it has been measured in dichloromethane for the
tred at 408 nm; these are assigned to MLCT absorp- closely related 4ꢀ-(Ph)trpy ligand complex, [Pt{4ꢀ-
tions. This pattern of absorption bands is typical of ter- (Ph)trpy}Cl]TFPB where TFPB is tetrakis-[3,5-bis(tri-
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J. S. Field et al. · Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
449
Fig. 2. Emission spectrum of [Pt{4-(o-MeC6H4)pzbipy}Cl]
SbF6 in dichloromethane solution (λex = 405 nm).
Fig. 3. Emission spectrum of [Pt{4-(o-MeC6H4)pzbipy}Cl]
SbF6 in a DME glass at 77 K (λex = 405 nm).
fluoromethyl)phenyl]borate; the spectrum exhibits a
weakly resolved vibronic structure with the zero-zero
band at 535 nm (τ = 85 ns) and is assigned as 3MLCT
in origin [10]. In order to make a direct comparison we
have synthesised and measured the emission spectrum
of [Pt{4-(Ph)pzbipy}Cl]BF4 in dichloromethane. The
spectrum is very similar to that shown in Fig. 2; the
emission maximises at 550 nm and the shoulder ap-
pears at ca. 580 nm i. e., it shifts to lower energies as
compared to that for the trpy analogue. We conclude
that the HOMO-LUMO energy gap in the pyrazinyl-
bipyridyl complex is narrower than in the terpyridyl
analogue due to the better π-acceptor ability of the
pyrazine unit, and that this results in a lower energy
for the emission. Somewhat surprisingly the lifetime
of 96 ns measured for [Pt{4ꢀ-(Ph)pzbipy}Cl]BF4 in di-
chloromethane is longer than that of 85 ns measured
for [Pt{4-(Ph)trpy}Cl]TFPB in the same solvent; the
energy gap law predicts an opposite trend [26].
bilised due to the formation of the rigid matrix [10, 18].
The frozen DME glass emission spectrum obtained for
the trpy analogue, [Pt{4ꢀ-(o-MeC6H4)trpy}Cl]SbF6,
is very similar in profile, the only significant differ-
ence being that the emission is shifted to somewhat
higher energies as reflected in a zero-zero transition
at 478 nm [13]. As discussed above this is consistent
with a narrowing of the HOMO-LUMO energy gap in
the pyrazinylbipyridyl complex, due to the better π-
acceptor properties of pyrazine as compared to pyri-
dine [19, 21].
Emission spectra have been recorded on a maroon-
coloured microcrystalline sample of [Pt{4-(o-
MeC6H4)pzbipy}Cl]SbF6 at 40 K intervals over the
temperature range 80 – 280 K, see Fig. 4. At 280 K a
structureless, narrow and asymmetric band that max-
imises at 674 nm is observed (τ = 80 ns). Lowering
the temperature causes a systematic red shift in the
The emission spectrum at 77 K of a 20 µM DME emission maximum, as well as a further narrowing
glass solution of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6 is of the band such that at 80 K the emission maximum
shown in Fig. 3. A highly structured band is observed occurs at 723 nm and the full-width-at-half-maximum
with the zero-zero transition at 501 nm and further pro- (fwhm) is ca. 1200 cm−1 (τ = 1.3 µs). The response
gressions at 539, 580, and 620 nm. The vibrational of the emission to lowering the temperature as well
spacings are of the order 1300– 1400 cm−1 which is as its profile is diagnostic for 3MMLCT emission
typical of a C–C or C–N stretching motion of a ter- i. e., d 2(Pt)-d 2(Pt) orbital interactions are present
pyridine and, presumably, a pyrazinylbipyridyl frame- in the zcrystal zand these interactions increase as the
work. Other evidence in deciding the nature of the temperature is lowered [3, 4, 13, 16]. A direct com-
emitting state is, (i) a Huang-Rhys ratio (I0−1/I0−0
)
parison can be made with the variable temperature
of ca. 0.95 that is close to 1.0 [4, 10, 14, 18], (ii) an solid emission spectra recorded for the red trpy
energy for the zero-zero transition that is somewhat analogue, [Pt{4ꢀ-(o-MeC6H4)trpy}Cl]SbF6 [13]. In
3
higher than that observed in dichloromethane solution this case MMLCT emission that shifts to the red as
(cf. Figs. 2 and 3) and (iii) a relatively long emission the temperature is lowered is also observed, but at
lifetime of 11 µs. Taken together the evidence sug- shorter wavelengths i. e., λ(em)max is 616 nm at 280 K
gests that the emitting state is an admixture of 3MLCT and 673 nm at 80 K [13]. Note that a crystal structure
3
and π-π∗ character, with the latter differentially sta- determination of [Pt{4ꢀ-(o-MeC6H4)trpy}Cl]SbF6
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450
J. S. Field et al. · Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
perature dependent 3MMLCT emission is observed in
the solid state.
Experimental Section
General
The organic solvents used in the syntheses were from
Aldrich and used as received except for acetonitrile that was
distilled by a literature method [28]. The Acetylpyrazine was
obtained from Aldrich and used as received, while the fol-
lowing organic reagents were also obtained from Aldrich
and distilled prior to use: 2-Acetylpyridine, benzaldehyde, 2-
tolualdehyde and α,α,α-trifluoromethyltolualdehyde. The
ammonium acetate was dried in a vacuum desiccator over
P2O5 for several days prior to use. [Pt(PhCN)2Cl2], AgSbF6
and AgBF4 were obtained from Strem Chemicals and also
Fig. 4. Emission spectra of solid [Pt{4-(o-MeC6H4)pzbipy}
used as received. The 2-R-1-{3-(2-pyridyl)-3-oxopropen-
yl}benzene (R = H, CH3 or CF3) was prepared as described
previously [13].
Cl]SbF measured at 40 K intervals from 80 – 280 K (λex
=
575 nm6).
at r. t. confirms that the platinum atoms define a
Instrumentation
linear chain structure and that the Pt···Pt distance
˚
˚
of 3.368 A is significantly shorter than 3.5 A, the
upper distance limit for effective d 2(Pt)-dz2(Pt) orbital
interactions [27]. We assume that zthe crystal structure
of the pyrazinylbipyridyl analogue also possesses a
linear chain of closely-spaced platinum atoms, given
the similar colour (maroon vs. red) and the same emis-
sion response to temperature for the two compounds.
If this is indeed the case, the implication is that the
dz2(Pt)-dz2(Pt) orbital interactions in solid [Pt{4-
(o-MeC6H4)pzbipy}Cl]SbF6 are stronger than in
[Pt{4ꢀ-(o-CH3-Ph)trpy}Cl]SbF6 since the 3MMLCT
emission occurs at lower energies for the former
complex. This view is consistent with the argument
that, because the pzbipy ligand is a better π-acceptor
than the trpy ligand, electron density on the metal
centre will be reduced in the pzbipy complex, thereby
Microanalyses for % C, H and N were performed in
the Microanalytical Laboratory at the University of Natal,
Pietermaritzburg. 1H and 13C NMR spectra ◦were recorded
on a Varian Gemini 200 spectrometer at 25 C with chem-
ical shifts in ppm referenced to TMS. Infrared spectra were
recorded as KBr discs on a Perkin Elmer Spectrum One FTIR
spectrometer. UV/vis absorption spectra were recorded at
22 ◦C using a Shimadzu-2101PC scanning spectrophotome-
ter and the spectrofluorimeter was a SLM Aminco SPF500C.
A finger-Dewar filled with liquid nitrogen permitted mea-
surements in a frozen DME glass. For the variable temper-
ature emission measurements the cryostat was an Oxford In-
struments DN1704 liquid-nitrogen-cooled system complete
with an Oxford Instruments temperature controller. See pre-
vious work for a description of the nitrogen-pumped dye
laser and associated equipment used for lifetime determina-
tions [29]. The method for determining lifetimes has been
promoting close Pt···Pt contacts as the intermetallic described previously [30].
repulsions are reduced. Whatever the explanation,
it is clear that the simple change of a pyridine for a
Syntheses
N-{1-pyrazinyl-1-oxo-2-ethyl}pyridinium iodide (PZPI):
pyrazine in the trpy ligand has a dramatic effect on the
energy of the solid emission.
Acetylpyrazine (4.76 g, 39 mmol) was added to a suspension
of iodine (5.0 g, 39 mmol) in pyridine (15 mL). The mix-
ture was refluxed for 90 min, allowed to cool, and the black
precipitate filtered off, washed with a small amount of cold
pyridine and dried in vacuo. The crude product was purified
by refluxing in a minimum volume of ethanol in the presence
of deactivated charcoal (ca. 1 – 2 % by weight) and filtered
through Celite®. The desired product precipitated as golden
flakes upon cooling. Yield: 6.12 g (48 %). – IR: ν(CO) =
1705 cm−1. – Anal. calcd. for C11H10N3OI: C 40.4, H 3.1,
Concluding Remarks
In conclusion we note how remarkably varied
the excited state properties of the [Pt{4-(o-MeC6H4)
pzbipy}Cl]SbF6 system are. Thus, in fluid solution the
cation exhibits 3MLCT emission that is subject to ex-
ciplex quenching, in a frozen glass the emission is pre-
dominantly intraligand in character and, finally, tem- N 12.8; found: C 40.1, H 2.9, N 12.7.
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J. S. Field et al. · Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
451
4-(2ꢀꢀꢀ-R-phenyl)-6-(2ꢀꢀ-pyrazinyl)bipyridine (R
=
H, trile (5 mL) and added to a suspension of [Pt(PhCN)2Cl2]
CH3, CF3): Ammonium acetate (10 g, excess) was added (100 mg, 0.21 mmol) in acetonitrile (100 mL). The mix-
to a suspension of 2-R-1-{3-(2-pyridyl)-3-oxopropenyl} ture was refluxed overnight under an inert atmosphere af-
benzene (2.0 mmol) and N-{1-pyrazinyl-1-oxo-2-ethyl} ter which the precipitate of AgCl that had formed was re-
pyridinium iodide (0.72 g, 2.2 mmol) in absolute ethanol moved by filtration. An approximately equimolar amount
(8 mL). The mixture was heated to reflux for 90 min (25 min of 4-(2ꢀꢀꢀ-CH3-phenyl)-6-(2ꢀꢀ-pyrazinyl)bipyridine (65 mg,
in the R = CH3 case) and allowed to cool. The impure ligand 0.21 mmol) was added as a solid and the mixture refluxed
precipitated as a grey solid which was recrystallised from for a further 24 h. After this period the solution was fil-
ethanol (95 %) to produce off-white blocks of analytically tered while still hot and the solvent partially removed under
pure ligand that was dried in vacuo.
reduced pressure resulting in the precipitation of [Pt{4-(o-
MeC6H4)pzbipy}Cl]SbF6 as a maroon-coloured solid. The
product was washed on a frit with copious amounts of dieth-
yl ether and then with smaller amounts of acetonitrile. The
resulting powder was recrystallised from hot acetonitrile.
Yield: 79 mg (50 %). – Anal. calcd. for C21H16ClF6N4PtSb:
C 31.90, H 2.04, N 7.09; found: C 31.81, H 1.84, N 7.04. –
For 4-phenyl-6-(2ꢀꢀ-pyrazinyl)bipyridine: Yield: 0.27 g
◦
(43 %). – M. p. 217 – 219 C. – Anal. calcd. for C20H14N4:
C 77.4, H 4.5, N 18.1; found: C 77.6, H 4.4, N 17.7. –
1H NMR (200 MHz, CDCl3): δ = 9.86 (d, 1H, H3 ) 8.78 (d,
ꢀꢀ
ꢀ
ꢀ
1H, H5) 8.71 (m, 1H, H6 ) 8.66 (m, 1H, H3) 8.65 (m, 1H, H3 )
ꢀꢀ ꢀꢀ
8.62 (m, 2H, H5 ,6 ) 7.81 – 7.92 (m, 2H, phenyl H’s) 7.85
ꢀ
1H NMR ([D6]DMSO): δ = 9.89 (d, 1H, H3 ) 9.11 (d, 1H,
ꢀꢀ
(m, 1H, H4 ) 7.44 – 7.55 (m, 3H, phenyl H’s) 7.35 (qd, 1H,
H5 ). – 13C NMR (50 MHz, CDCl3): δ = 150.5 – 156.2 (5C,
ꢀꢀ ꢀꢀ
H6 ) 8.85 (s, 1H, H5) 8.83 (d, 1H, H5 ) 8.79 (s, 1H, H3)
ꢀ
ꢀ ꢀ
8.76 (m, 1H, H6 ) 8.71 (m, 1H, H3 ) 8.44 (td, 1H, H4 ) 7.86
ꢀ
ꢀ
ps, pyridyl and pyrazinyl quat. C’s) 149.1 (s, 1C, C6 ) 143.5 –
144.5 (ts, 3C, pyrazinyl CH’s) 138.1 (s, 1C, phenyl quat. C)
ꢀ
(m, 1H, H5 ) 7.40 – 7.90 (m, 4H, phenyl H’s) 2.45 (s, 3H,
ꢀ
CH3). – IR (KBr, cm−1): ν[4-(o-MeC6H4)pzbipy] = 1610s,
1560w, 1473m, 1420m, 889w, 768s; ν(SbF6−) = 662vs. –
UV/vis (50 µM in MeCN): λmax (ε) = 262 (2.8 × 104),
285 (3.0 × 104), 308sh (1.7 × 104), 325sh (1.5 × 104), 338
(1.7 × 104), 356sh (8.0 × 103), 387sh (3.3 × 103), 408 nm
(3.6×103).
137.0 (s, 1C, C4 ) 127.2 – 129.3 (ts, 5C, phenyl CH’s) 124.0
ꢀ
ꢀ
(s, 1C, C5 ) 121.4 (s, 1C, C3 ) 119.5 (s, 1C, C5) 119.2 (s, 1C,
C3).
For 4-(2ꢀꢀꢀ-CH3-phenyl)-6-(2ꢀꢀ-pyrazinyl)bipyridine:
Yield: 0.23 g (35 %). – M. p. 174 – 176 C. – Anal. calcd.
◦
for C21H16N4: C 77.8, H 5.0, N 17.3; found: C 77.7, H 4.9,
N 17.2. – 1H NMR (200 MHz, CDCl3): δ = 9.86 (d, 1H,
[Pt{4-(Ph)pzbipy}Cl]BF4:
Silver
tetrafluoroborate
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ ꢀꢀ
(41 mg, 0.21 mmol) was dissolved in acetonitrile (5 mL)
and added to a suspension of [Pt(PhCN)2Cl2] (100 mg,
0.21 mmol) in acetonitrile (100 mL). The mixture was
refluxed overnight under an inert atmosphere after which
the precipitate of AgCl that had formed was removed by
filtration. An approximately equimolar amount of 4-phenyl-
6-(2ꢀꢀ-pyrazinyl)bipyridine (62 mg, 0.21 mmol) was added
as a solid and the mixture refluxed for a further 24 h. After
this period the solution was filtered while still hot and the
solvent partially removed under reduced pressure resulting
in the precipitation of [Pt{4-(Ph)pzbipy}Cl]BF4 as a yellow
solid. The product was washed on a frit with copious
amounts of diethyl ether and then with smaller amounts
of acetonitrile. The resulting powder was recrystallised
from hot acetonitrile. Yield: 60 mg (48 %). – Anal. calcd.
for C20H14BClF4N4Pt: C 38.27, H 2.25, N 8.93; found:
C 38.62, H 2.17, N 8.50. – 1H NMR ([D6]DMSO): δ = 9.92
H3 ) 8.65 (m, 1H, H6 ) 8.64 (m, 1H, H3 ) 8.57 (d, 2H, H5 ,6
)
ꢀ
8.51 (d, 1H, H5) 8.39 (d, 1H, H3) 7.84 (td, 1H, H4 ) 7.20 –
ꢀ
7.40 (m, 5H, H5 and phenyl H’s) 2.34 (s, 3H, methyl H’s). –
13C NMR (50 MHz, CDCl3): δ = 151.0 – 155.6 (ps, 5C,
ꢀ
pyridyl and pyrazinyl quat. C’s) 149.1 (s, 1C, C6 ) 144.3 (s,
1C, pyrazinyl CH) 143.5 (ss, 2C, pyrazinyl CH’s) 139.1 (s,
1C, phenyl quat. C) 136.8 (s, 1C, C4 ) 135.0 (s, 1C, phenyl
quat. C) 125.9 – 130.5 (qs, 4C, phenyl CH’s) 123.9 (s, 1C,
ꢀ
ꢀ
ꢀ
C5 ) 122.1 (s, 1C, C5) 121.8 (s, 1C, C3) 121.2 (s, 1C, C3 )
20.3 (s, 1C, CH3).
For 4-(2ꢀꢀꢀ-CF3-phenyl)-6-(2ꢀꢀ-pyrazinyl)bipyridine:
Yield: 0.16 g (21 %). – M. p. 298 – 301 ◦C. – Anal. calcd. for
C21H13N4F3: C 66.7, H 3.5, N 14.8; found: C 66.9, H 3.3,
N 14.7. – 1H NMR (200 MHz, CDCl3): δ = 9.88 (d, 1H,
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ ꢀꢀ
H3 ) 8.67 (m, 2H, H3 ,6 ) 8.60 (m, 2H, H5 ,6 ) 8.40 – 8.53
ꢀ
(dm, 2H, H3,5) 7.88 (m, 1H, H4 ) 7.40 – 7.85 (m, 4H, phenyl
H’s) 7.34 (qd, 1H, H5 ). – 13C NMR (50 MHz, CDCl3): δ =
ꢀ
ꢀꢀ
ꢀꢀ
(d, 1H, H3 ) 9.10 (d, 1H, H6 ) 9.02 (s, 1H, H5) 8.92 (s, 1H,
150.0 – 155.5 (ps, 5C, pyridyl and pyrazinyl quat. C’s) 149.2
ꢀꢀ
ꢀ
ꢀ
H3) 8.76 (d, 1H, H5 ) 8.70 (m, 1H, H3 ) 8.66 (m, 1H, H6 )
ꢀ
(s, 1C, C6 ) 143.5 – 144.6 (ts, 3C, pyrazinyl CH’s) 138.6 (s
(low intensity), 1C, C1 ) 137.0 (s, 1C, C4 ) 128.4 – 131.6
ꢀ
ꢀꢀꢀ,6ꢀꢀꢀꢀ
8.44 (td, 1H, H4 ) 8.06 – 8.18 (m, 2H, H2
) 7.82 (qd,
ꢀꢀꢀ
ꢀ
1H, H5 ) 7.64 – 7.73 (m, 3H, H3 ,4 ,5 ). – IR (KBr, cm−1):
ν[4-(Ph)pzbipy] = 1610s, 1560w, 1474m, 1418m, 889w,
791s; ν (BF4−) = 1053vs. – UV/vis (50 µM in MeCN): λmax
(ε) = 262 (3.3 × 104), 284 (3.4 × 104), 306sh (2.4 × 104),
321sh (2.1 × 104), 334 (2.0 × 104), 384sh (4.8 × 103), 404
(6.0×103).
2
ꢀ
ꢀꢀ ꢀꢀ ꢀꢀ
ꢀꢀꢀ
(ts, 3C, phenyl CH’s) 128.2 (q, JC−F = 30.6 Hz, 1C, C2
)
126.2 (q, 3JC−F = 5.3 Hz, 1C, C3 ) 124.1 (s, 1C, C5 ) 124.0
ꢀꢀꢀ
ꢀ
(q, 1JC−F = 273.9 Hz, 1C, CF3) 121.5 – 122.0 (ss, 2C, C3,5
)
ꢀ
121.4 (s, 1C, C3 ).
[Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6: Silver hexafluoroan-
timonate (73 mg, 0.21 mmol) was dissolved in acetoni-
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452
J. S. Field et al. · Synthesis and Luminescence Properties of [Pt{4-(o-MeC6H4)pzbipy}Cl]SbF6
Acknowledgements
sity of KwaZulu-Natal. DRM acknowledges the Petroleum
Research Foundation (Grant No. ACS-PRF 4036-AC3). We
also express our thanks to James Ryan for performing the
microanalyses.
We gratefully acknowledge the financial support of the
South African National Research Foundation and the Univer-
[16] J. S. Field, J.-A. Gertenbach, R. J. Haines, L. P. Led-
waba, N. T. Mashapa, D. R. McMillin, O. Q. Munro,
G. C. Summerton, J. Chem. Soc., Dalton Trans. 2003,
1176.
[17] V. W.-W Yam, K. M.-C. Wong, N. Zhu, Angew. Chem.
Int. Ed. 2003, 42, 1400.
[1] Selected reviews are: D. M. Roundhill in Photochem-
istry and Photophysics of Metal Complexes, Modern
Inorganic Chemistry Series (Ed.: J. P. Fackler), Plenum
Press, New York, N. Y, 1994, chapter 5; V. Balzani,
A. Juris, M. Venturi, S. Campagna, S. Serroni, Chem.
Rev. 1996, 759.
[18] M. H. Wilson, L. P. Ledwaba, J. S. Field, D. R.
McMillin, J. Chem. Soc., Dalton Trans. 2005, 2754.
[19] S. D. Ernst, W. Kaim, Inorg. Chem. 1989, 28, 1520.
[20] R. J. Crutchley, A. B. P. Lever, J. Am. Chem. Soc. 1980,
102, 7128.
[2] V. M. Miskowski, V. H. Houlding, Inorg. Chem. 1989,
28, 1529.
[3] V. H. Houlding, V. M. Miskowski, Coord. Chem. Rev.
1991, 111, 145.
[4] H.-K. Yip, L.-K. Cheng, K.-K. Cheung, C.-M. Che, J.
Chem. Soc., Dalton Trans. 1993, 2933.
[5] J. A. Bailey, M. G. Hill, R. E. Marsh, V. M. Miskowski,
W. P. Schaefer, H. B. Gray, Inorg. Chem. 1995, 34,
4591.
[21] R. J. Crutchley, A. B. P. Lever, Inorg. Chem. 1982, 21,
2276.
[22] H. E. Toma, A. B. P. Lever, Inorg. Chem. 1986, 25,
176; H. E. Toma, P. R. Auburn, E. S. Dodsworth, M. N.
Golovin, A. B. P. Lever, Inorg. Chem. 1987, 26, 4257;
H. E. Toma, P. S. Santos, A. B. P. Lever, Inorg. Chem.
1988, 27, 3850.
[23] R. Liegghio, P. G. Potvin, A. B. P. Lever, Inorg. Chem.
2001, 40, 5485.
[24] F. Kro¨hnke, Synthesis 1976, 1.
[25] M. G. B. Drew, P. B. Iveson, M. J. Hudson, J. O. Liljen-
zin, L. Spjuth, P.-Y. Cordier, A. Enarsson, C. Hill, C.
Madic, J. Chem. Soc., Dalton Trans. 2000, 821.
[26] J. V. Caspar, T. J. Meyer, J. Am. Chem. Soc. 1983, 105,
5583; J. Jortner, S. A. Rice, R. M. Hochstrasser, Adv.
Photochem. 1969, 7, 149.
[6] D. K. Crites, C. T. Cunningham, D. R. McMillin, Inorg.
Chim. Acta. 1998, 273, 346.
[7] G. Arena, G. Calogero, S. Campagna, L. Monsu´ Sco-
laro, V. R. Romeo, Inorg. Chem. 1998, 37, 2763.
[8] V. W.-W. Yam, R. P.-L. Tang, K. M.-C. Wong, K.-K.
Cheung, Organometallics 2001, 20, 4476.
[9] R. Bu¨chner, C. T. Cunningham, J. S. Field, R. J. Haines,
D. R. McMillin, G. C. Summerton, J. Chem. Soc., Dal-
ton Trans. 1999, 711.
[10] J. F. Michalec, S. A. Bejune, D. G. Cuttell, G. C. Sum-
merton, J.-A. Gertenbach, J. S. Field, R. J. Haines, D. R.
McMillin, Inorg. Chem. 2001, 40, 2193.
[27] D. S. Martin, in Extended Interations between Metal
Ions, ACS Symp. Ser. 5 (Ed.: L. V. Interannte), Ameri-
can Chemical Society, Washington, D. C, 1974, p. 254.
[28] L. Carlsen, H. Egsgaard, J. R. Anderson, Anal. Chem.
1979, 51, 1593.
[29] K. L. Cunningham, C. R. Hecker, D. R. McMillin, In-
org. Chim. Acta. 1996, 242, 143.
[30] F. Liu, K. L. Cunningham, W. Uphues, G. W. Fink,
J. Schmolt, D. R. McMillin, Inorg. Chem. 1995, 34,
2015.
[11] S. E. Hobert, J. T. Carney, S. D. Cummings, Inorg.
Chim. Acta 2001, 318, 89.
[12] D. K. Crites Tears, D. R. McMillin, Coord. Chem. Rev.
2001, 211, 195.
[13] J. S. Field, R. J. Haines, D. R. McMillin, G. C. Summer-
ton, J. Chem. Soc., Dalton Trans. 2002, 1369.
[14] D. R. McMillin, J. J. Moore, Coord. Chem. Rev. 2002,
229, 113.
[15] V. W.-W Yam, K. M.-C. Wong, N. Zhu, J. Am. Chem.
Soc. 2002, 124, 6506.
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