Adams et al.
reductant [Co(C5Me5)2] to the top, and allowing the solution to
warm until a signal was observed. Microanalysis was carried out
by the microanalytical laboratory of the University of Bristol School
of Chemistry. Electrochemical studies were carried out using an
EG&G model 273A potentiostat linked to a computer using EG&G
Model 270 Research Electrochemistry software in conjunction with
a three-electrode cell. The auxiliary electrode was a platinum wire
and the working electrode a platinum disk (1.6 mm diameter). The
reference electrode was an aqueous saturated calomel electrode
separated from the test solution by a fine porosity frit and an agar
bridge saturated with KCl. Solutions in CH2Cl2 were 1.0 × 10-3
trograph, and Andor iDUS CCD camera. The spectrograph and
CCD detection system was calibrated with a Bentham CL2 tungsten
calibration lamp. The emission spectra were corrected for the overall
system sensitivity.
Luminescence quantum yields were determined relative to
[Ru(bpy)3Cl2] in air saturated water, φo ) 0.028, or relative to a
solution of [Pt(MesBIAN)Cl2] in deoxygenated CH2Cl2 (φ ) 3 ×
10-4).10 Luminescence lifetimes were measured with a Mini-τ
fluorimeter (Edinburgh Instruments) containing a picosecond diode
laser (410 nm, 80 ps) as an excitation source; the emission
wavelength range was selected by glass filters. Experimental
uncertainties are estimated to be 20% for emission quantum yields
and 15% for luminescence lifetimes.
The nanosecond and picosecond TRIR experiments were per-
formed at the Central Laser Facility of the Rutherford Appleton
Laboratory (RAL), STFC, U.K. The experiments were carried out
in tetrahydrofuran (THF) or CH2Cl2 solutions under an inert
atmosphere, with a standard concentration of approximately 1 mM;
concentration dependence studies were done in the range between
1 mM and 46 µM.
The picosecond-TRIR setup at RAL has been described in detail
elsewhere.43 Briefly, part of the output from a 1 kHz, 800 nm, 150
fs, 1 mJ Ti:Sapphire oscillator/regenerative amplifier was used to
pump a white light continuum seeded BBO OPA. The signal and
idler produced by this OPA were difference frequency mixed in a
type I AgGaS2 crystal to generate tuneable mid-infrared pulses (ca.
150 cm-1 fwhm, 0.1 µJ). Second harmonic generation of the
residual 800 nm light provided 400 nm pulses, which were used to
excite the sample (typical excitation energy 3 µJ, focus 100 µm2).
Changes in infrared absorption were recorded by normalizing the
outputs from a pair of 64-element HgCdTe linear array detectors
on a shot-by-shot basis. The nanosecond TRIR setup, described in
detail elsewhere,59 combines the PIRATE TRIR spectrometer and
nanosecond AOT-YVO-20QSP/MOPA Nd:Vanadate diode pumped
microlaser, with a pulse duration of 0.6 ns and energies of about
0.6 µJ/pulse.
mol dm-3 in the compound and 0.1 mol dm-3 in [NBun ][PF6] as
4
the supporting electrolyte. Under these conditions, Eo′ for the one-
electron oxidation of [Fe(η-C5H5)2], added to the test solutions as
an internal calibrant, is 0.47 V.58
Syntheses. [Pt(MesBIAN)(-Ct C-C6H5)2] 4. A 0.118 g quan-
tity (0.173 mmol) of [Pt(MesBIAN)Cl2] and a catalytic amount (<1
mg) of copper(I) iodide were dissolved in 20 mL of CH2Cl2 and 1
mL of triethylamine. To this was added 0.076 mL (0.69 mmol) of
phenylacetylene, and the mixture stirred for 24 h, during which
time it became purple. It was then evaporated to dryness and purified
by column chromatography on grade III alumina (25 cm × 4 cm),
using CH2Cl2 as eluent. The product was collected as a purple band,
which was reduced in volume on a rotary evaporator to ap-
proximately 25 mL. An approximately equal volume of hexane was
then added and evaporation slowly continued until the desired
product separated out as dark purple microcrystals. These were
isolated by filtration, washed with hexane and dried to give 0.106
g (0.130 mmol, 75%) of product.
[Pt(MesBIAN)(sCt CsC6H4sCN-p)2] 1, [Pt(MesBIAN)(sCt
CsC6H4sCF3-p)2] 3, and [Pt(MesBIAN)(sCt CsSiMe3)2] 2 were
prepared similarly from [Pt(MesBIAN)Cl2] and the appropriate
alkyne. So was [Pt(MesBIAN)(sCt CsC6H4sCH3-p)2] 5, except
that the precipitation from dichloromethane was effected with
diethyl ether.
[{Pt(MesBIAN)(sCt CsSiMe3)2}-η2,η2-CuCl] 2a. A 0.054 g
quantity (0.079 mmol) of [Pt(MesBIAN)Cl2], 0.25 mL of trimeth-
ylsilylacetylene (1.75 mmol), and 0.023 g of copper(I) chloride (0.23
mmol) were stirred for 16 h in 10 mL of CH2Cl2 and 1 mL of
triethylamine. The resulting brown solution was then evaporated
to dryness and washed three times with saturated sodium chloride
solution and once with distilled water. It was then dried over
magnesium sulfate, which was removed by filtration prior to the
solution being evaporated to dryness again. Trituration of the residue
with diethyl ether gave 0.030 g (0.033 mmol) of 2a as a brown
solid.
[Pt(MesBIAN)I2] 6. To a solution of 0.056 g (0.068 mmol) of
4 in 5 mL of CH2Cl2 was added 5 mL of a 17 mM solution of
iodine (0.085 mmol). The resulting solution was stirred for 36 h,
and then 40 mL of hexane was added. Continued stirring caused
the deposition of a dark solid, which was isolated by filtration,
washed with hexane, and dried in vacuo to give 0.040 g (0.046
mmol, 68%) of 6. Treatment of the remaining solution with
activated charcoal, filtration and evaporation yielded a light colored
solid. This was identified as 1,4-diphenylbuta-1,3-diyne by NMR,
IR (ν{Ct C} ) 2195s cm-1) and EI-MS (M+ ) 202).
Computational Studies. All calculations were performed with
Gaussian 03 (Revision C.02)60 and used the popular B3LYP density
functional.61-63 The Stuttgart-Dresden (SDD) basis set64 was used
with a relativistic effective core potential for Pt, and all ligand atoms
(C, H, N) were described by the all-electron 6-31G* basis set. In
agreement with results reported by other groups, we found that
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at room temperature on CH2Cl2 solutions degassed by freeze-
pump-thaw methods. Emission spectra were recorded on a home-
built system (Sheffield) comprising a Coherent CW Ar ion laser
(<10 mW at the sample, 514.5 nm), Bentham TMC600 spec-
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8256 Inorganic Chemistry, Vol. 47, No. 18, 2008