Synthesis, electrochemistry and luminescence of [Pt{4′-(R)trpy}(CN)] + (R = Ph, o-CH3C6H4, o-ClC 6H4 or o-CF3C6H4; Trpy = 2,2′:6′,2″-terpyridine): Crystal structure of [Pt{4′-(Ph)trpy}(CN)]BF4·CH3CN

Article abstract of DOI:10.1039/b611244g

The synthesis and characterization of [Pt{4′-(R)trpy}(CN)]X (R = Ph, X = BF₄ or SbF₆; R = o-CH₃C₆H ₄, X = SbF₆; R = o-ClC₆H₄, X = SbF₆; or R = o-CF₃C₆H₄, X = SbF ₆) are described where trpy = 2,2′:6′,2″- terpyridine. Single crystals of [Pt{4′-(Ph)trpy}(CN)]BF ₄·CH₃CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4′-(Ph)trpy}(CN)]BF ₄. An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9° of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4′-(R)trpy}(CN)]⁺ cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E_1/2 values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4′-(Ph)trpy}(CN)]⁺ ～ [Pt{4′-(o-CH ₃C₆H₄)trpy}(CN)]⁺ < [Pt{4′-(o-ClC₆H₄)trpy}(CN)]⁺ < [Pt{4′-(o-CF₃C₆H₄)trpy}(CN)] ⁺. All the [Pt(4′-(R)trpy}(CN)]⁺ cations are photoluminescent in dichloromethane. Emission by [Pt{4′-(Ph)trpy}(CN)] ⁺ is from an excited state with largely ³MLCT orbital parentage, but with some intraligand ³π-π* character mixed-in (τ = 0.1 s). In contrast, the other three cations display emission that appears exclusively intraligand ³π-π* in origin (τ ～ 0.8 s). Emission spectra have been recorded in a low concentration frozen DME {1: 5: 5 (v/v) DMF-MeOH-EtOH} glass. For the R = o-CH ₃C₆H₄, o-ClC₆H₄ and o-CF₃C₆H₄ cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4′-(Ph)trpy}(CN)] ⁺ cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more "domed" pattern; this has been interpreted in terms of a higher percentage of intraligand ³π-π* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric ³π-π* and ³MMLCT emission, respectively. The Royal Society of Chemistry 2007.

Full text of DOI:10.1039/b611244g

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Synthesis, electrochemistry and luminescence of [Pt{4ꢀ-(R)trpy}(CN)]+ (R =
Ph, o-CH3C6H4, o-ClC6H4 or o-CF3C6H4; trpy = 2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine):
crystal structure of [Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN
John S. Field,*a Raymond J. Haines,a Lesibana P. Ledwaba,a Robert McGuire, Jr.,b Orde Q. Munro,a
Murray R. Lowa and David R. McMillinb
Received 3rd August 2006, Accepted 2nd November 2006
First published as an Advance Article on the web 16th Novemeber 2006
DOI: 10.1039/b611244g
The synthesis and characterization of [Pt{4ꢀ-(R)trpy}(CN)]X (R = Ph, X = BF4 or SbF6; R =
o-CH3C6H4, X = SbF6; R = o-ClC6H4, X = SbF6; or R = o-CF3C6H4, X = SbF6) are described where
trpy = 2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine. Single crystals of [Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN were grown by
vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4ꢀ-(Ph)trpy}(CN)]BF4. An X-ray
crystal structure determination of the solvated complex confirms the near linear coordination of the
cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9◦
of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in
DMF/0.1 M TBAH for the [Pt{4ꢀ-(R)trpy}(CN)]+ cations. Two quasi-reversible one-electron reduction
(cathodic) waves are observed with E1/2 values that show the trend expected for an increasingly lower
energy of the trpy-based LUMO of the complex i.e., [Pt{4ꢀ-(Ph)trpy}(CN)]+ ∼ [Pt{4ꢀ-(o-CH3-
C6H4)trpy}(CN)]+ < [Pt{4ꢀ-(o-ClC6H4)trpy}(CN)]+ < [Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+. All the
[Pt(4ꢀ-(R)trpy}(CN)]+ cations are photoluminescent in dichloromethane. Emission by
[Pt{4ꢀ-(Ph)trpy}(CN)]+ is from an excited state with largely 3MLCT orbital parentage, but with some
intraligand 3p–p* character mixed-in (s = 0.1 ls). In contrast, the other three cations display emission
that appears exclusively intraligand 3p–p* in origin (s ∼ 0.8 ls). Emission spectra have been recorded in
a low concentration frozen DME {1 : 5 : 5 (v/v) DMF–MeOH–EtOH} glass. For the R = o-CH3C6H4,
o-ClC6H4 and o-CF3C6H4 cations the envelope of vibronic structure and energies of the vibrational
components are essentially the same as that recorded in dichloromethane. However, for the
[Pt{4ꢀ-(Ph)trpy}(CN)]+ cation, there is a blue-shift in the energies of the vibrational components as
compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure
to a more “domed” pattern; this has been interpreted in terms of a higher percentage of intraligand
3p–p* character in the emitting state for the glass. Increasing the concentration of the glass invariably
leads to aggregation of the cations and the consequent development of new low energy bands, such that
at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are
assigned to excimeric 3p–p* and 3MMLCT emission, respectively.
3
weakly in dichloromethane (DCM) from an intraligand p–p*
Introduction
state, [Pt{4ꢀ-(dma)trpy}(CN)]+ (dma = dimethylamino) emits
Terpyridyl or substituted terpyridyl (trpy, where trpy = 2,2ꢀ:6ꢀ,2ꢀꢀ-
strongly in DCM from a largely ligand-based charge-transfer
excited state with an unusually long lifetime of 22 ls.21 Here we
report the electrochemical and photoluminescence properties of
the [Pt{4ꢀ-(R)trpy}(CN)]+ cations where R = Ph, o-CH3C6H4, o-
ClC6H4 or o-CF3C6H4 i.e., a phenyl or ortho-substituted phenyl
group. Also reported, for the first time, is the crystal structure of a
terpyridyl ligand complex of platinum(II) with the cyanide ion as
a co-ligand, in particular of [Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN.
terpyridine) ligand complexes of platinum(II) with a chloride ion
as the fourth ligand bonded to platinum have received consider-
able attention insofar as their photoluminescence properties are
concerned.1–15 Similarly, a number of reports have appeared that
describe the photoluminescence properties of compounds where a
r-acetylide ligand is bound to a Pt(trpy) unit.16–20 However, only
one report has appeared to date on the photophysics of platinum
terpyridine complexes that include the strong-field cyanide ion
as a co-ligand.21 Their luminescence properties vary according
to the substituent in the 4ꢀ-position of the terpyridyl ligand.
Thus, whereas [Pt(trpy)(CN)]+ and [Pt{(4ꢀ-(CN)trpy}(CN)]+ emit
Results and discussion
The compounds [Pt{4ꢀ-(R)trpy}(CN)]SbF6 (R = Ph, yellow; o-
CH3C6H4, red; o-ClC6H4, orange or o-CF3C6H4, yellow) and
[Pt{4ꢀ-(Ph)trpy}(CN)]BF4 (yellow) were synthesized in good yields
by means of a metathesis reaction in which the chloride ion
precursor, [Pt{4ꢀ-(R)trpy}Cl]SbF6 or [Pt{4ꢀ-(Ph)trpy}Cl]BF4, was
aSchool of Chemistry, University of KwaZulu-Natal, Private Bag X01,
Pietermaritzburg, 3201, South Africa. E-mail: fieldj@ukzn.ac.za
bDepartment of Chemistry, Purdue University, West Lafayette, Indiana,
47907-1393, USA. E-mail: mcmillin@purdue.edu
192 | Dalton Trans., 2007, 192–199
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in [Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN, consistent with its yellow
colour. On the other hand, [Pt{4ꢀ-(Ph)trpy)Cl]BF4·CH3CN is red,
reacted in refluxing acetonitrile with one equivalent of silver
cyanide. The compounds were characterised bymeans of elemental
analysis, IR, 1H NMR and 13C NMR spectroscopy. These data are
listed in the Experimental section.
2
2
the colour often associated with the presence of dz (Pt)–dz (Pt)
orbital interactions in the crystal; see ref. 24 and 25 for example.
Crystal structure of [Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN
Electrochemistry
Yellow needle-shaped single crystals of [Pt{4ꢀ-(Ph)trpy}-
Cyclic voltammograms of the hexafluoroantimonate salt of
the [Pt{4ꢀ-(Ph)trpy}(CN)]+ cation were recorded in dimethylfor-
mamide (DMF) as a function of scan rate; the results obtained
for a 1 mM solution are shown in Fig. 2. At 1000 mV s−1
two quasi-reversible reduction waves are observed with the first
somewhat broader than the second. Other related platinum(II)
terpyridine complexes similarly exhibit a pair of quasi-reversible
reduction waves that are assigned as one-electron transfers to
a largely ligand-based orbital.5,11,21,26 Accordingly, we make the
same assignment and calculate E1/2 (vs. Fc+/0) values of −1.14 and
−1.68 V for the two waves. These values are significantly anodic of
the corresponding E1/2 values of −1.22 and −1.76 V measured in
DMF for the chloride ion analogue, [Pt{4ꢀ-(Ph)trpy}Cl]+.5 The
implication is that the energy of the largely terpyridyl ligand-
based LUMO for the cyanide ion complex,27 is lower than that
for the chloride ion species, an expected result in view of the fact
that the cyanide ion is strongly electron-withdrawing whereas the
chloride ion is considered a p-donor ligand. The E1/2 values are
also anodic of those recorded in DMF for the parent cyanide
complex, [Pt(trpy)(CN)]+ but only marginally so; the latter values
are −1.16 and −1.72 V.21 Though the anodic shift is small it is
consistent with the extended p-delocalisation and hence lower
energy of the terpyridyl ligand-based LUMO brought about by
the presence of phenyl group in the 4ꢀ-position of the terpyridyl
moiety.
(CN)]BF4·CH3CN were grown by slow diffusion of diethyl
ether into
acetonitrile.
a
A
concentrated solution of the compound in
perspective view of the cation in [Pt{4ꢀ-
(Ph)trpy}(CN)]BF4·CH3CN is given in Fig. 1 with a selection
of intramolecular bond lengths and angles being listed in the
caption. None of these shows any unusual features and are
similar to those measured for other terpyridyl ligand complexes of
platinum(II).1,2,4,5,7,16,19 As expected the Pt–C≡N linkage is nearly
linear with a Pt–C(22)–N(4) angle of 176.1(8)◦. The phenyl ring is
only slightly twisted out of the plane of the terpyridyl moiety as
evidenced by (i) a dihedral angle between the mean planes through
the phenyl ring carbon atoms and the non-hydrogen atoms of the
central pyridine ring of 2.1◦ and (ii) a C(9)–C(8)–C(16)–C(17)
torsion angle of 1.9◦. The corresponding torsion angles calculated
from crystal structure determinations of the free 4ꢀ-(Ph)trpy
ligand,22 and for the cation in [Pt{4ꢀ-(Ph)trpy}Cl]BF4·CH3CN,4
are considerably larger at 10.9 and 33.4◦, respectively. Pre-
sumably crystal packing effects are responsible for these dif-
ferences. Noteworthy is that the packing of the cations in
[Pt{4ꢀ-(Ph)trpy}(CN)]BF4·CH3CN is very different from that for
the chloride analogue, [Pt{4ꢀ-(Ph)trpy}Cl]BF4·CH3CN.4 Thus,
whereas in the former the cations are well-separated (the shortest
˚
intermolecular Pt · · · Pt distance is 4.766 A) in the latter they are
stacked as an extended chain of tetramers with Pt · · · Pt distances
4
˚
within the tetramers of ca. 3.3 A. The upper Pt · · · Pt distance
2
2
limit for significant dz (Pt)–dz (Pt) orbital interactions is about
23
˚
2
2
3.5 A. Clearly, dz (Pt)–dz (Pt) orbital interactions are absent
Fig. 2 Cyclic voltammograms of [Pt{4ꢀ-(Ph)trpy}(CN)]+ (1 mM in DMF
containing 0.1 M TBAH) as a function of scan rate.
We now discuss the cyclic voltammograms recorded at lower
scan rates for the [Pt{4ꢀ-(Ph)trpy}(CN)]+ cation. As shown in
Fig. 2, an additional irreversible wave ca. 0.14 V cathodic of the
first wave is clearly visible at a scan rate of 100 mV s−1. Note that its
height decreases as the scan rate increases such that at 1000 mV s−1
it is no longer discernable as a distinct peak. A similar peak was
observed in the cyclic voltammogram recorded for [Pt(trpy)(CN)]+
also in DMF.21 A likely explanation for the peak is that a chemical
process is coupled to the first reduction step, in particular dimer
Fig.
1
ORTEP view of the cation in [Pt{4ꢀ-(Ph)trpy}(CN)]-
BF4·CH3CN. Non-hydrogen atoms are drawn as 50% ellipsoids while the
hydrogen atoms are drawn as spheres of arbitrary radius. Interatomic
◦
˚
distances (A) and angles ( ): Pt–N(1) 2.026(6), Pt–N(2) 1.936(5), Pt–N(3)
2.028(6), Pt–C(22) 2.048(8); N(1)–Pt–N(2) 80.6(2), N(1)–Pt–N(3) 161.0(3),
N(2)–Pt–N(3) 80.5(2), Pt–C(22)–N(4) 176.1(8).
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formation due to a rapid reaction at the electrode surface between
Photophysics
[Pt{4ꢀ-(Ph)trpy}(CN)] and [Pt{4ꢀ-(Ph)trpy}(CN)]+ to form [Pt{4ꢀ-
The absorption spectrum measured in dichloromethane (DCM)
for [Pt{4ꢀ-(Ph)trpy}(CN)]+ is representative and is shown in
Fig. 3; a listing of the wavelengths of the absorption maxima
for all the cations is given in Table 2. Typical of platinum(II)
terpyridine complexes is the presence of mainly intraligand p–
p* absorptions at shorter wavelengths and weaker metal-to-ligand
charge-transfer [1MLCT/1d–p*(trpy)] absorptions bands in the
range 350–450 nm.1,3,12,21 In DCM the latter occur at 365 and
380 nm i.e., at a significantly higher energy than the corresponding
bands at 397 and 412 nm measured for the chloride ion analogue,
[Pt{4ꢀ-(Ph)trpy}Cl]+.5 A likely explanation for the blue shift is that
the stronger p-acceptor properties of the cyanide (as compared
to the chloride) causes a larger ligand field splitting of the d-
orbitals and a concomitant stabilization of the dp orbitals of the
metal (more correctly molecular orbitals with significant dp(Pt)
atomic orbital character).29 Note that this effect must dominate
the energy of the 1MLCT absorption since, as discussed above, the
electrochemical data suggest that the energy of the trpy ligand-
based LUMO is actually lower for the cyanide ion complex. The
corresponding1MLCT absorptions ofthe parent cyanidecomplex,
[Pt(trpy)(CN)]+, occur at 360 and 375 nm i.e., at slightly higher
energies than those shown in Fig. 1.21 This is consistent with the
+
(Ph)terpy}CN]2 ; and that it is the reduction of the latter that gives
rise to the additional peak. Certainly, other workers have invoked
dimer formation to explain the spectroelectrochemical results
obtained for [Pt(trpy)Cl]+.26 Note that doubling the concentration
to 2 mM has as a result that the additional cathodic wave increases
in height relative to that for the first wave for a given scan rate.
This is also consistent with dimer formation.28
With regard to the cyclic voltammograms recorded in DMF
of the other cations viz [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+, [Pt{4ꢀ-
(o-ClC6H4)trpy}(CN)]+ and [Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+, they
all display two reversible one-electron reduction waves over the
full scan rate range of 100 to 1000 mV s−1; note that they are not
complicated by the intervention of an additional wave cathodic of
the first reduction wave. The implication is that dimer formation
does not occur on reduction of these cations. We speculate that,
due to steric interactions with adjacent hydrogens of the terpyridyl
moiety, the ortho-substituent of the 4ꢀ-phenyl group forces the
phenyl group out of the plane of the terpyridyl moiety, thus
rendering the cation as a whole non-planar. The upshot is that the
cations do not p-stack as easily as the flat [Pt{4ꢀ-(Ph)terpy}(CN)]+
cation, thus hindering dimer formation. A summary of the
electrochemical data for all four cations is given in Table 1.
Note the trend in E1/2 values: [Pt{4ꢀ-(Ph)trpy}(CN)]+ ∼ [Pt{4ꢀ-(o-
CH3C6H4)trpy}(CN)]+ < [Pt{4ꢀ-(o-ClC6H4)trpy}(CN)]+ < [Pt{4ꢀ-
(o-CF3C6H4)trpy}(CN)]+. The order reflects an increasingly lower
energy for the largely p*-trpy LUMO of the complex and is the
expected one, given an order of electron-withdrawing ability of
o-CF3C6H4 > o-ClC6H4 > o-CH3C6H4 ∼ Ph.
Table 1 Electrochemical data in DMF with 0.1 M TBAH
Complex
E1a/V (vs. Fc+/0
)
E2a/V (vs. Fc+/0
)
[Pt{4ꢀ-(Ph)trpy}Cl]+ (ref. 5)
[Pt(trpy)(CN)]+ (ref. 21)
−1.21 (88, 1.2)b,c
−1.16 (90, 0.9)b,c
−1.14 (108, 1.1)b,e
−1.10 (100, 1.1)b,e
−1.08 (98, 1.1)b,e
−1.75 (68, 1.0)b,c
−1.72 (60, 1.2)b,c
−1.68 (60, 1.0)b,e
−1.74 (64, 1.0)b,e
−1.62 (64, 1.0)b,e
[Pt{4ꢀ-(Ph)trpy}(CN)]+
−1.14 (126, 1.3)b,d −1.68 (66, 1.0)b,d
[Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+
[Pt{4ꢀ-(o-ClC6H4)trpy}(CN)]+
[Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+
a E1/2 = (Epa + Epc)/2 where Epa and Epc are the peak anodic and peak
cathodic potentials, respectively. b
Epa–Epc separation in mV and ic/ia ratio
in brackets. c Scan rate = 50 mV s−1
.
d Scan rate = 1000 mV s−1
.
e Scan
Fig. 3 Absorption spectrum of [Pt{4ꢀ-(Ph)trpy}(CN)]+ in dichloro-
rate = 100 mV s−1
.
methane solution.
Table 2 Photophysical data for platinum terpyridine complexes in DCM at room temperature
Complex
kabs a/nm
kem b/nm
sc/ls
φd
kr = (φ/s)e/s−1
max
max
[Pt{4ꢀ-(Ph)trpy}Cl]+ (ref. 5)
[Pt(trpy)(CN)]+ (ref. 21)
283, 309, 322, 336; 397sh, 412
298, 312, 330, 345; 360sh, 375
245, 275, 309, 322, 344; 365, 380
247, 277, 302sh, 316, 328, 345; 365, 379
244, 278, 315, 331, 346; 367, 377
245, 279, 314, 330, 346: 362, 377
535, 570sh, 608sh
465, 500, 530, 570sh
490, 525, 575
0.085
0.015
0.1
0.7
0.8
0.0031
0.0004
0.0028
0.0008
0.0003
0.0005
3.6 × 104
2.6 × 104
2.8 × 104
1.1 × 103
3.8 × 102
6.3 × 102
[Pt{4ꢀ-(Ph)trpy}(CN)]+
[Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+
465, 500, 540
f
[Pt{4ꢀ-(o-ClC6H4)trpy}(CN)]+
471, 504, 535
468, 501, 534
f
[Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+
0.8
f
a Absorption maxima; semicolon sets off CT bands. b Emission maxima. Italic values refer to the most intense band. c Excited state lifetime 10%.
d Emission yield 10%. e Estimate of radiative rate constant, see ref. 32. f Emission spectra in DCM have not been recorded for the chloride ion analogue
of these complexes.
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comparison of E1/2 values made above i.e., the energy of the trpy
ligand-based LUMO for [Pt{4ꢀ-(Ph)trpy}(CN)]+ is slightly lower
than that of [Pt(trpy)(CN)]+.
The [Pt{4ꢀ-(Ph)trpy}(CN)]+ complex also exhibits photolumi-
nescence in DCM as shown in Fig. 4. Well resolved vibrational
components attributable to the 0–0 and 0–1 transitions appear
at 490 and 525 nm along with a shoulder at 575 nm. Increasing
the excitation wavelength from 340 to 390 nm results in a gradual
decrease in the intensity of the emission but has no effect on the
positions of the peaks. We assign the emission as mainly 3MLCT in
origin. Consistent with this assignment, the envelope of vibronic
structure shows a monotonic decrease in intensity with increase
in wavelength.1,3,5,21 However, the Huang–Rhys ratio (i.e., I0–1/I0–0
)
of 0.96 is close to 1.0, which indicates that the emitting state has
significant intraligand 3p–p* character mixed-in as well.1,3,5,21 The
emission exhibited by the [Pt{4ꢀ-(Ph)trpy}(CN)]+ complex in fluid
solution is the more interesting because it differs from that of the
parent species [Pt(trpy)(CN)]+ which emits from an intraligand
3p–p* state at higher energy (see Table 2). As previously noted,21
it is possible to observe 3p–p* emission from [Pt(trpy)(CN)]+,
Fig.
5
Emission spectrum of [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+ in
dichloromethane solution: kex = 340 nm.
shape i.e., a longer wavelength vibronic component becomes
the most intense transition (see Table 2). Also significant is
that the energy spacing within the progression is of the order
of 1400 cm−1 which is typical of the C–C and C–N stretching
motion of the terpyridine framework. As others have discussed,
a Franck–Condon envelope of this type is the signature for
polypyridine-centred 3p–p* emission.30,33–35 Accordingly, the emis-
sions exhibited by the [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+, [Pt{4ꢀ-(o-
ClC6H4)trpy}(CN)]+ and [Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+ cations
have similar energies as that recorded for the parent
[Pt(trpy)(CN)]+ complex (see Table 2). The difference in the
emission energy relative to [Pt{4ꢀ-(Ph)trpy}(CN)]+ is prob-
ably due to the planarity of the latter; crystal struc-
ture determinations of [Pt{4ꢀ-(o-CH3C6H4)trpy}Cl]SbF6,7 [Pt{4ꢀ-
(o-CH3C6H4)trpy}Cl]BF4,7 [Pt{4ꢀ-(o-ClC6H4)trpy}Cl]SbF6,9 and
[Pt{4ꢀ-(o-CF3C6H4)trpy}Cl]SbF6,7 reveal that the other cations
must be markedly non-planar.
Insofar as the room-temperature excited state lifetimes are
concerned, those measured for the [Pt{4ꢀ-(R)trpy}(CN)]+ cations
as well as for [Pt{4ꢀ-(Ph)trpy}Cl]+, follow the pattern expected
from the prediction of the energy-gap law,36 in that the emission
lifetimes decrease as the energy of the emission decreases (see
Table 2). The trend is remarkable because the orbital parentage
is also changing. One anomaly is that the lifetime of 0.015 ls
for the emitting state of the parent [Pt(trpy)(CN)]+ cation is low
by comparison with the lifetimes of 0.1–0.8 ls measured for the
[Pt{4ꢀ-(R)trpy}(CN)]+ cations. The relatively short excited state
lifetime of the [Pt(trpy)(CN)]+ complex has been rationalized in
terms of the thermal population of a non-radiative 3d–d state,21 in
accordance with findings for related transition metal coordination
compounds.37 However, if that were the case, the complexes with an
ortho-substituted phenyl group in the 4ꢀ-position of the terpyridyl
ligand might also be expected to exhibit short lifetimes. Other
work on complexes of platinum(II) with aryl substituents in the 4ꢀ-
position of the terpyridyl ligand i.e., [Pt{4ꢀ-(Rꢀ)trpy}Cl]+ systems
where Rꢀ = 1-naphthyl, 2-naphthyl or 1-phenanthrenyl, may be
relevant in this regard.5 The dramatically enhanced lifetimes of
up to 64 ls within that series have been explained in terms of
emitting states having an admixture of aryl-to-trpy intraligand
charge-transfer (ILCT) character. Perhaps, a similar effect is at
work in the complexes with the ortho-substituted phenyl groups
in the 4ꢀ position of the trpy ligand. Another possibility is that
the thermally assisted decay of the photoexcited [Pt(trpy)(CN)]+
1
even though the lowest energy absorption has d–p* character,
because the singlet–triplet splitting is comparatively small for
d–p* excitation.30,31 What makes the [Pt{4ꢀ-(Ph)trpy}(CN)]+ sys-
1
tem different is an appreciably lower energy d–p* absorption.
The chloride analogue [Pt{4ꢀ-(Ph)trpy}Cl]+ also exhibits 3MLCT
emission in DCM,5 consistent with the low energy of the CT
absorptions recorded for the complex (see Table 2). The radiative
rate constants in Table 2 tend to support the proposed state
assignments. Note that the kr value for the triplet emission drops
by more than an order of magnitude as the participation of the
heavy metal decreases and the orbital parentage changes from
3
3
predominantly d–p* to predominantly p–p* in character. The
kr value calculated for [Pt(trpy)(CN)]+ in Table 2 is anomalously
high, but note that the reported lifetime is an extrapolated value,
as opposed to a directly measured quantity.21 Also, for this system
the simple kinetic model that gives rise to the kr = φ/s equation
may not be applicable if the 3p–p* emitting state is in equilibrium
with a nearby deactivating state, vide infra.32
Fig. 4 Emission spectrum of [Pt{4ꢀ-(Ph)trpy}(CN)]+ in dichloromethane
solution; kex = 340 nm.
In contrast, the emission spectra recorded for the [Pt{4ꢀ-(o-
CH3C6H4)trpy}(CN)]+, [Pt{4ꢀ-(o-ClC6H4)trpy}(CN)]+ and [Pt{4ꢀ-
3
(o-CF3C6H4)trpy}(CN)]+ cations clearly exhibit p–p* character;
see Fig. 5 for the signal from the 4ꢀ-(o-CH3C6H4)trpy complex.
Here the envelope of the vibronic structure has a ‘domed’
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Dalton Trans., 2007, 192–199 | 195
©

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complex occurs via a higher lying vibrational level of the emitting
state rather than a 3d–d excited state.38 With that type of pathway,
the efficiency could be very dependent on the ligand structure.
Emission spectra have been recorded in a frozen DME {1 : 5 : 5
(v/v) DMF–MeOH–EtOH} glass as a function of concentration
for the hexafluoroantimonate salts of the [Pt{4ꢀ-(R)trpy}(CN)]+
cations. The spectra obtained for the [Pt{4ꢀ-(Ph)trpy}(CN)]+
cation are shown in Fig. 6. At the lowest concentration of
0.005 mM, a structured band is observed with vibrational compo-
nents at 478, 505 and 543 nm. There is no measurable difference
in the intensities of the first two (0–0 and 0–1) components, and
the band positions are slightly blue-shifted when compared to
those recorded for the [Pt{4ꢀ-(Ph)trpy}(CN)]+ cation in DCM
(see Table 2). The blue-shift in energy as well as the change in
emission profile towards a more “domed” envelope suggests that
there is more 3p–p* character in the dilute glass emission, though
Fig. 7 Emission spectra of [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+ in DME at
77 K as a function of concentration: kex = 340 nm.
3
the emitting state remains one of mixed MLCT/3p–p* orbital
similar to that recorded for the [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+
cation in DCM (see Table 2 and Fig. 5). Thus, the same
assignment of emission from a terpyridyl ligand-based 3p–p* state
applies. As for the [Pt{4ꢀ-(Ph)trpy}(CN)]+ cation, increasing the
concentration of [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+ in frozen DME
leads to aggregate formation and hence to the development of two
new low energy bands, in particular at 647 and 711 nm, the latter
as a shoulder. Finally, the frozen DME glass emission spectra have
also been recorded as a function of concentration for the [Pt{4ꢀ-(o-
ClC6H4)trpy}(CN)]+ and [Pt{4ꢀ-(o-CF3C6H4)trpy}(CN)]+ cations,
but since these display essentially the same features as those shown
in Fig. 7 for the [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]+ cation, they are
not discussed further here.
parentage. Increasing the concentration of the glass results in the
development of two new longer wavelength bands; in particular
bands at 653 and 713 nm. These bands are associated with different
types of aggregates that form when the concentration is increased.
At the suggestion of a Referee, excitation spectra of a concentrated
solution of the [Pt{4ꢀ-(Ph)trpy}(CN)]+ cation were recorded at
77 K in a DME glass. At an emission wavelength of 505 nm,
the excitation spectrum revealed charge-transfer excitation bands
in the vicinity of 390 nm, similar to what has been observed in
fluid solution at room temperature. This observation establishes
that the monomeric complex is present in the glass. However,
other species are also present because the same bands do not
appear in the excitation spectrum obtained while monitoring at
720 nm. In their stead, the excitation spectrum shows a broad
band centred at around 440 nm which is attributable to aggregated
species i.e., oligomers of an undetermined length. Consistent with
the excitation data, the sample was virtually colorless at room tem-
perature but clearly took on a reddish hue at 77 K. Similar aggre-
gation effects have been observed in the high concentration glass
spectra recorded for [Pt{4ꢀ-(Ph)trpy}Cl]+ in butyronitrile,4 and
[Pt(trpy)Cl]+ in DME.2 The emission from the 4ꢀ-(o-CH3C6H4)trpy
ligand complex in a low-temperature glass appears in Fig. 7.
At low concentrations (≤0.013 M) the spectrum consists of a
structured ‘domed’ pattern with vibronic components at 465, 496
and 534 nm and a weak progression at 576 nm. As such it is very
Experimental
Methods
The 4ꢀ-phenyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine was prepared by the method
of Constable,22 4ꢀ-o-methylphenyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine and 4ꢀ-
o-trifluoromethylphenyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine by the Kro¨hnke
method described in ref. 7, and 4ꢀ-o-chlorophenyl-2,2ꢀ:6ꢀ,2ꢀꢀ-
terpyridine by the Kro¨hnke method described in ref. 9.
The chloride ion platinum complex precursors were prepared
according to procedures described in the literature: [Pt{4ꢀ-
(Ph)trpy}Cl]SbF6 and [Pt{4ꢀ-(Ph)-trpy}Cl]BF4 (ref. 4); [Pt{4ꢀ-
(o-CH3C6H4)trpy}Cl]SbF6 and [Pt{4ꢀ-(o-CF3C6H4)trpy}Cl]SbF6
(ref. 7) and [Pt{4ꢀ-(o-ClC6H4)trpy}Cl]SbF6 (ref. 9). The acetonitrile
used as the solvent and for the purposes of crystal growth
was purified by the method of Carlsen and co-workers.39 Other
solvents were dried and purified using standard procedures.40 The
silver cyanide was obtained from FLUKA chemicals and used as
received. The tetrabutylammonium hexafluorophosphate (TBAH)
used for the electrochemistry studies was of electrochemical grade
(FLUKA); the DMF of Biotech grade (ALDRICH).
[Pt{4ꢀ-(R)trpy}(CN)]SbF6 (R = Ph, o-CH3C6H4, o-ClC6H4 or o-
CF3C6H4). To a suspension of [Pt{4ꢀ-(R)trpy}Cl]SbF6 (100 mg)
in acetonitrile (10 mL) was added an equimolar amount of AgCN
dissolved in 10 mL of boiling acetonitrile and the mixture heated
to reflux for 24 h. After cooling to room temperature the resulting
AgCl precipitate was removed by filtration, and the volume
of the solvent reduced in vacuo to induce the precipitation of
Fig. 6 Emission spectra of [Pt{4ꢀ-(Ph)trpy}(CN)]+ in DME at 77 K as a
function of concentration: kex = 340 nm.
196 | Dalton Trans., 2007, 192–199
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©

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[Pt{4ꢀ-(R)trpy}(CN)]SbF6 as a microcrystalline solid. The pre-
cipitate was collected by filtration and washed with a minimum
amount of ice-cold acetonitrile and finally dried in vacuo. The
resultant solid was purified by extraction into hot acetonitrile
that was then allowed to slowly cool to room temperature, a
process that afforded a pure crystalline solid that was collected
by filtration and dried in vacuo. Analytical and spectroscopic data
are as follows. [Pt{4ꢀ-(Ph)trpy}(CN)]SbF6: Yield 83 mg (86%).
Colour, yellow. Anal. Calc. for C22H15N4F6PtSb: C, 34.5; H, 2.0;
N, 7.3%. Found: C, 34.1; H, 1.9; N, 6.9%. 1H NMR (DMSO-d6): d
yellow. Anal. Calc. for C22H15BF4N4Pt: C, 42.8; H, 2.5; N, 9.1%.
Found: C, 43.2; H, 2.6; N, 9.1%. H NMR (DMSO-d6): d 9.04
1
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
(2H, s, H3 /5 ), 8.91 (2H, d, H6/6 ), 8.87 (2H, d, H3/3 ), 8.57 (2H,
ꢀ
ꢀꢀ
ꢀꢀ
m, H4/4 ), 8.19–8.17 (phenyl H s), 7.91 (2H, m, H5/5 ), 7.71–7.69
(phenyl Hꢀs). 13C NMR (DMSO-d6): d 158.3 (1C, s, pyridyl quat.
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
C4 ), 155.0 (2C, s, C6/6 ), 154.7–154.2 (4C, singlets, C2/2 /6 /2 ), 142.8
ꢀ
ꢀꢀ
ꢀꢀꢀ
(2C, s, C4/4 ), 134.9 (1C, s, phenyl quat. C1 ), 131.7 (phenyl C s),
ꢀ
ꢀꢀ
ꢀꢀ
130.3 (2C, s, C5/5 ), 129.5–128.1 (phenyl C s), 126.4 (2C, s, C3/3 ),
121.5 (2C, s, C3 /5 ), 120.7 (1C, s, quat. CCN). IR (KBr, cm−1):
m[C≡N]: 2139ms; m[4ꢀ-(Ph)trpy]: 1607s, 1557m, 1479ms, 1417s,
894vw; m[BF4−]: 1055vs.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
9.02 (2H, s, H3 /5 ), 8.87 (2H, d, H6/6 ), 8.85 (2H, d, H3/3 ), 8.55 (2H,
The [Pt{4ꢀ-(R)trpy}(CN)]SbF6 complexes are soluble in DCM
as the TFPB salts after metathesis with Na[TFPB]·nH2O where
TFPB = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. The UV-
vis absorption and emission spectra were recorded on deoxy-
genated DCM solutions of the complexes obtained in this way.
An excitation wavelength of 340 nm was used to record the DCM
fluid and DME glass emission spectra, unless otherwise stated.
A long-wave-pass filter of 400 nm was used to remove scattered
light. The method of determining lifetimes has been described
previously.41 The method used for measuring quantum yields is
described in ref. 21.
ꢀ
ꢀꢀ
ꢀꢀ
m, H4/4 ), 8.18–8.16 (phenyl H s), 7.90 (2H, m, H5/5 ), 7.70–7.69
(phenyl Hꢀs). 13C NMR (DMSO-d6): d 158.2 (1C, s, pyridyl quat.
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
C4 ), 155.0 (2C, s, C6/6 ), 154.6–154.2 (4C, singlets, C2/2 /6 /2 ), 142.8
ꢀ
ꢀꢀ
ꢀꢀꢀ
(2C, s, C4/4 ), 134.8 (1C, s, phenyl quat. C1 ), 131.8 (phenyl C s),
130.4 (2C, s, C5/5 ), 129.5–128.1 (phenyl C s), 126.4 (2C, s, C3/3 ),
ꢀ
ꢀꢀ
ꢀꢀ
121.4 (2C, s, C3 /5 ), 120.5 (1C, s, quat. CCN). IR (KBr, cm−1):
m[C≡N]: 2145ms; m[4ꢀ-(Ph)trpy]: 1607s, 1557ms, 1477ms, 1415s,
883m; m[SbF6−]: 652vs. [Pt{4ꢀ-(o-CH3C6H4)trpy}(CN)]SbF6: Yield
89.3 mg (90%). Colour, red. Anal. Calc. for C23H17N4F6PtSb:
ꢀ
ꢀ
1
C, 35.4; H, 2.2; N, 7.2. Found: C, 35.6; H, 2.3; N, 7.0%]. H
ꢀꢀ
ꢀ
ꢀ
NMR (DMSO-d6): d 8.93 (2H, d, H6/6 ), 8.78 (2H, s, H3 /5 ),
ꢀꢀ
ꢀꢀ
ꢀꢀ
For voltammetry, the electrolyte was 0.1 M tetrabutylam-
monium hexafluorophosphate (TBAH) in DMF. The working
electrode was a platinum disc (diameter = 6.0 mm) and the
auxiliary electrode a spiral platinum wire. The pseudo-reference
electrode used during the experiments was a Ag/AgCl spiral wire
sealed in a glass tube fitted with a frit and containing the 0.1 M
TBAH in DMF solution. The primary scans were made relative
to this electrode; however, ferrocene was added at the end of each
experiment as an internal standard. Thus, the potentials given in
Table 1 and in Fig. 2 are shown relative to the Fc+/0 couple.
8.75 (2H, d, H3/3 ), 8.54 (2H, m, H4/4 ), 7.92 (2H, m, H5/5 ),
7.52–7.46 (4H, m, phenyl Hꢀs), 2.43 (3H, s, HCH3). 13C NMR
(DMSO-d6): d 158.4 (1C, s, pyridyl quat. C4 ), 156.4–155.1 (4C,
ꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
singlets, quat. C2/2 /6 /2 ), 154.2 (2C, s, C6/6 ), 142.9 (2C, s, C4/4 ),
ꢀꢀꢀ
ꢀꢀꢀ
136.9 (1C, s, phenyl quat. C1 ), 135.4 (1C, s, phenyl quat. C2 ),
130.4 (2C, s, C5/5 ), 130.1–126.6 (singlets, phenyl C s), 126.4 (2C, s,
ꢀ
ꢀꢀ
ꢀꢀ
ꢀ
ꢀ
C3/3 ), 124.8 (2C, s, C3 /5 ), 119.9 (1C, s, quat. CCN), 19.87 (1C, s,
CCH3). IR (KBr, cm−1): m[C≡N]: 2137m; m[4ꢀ-(o-CH3C6H4)trpy]:
1607s, 1558w, 1478m, 1418s, 885m; m[SbF6−]: 652vs. [Pt{4ꢀ-(o-
ClC6H4)trpy}(CN)]SbF6: Yield 78.8 mg (89%). Colour, orange.
Anal. Calc. for C22H14N4F6ClPtSb: C, 33.0; H, 1.8; N, 7.0%.
Found: C, 32.6; H, 1.7; N, 6.6%. H NMR (DMSO-d6): d 8.91
(2H, s, H3 /5 ), 8.89 (2H, d, H6/6 ), 8.74 (2H, d, H3/3 ), 8.54 (2H,
m, H4/4 ), 7.91 (2H, m, H5/5 ), 7.79–7.65 (4H, m, phenyl H s). 13C
NMR (DMSO-d6): d 158.1 (1C, s, pyridyl quat. C4 ), 155.1 (2C, s,
C6/6 ), 154.3–153.4 (4C, singlets, quat. C2/2 /6 /2 ), 142.9 (2C, s,
C4/4 ), 135.7 (1C, s, phenyl quat. C1 ), 132.0 (1C, s, phenyl quat.
C2 ), 131.5–131.0 and 130.3–128.1 (4C, singlets, phenyl C s), 130.4
(2C, s, C5/5 ), 126.4 (2C, s, C3/3 ), 125.1 (2C, s, C3 /5 ), 120.3 (1C, s,
quat. CCN). IR (KBr, cm−1): m[C≡N]: 2136ms; m[4ꢀ-(o-ClC6H4)trpy]:
1609s, 1558w, 1478ms, 1415s, 1032ms; m[SbF6−]: 654vs. [Pt{4ꢀ-(o-
CF3C6H4)trpy}(CN)]SbF6: Yield 86.0 mg (92%). Colour, yellow.
Anal. Calc. for C23H14N4F9PtSb: C, 33.1; H, 1.7; N, 6.7%. Found:
1
Instrumentation
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀ
ꢀꢀ
ꢀꢀ
Microanalyses for %C, H and N were performed by Galbraith
Laboratories Inc., Knoxville, Tennessee, USA. 1H (500 MHz)
and 13C (125 MHz) NMR spectra were◦ recorded on a Varian
UNITY INOVA 500 spectrometer at 25 C with chemical shifts
referenced to the solvent. IR 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 spectrophotometer and the spectrofluorimeter
was a Varian Cary Eclipse. A finger-Dewar filled with liquid
nitrogen permitted measurements in a frozen DME glass. See
previous work for a description of the nitrogen-pumped dye
laser and associated equipment used for lifetime determinations.42
The cyclic voltammetry unit was a BAS100B Electrochemical
Analyser.
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀꢀ
ꢀ
ꢀꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀ
ꢀ
1
C, 32.7; H, 1.6; N, 6.3%. H NMR (DMSO-d6): d 8.97 (2H, d,
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
H6/6 ), 8.84 (2H, s, H3 /5 ), 8.72 (2H, d, H3/3 ), 8.55 (2H, m, H4/4 ),
8.21 (1H, d, phenyl Hꢀs), 7.95 (2H, m, H5/5 ), 7.88–7.66 (m, phenyl
ꢀꢀ
Hꢀs). C NMR (DMSO-d6): d 158.0 (1C, s, pyridyl quat. C4 ),
13
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
155.2 (2C, s, C6/6 ), 154.2–154.1 (4C, singlets, quat. C2/2 /6 /2 ), 142.9
ꢀꢀ
ꢀꢀꢀ ꢀꢀꢀ
), 133.0–130.5 (3C,
/2
(2C, s, C4/4 ), 135.9 (2C, s, phenyl quat. C1
Crystallography
singlets, phenyl Cꢀs), 130.4 (2C, s, C5/5 ), 126.6 (1C, s, phenyl C),
ꢀꢀ
Intensity data were obtained for single crystals of [Pt{4ꢀ-
(Ph)trpy}(CN)]BF4·CH3CN on an Oxford Diffraction Xcalibur
2 CCD four circle diffractometer in the range 4 ≤ h ≤ 32◦ using
graphite monochromated Mo-Ka radiation. The intensity data
collection, as well as the determination of the unit cell parameters
and the data reduction were processed by the CrysalisRED
v. 170 software supplied by Oxford Diffraction.43 Lorentz and
ꢀꢀ
ꢀ
ꢀ
126.3 (2C, s, C3/3 ), 124.5 (2C, s, C3 /5 ), 120.3 (1C, s, quat. CCN).
IR (KBr, cm−1): m[C≡N]: 2139ms; m[4ꢀ-(o-CF3C6H4)trpy]: 1608s,
1480s, 1420s, 1316s, 1073m, 1034s, 887w; m[SbF6−]: 658vs.
[Pt{4ꢀ-(Ph)trpy}(CN)]BF4. The same procedure was followed
as described above for the SbF6− salts except that the starting com-
plex was [Pt{4ꢀ-(Ph)trpy}Cl]BF4. Yield 82.9 mg (86%). Colour,
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 192–199 | 197
©

View Article Online
Table 3 Crystal structure data and refinement details for [Pt{4ꢀ-
(Ph)trpy}(CN)]BF4·CH3CN
Foundation for Grant No. ACS-PRF 4036-AC3 and the NSF
for Grant No. 0550241-CHE.
Formula
C24H18BF4N5Pt
References
M
658.33
280
1 H.-K. Yip, L.-K. Cheng, K.-K. Cheung and C.-M. Che, J. Chem. Soc.,
Dalton Trans., 1993, 2933.
2 J. A. Bailey, M. G. Hill, R. E. Marsh, V. M. Miskowski, W. P. Schaefer
and H. B. Gray, Inorg. Chem., 1995, 34, 4591.
3 D. R. McMillin and J. J. Moore, Coord. Chem. Rev., 2002, 229, 113.
4 R. Bu¨chner, C. T. Cunningham, J. S. Field, R. J. Haines, D. R. McMillin
and G. C. Summerton, J. Chem. Soc., Dalton Trans., 1999, 711.
5 J. F. Michaelec, S. A. Bejune, D. G. Cuttell, G. C. Summerton, J.-A.
Gertenbach, J. S. Field, R. J. Haines and D. R. McMillin, Inorg. Chem.,
2001, 40, 2193.
6 S. E. Hobert, J. T. Carney and S. D. Cummings, Inorg. Chim. Acta,
2001, 318, 89.
7 J. S. Field, R. J. Haines, D. R. McMillin and G. C. Summerton, J. Chem.
Soc., Dalton Trans., 2002, 1369.
8 J. F. Michaelec, S. A. Bejune and D. R. McMillin, Inorg. Chem., 2000,
39, 2708.
9 J. S. Field, J.-A. Gertenbach, R. J. Haines, L. P. Ledwaba, N. T.
Mashapa, D. R. McMillin, O. Q. Munro and G. C. Summerton, Dalton
Trans., 2003, 1176.
10 S.-W. Lai, M. C. W. Chan, K.-K. Cheung and C.-M. Che, Inorg. Chem.,
1999, 38, 4262.
11 D. K. Crites, C. T. Cunningham and D. R. McMillin, Inorg. Chim.
Acta, 1998, 273, 346.
12 T. K. Aldridge, E. M. Stacey and D. R. McMillin, Inorg. Chem., 1994,
33, 722.
13 G. Arena, G. Calogero, S. Campagna, L. Monsu´ Scolaro and V. R.
Romeo, Inorg. Chem., 1998, 37, 2763.
14 R. Bu¨chner, J. S. Field, R. J. Haines, C. T. Cuninngham and D. R.
McMillin, Inorg. Chem., 1997, 36, 3952.
15 D. K. C. Tears and D. R. McMillin, Coord. Chem. Rev., 2001, 211, 195.
16 V. W.-W. Yam, R. P.-L. Tang, K. M.-C. Wong and K.-K. Cheung,
Organometallics, 2001, 20, 4476.
T/K
Crystal size/mm
Crystal system
Space group
a/A
b/A
0.60 × 0.20 × 0.16
Triclinic
¯
P1
˚
˚
˚
7.304(3)
13.015(3)
13.057(3)
72.15(2)
76.32(2)
81.03(2)
1143.2(6)
2
1.912
6.193
632
11424
7010
5941
0.0335
0.0553, 0.1540
0.0644, 0.1599
318,0
c/A
a/◦
b/◦
c /◦
3
˚
U/A
Z
Dc/g cm−3
l/mm−1
F(000)
Reflections measured
Unique reflections
Reflections with F2 ≥ 2r(F2)
Rint
R1, wR2 [F2 ≥ 2r(F2)]a
R1, wR2 (all data)a
No. refined parameters,
restraints
Goodness-of-fit on F2
1.103
−3
˚
˚
Max. Dq/e A
Min. Dq/e A
3.85 (Pt)
−1.96 (Pt)
ꢀ
−3
ꢀ
ꢀ
2
a R1
=
||Fo|
−
|Fc||/ |Fo|. wR2
=
[( [w(Fo
−
Fo2)2]/
ꢀ
2
(
[w(Fo2)2]]1/2. w = 1/[(r2(Fo2) + (0.1P)2] where P = (Fo + 2Fc2)/3.
17 V. W.-W. Yam, K. M.-C. Wong and N. Zhu, J. Am. Chem. Soc., 2002,
124, 6506.
18 Q.-Z. Yang, L.-Z. Wu, Z.-X. Wu, L.-P. Zang and C.-H. Tung, Inorg.
Chem., 2002, 41, 5653.
19 Q.-Z. Yang, Q.-X. Tong, L.-Z. Wu, Z.-X. Wu, L.-P. Zang and C.-H.
Tung, Eur. J. Inorg. Chem., 2004, 1948.
20 V. W.-W. Yam, K. M.-C. Wong and N. Zhu, Angew. Chem., Int. Ed.,
2003, 42, 1400.
21 M. H. Wilson, L. P. Ledwaba, J. S. Field and D. R. McMillin, Dalton
Trans., 2005, 2754.
22 E. C. Constable, J. Lewis, M. C. Liptrot and P. R. Raithby, Inorg. Chim.
Acta, 1990, 178, 47.
23 D. S. Martin, in Extended Interactions between Metal Ions, ed.
L. V. Interannte, ACS Symp. Ser. 5, American Chemical Society,
Washington, DC, 1974, p. 254.
polarization as well as absorption corrections, the latter by means
of a numerical face-indexing method, were also effected using
the same software. Crystal data and details of the refinement
are reported in Table 3. To attain the temperature of 280 K the
crystal was cooled in a stream of nitrogen supplied by an Oxford
Instruments cryostat cooling system, fitted with a thermocouple
and temperature controller, which allowed the temperature of the
nitrogen in the immediate vicinity of the crystal to be measured.
The intensities of selected reflections were monitored from three
reference frames spanning the period of time (ca. 14 h) required to
collect a complete intensity data set. No statistically significant
variation in the intensities of these standard reflections was
observed indicating that no crystal decomposition had occurred.
The structure was solved by Patterson and Fourier methods and
refined by full-matrix least-squares using SHELX-97,44 with all
non-hydrogen atoms assigned anisotropic temperature factors and
with the hydrogen atoms (in calculated positions) assigned a single
overall isotropic temperature factor. The crystal structure diagram
was produced by the ORTEP32 program.45
24 W. B. Connick, R. E. Marsh, W. P. Schaefer and H. B. Gray, Inorg.
Chem., 1997, 36, 913.
25 V. M. Miskowski and V. H. Houlding, Inorg. Chem., 1991, 30, 4446;
V. H. Houlding and V. M. Miskowski, Coord. Chem. Rev., 1991, 111,
145.
26 M. G. Hill, J. A. Bailey, V. M. Miskowski and H. B. Gray, Inorg. Chem.,
1996, 35, 4585.
27 Calculations by Hill et al. on the [Pt(trpy)Cl]+ cation show that the
LUMO for the complex is largely p*-trpy in character but with some
platinum(II) d-orbital character mixed-in; see ref. 26.
28 A Beer’s law plot spanning the concentration range 0.1 to 2 mM is
linear, suggesting that aggregation to a dimer does not occur until the
initial reduction of the cation takes place.
CCDC reference number 616745.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b611244g
29 C. D. Cowman and H. B. Gray, Inorg. Chem., 1976, 15, 2823.
30 J. J. Moore, J. J. Nash, P. E. Fanwick and D. R. McMillin, Inorg. Chem.,
2002, 41, 6387.
31 J. DePriest, G. Y. Zheng, N. Goswami, D. M. Eichorn, C. Woods and
D. P. Rillema, Inorg. Chem., 2000, 39, 1955.
Acknowledgements
32 J. R. Kirchoff, R. E. Gamache, M. W. Blaskie, A. A. del Paggio, R. K.
Lengel and D. R. McMillin, Inorg. Chem., 1983, 22, 2380.
33 H. Yersin and D. Donges, Top. Curr. Chem., 2001, 81.
34 M. K. DeArmond and J. E. Hills, J. Chem. Phys., 1971, 54, 2247.
We acknowledge financial support from the University of
KwaZulu-Natal and the South African National Research Foun-
dation. The Purdue authors thank the Petroleum Research
198 | Dalton Trans., 2007, 192–199
This journal is
The Royal Society of Chemistry 2007
©

View Article Online
35 M. Maestri, D. Sandrini, V. Balzani, A. von Zelwesky, C. Deuschel-
Cornioley and P. Jolliet, Helv. Chim. Acta, 1988, 71, 1053.
36 J. V. Caspar and T. J. Meyer, J. Am. Chem. Soc., 1983, 105, 5583; J.
Jortner, S. A. Rice and R. M. Hochstrasse, Adv. Photochem., 1969, 7,
149.
37 A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A. von
Zelewsky, Coord. Chem. Rev., 1988, 84, 85.
38 Y.-Z. Hu, M. H. Wilson, R. Zong, C. Bonnefous, D. R. McMillin and
R. P. Thummel, Dalton Trans., 2005, 354.
39 L. Carlsen, H. Egsgaard and J. R. Anderson, Anal. Chem., 1979, 51,
1593.
40 D. D. Perrin, W. L. F. Armarego and D. R. Perrin, Purification of
Laboratory Chemicals, Pergamon, New York, 2nd edn, 1980.
41 F. Liu, K. L. Cunningham, W. Uphues, G. W. Fink, J. Schmolt and
D. R. McMillin, Inorg. Chem., 1995, 34, 2015.
42 K. L. Cunningham, C. R. Hecker and D. R. McMillin, Inorg. Chim.
Acta, 1996, 242, 143.
43 Oxford Diffraction Ltd., Abingdon, Oxon OX14 1RL, UK,
2003.
44 G. M. Sheldrick, SHELXS-97, A program for crystal structure determi-
nation and refinement, University of Go¨ttingen, 1997.
45 L. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 192–199 | 199
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