Facile synthesis, structure, and luminescence properties of Pt(diimine)bis(arylacetylide) chromophore-donor dyads

Article abstract of DOI:10.1021/ic048886l

The luminescent complex Pt(dpphen)bis(arylacetylide) complex (1) (dpphen = 4,7-diphenylphenanthroline and arylacetylide = 4-ethynylbenzaldehyde) has been synthesized and characterized structurally and spectroscopically. Complex 1 has been employed in the synthesis of donor-chromophore (D-C) dyads through Schiff base condensations of different anilines to give imine-linked dyads 2-4 and through imine reduction with borohydride, to give the corresponding amine-linked dyads 2a-4a. Crystal structure determinations of 1-4 and 4a establish a distorted square-planar geometry around the Pt(II) ion in each system with cis arylacetylide ligands and a diimine-constrained N-Pt-N bond angle of ca. 79.5°. Complex 1 is strongly emissive having a relative quantum yield (φ) of 36% and an excited-state lifetime of 3.1 μs. In accord with the notion of photoinduced electron transfer from the aniline-based donor to the photoexcited chromophore, the emission of dyads 2-4 and 2a-4a is effectively quenched in all solvents tested. The intense absorption at 400 nm (30000-70000 L/mol·cm) for 2 and 2a has been assigned as an intraligand π-π* transition, whereas the lowest-energy transitions for all other dyads correspond to Pt-to-π*(diimine) MLCT transitions. Although the dyads can be synthesized in a facile manner, photolysis experiments reveal that both the imine and amine linkages are photochemically unstable, resulting in hydrolysis and regeneration of the aldehyde-containing chromophore 1.

Full text of DOI:10.1021/ic048886l

Inorg. Chem. 2005, 44, 2628−2638
Facile Synthesis, Structure, and Luminescence Properties of
Pt(diimine)bis(arylacetylide) Chromophore Donor Dyads
−
Thaddeus J. Wadas, Soma Chakraborty, Rene J. Lachicotte, Quan-Ming Wang, and
Richard Eisenberg*
Department of Chemistry, UniVersity of Rochester, Rochester, New York 14627
Received August 13, 2004
The luminescent complex Pt(dpphen)bis(arylacetylide) complex (1) (dpphen
) 4,7-diphenylphenanthroline and
arylacetylide
Complex 1 has been employed in the synthesis of donor
condensations of different anilines to give imine-linked dyads 2
to give the corresponding amine-linked dyads 2a 4a. Crystal structure determinations of 1
distorted square-planar geometry around the Pt(II) ion in each system with cis arylacetylide ligands and a diimine-
constrained N Pt N bond angle of ca. 79.5 . Complex 1 is strongly emissive having a relative quantum yield (
of 36% and an excited-state lifetime of 3.1 s. In accord with the notion of photoinduced electron transfer from the
aniline-based donor to the photoexcited chromophore, the emission of dyads 2 4 and 2a 4a is effectively quenched
in all solvents tested. The intense absorption at 400 nm (30000 70000 L/mol cm) for 2 and 2a has been assigned
as an intraligand π−π* transition, whereas the lowest-energy transitions for all other dyads correspond to
Pt-to- *(diimine) MLCT transitions. Although the dyads can be synthesized in a facile manner, photolysis experiments
)
4-ethynylbenzaldehyde) has been synthesized and characterized structurally and spectroscopically.
chromophore (D C) dyads through Schiff base
4 and through imine reduction with borohydride,
4 and 4a establish a
−
−
−
−
−
−
−
°
φ)
µ
−
−
−
‚
π
reveal that both the imine and amine linkages are photochemically unstable, resulting in hydrolysis and regeneration
of the aldehyde-containing chromophore 1.
Introduction
of two- and three-component systems (dyads and triads) for
photoinduced charge separation.11,15,18-25 In these investiga-
tions, the photochemically active component is generally a
transition metal chromophore with a d6 metal ion [primarily
Ru(II), Os(II), and Re(I)] and an unsaturated diimine ligand
for charge-transfer excitation. The other components in these
Photosynthesis involves the conversion of light energy into
chemical potential energy and is accomplished through a
series of events including photon capture, electron-hole pair
creation, charge separation, charge accumulation, and ca-
talysis of the energy-storing reaction.1-17 Over the past two
decades, efforts in the development of artificial photosyn-
thetic systems have included the design, synthesis and study
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* Author to whom correspondence should be addressed. Email:
eisenberg@chem.rochester.edu.
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2628 Inorganic Chemistry, Vol. 44, No. 8, 2005
10.1021/ic048886l CCC: $30.25
© 2005 American Chemical Society
Published on Web 03/23/2005

Pt(diimine)bis(arylacetylide) Chromophore-Donor Dyads
systems for charge separation by electron transfer are
commonly organic moieties such as phenothiazines and
arylamines as donors and fullerenes, porphyrins, and qui-
nones as acceptors.8,11,26-35
Pt(diimine)bis(acetylide) complexes gives rise to intense
luminescence in fluid solution with high emission quantum
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standard] and excited-state lifetimes between 0.1 and
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2+
A different class of chromophores that has been studied
by us and others consists of diimine-based square-planar
Pt(II) complexes having the general formula Pt(diimine)L2.36-40
The diimine in these complexes corresponds to 2,2′-bipy-
ridine, 1,10-phenanthroline, or derivatives thereof. For these
chromophores, the LUMO is localized on a π* orbital of
the diimine ligand, and the HOMO has varying extents of
metal character influenced by the ancillary ligand L. For
systems with L2 ) dithiolate, the HOMO exhibits mixed
metal and dithiolate character, whereas for the bis(arylacetyl-
ide) complexes (L ) CtCAr), the HOMO is localized
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also observed to be nonemissive in fluid solution, and
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with a 75-ns lifetime in DMF solution. Based on a simple
3
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Inorganic Chemistry, Vol. 44, No. 8, 2005 2629

Wadas et al.
further purification. All solvents were of spectroscopic grade or
better, triethylamine was distilled under nitrogen from potassium
hydroxide, and methylene chloride, toluene, and acetonitrile were
purified by passing the degassed solvent through columns of
activated alumina and molecular sieves under argon as described
in the literature.62 The compounds Pt(DMSO)2Cl2, Pt(dpphen)-
Cl2,and 4-ethynylbenzaldehyde were prepared according to literature
methods.63-67 The syntheses of Pt(dpphen)(arylacetylide)2 com-
plexes and all dyads were performed under nitrogen or argon with
degassed solvents following a procedure similar to that previously
reported.55,68-70
electrochemical analysis, it was estimated that the CS state
-
of the triad (PTZ+‚-C-NO2 ‚) transiently stored ca. 1.7 V
of energy.
1
Physical Measurements. H NMR spectra were recorded on a
Bruker AMX-400 or Avance 400 spectrometer (400 MHz), and
infrared spectra were obtained from Nujol mulls, dry film, or KBr
pellets using a Mattson Galaxy 6020 FTIR spectrometer. Field
desorption mass spectrometry was performed by Kodak Analytical
Services, Rochester, NY, and elemental analyses were provided
by Desert Analytics, Tucson, AZ. Cyclic voltammetry experiments
were conducted on a EG & G PAR 263 A potentiostat/galvanostat
using a three-electrode single-cell compartment, and all samples
were degassed with argon. A Pt wire working electrode, a Pt wire
auxiliary electrode, and Ag/AgNO3/acetonitrile reference electrode
were used, and the scan rate used was 50 mV/s. For all measure-
ments, tetrabutylammonium hexafluorophosphate was used as the
supporting electrolyte with ferrocene as an internal reference, and
all redox potentials are reported relative to the ferrocenium/ferrocene
(Fc+/Fc) couple (0.4 V versus SCE). Absorption spectra were
recorded using a Hitachi U2000 scanning spectrophotometer
(200-1100 nm). Steady-state luminescence spectra were measured
on a Spex Fluoromax-P fluorometer and corrected for instrument
response. Lifetime data of the chromophore were obtained using
an excimer-pumped dye laser system (1-3 mJ/pulse) with the
excited-state decay fit to single exponentials. The metal complex
concentration was 3 × 10-5 M, and each sample was subjected to
at least four freeze-pump-thaw cycles. Photolysis experiments
were conducted in wet and anhydrous methylene chloride using a
1-cm quartz cuvette equipped with a high-vacuum valve and an
Oriel Hg/Xe lamp with a filter to absorb all wavelengths below
300 nm. For studies examining dyad stabilities, absorption and
emission spectra were recorded before and immediately after 1 h
of irradiation and at arbitrary time points over the course of 3 days.
Samples were kept in the absence of light until measurements were
taken.
In the second study,40,61 D-C dyads were prepared and
studied in which 4,4′-diethoxycarbonylbipyridine and
4,4′-di-tert-butylbipyridine were the diimine ligands and
phenothiazine and 2-trifluoromethylphenothiazine func-
tioned as the one-electron donors. When the diimine was
4,4′-di-tert-butylbipyridine, emission intensity was observed
to be solvent-dependent, with significant luminescence
quenching occurring in polar solvents but not in nonpolar
solvents. Intramolecular electron transfer was observed by
transient absorption spectroscopy, and analysis of the pho-
tophysical and electrochemical data suggested that, whereas
charge separation appeared to be in the Marcus normal
region, charge recombination was found to be in the inverted
region.
Although these Pt(II) diimine dyads and triads provided
meaningful data and insight for photoinduced charge separa-
tion, their syntheses were arduous, utilizing a sequence of
Pd2+-catalyzed Sonogashira-Hagihara coupling steps, each
with problems of purification and catalyst metal ion removal.
As an alternative approach, we describe in this paper the
synthesis and study of dyad systems constructed using Schiff
base condensations to an aldehyde-containing Pt(diimine)-
bis(arylacetylide) chromophore. We have previously de-
scribed related Pt(diimine)(CtCsp-C6H4CHO)2 complexes
TMS-C≡CsC6H4sp-(CHdNsC6H4NMe2) (L-2sCCsTMS).
A 100-mL round-bottom flask was charged with 4-trimethylsilyl-
ethynylbenzaldehyde (1 g, 4 mmol), NMe2ani (1.18 g, 5.6 mmol),
and ZnCl2 (10 mg). Twenty-five milliliters of CH2Cl2 containing
0.8 mL of Et3N was added, and the resulting solution was allowed
to stir at room temperature for 12 h. The solvent was removed,
and the resultant solids were chromatographed on a Biotage
40S column (alumina, 40 µm, 60 Å) eluting with a solvent mixture
of hexanes/CH2Cl2 (1:2 v/v) to give an orange solid. Yield:
3
that were brightly emissive in fluid solution with a MLCT
state characteristic of other arylacetylide derivatives,56 and
this study builds on that work. Representative D-C dyads
were synthesized and structurally characterized, and their
luminescence properties and relative stabilities upon irradia-
tion are described.
1
Experimental Section
79 mg (50%). H NMR (CD2Cl2): δ 8.49 (1H, s), 7.61 (2H, d,
J ) 12 Hz), 7.52 (2 H, d, J ) 8.0 Hz), 7.25 (2H, s), 6.76 (2H, s),
2.98 (6H, s), 0.25 (9H, s). MS (EI) m/z (%): 320 (100).
HsC≡CsC6H4sp-(CH2sNHsC6H4NMe2) (L-2asCCsH).
A 100-mL round-bottom flask was charged with L-2sCCsTMS
(0.05 g, 0.156 mmol), NaBH4 (0.06 g, 1.56 mmol), and 50 mL of
dry methanol. The resultant solution was allowed to stir at room
Reagents. Potassium tetrachloroplatinate (Johnson Matthey);
4,7-diphenylphenanthroline (dpphen), 4-trimethylsilylethynylben-
zaldehyde, copper(I) iodide, aniline (ani), N,N′-(dimethylamino)-
1,4-phenylenediamine (NMe2ani) dihydrochloride, p-anisidine
(MeOani), N-benzylidene aniline (L-4), N-benzylidene-p-anisidine
(L-3), N,N′-dimethylformamide, absolute methanol, absolute etha-
nol, chloroform, triethylamine, zinc(II) chloride, glacial acetic acid
(HOAc), and sodium triacetoxyborohydride (all from Aldrich);
1,4-benzene diamine (L-2) (ChemBridge Corporation); and tet-
rabutylammonium hexafluorophosphate (Fluka) were used without
(69) Sonogashira, K.; Yatake, T.; Tohda, Y.; Takahashi, S.; Hagihara, N.
J. Chem. Soc., Chem. Commun. 1977, 291.
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S.; Hagihara, N. J. Org. Chem. 1978, 145, 101-108.
2630 Inorganic Chemistry, Vol. 44, No. 8, 2005

Pt(diimine)bis(arylacetylide) Chromophore-Donor Dyads
temperature for 24 h, after which solvent was removed and the
residue was dissolved in CH2Cl2 and filtered through a 2-in. pad
of alumina. The resultant solution was dried to give a yellow solid.
to cool, the solution was filtered and concentrated, and ethanol was
added. The solids were collected on a medium-porosity glass frit,
washed with diethyl ether, recrystallized from a methanol/CH2Cl2
mixture, washed with methanol and diethyl ether, and dried under
vacuum. X-ray-quality crystals were grown by the vapor diffusion
of diethyl ether into a saturated solution of 4 in CHCl3 at room
1
Yield: 39 mg (50%). H NMR CDCl3: δ 7.47 (2H, d, J ) 8.12
Hz), 7.35 (2H, d, J ) 8.04 Hz), 6.74 (2H, d, J ) 8.88 Hz), 6.62
(2H, d, J ) 8.8 Hz), 4.32 (2H, s), 3.07 (1H, s), 2.84 (6H, s), 1.56
(1H, s). MS (EI) m/z (%): 250 (100).
1
temperature. Yield: 107 mg (90%). H NMR (CD2Cl2): δ 10.01
(2H, d, J ) 8 Hz), 8.46 (2H, s), 8.09 (2H, s), 7.93 (4H, d, J ) 4
Hz), 7.86 (2H, d, J ) 8 Hz), 7.67 (14H, pseudo t, J ) 8 Hz), 7.43
(4H, pseudo t, J ) 8 Hz), 7.27 (4H, d, J ) 8 Hz). FT IR (dry film,
cm-1): 1608 (υCdN), 2106 (υC≡C). MS (FD) m/z (%) 936.0 ([M]+,
100). Anal. Calcd for PtC54H36N4‚CHCl3: C, 62.59; H, 3.53; N,
5.30. Found: C, 63.02; H, 3.81; N, 5.55.
Pt(dpphen)(C≡CC6H4CHO)2 (1). A Schlenk tube was charged
with Pt(dpphen)Cl2 (0.100 g, 0.17 mmol), 4-ethynylbenzaldehyde
(0.21 g, 1.6 mmol), CuI (10 mg), and 10 mL of a solvent mixture
of DMF/NEt3 (8:2 v/v). The resultant heterogeneous solution was
allowed to stir for 24 h at 65 °C, after which it was filtered through
a medium-porosity glass frit. The precipitate was washed with
methanol, ethanol, and diethyl ether, recrystallized from CH2Cl2,
washed with methanol and diethyl ether, and dried under vacuum.
X-ray-quality crystals were grown by the vapor diffusion of diethyl
ether into saturated solutions of 1 in CH2Cl2 at room temperature.
Pt(dpphen)[C≡CC6H4sp-(CH2sNHsC6H4NMe2)]2 (2a). A
50-mL round-bottom flask was charged with 2 (0.05 g, 0.63 mmol),
sodium triacetoxyborohydride (0.676 g, 3.1 mmol), and 50 mL of
dichloromethane. The resultant solution was stirred for 48 h. The
solution was then poured over water and extracted with dichlo-
romethane (5 × 50 mL), dried with MgSO4, filtered, and evaporated
to dryness to give the desired product. The crude material was
recrystallized from a CH2Cl2/C2H5OH (1:1 v/v) solution. Yield:
1
Yield: 109 mg (83%). H NMR (CD2Cl2): δ 9.96 (2H, s), 9.92
(2H, d, J ) 5.2 Hz), 8.09 (2H, s), 7.92 (2H, d, J ) 4.80 Hz), 7.82
(4H, d, J ) 8.4 Hz), 7.66 (4H, d, J ) 8.0 Hz), 7.63 (10H, M). FT
IR (dry film, cm-1): 1689 (υCHO), 2125, 2113 (υC≡C). MS (FD)
m/z (%): 786.0 ([M]+, 100). Anal. Calcd for PtC42H26N2O2‚CH3-
OH: C, 64.20; H, 3.33; N, 3.56. Found: C, 63.71; H, 3.51; N,
3.45.
1
60 mg (60%). H NMR (CD2Cl2): δ 10.00 (2H, d, J ) 5.32 Hz),
8.06 (2H, s), 7.87 (2H, d, J ) 5.4 Hz), 7.61 (10H, m), 7.49 (4H,
d, J ) 8.08 Hz), 7.31 (4H, d, J ) 8.2 Hz), 6.70 (4H, d, J ) 8.72
Hz), 6.62 (4H, d, J ) 8.72 Hz), 4.28 (4H, s), 2.78 (12H, s), 1.5
(2H, s). FT IR (dry film, cm-1): 2109 (υC≡C), 2963 (υC-H), 3390
(υN-H). MS (FD) m/z (%): 1024.4 ([M]+, 100). Anal. Calcd for
PtC58H50N6‚2CH2Cl2‚3.5C2H5OH: C, 59.28; H, 5.58; N, 6.19.
Found: C, 59.82; H, 5.52; N, 5.71.
Pt(dpphen)[C≡CC6H4sp-(CH2sNHsC6H4OMe)]2 (3a). The
same procedure as employed for 2a was followed except that
complex 3 (0.05 g, 0.63 mmol) was used as the starting material.
Yield: 55 mg (55%). 1H NMR (CD2Cl2): δ 10.13 (2H, d, J ) 5.4
Hz), 8.16 (2H, s), 7.99 (2H, d, J ) 5.4 Hz), 7.73 (10H, m), 7.62
(4H, d, J ) 8.08 Hz), 7.42 (4H, d, J ) 7.41 Hz), 6.85 (4H, d,
J ) 8.96 Hz), 6.72 (4H, d, J ) 8.96 Hz), 4.39 (4H, s), 3.81 (6H,
s), 1.63 (2H, s). FT IR (dry film, cm-1): 1244 (υOCH3), 2112 (υC≡C),
2928 (υC-H), 3390 (υN-H). MS (FD) m/z (%): 1000 ([M]+, 100).
Anal. Calcd for PtC56H44N4O2‚CH2Cl2‚3C2H5OH‚0.5H2O: C, 61.40;
H, 5.33; N, 4.54. Found: C, 61.65; H, 5.32; N, 3.92.
Pt(dpphen)(C≡CC6H4CH2sp-NHsC6H5)2 (4a). The same
procedure as employed for 2a was followed except that complex 4
(0.05 g, 0.63 mmol) was used as the starting material. X-ray-quality
crystals were grown by the slow liquid diffusion of ethanol into a
saturated solution of 4a in dichloromethane at room temperature.
Yield: 70 mg (70%). 1H NMR (CD2Cl2): δ 10.05 (2H, d,
J ) 5.32 Hz), 8.09 (2H, s), 7.91 (2H, d, J ) 5.44 Hz), 7.64 (10H,
m), 7.54 (4H, d, J ) 8.08 Hz), 7.34 (4H, d, J ) 8.08 Hz), 7.18
(4H, t, J ) 8, 7.96 Hz), 6.70 (6H, m), 4.36 (4H, s), 1.55 (2H, s).
FT IR (dry film, cm-1): 2112 (υC≡C), 2928 (υC-H), 3390 (υN-H).
MS (FD) m/z (%): 938.29 ([M]+, 100). Anal. Calcd for
PtC54H40N4: C, 69.00; H, 4.29; N, 5.96. Found: C, 68.53; H, 4.11;
N, 5.76.
Pt(dpphen)[C≡CC6H4sp-(CHdNsC6H4NMe2)]2 (2). A 50-
mL round-bottom flask was charged with 1 (0.05 g, 0.63 mmol),
ZnCl2 (10 mg), NMe2ani‚2HCl (0.0531 g, 2.5 mmol), and 20 mL
of CH2Cl2/MeOH (4:1 v/v) containing NEt3 (0.25 g, 2.5 mmol),
and the resultant solution was allowed to stir for 40 h at room
temperature. The product was isolated on a medium-porosity glass
frit; washed with small amounts of methanol, ethanol, and diethyl
ether; recrystallized from a methanol/CH2Cl2 mixture; washed with
methanol and diethyl ether; and dried under vacuum. X-ray-quality
crystals were grown by diffusion of ethanol into a saturated solution
of 2 in CH2Cl2 at room temperature. Yield: 117 mg (90%).
1H NMR (CD2Cl2): δ 9.95 (2H, d, J ) 4 Hz), 8.50 (2H, s), 8.08
(2H, s), 7.90 (2H, d, J ) 4 Hz), 7.83 (4H, d, J ) 8 Hz), 7.64 (14H,
m), 7.28 (4H, d, J ) 8 Hz), 6.77 (4H, d, J ) 8 Hz), 2.90 (12H, s).
FT IR (dry film, cm-1): 1617, 1600 (υCdN), 2120 (sh), 2100 (υC≡C).
MS (FD) m/z (%): 1021.2 ([M]+, 100). Anal. Calcd for
PtC58H46N6‚2CH3OH: C, 66.34; H, 5.01; N, 7.73. Found: C, 66.22;
H, 4.38; N, 7.89.
Pt(dpphen)[C≡CC6H4sp-(CHdNsC6H4OMe)]2 (3). A 50-mL
round-bottom flask was charged with 1 (0.05 g, 0.63 mmol), ZnCl2
(10 mg), MeOani (0.0531 g, 2.5 mmol), and 20 mL of CH2Cl2
containing 2 drops of HOAc, and the resultant solution was allowed
to stir for 40 h at room temperature. The product was isolated on
a medium-porosity glass frit; washed with small amounts of
methanol, ethanol, and diethyl ether; recrystallized from a methanol/
CH2Cl2 mixture; washed with methanol and diethyl ether; and dried
under vacuum. X-ray-quality crystals were grown by the liquid
diffusion of ethanol into a saturated solution of 3 in CH2Cl2 at room
1
temperature. Yield: 114 mg (90%). H NMR (CD2Cl2): δ 9.98
(2H, d, J ) 4 Hz), 8.48 (2H, s), 8.09 (2H, s), 7.92 (2H, d, J ) 8
Hz), 7.84 (4H, d, J ) 8 Hz), 7.64 (14H, m), 7.25 (4H, d, J ) 8
Hz), 6.95 (4H, d, J ) 12 Hz), 3.82 (6H, s). MS (FD) m/z (%):
996.2 ([M]+, 100). FT IR (dry film, cm-1): 1620, 1600 (υCdN),
2100 (υC≡C). Anal. Calcd for PtC56H40N4O2‚CH3OH: C, 66.59; H,
4.31; N, 5.44. Found: C, 66.80; H, 4.25; N, 5.42.
Pt(dpphen)[C≡CC6H4sp-(CHdNsC6H5)]2 (4). A 25-mL round-
bottom flask was charged with 1 (0.050 g, 0.63 mmol), ZnCl2
(10 mg), 3 mL of aniline, and 20 mL of CHCl3. The resulting
solution was allowed to stir for 36 h at 60 °C. After being allowed
X-ray Structural Determinations of 1-4 and 4a. Crystals of
each complex were mounted under paratone-8277 oil on a glass
fiber and immediately placed in a cold nitrogen stream at -80 °C
on the X-ray diffractometer. It should be noted that 3 undergoes
rapid solvent loss. The X-ray intensity data were collected on a
standard Siemens SMART CCD area detector system equipped with
a normal-focus molybdenum-target X-ray tube operated at 2.0 kW
(50 kV, 40 mA). Data (1.3 hemispheres) were collected using a
narrow-frame method with scan widths of 0.3° in ω and exposure
times of 30 s/frame using a detector-to-crystal distance of 5.09 cm
Inorganic Chemistry, Vol. 44, No. 8, 2005 2631

Wadas et al.
Table 1. Crystallographic Data for Complexes 1-4 and 4a‚Et2O
1
2
3
4
4a‚Et2O
emp formula
fw
T, K
C42H26N2O2Pt
785.74
293
C58H46N6Pt
1022.10
293
C56H40N4O2Pt
996.01
293
C54H36N4Pt
935.96
193
C58H50N4OPt
1014.11
193
µ, Å
0.71073
triclinic
P1h
0.71073
monoclinic
C2/c
0.71073
monoclinic
P2(1)/c
4
19.4441(10)
16.3369(9)
15.2547(8)
90.00
108.6090(10)
90.00
4592.4(4)
1.441
0.71073
monoclinic
C2/c
0.71073
triclinic
P1h
cryst syst
space group
Z
2
4
4
2
a, Åa
9.4406(4)
11.6495(5)
14.6801(7)
101.0600(10)
95.9300(10)
95.4580(10)
1565.06(12)
1.667
30.1689(18)
15.5466(8)
9.7179(5)
90.00
91.365(2)
90.00
22.954(6)
19.501(5)
11.044(3)
90.00
118.036(3)
90.00
10.5336(13)
11.6625(15)
19.425(2)
98.245(2)
90.598(2)
105.602(2)
2271.6(5)
1.483
b, Åa
c, Åa
R, dega
â, dega
γ, dega
V, Å3
4556.6(4)
1.490
3.126
4363.5(19)
1.425
F
calcd, g cm-3
µ, mm-1
4.524
3.102
3.256
3.135
abs correction
transm range
θ range, deg
no. data
SADABSb
0.570-0.928
1.79-28.27
7117
SADABSb
0.737-0.928
2.41-28.29
5381
SADABSb
0.787-0.928
1.67-28.27
10551
SADABSb
c
SADABSb
0.468-1.000
1.83-28.32
10529
2.01-28.28
5270
no. params
424
1.064
0.0336,
0.0937
0.0344,
0.0943
296
1.089
0.0208,
0.0546
0.0229,
0.0554
570
1.054
0.0204,
0.0505
0.0271,
0.0521
267
0.944
577
1.052
0.0334,
0.0724
0.0407,
0.0752
GOFd
R1, wR2 [I > 2σ(I)]e
0.0515,f
0.1187f
0.1256,f
0.1366f
R1, wR2 (all data)e
a It has been noted that the integration program SAINT produces cell constant errors that are unreasonably small because systematic error is not included.
More reasonable errors might be estimated at 10 times the reported value. b The SADABS program is based on the method of Blessing; see Blessing, R. H.
Acta Crystallogr. A 1995, 51, 33. c The transmission coefficient cannot be specified because the crystal dimensions were lost. d GOF ) {∑[w(Fo2 - Fc )2]/
2
(n - p)}1/2, where n and p denote the number of data points and the number of parameters, respectively. e R1 ) (∑||Fo| - |Fc||)/∑|Fo|; wR2 )
2
2
2
2
2
{∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2, where w ) 1/[σ2(Fo ) + (aP)2 + bP] and P ) [max(0,Fo ) + 2Fc ]/3. f Solvent disorder within the crystal lattice and small
crystal size contribute to higher R factors in this case, but the overall structural connectivity is confirmed and in agreement with the crystal structures of 2
and 3.
(maximum 2θ angle of 56.5°). The total data collection time was
approximately 13 h for each complex. Frames were integrated to a
maximum 2θ angle with the Siemens SAINT program and corrected
for absorption with the program SADABS. The structures were
solved by direct methods and refined employing full-matrix least-
squares on F2. All non-H atoms of the metal complexes were refined
with anisotropic thermal parameters, and the non-H atoms of the
solvent (if present) were refined isotropically. The hydrogen atoms
were included in idealized positions. Solvent molecules that did
not refine regardless of disorder model were compensated using
the SQUEEZE program. Final residuals along with unit cell, space
group, data collection, and refinement parameters are presented in
Table 1.
C6H5CHdNsp-C6H4sR′, (L-4, R ) H, R′ ) H; L-3,
R ) H, R′ ) OMe; L-2, R ) H, R′ ) NMe2; L-2-CC-
TMS, R ) TMS-CtC-, R′ ) NMe2) were purchased from
respective suppliers or synthesized while amine L-2a-
CC-H was prepared by the reaction of L-2-CC-TMS
with borohydride (Scheme 3).
All of the complexes were characterized by NMR, IR,
electronic absorption, and emission spectroscopies, mass
spectroscopy, and elemental analyses. Additionally, com-
plexes 1-4 and 4a were structurally characterized by X-ray
crystallography. All of the spectroscopic data are consistent
with the X-ray structural results described below.
Molecular Structures of 1-4 and 4a. The molecular
structures of the aldehyde-containing complex 1, the imine
dyad 2, and the amine dyad 4a are shown in Figures 1-3,
respectively, with important bond lengths and angles for 1,
2, and 4a reported in Table 2. Perspective drawings of the
other imine dyads 3 and 4 and complete crystallographic
information including all bond distances and angles for all
structures are given in the Supporting Information. Each
complex consists of a square-planar Pt(II) ion with a dpphen
chelate and two cis acetylide ligands. The average Pt-N
distance of 2.064(10) Å in the complexes agrees well with
Results and Discussion
Synthesis and Characterization. Complex 1 was syn-
thesized according to a previously reported route in which
the chloride ligands were exchanged by the arylacetylide
groups using a CuI-catalyzed procedure, as indicated in
Scheme 1.55,68-70 The synthesis of the imine-containing
donor-chromophore dyads (2-4) was accomplished by
standard Schiff base chemistry to afford the desired products
in excellent yields. Synthesis of the amine dyads (2a-4a),
which is shown in Scheme 2, also proceeds smoothly in the
presence of the borohydride reducing agent. Tolerance of
the Pt complexes for reagents such as borohydride and acetic
acid demonstrates the robust nature of the former. The
complexes are soluble in CH2Cl2 and DMF and only
sparingly soluble in toluene. In addition, several benzaldimine
compounds L-4, L-3, L-2, and L-2-CC-TMS, p-Rs
those of other Pt phenanthroline complexes such as
71
2.063(3), 2.033(6), and 2.040(5) Å in Pt(phen)Cl2
,
Pt(phen)(CtCC6H4CH3)2,55 and Pt(dbbpy)(CtCC6H4CH3)2,72
respectively. The Pt-C(acetylide) distances in all of the
(71) Hazell, A.; Mukhopadhyay, A. Acta Crystallogr. 1980, B36, 1647-
1649.
2632 Inorganic Chemistry, Vol. 44, No. 8, 2005

Pt(diimine)bis(arylacetylide) Chromophore-Donor Dyads
Scheme 1
Scheme 2
structures reported here average 1.954(5) Å and this is in
good agreement with previously reported Pt-C(acetylide)
distances of 1.946(7) and 1.948(3) Å for Pt(phen)(Ct
CC6H4CHO)256 and Pt(phen)(CtCC6H4CH3)2,55 respectively.
Deviations from a square-planar geometry for Pt(II) are
relatively minor, with a mean C-Pt-C angle of 90.18(7)°
and an average N-Pt-N bite angle of 79.27(9)°, the latter
resulting from the built-in constraint of the chelated phenan-
throline ligand. The average CdN (imine)73-78 and CsN
(amine)79 bond distances, 1.255(3) and 1.423(5) Å, respec-
(72) James, S. L.; Younus, M.; Raithby, P. R.; Lewis, J. J. Org. Chem.
1997, 543, 233-235.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2633

Wadas et al.
Scheme 3
Figure 2. Crystal structure of 2 showing 80% probability ellipsoids.
Hydrogen atoms and solvent molecules of crystallization have been omitted
for clarity.
Figure 1. Crystal structure of 1 showing 80% probability ellipsoids.
Hydrogen atoms and solvent molecules of crystallization have been omitted
for clarity.
Figure 3. Crystal structure of 4a showing 80% probability ellipsoids.
Hydrogen atoms and solvent molecules of crystallization have been omitted
for clarity.
tively, agree well with previously reported examples. Finally,
the phenyl rings located in the 4 and 7 positions of the
phenanthroline ring are canted approximately 51° out of the
phenanthroline plane most likely because of unfavorable
steric interactions between the ortho protons located on those
phenyl rings and the 5- and 6-position protons in the
phenanthroline backbone.
Electrochemistry. All of the compounds were investigated
by cyclic voltammetry, and the results are reported in Table
(73) Koh, L. L.; Ranford, J.; Robinson, W.; Svensson, J. O.; Tan, A. L.
C.; Wu, D. Inorg. Chem. 1996, 35 (22), 6466-6472.
(74) Caravan, P.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1997, 36 (21), 4912.
2634 Inorganic Chemistry, Vol. 44, No. 8, 2005

Pt(diimine)bis(arylacetylide) Chromophore-Donor Dyads
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes
1, 2, and 4a‚Et2O
bond lengths
bond angles
Complex 1
Pt(1)-C(25)
1.961(5)
1.959(4)
2.068(3)
2.068(3)
1.195(6)
1.192(6)
C(34)-Pt(1)-C(25)
C(25)-Pt(1)-N(1)
C(34)-Pt(1)-N(2)
N(1)-Pt(1)-N(2)
C(25)-Pt(1)-N(2)
C(34)-Pt(1)-N(1)
87.18(17)
97.10(16)
96.32(15)
79.40(13)
176.09(14)
175.72(13)
Pt(1)-C(34)
Pt(1)-N(1)
Pt(1)-N(2)
C(25)-C(26)
C(34)-C(35)
Complex 2
Pt(1)-C(13)
Pt(1)-N(1)
C(13)-C(14)
1.951(2)
2.0618(18)
1.206(3)
C(13)-Pt(1)-C(13) #1
C(13) #1-Pt(1)-N(1)
N(1)-Pt(1)-N(1) #1
C(13)-Pt(1)-N(1)
92.93(13)
93.83(8)
79.56(10)
172.75(8)
Complex 4a‚Et2O
C(16)-Pt(1)-C(1)
Pt(1)-C(1)
Pt(1)-C(16)
Pt(1)-N(1)
Pt(1)-N(2)
C(1)-C(2)
C(16)-C(17)
1.956(4)
1.939(3)
2.070(3)
2.062(3)
1.205(5)
1.209(5)
87.68(14)
95.58(12)
97.56(13)
79.42(11)
174.74(13)
173.91(12)
C(16)-Pt(1)-N(2)
C(1)-Pt(1)-N(1)
N(2)-Pt(1)-N(1)
C(1)-Pt(1)-N(2)
C(16)-Pt(1)-N(1)
Table 3. Quantum Yields and Redox Potentials (V vs Fc+/Fc)a
compound
φem (%)b
E (V)/∆E (mV)
1
2
3
4
2a
3a
4a
L-2
L-3
L-4
36
0.002
0.02
1.04,c -1.7 (100)
0.28,d -1.75 (100)
0.26,d 0.80,d -1.74 (80)
0.61,d -1.73 (90)
-0.24,d 0.36,d -1.76 (90)
0.24,d -1.76 (110)
0.45,d -1.75 (110)
0.24,d 0.55d
0.07
0.0036
0.032
0.4008
0.87,d 1.51d
1.30d
a In 2:1 dichloromethane/acetonitrile solution at 50 mV/s containing
0.1 M tetrabutylammonium hexafluorophosphate at 298 K. b Determined
using Ru(bpy)3 as the standard. c Irreversible and poorly defined under
2+
experimental conditions. d Irreversible under experimental conditions.
3 with all potentials given relative to the Fc+/Fc couple used
as an internal standard. The complexes show irreversible
oxidation and quasireversible reduction processes. The
electrochemical behavior of complex 1 is similar to that
reported previously for similar systems.55 Complex 1 shows
one poorly defined irreversible oxidation wave at 1.04 V
and one reversible reduction corresponding to the addition
of an electron to an orbital of the diimine ligand at -1.7 V.
The amine and imine complexes undergo oxidation fol-
lowing the order of oxidation: 2 (NMe2ani) more easily than
3 (MeOani) more easily than 4 (ani).80,81 This trend is further
confirmed from the respective imine ligands, which follow
the same order, as oxidation of L-2 is easier than that of
Figure 4. (A) Room-temperature absorption spectrum of 1 in CH2Cl2.
(B) Normalized room-temperature absorption spectra of 2 in DMF,
CH2Cl2, and toluene. (C) Normalized room-temperature absorption spectra
of 2a in DMF, CH2Cl2, and toluene.
L-3, which, in turn, is easier than that of L-4. With regard
to the imine ligands as well as the imine complexes, the first
oxidation is most probably donor-based, following a trend
reflecting the relative ease of aryl oxidation as one moves
from aniline to MeO- and NMe2-anilines. There is also a
second oxidation wave for the imine ligands L-2 and L-3 as
well as the imine complex 3. For the amine complexes, the
lowest irreversible oxidation follows the same trend as that
seen for the imine complexes, with oxidation of 2a at a lower
potential than that of 3a, which is again lower (less anodic)
than that of 4a. The amine complex 2a also shows a second
oxidation wave. However, the basis of the second oxidation
waves for both complexes 3 and 2a and ligands L-2 and
L-3 is not established at this point.
(75) Fernandez-G, J. M.; del Rio-Portilla, F.; Quiroz-Garcia, B.; Toscano,
R. A.; Salcedo, R. J. Mol. Struct. 2001, 561 (1-3), 197-207.
(76) Dahan, F.; Dyer, P. W.; Hanton, M. J.; Jones, M.; Mingos, D. M. P.;
White, A. J. P.; Williams, D. J.; Williamson, A.-M. Eur. J. Inorg.
Chem. 2002, 3, 732-742.
(77) Albietz, P. J., Jr.; Yang, K.; Eisenberg, R. Organometallics 1999, 18
(15), 2747-2749.
(78) Albietz, P. J., Jr.; Yang, K.; Lachicotte, R. J.; Eisenberg, R.
Organometallics 2000, 19 (18), 3543-3555.
Absorption Spectra. The absorption spectra of all of the
complexes have been measured in methylene chloride, DMF,
and toluene (Figures 4, S4, and S5). The high-energy bands
(λ < 370 nm) assignable as diimine-, imine-, amine-, and
acetylide-based intraligand transitions are readily apparent.
(79) Marcazzan, P.; Patrick, B. O.; James, B. R. Organometallics 2003,
22, 1177-1179.
(80) Meites, L.; Zuman, P.; Rupp, E. B. CRC Handbook Series in Organic
Electrochemistry; CRC Press: Boca Raton, FL, 1982.
(81) Brookes, B. A.; Lawrence, N. S.; Compton, R. G. J. Phys. Chem. B
2000, 104, 11258-11267.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2635

Wadas et al.
Complexes 1, 3, 3a, 4, and 4a exhibit an absorption around
400 nm that has been assigned as the Pt f π*(diimine)
1MLCT transition.55,59 The transition comprising the 400-
nm band progressively shifts to lower energy as the electron-
donating ability of the arylacetylide ligand increases
[1 (400 nm) > 4 (425 nm) > 3 (434 nm)]. The MLCT
absorption of complexes 1, 3, 3a, 4, and 4a undergoes a shift
in λmax as solvent polarity is changed (Figures 4, S4, and
S5). This shift to higher energy with increasing solvent
polarity corresponds to negative solvatochromism, suggesting
that the ground state is more polar than the respective excited
states. Similar solvatochromism has been described for other
Pt(diimine)bis(acetylide) complexes as well as for Pt-
(diimine)dithiolate systems.44,45,55
In the case of 2 and 2a, an intense absorption around
400 nm (ꢀ ) 7 × 104 L/mol‚cm) is seen. The intensity of
this band is much larger than that of the MLCT transition
of 1, 3, 3a, 4, and 4a (ꢀ ) 8000-20000 L/mol‚cm) and
exhibits only a very minor dependence on solvent polarity
(Figure S3). In view of these differences from the MLCT
transitions in other Pt(diimine)bis(acetylide) complexes, the
intense 400-nm band for 2 and 2a is not assigned to be the
same MLCT transition.
To further probe the nature of the intense 400-nm
transition, the absorption spectra of L-4, L-3, L-2, and
L-2-CC-TMS were recorded in methlyene chloride, and
their normalized absorption spectra are presented in Figure
5. All three imine (L-4-L-2) analogues display the same
transition, which becomes more intense and shifts to lower
energy as the degree of electron donation increases [L-4
(313 nm) > L-3 (336 nm) > L-2 (380 nm)]. Figure 5 also
demonstrates that this transition continues to shift to lower
energy [L-2 (380 nm) > L-2-CC-TMS (403 nm)] when
an electron-withdrawing acetylide group is positioned para
to the imine bond. Finally, the normalized absorption spectra
of L-2-CC-TMS, L-2a-CC-H, and complexes 2 and 2a
are compared in Figure 5. Both L-2-CC-TMS and
L-2a-CC-H exhibit the same feature at approximately
400 nm, suggesting that this transition in 2 and 2a is ligand-
based and obscures the less strongly allowed MLCT transi-
tions. Based on literature reports, the intense band at
400 nm occurs in highly conjugated systems and has been
assigned as a low-lying π-π* transition.82,83
Emission Spectroscopy of 1. Complex 1, like other Pt-
(diimine)bis(acetylide) complexes, is highly emissive in fluid
solution and displays a broad structureless emission. The
relative quantum yield for emission of 1 in CH2Cl2 was
measured using Ru(bpy)32+ as the standard (φ ) 0.062) and
found to be 36%, which is similar to what has been reported
for other complexes of this type.84 Complex 1 has an excited
state with a long lifetime of 3.1 µs that is approximately 10
times longer-lived, as well as 10 times more luminescent,
than that of the corresponding phenanthroline complex,
Pt(phen)(CtCsp-C6H4CHO)2.56 The basis of the long
Figure 5. (A) Normalized room-temperature absorption spectra of L-4,
L-3, L-2, and L-2-CC-TMS in CH2Cl2. (B) Normalized room-temperature
absorption spectra of 2 and L-2-CC-TMS in CH2Cl2 at room temperature.
(C) Normalized room-temperature absorption spectra of 2a and
L-2a-CC-H in CH2Cl2 at room temperature.
excited-state lifetime can be found in a rationalization put
forward by McCusker to explain the long excited-state
lifetimes of related Ru(II) dpphen systems.85,86 Specifically,
in the excited state, the phenyl substituents on the dpphen
ligand rotate into the plane of the phenathroline to create a
more highly conjugated ligand, resulting in greater delocal-
ization of the excited-state electron. Based on the measured
em
rel
values of τ and φ , the radiative and nonradiative rate
constants for 1 are calculated to be kr ) 1.2 × 105 s-1 and
knr ) 2.1 × 105 s-1.
Emission of Dyads, Quenching, and Photodecomposi-
tion. Substantial luminescence quenching is observed for all
of the D-C dyads when compared to 1, and this can be seen
(82) Smith, W. F. Tetrahedron 1963, 19, 445-454.
(85) Damrauer, N. H.; McCusker, J. K. J. Phys. Chem. A 1999, 103 (42),
8440-8446.
(86) Damrauer, N. H.; Boussie, T. R.; Devenney, M.; McCusker, J. K. J.
Am. Chem. Soc. 1997, 119 (35), 8253-8268.
(83) Reeves, R. L.; Smith, W. F. J. Am. Chem. Soc. 1963, 85, 724-728.
(84) Chan, S.-C.; Chan, M. C. W.; Wang, Y.; Che, C.-M.; Cheung, K.-K.;
Zhu, N. Chem. Eur. J. 2001, 7, 4180-4190.
2636 Inorganic Chemistry, Vol. 44, No. 8, 2005

Pt(diimine)bis(arylacetylide) Chromophore-Donor Dyads
Figure 6. Emission spectrum of the chromophore in CH2Cl2 at room
temperature and spectra of 2 in solvents of varying polarity. Multiplication
factors are arbitrary so that the emission spectra can be observed for each
solvent and compared relative to that of chromophore 1.
from Figures 6 and S6, but unlike other dyads based on the
Pt(diimine)bis(acetylide) chromophore,61 luminescence quench-
ing is not solvent-dependent. A tabulation of relative quantum
yields obtained in degassed methylene chloride is presented
in Table 3 and correlates well with the standard potentials
of the donors aniline, MeO-aniline and NMe2-aniline.
Because NMe2-aniline is the most easily oxidized of the three
3
donors, reductive quenching of the MLCT excited state
would be the most efficient in this dyad, yielding a
substantially lower relative quantum yield for emission.
Conversely, aniline is the most difficult to oxidize, making
reductive quenching of the excited state less facile with
consequent increased luminescence. As expected, the imine
dyads were observed to have lower relative quantum yields
than their amine analogues, suggestive of greater quenching
due to conjugation between the donor and metal center.
However, even with the most luminescent D-C dyad, the
relative emission quantum yield was observed to be less than
0.5%, clearly indicating that the Pt chromophore undergoes
effective reductive quenching with photooxidation of the
donor. As has been observed for other Pt(diimine) systems,
the quenching occurs through an electron-transfer mechanism
and not through energy transfer.49,56,87 Attempts to observe
the charge-separated state directly in these systems, however,
proved unsuccessful, and in the course of these measure-
ments, it was found that the dyads were unstable chemically
upon irradiation.
To investigate the photoinstability of these dyads, photo-
lysis experiments were conducted on all of the samples, and
a representative set of these experiments (imine complex 2
and amine complex 2a) is discussed below. When complex
2 is irradiated in dry methylene chloride, the 400-nm
transition is seen to decrease only during irradiation (Figure
S7A), but in the presence of water, the same band continues
to decrease even after irradiation ceases, indicating that a
thermal reaction is taking place in the absence of further
irradiation (Figure S7B).
Figure 7. Room-temperature emission spectra of 2 and 2a in CH2Cl2
recorded during a photostability study with broad-spectrum irradiation
(300-700 nm): (A) complex 2 in anhydrous CH2Cl2, (B) complex 2 in
wet CH2Cl2, (C) complex 2a in wet CH2Cl2.
cence increases slightly with a blue shift from 586 to
567 nm, suggesting that a new species slowly forms after
photolysis (Figure 7A). When a similar photolysis of 2 in
wet dichloromethane is conducted, bright luminescence
returns to the solution with an emission maximum of
550 nm, identical to that of chromophore 1 (Figure 7B). The
new species formed was identified by FTIR spectroscopy.
The band at 1620 cm-1 corresponding to the imine CdN
stretch for 2 diminishes upon photolysis in wet dichlo-
romethane, and a new peak at 1683 cm-1, corresponding to
the aldehyde CdO stretch of chromophore 1, appears. Thus,
2 is undergoing hydrolysis to regenerate a small concentration
of the brightly emissive chromophore. However, attempts
to identify the weakly emissive species formed upon irradia-
tion of dry CH2Cl2 samples of 2 have not met with success.
Prior to irradiation, complex 2 in dry methylene chloride
is very weakly emissive, whereas after photolysis, lumines-
(87) Scaiano, J. C. CRC Handbook of Organic Photochemistry; CRC
Press: Boca Raton, FL, 1989.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2637

Wadas et al.
In the case of the amine dyad 2a, similar evidence of
photoinstability was obtained. Immediately after 2a was
irradiated for 1 h in wet CH2Cl2 with visible light, a marked
decrease in the absorbance band at 400 nm was seen (Figure
S7C), and the emission maximum was seen to exhibit a great
increase in intensity with an immediate blue shift of the
emission maximum to a value similar to that of the parent
chromophore 1 (Figure 7C).
Photohydrolysis has been observed previously in solutions
of metal complexes.88-92 Based on these reports, it is believed
that, for the imine-linked dyads, the formation of 1 proceeds
through an iminium ion generated upon photoinduced
electron transfer from the donor to the Pt metal center,
followed by reaction with H2O. For the amine-linked dyads,
the same reaction manifold is accessible following initial
arylamine oxidation followed by proton loss and subsequent
electron and proton loss steps to generate the corresponding
imine. Because the instability of the complexes was observed
only under photolytic conditions in contrast to samples that
exhibited stability in the dark, we conclude that the observed
decomposition reaction is a photochemically driven hydroly-
sis process.
(acetylide)-based donor-chromophore (D-C) dyads. The
parent aldehyde, Pt(dpphen)(CtCC6H4CHO)2 (1), is brightly
luminescent with a long-lived excited state in CH2Cl2 (3 µs),
whereas emission of the corresponding D-C dyads is
effectively quenched by the attached aniline donors in all
solvents tested. The dyad complexes exhibit a dpphen-based
reversible one-electron reduction and an irreversible oxidation
of the attached aniline donors. Complexes 2 and 2a display
an intense absorption around 400 nm that is shown to be a
π-π* transition localized on the highly conjugated ligand
system, whereas all other dyads exhibit the expected
Pt f π*(dpphen) MLCT transitions. Although the synthesis
of the imine and the corresponding amine dyads 2/2a-4/4a
is facile, irradiation experiments of the D-C dyads using a
broad spectrum of visible light suggest that both the imine
and the amine linkages are highly susceptible to photo-
hydrolysis. This difficulty essentially makes this approach
undesirable for further development in the construction of
systems for photoinduced charge separation.
Acknowledgment. We thank the Department of Energy,
Division of Chemical Sciences, for support of this research
and Ms. Christine Flaschenreim for assistance with structural
aspects of this study.
Conclusions
The present work describes the use of Schiff base
condensation as a means of generating new Pt(diimine)bis-
Supporting Information Available: Crystal data, atomic
coordinates, bond distances, bond angles, and anisotropic displace-
ment parameters for 1-4 and 4a in CIF format. ORTEP diagrams
of complexes 3 and 4, absorption spectra of complexes 3/3a and
4/4a in different solvents, and emission spectra of 1, 3, and 4 in
different solvents. This material is available free of charge via the
Internet at http://pubs.acs.org.
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IC048886L
2638 Inorganic Chemistry, Vol. 44, No. 8, 2005