Heteroleptic platinum(II) and palladium(II) complexes with thiacrown and diimine ligands

Article abstract of DOI:10.1016/j.poly.2011.08.030

We wish to report the synthesis, crystal structures, spectroscopic and electrochemical properties of several new Pt(II) heteroleptic complexes containing the thiacrown, 9S3 (1,4,7-trithiacyclononane) with a series of substituted phenanthroline ligands and

Full text of DOI:10.1016/j.poly.2011.08.030

Polyhedron 31 (2012) 89–97
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Polyhedron
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Heteroleptic platinum(II) and palladium(II) complexes with thiacrown and
diimine ligands
a
a
b
b
Gregory J. Grant a, , Natalie N. Talbott , Marko Bajic , Larry F. Mehne , Thomas J. Holcombe ,
⇑
Donald G. VanDerveer c
a Department of Chemistry, The University of Tennessee at Chattanooga, TN 37403, USA
b Department of Chemistry, Covenant College, Lookout Mountain, Georgia 30750, USA
c Department of Chemistry, Clemson University, Clemson, SC 29366, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 July 2011
Accepted 30 August 2011
Available online 10 September 2011
We wish to report the synthesis, crystal structures, spectroscopic and electrochemical properties of sev-
eral new Pt(II) heteroleptic complexes containing the thiacrown, 9S3 (1,4,7-trithiacyclononane) with a
series of substituted phenanthroline ligands and related diimine systems. These five ligands are
5,6-dimethyl-1,10-phenanthroline(5,6-Me2-phen),
4,7-dimethyl-1,10-phenanthroline(4,7-Me2-phen),
4,7-diphenyl-1,10-phenanthroline(4,7-Ph2-phen), 2,20-bipyrimidine(bpm), and pyrazino[2,3-f]quinoxa-
line or 1,4,5,8-tetraazaphenanthrene(tap). All complexes have the general formula [Pt(9S3)(N2)](PF6)2
(N2 = diimine ligand) and form similar structures in which the Pt(II) center is surrounded by a cis arrange-
ment of the two N donors from the diimine chelate and two sulfur atoms from the 9S3 ligand. The third
9S3 sulfur in each structure forms a longer interaction with the platinum resulting in an elongated square
pyramidal structure, and this distance is sensitive to the identity of the diimine ligand. In addition, we
report the synthesis, structural, electrochemical, and spectroscopic properties of related Pd(II) 9S3 com-
plex with tap. The 195Pt NMR chemical shifts for the six Pt(II) complexes show a value near ꢀ3290 ppm,
consistent with a cis-PtS2N2 coordination sphere although more electron-withdrawing ligands such as tap
show resonances shifted by almost 100 ppm downfield. The physicochemical properties of the complexes
generally follow the electron-donating or withdrawing properties of the phenanthroline substituents.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Thioether complexes
Platinum complexes
Trithiacyclononane
Platinum nuclear magnetic resonance
Diimine complexes
Crown thioethers
1. Introduction
the Van der Waals radii for a metal–sulfur interaction [12]. The dis-
tance is a function of the donor ability of the ancillary ligand, with
The thiacrown ligand, 1,4,7-trithiacyclononane (9S3), has been
extensively studied for over 30 years [1–6]. A particular focus of
thiacrown coordination behavior deals with its complexes of Pt(II)
and Pd(II) [4,7–10]. Long distance interactions between the d8 me-
tal ion and axial sulfur donors in the coordinated 9S3 result in the
unusual spectroscopic and electrochemical properties displayed by
the complexes [11]. These 9S3 complexes show two equatorial me-
tal–sulfur bond distances that fall in the expected ranges (2.2–
2.5 Å for both ions), but there are longer axial sulfur interactions
which are quite sensitive to the donor properties of the second
or ancillary ligand. The long distance interactions result in hetero-
leptic 9S3 Pt(II) and Pd(II) structures typically best described as
elongated square pyramids with [S4 + S1] coordination. For the
Pt(II) thiacrown complexes, these axial sulfur distances vary be-
tween 2.6 and 3.3 Å. All of the observed Pt–S and Pd–S axial dis-
tances fall between the covalent bond distance and the sum of
poor donors such as SbPh3 displaying the shortest axial distances
and good donors like halides showing the longest ones [13,14].
One important set of ancillary ligands that have been used in
these types of Pt(II) and Pd(II) 9S3 complexes are diimines such
as 2,2-bipyridine (bipy) and 1,10-phenanthroline (phen). Indeed,
early reports from the Gray and Schröder research groups exam-
ined Pd(II) and Pt(II) 9S3 behavior with unsubstituted bipy and
phen [15,16]. More recent reports by our group and others have ex-
tended the ligating properties of diimines as ancillary ligands in
9S3 complexes of d8 metal ions [17,18], and last year Connick
and co-workers reported unusual photochemical behavior in the
Pt 9S3 complex with 5-nitro-phen due to its interaction with
[SbCl5]2ꢀ [19]. We have also been interested in the related com-
plexes with cyclometallating ligands such as 2-phenylpyridine
[20,21]. Our research group has previously identified three differ-
ent modes of intermolecular p–p stacking arrangements in diimine
and cyclometallating complexes with 9S3 and Pt(II) and Pd(II) [22].
Complexes with long distance metal–sulfur interaction can serve
as models for transition states of associative substitution reactions
involving d8 metal ions since they involve dangling nucleophiles
⇑
Corresponding author.
E-mail address: Greg-Grant@utc.edu (G.J. Grant).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.030

90
G.J. Grant et al. / Polyhedron 31 (2012) 89–97
Scheme 1. Diimine ligands discussed in this report.
[15]. Diimine ligand complexes with these ions are of interest due
to a wide range of applications including tumor cytotoxicity [23],
the development of molecular photochemical devices [24], and
supramolecular complexes [25,26]. A listing for the six different
diimines used in our study is given in Scheme 1. Here we report
the syntheses, structural, electrochemical, and spectroscopic prop-
erties for five new Pt(II) heteroleptic complexes containing a series
of diimine ligands. The ligands studied are 5,6-di-1,10-phenan-
in electrolytic solution. All reported potentials were internally ref-
erenced to the FeCp2+/FeCp2 couple which under these conditions
gave an approximate E0 of +0.093 V relative to the reference elec-
trode. The electrochemical window was generally +1.4 to ꢀ1.6 V
versus the FeCp2+/FeCp2 couple.
2.2. Preparation of Pt(II) 9S3 complexes with diimine ligands
throline(5,6-Me2-phen),
4,7-dimethyl-1,10-phenanthroline(4,7-
2.2.1. Preparation of [Pt(9S3)(5,6-Me2-phen)](PF6)2 (1)
Me2-phen), 4,7-diphenyl-1,10-phenanthroline(4,7-Ph2-phen),
A
mixture of potassium tetrachloroplatinate (99.6 mg,
pyrazino[2,3-f]quinoxaline or 1,4,5,8-tetraazaphenanthrene(tap),
2,20-bipyrimidine(bpm), and 5-nitro-1,10-phenanthroline(5-NO2-
phen). The complexes all have the general formula
Pt(9S3)(N2)](PF6)2 where N2 is the diimine chelate. While this work
was being prepared, Connick and co-workers reported the synthe-
sis and properties of the 5-NO2-phen complex, including its crystal
structure [19]. We include only new multinuclear NMR data on
that compound in this paper. Lastly, we also report the synthesis,
crystal structure, and physicochemical properties of the related
Pd(II) 9S3 complex with tap.
0.240 mmol) and 5,6-Me2-Phen (50.0 mg, 0.240 mmol) was re-
fluxed in 26 mL of H2O and 2 N HCl (25:1 v/v) for 1 h. The insoluble,
yellow [Pt(5,6-Me2-phen)Cl2] was filtered and washed with ether
(3 ꢁ 3 mL) to yield 90 mg (79%) of product. Under nitrogen, a mix-
ture of [Pt(5,6-Me2-phen)Cl2] (90.0 mg, 0.190 mmol) and 9S3
(32.5 mg, 0.180 mmol) was refluxed in 30 mL of MeOH:CH3CN:H2O
(1:1:1 v:v) for 40 min. The flask was slightly cooled before ammo-
nium hexafluorophosphate (65.0 mg, 0.400 mmol) was added, and
the solution refluxed for 30 min. The sample was cooled to room
temperature and filtered. An insoluble, yellow powder of the start-
ing Pt(II) complex was removed by filtration. The soluble portion
was filtered a second time, concentrated to dryness, redissolved
in MeNO2, and crystallized via ether diffusion to produce X-ray
quality crystals. A mass of 33.2 mg (21.1%) of [Pt(9S3)(5,6-Me2-
phen)](PF6)2 was obtained as an orange solid. Anal. Calc. for
2. Experimental
2.1. Materials and measurements
All ligands, solvents and other reagents were purchased from
Aldrich Chemical Company and other commercial sources and
used as received. The starting 9S3 complexes [Pt(9S3)Cl2] and
[Pd(9S3)Cl2] were prepared according to the published procedures
[27]. All starting diimine Pt(II) complexes, [Pt(diimine)Cl2] were
synthesized based upon a published procedure for the related bipy
complexes [17]. Elemental analyses were performed by Atlantic
Microlab, Inc. of Atlanta, GA. Fourier transform IR spectra were ob-
tained as KBr powders using pre-weighed 500 mg packets and a
Nicolet Impact 410 spectrometer equipped with an ATR accessory.
Electronic spectra were obtained in acetonitrile using a Shimadzu
UV-2101PC ultraviolet–visible spectrophotometer. All 13C{1H}
and 1H NMR spectra were recorded on a JEOL ECX-400 NMR spec-
trometer using CD3NO2 for both the deuterium lock and reference.
All proton connectivities are confirmed through 13C DEPT NMR
experiments. All six 195Pt{1H} NMR spectra were externally refer-
enced to [PtCl4]2ꢀ at ꢀ1624 ppm [28]. Electrochemical data were
obtained using a Bioanalytical Systems Epsilon potentiostat and
analyzer. The supporting electrolytic solution was 0.1 M tetra-n-
butylammonium tetrafluoroborate in acetonitrile, and sample con-
centrations were approximately 2 mM. All voltammograms were
recorded at a scan rate of 100 mV/s except where noted. The stan-
dard three-electrode configuration used is as follows: 1.6 mm
diameter Pt disk working electrode, Pt wire auxiliary electrode,
and a pseudo-reference electrode comprised of Ag/0.01 M Ag(I)
C
18F12H24N2P2PtS3: C, 27.50; H, 2.77; N, 3.21; S, 11.01. Found: C,
27.65; H, 2.68; N, 3.38; S, 10.84%. 1H NMR (CD3NO2): d (ppm),
9.31 (d with 195Pt satellites, JPt–H = 33 Hz, JH–H = 5.5 Hz, phen-C2
proton, 2H), 9.20 (d, JH–H = 8.3 Hz, phen-C4 proton, 2H), 8.17 (dd,
3
3
3
3JH–H = 5.5 and 8.3 Hz, phen-C3 proton, 2H), 3.52–3.43 (m, 9S3,
6H) and 3.38–3.30 (m, 9S3, 6H), 2.93 (s, –Me, 6H). 13C{1H} NMR
(CD3NO2): d (ppm), 150.74 (s, phen-C2, –CH, 2C), 148.62 (s, phen,
–C–, 2C), 139.90 (s, phen-C4, –CH–, 2C), 135.04 (s, phen, –C–, 2C),
133.34 (s, phen, –C–, 2C), 128.11 (s, phen-C3, –CH–, 2C), 34.53 (s,
9S3, –CH2–, 6C), 15.64 (s, –Me, –CH3–, 2C). 195Pt{1H} NMR
(CD3NO2), d (
absorption spectrum measured in acetonitrile showed two kmax’s
at 400 nm ( = 3200) and 283 nm ( = 29000) along with a shoulder
v1/2): singlet at ꢀ3286 ppm (641 Hz). The electronic
e
e
peak at 291 nm (e = 26000). The complex showed an irreversible
oxidation at +1.13 V versus Fc/Fc+ and an irreversible reduction
at ꢀ1.29 V versus Fc/Fc+.
2.2.2. Preparation of [Pt(9S3)(4,7-Me2-phen)](PF6)2 (2)
A
mixture of potassium tetrachloroplatinate (99.0 mg,
0.240 mmol) and 4,7-Me2-Phen (50.0 mg, 0.240 mmol) was refluxed
in 26 mL of H2O and 2 N HCl (25:1 v/v) for 1 h. The insoluble, yellow
solid of [Pt(4,7-Me2-Phen)Cl2] was filtered and washed with ether
(3 ꢁ 3 mL) to yield 85.5 mg (75.0%) of product. Next, under nitrogen,
a mixture of [Pt(4,7-Me2-Phen)Cl2] (73.6 mg, 0.155 mmol) and 9S3
(27.0 mg, 0.150 mmol) was refluxed in 60 mL of MeOH:CH3CN:H2O

G.J. Grant et al. / Polyhedron 31 (2012) 89–97
91
(1:1:1 v:v) for 40 min. After 20 min of refluxing, the solution became
bright yellow in color, and all solids had dissolved. The flask was
slightly cooled before ammonium hexafluorophosphate (52.0 mg,
0.319 mmol) was added to the flask, and the solution was then re-
fluxed under nitrogen for 20 min. The sample was cooled to ambient
temperature and concentrated to 1/3 its original volume. The yellow
solid was filtered and washed with cold EtOH (1 ꢁ 10 mL), H2O
(1 ꢁ 10 mL), and dried with ether (3 ꢁ 3 mL) to yield 45 mg (34%)
of [Pt(9S3)(4,7-Me2-phen)](PF6)2. Golden-yellow crystals suitable
for X-ray diffraction were grown by ether diffusion into a nitrometh-
ane solution. Anal. Calc. for C20H24F12N2P2PtS3: C, 27.50; H, 2.77; S,
11.01; N, 3.21. Found: C, 27.72; H, 2.65; S, 11.26; N, 3.34%. 1H NMR
at 536 nm (
and a shoulder peak at 227 nm (
e
= 2200), 401 nm (
e
= 3100), and 298 nm (
e
= 32000)
e
= 40000). Since a crystal
structure could not be obtained for this compound, we have in-
cluded its 13C{1H} DEPT NMR spectrum in the ESI Section.
2.2.4. Preparation of [Pt(9S3)(2,20-bpm)](PF6)2 (4)
A mass of [Pt(9S3)Cl2] (100 mg, 0.224 mmol) and 2,20-bipyrimi-
dine (bpm) (35.4 mg, 0.224 mmol) were refluxed in 60 mL of
MeOH:CH3CN:H2O (1:1:1 v:v) for 1 h. During reflux, the solution
became dark orange/pink in color. The sample was concentrated
to 1/4 of its original volume, and a mass of NH4PF6 (146 mg,
0.896 mmol) was added to the flask. Cooling to 0 °C produced dark
orange crystals of the desired product. These were filtered, rinsed
with cold EtOH (1 ꢁ 5 mL) and then ether (3 ꢁ 15 mL) to yield
107 mg (58.0%) of [Pt(9S3)(2,20-bpm)](PF6)2. Crystallization using
ether diffusion into nitromethane produced bright orange crystals
suitable for X-ray diffraction. Anal. Calc. for C14H18F12N4P2PtS3: C,
20.42; H, 2.20; N, 6.80; S, 11.68. Found: C, 19.94; H, 2.17, N, 6.40;
S, 11.91%. 1H NMR (CD3NO2): d (ppm), 9.46 (dd, 3JH–H = 6 Hz, bpm-
3
(CD3NO2): d (ppm), 9.16 (d with 195Pt satellites, JPt–H = 31 Hz,
3JH–H = 5.5 Hz, phen-C2 proton, 2H), 8.47 (s, phen-C5 proton, 2H),
3
7.98 (d, JH–H = 5.6 Hz, phen-C3 proton, 2H), 3.49–3.40 (m, 9S3, 6H)
and 3.35–3.27 (m, 9S3, 6H), 3.04 (s, –CH3, 6H). 13C{1H} NMR
(CD3NO2): d (ppm), 155.01 (s, phen, –C–, 2C), 151.33 (s, phen-C2, –
CH, 2C), 147.67 (s, phen, –C–, 2C), 132.90 (s, phen, –C–, 2C), 128.70
(s, phen-C5, –CH–, 2C), 126.30 (s, phen-C3, –CH–, 2C), 34.49 (s, 9S3,
–CH2, 6C), 19.62 (s, –CH3, 2C). 195Pt{1H} NMR (CD3NO2), d (
v
1/2): sin-
C6 proton, 2H), 9.33 (dd with 195Pt satellites, JPt–H = 36 Hz,
3
glet at ꢀ3298 ppm (657 Hz). The electronic absorption spectrum
3JH–H = 6 Hz, 4JH–H = 4 Hz, bpm-C3 proton, 2H), 8.04 (dd,
4
measured in acetonitrile showed two kmax’s at 383 nm (
and 276 nm ( = 47400) and shoulder peaks at 355 nm (
302 nm ( = 12000) and 284 nm (e = 39000). The complex showed
e
= 3930)
3JH–H = 6 Hz, JH–H = 4 Hz, bpm-C4 proton, 2H), 3.50–3.38 (m, 9S3,
e
e
= 3240),
6H), and 3.33–3.22 (m, 9S3, 6H). 13C{1H} NMR (CD3NO2): d (ppm),
163.29 (bpm-C5, –CH), 162.02 (bpm-C1, –C–), 158.25 (bpm-C3, –
CH), 127.07 (bpm-C4, –CH), 34.67 (9S3, –CH2–, 6C). 195Pt{1H}
e
an irreversible oxidation at +1.09 V versus Fc/Fc+ and an irreversible
reduction at ꢀ1.24 V versus Fc/Fc+.
NMR (CD3NO2), d (
v
1/2): singlet at ꢀ3277 ppm (567 Hz). mmax
,
cmꢀ1: strongest IR bands at 1583, 1560, 1456, 1417, 1261, 1029,
846 (s, PF6ꢀ), 742, 675 (C–S), 605. The electronic absorption spec-
trum measured in acetonitrile showed two kmax’s at 426 nm
2.2.3. Preparation of [Pt(9S3)(4,7-Ph2-phen)](PF6)2 (3)
A
mixture of potassium tetrachloroplatinate (62.3 mg,
0.150 mmol) was refluxed with 4,7-Ph2-Phen (50.0 mg,
0.150 mmol) in 26 mL of H2O and 2 N HCl (25:1 v/v) for 1 h. The
insoluble solid was filtered and washed with three times with
3 mL ether to yield 54 mg (60%) of yellow [Pt(4,7-Ph2-Phen)Cl2].
Under nitrogen, [Pt(4,7-Ph2-Phen)Cl2] (54 mg, 0.090 mmol) and
9S3 (16.3 mg, 0.090 mmol) were refluxed in 30 mL of
MeOH:CH3CN:H2O (1:1:1 v:v) for 3 h. After 20 min of refluxing,
the solution became bright yellow in color with dissolution of
the starting Pt(II) complex. The reaction was slightly cooled,
ammonium hexafluorophosphate (44.0 mg, 0.270 mmol) was
added, and the mixture refluxed for another hour. The sample
was concentrated to 1/3 of its original volume, resulting in the pre-
cipitation of the [Pt(4,7-Ph2-Phen)Cl2] complex as a bright yellow
precipitate. The precipitate was removed by filtration, and the fil-
trate evaporated to dryness. Traces of a white crystalline solid, pre-
sumably ammonium chloride, were removed by rinsing the sample
with H2O (3 ꢁ 5 mL). The sample was then redissolved in 3 mL of
nitromethane, and ether slowly diffused into the sample. After
14 h of crystallization, several crystal habits were visible including
yellow needles of the starting [Pt(4,7-Ph2-Phen)Cl2], orange prisms
of [Pt(9S3)2](PF6)2, and red crystals of the desired product of
[Pt(9S3)(4,7-Ph2-phen)](PF6)2. The supernatant was removed, and
the crystals were washed with MeOH (4 ꢁ 3 mL) and ether
(4 ꢁ 3 mL). Mechanical separation of the red crystals yielded
12 mg (13%) of [Pt(9S3)(4,7-Ph2-phen)](PF6)2. Anal. Calc. for
(
(
e
e
= 1720) and 227 nm (e = 25300) and a shoulder peak at 246 nm
= 21800). The complex shows a single one electron oxidation
wave at +0.98 V versus Fc/Fc+ and an irreversible reduction at
ꢀ1.00 V versus Fc/Fc+.
2.2.5. Preparation of [Pt(9S3)(tap)](PF6)2 (5)
A
mixture of [Pt(9S3)Cl2] (50.0 mg, 0.112 mmol) and tap
(20.4 mg, 0.112 mmol) was refluxed in 25 mL of MeNO2 for 1 h.
During reflux, the solution turned bright yellow with dissolution
of all solids. After cooling to room temperature, a mass of NH4PF6
(36.5 mg, 0.224 mmol) was added, and the solution was refluxed
for an additional 20 min. Cooling at 0 °C overnight resulted in the
formation of an orange precipitate of [Pt(9S3)2](PF6)2. The precipi-
tate was filtered and rinsed with cold MeNO2 (2 ꢁ 5 mL). The
filtrate, which was bright yellow in color, was concentrated to
1/3 its original volume, and ether diffused in the solution. Crystals
formed which were then redissolved in MeCN. Diffusion of ether
into a MeCN solution produced red needles suitable for X-ray dif-
fraction studies.
A second method was used to prepare complex 5. A mass of
[Pt(9S3)Cl2] (100 mg, 0.224 mmol) was refluxed with tap
(40.8 mg, 0.224 mmol) for 1 h in 60 mL of a total volume of a
1:1:1 ratio of methanol, acetonitrile, and water. During reflux,
the color of changed to a dark orange color with all insoluble solids
dissolving. The sample was concentrated to ½ of its original vol-
ume, and a mass of ammonium hexafluorophosphate (146 mg,
0.896 mmol) was added to the flask. The reaction was refluxed
for 1 h with some turbidity present. Upon cooling, an orange pre-
cipitate of [Pt(9S3)2](PF6)2 formed. The orange precipitate was
washed once with cold ethanol (5 mL) and then with ether
(15 mL) to yield 81.0 mg of [Pt(9S3)2](PF6)2 as a side product. The
orange filtrate was concentrated to 1/3 of its original volume to
yield a second crop of Pt(9S3)2](PF6)2 as a bright orange solid
weighing 8.8 mg. This was washed with cold ethanol (5 mL) and
then with ether (15 mL). The remaining dark orange filtrate was
evaporated to dryness to yield 30 mg (15.8%) yield of
[Pt(9S3)(tap)](PF6)2 as a maroon solid. The same complex cation
C
30H28F12N2P2PtS3: C, 36.11; H, 2.83; N, 2.81; S, 9.64. Found: C,
36.22 H, 2.99, N, 2.99; S, 9.50%. 1H NMR (CD3NO2): d (ppm), 9.44
(d with 195Pt satellites, JPt–H = 35 Hz, JH–H = 5.5 Hz, phen-C2 pro-
ton, 2H), 8.34 (s, phen-C6 proton, 2H), 8.19 (d, JH–H = 5.6 Hz,
3
3
3
phen-C3 proton, 2H), 7.77–7.69 (m, Ph, 10H), 3.55–3.46 (m, 9S3,
6H) and 3.41–3.32 (m, 9S3, 6H). 13C{1H} NMR (CD3NO2): d (ppm),
155.77 (s, phen, –C–), 151.54 (s, phen, –CH), 136.45 (s, phen, –C–),
131.93 (s, Ph, –CH), 131.88 (s, phen, –C–), 131.22 (s, Ph, –C–),
131.20 (s, Ph, –CH), 130.70 (s, Ph, –CH), 128.38 (s, phen, –CH),
128.00 (s, phen, –CH), 34.19 (s, 9S3, –CH2). 195Pt{1H} NMR
(CD3NO2), d (
v1/2): singlet at ꢀ3288 ppm (501 Hz). The electronic
absorption spectrum measured in acetonitrile showed three kmax’s

92
G.J. Grant et al. / Polyhedron 31 (2012) 89–97
could also be prepared as a triflate salt using a similar procedure to
the one reported for the Pd(II) complexes (see below, Section
2.3.1). 1H NMR (CD3NO2): d (ppm), 9.59 (d with 195Pt satellites,
but a series of four irreversible reduction waves were observed
at ꢀ0.59, ꢀ0.78, ꢀ1.20, and ꢀ1.40 V versus Fc/Fc+.
3
4JPt–H = 10 Hz, JH–H = 2.8 Hz, tap-C3 proton, 2H), 9.37 (d with 195Pt
2.4. X-ray structural determinations
3
3
satellites, JPt–H = 32 Hz, JH–H = 2.8 Hz, tap-C2 proton, 2H), 8.73 (s,
tap-C5 proton, 2H), 3.55–3.46 (m, 9S3, 6H) and 3.43–3.34 (m, 9S3,
6H), 3.04 (s, –CH3, 6H). 13C{1H} NMR (CD3NO2): d (ppm), 153.11
(tap, –CH–), 151.42 (tap, –C–), 148.72 (tap, –C–), 145.19 (tap, –
CH–), 134.77 (tap, –CH–), 35.20 (9S3, –CH2–). 195Pt{1H} NMR
Table 1 contains crystal data, collection parameters, and refine-
ment criteria for the structures of 1–2, 4–5, and 7. For all struc-
tures, X-ray intensity data were measured at low temperature in
the range of 163–183 K with graphite-monochromated Mo K
a
(CD3NO2), d (
v
1/2): singlet at ꢀ3198 ppm (446 Hz).
m :
max, cmꢀ1
radiation (k = 0.71073 Å) on Rigaku AFC8S diffractometer
a
strongest IR bands at 1623, 1406, 839 (s, PF6ꢀ), 664 (s, C–S). The
electronic absorption spectrum measured in acetonitrile showed
equipped with a 1 K Mercury CCD detector. The structure was
solved using direct methods and refinement was done using full-
matrix least-squares techniques (on F2) [29]. Data were corrected
for absorption, using semi-empirical methods [29]. Structure solu-
tion, refinement and the calculation of derived results were per-
formed with the SHELXTL package of computer programs [30]. All
non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were placed in ideal positions
and refined a riding atoms with relative isotropic displacement
parameters.
two kmax’s at 464 nm (
e
= 1620) and 290 nm (
e = 18900) along with
a weak shoulder at 338 nm (
e
= 5480). The complex showed no
oxidation behavior, but an irreversible reduction at ꢀ0.95 V versus
Fc/Fc+.
2.2.6. Preparation of [Pt(9S3)(5-NO2-phen)](PF6)2 (6)
The synthesis of the complex has recently been reported [19].
We include only previously unpublished data in this report.
13C{1H} NMR (CD3NO2): d (ppm), 154.77 (phen, –CH, 1C), 153.23
(phen, –CH, 1C), 149.67 (phen, –C–, 1C), 148.66 (phen, –C–, 1C),
146.33 (phen, –C–, 1C), 144.82 (phen, –CH, 1C), 139.72 (phen, –
CH, 1C), 130.19 (phen, –C–, 1C), 129.90 (phen, –CH, 1C), 129.70
(phen, –CH, 1C), 129.08 (phen, –CH, 1C), 126.22 (phen, –C–, 1C),
3. Results and discussion
3.1. Syntheses
34.63 (9S3, –CH2–, 6C). 195Pt{1H} NMR (CD3NO2), d (
v1/2): singlet
Two general routes were employed in the synthesis of the com-
pounds, and both were based upon prior reports [17,27]. These are
at ꢀ3255 ppm (552 Hz). The reaction between the complex and
tris(4-bromophenyl)aminium hexachloroantimonate was also re-
ported [19]. We have repeated that procedure in an attempt to
study the reaction using 195Pt NMR spectroscopy. After a 1-week
reaction between the two species, we observe a color change to a
dark orange solution and a significant loss in strength of the
195Pt NMR resonance at ꢀ3255 ppm, with only a weak, broad peak
remaining for the original complex. No other resonances were
observed.
shown in Scheme
2 for the synthesis of [Pt(9S3)(5,6-Me2-
phen)](PF6)2 from [Pt(5,6-Me2-phen)Cl2] and the synthesis of
[Pt(9S3)(tap)](PF6)2 from [Pt(9S3)Cl2]. The former procedure gen-
erally worked better for the diimine ligands containing electron-
donating groups while the latter worked better for diimines with
electron-withdrawing components. In the synthesis of the Pt(II)
complexes containing both Me2-phen ligands, the crude synthetic
products were contaminated with either the starting and unre-
acted dichloro diimine complex (usually yellow needles) or the
bis 9S3 complex of Pt(II) (orange prisms). Furthermore, the synthe-
sis of [Pt(9S3)(4,7-Ph2-phen)](PF6)2 poses similar problems, but to
an even larger degree with greater amounts of side products pres-
ent. We attempted additional syntheses of Pt(II) 9S3 complexes of
these types with three more diimine ligands. These were: 2,9-Me2-
phen, 2,9-Me2-4,7-Ph2-phen, and 2,2-biquinioline (structures
shown in Experimental Supplementary Information). It should be
noted that all three ligands contain substituents at the 2,9 posi-
tions within the aromatic ring system. The reaction between
[Pt(9S3)Cl2] and 2,9-Me2-phen failed completely as evidenced by
no soluble colored reaction products. Reactions with the other
two diimines failed to produce clean products. In contrast, the di-
chloro Pt(II) complexes with 2,9-Me2-phen and 2,9-Me2-4,7-Ph2-
phen are known, suggesting that the 9S3 ligand plays the key role
in the difficulty in complex synthesis [31]. The Pt(II) 9S3 complexes
are all air-stable and range in color from light orange to maroon.
The composition of all the new complexes is confirmed using a
variety of spectroscopic techniques, elemental analyses, and, for
five compounds, X-ray crystal structures as described below.
2.3. Preparation of Pd(II) 9S3 diimine complexes
2.3.1. Preparation of [Pd(9S3)(tap)](OTf)2 (7)
A mixture of [Pd(9S3)Cl2] (50.0, 0.140 mmol) and silver triflate
(71.9 mg, 0.280 mmol) was reacted at room temperature in
10 mL of nitromethane for 2 h with stirring. The flask was pro-
tected from light with aluminum foil. While stirring, the solution
became deep maroon in color, and finally light purple with a white
precipitate present. The reaction mixture was filtered to remove
the AgCl precipitate. It was washed with cold ethanol
(2 ꢁ 10 mL), ether (10 mL), and air dried to recover 92% of the
anticipated mass (37 mg) of AgCl. A mass of 12.8 mg of tap ligand
(0.0702 mmol) was next added to the filtrate, and the reaction stir-
red overnight. The solution was concentrated to ½ volume, and
ether diffused slowly into the solution. Reddish-black crystals suit-
able for X-ray diffraction where obtained. These were washed with
ether and air-dried to yield 34.8 mg (58.8%) of [Pd(9S3)(tap)](OTf)2
as a deep purple-red solid. The sample used for elemental analysis
was dried at 60° at 0.1 mm pressure for 1 h. Anal. Calc. for
C
18H18F6N4O6PdS5: C, 28.18; H, 2.37; N, 7.30; S, 20.90. Found: C,
28.36; H, 2.24, N, 7.00; S, 20.84%. 1H NMR (CD3NO2): d, 9.55 (d,
3.2. Structures
3JH–H = 2.7 Hz, tap-C3 proton, 2H), 9.07 (d, JH–H = 2.7 Hz, tap-C2
3
proton, 2H), 8.71 (s, tap-C5 proton, 2H), 3.65–3.57 (m, 9S3, 6H),
and 3.54–3.47 (m, 9S3, 6H). 13C {1H} NMR (CD3NO2): d, 152.59
(tap, –CH), 148.53 (tap, –C–), 145.60 (tap, –CH), 141.85 (tap, –C–),
134.58 (tap, –CH), 36.27 (s, 9S3, 6C). The electronic absorption
spectrum measured in acetonitrile showed three kmax’s at
Crystallographic data for the five complexes are presented in
Table 1, their thermal ellipsoid plots are presented in Figs. 1–5,
and selected structural features are summarized in Table 2. A
search of the Cambridge Structural Database revealed that there
are only three Pt(II) 9S3 structures and only two Pd(II) 9S3 struc-
tures with phenanthroline ligands [32]. All complexes show an
elongated square pyramidal structure which is typical for hetero-
leptic crown trithioether complexes of Pt(II) and Pd(II) [16–18],
552 nm (
with shoulder peaks at 277 nm
= 22000). The complex showed no oxidative electrochemistry,
e
= 180), 410 nm (
e
= 1100), 289 nm (
e = 19000) along
(
e
= 18000), and 225 nm
(e

G.J. Grant et al. / Polyhedron 31 (2012) 89–97
93
Table 1
Crystal data, data collection, and refinement parameters for [Pt(9S3)(5,6-Me2-phen](PF6)2 (1), [Pt(9S3)(4,7-Me2-phen](PF6)2ꢂCH3NO2 (2), [Pt(9S3)(2,20-bpm)](PF6)2ꢂ1.5CH3NO2 (4),
[Pt(9S3)(tap)](PF6)2ꢂ2CH3CN (5), and [Pd(9S3)(tap)](OTf)2ꢂCH3NO2ꢂH2O (7).
Compound
1
2
4
5
7
Formula
Habit, color
Lattice type
Space group
a (Å)
C
20H24F12N2P2PtS3
C22H27F12N3P2PtS3
chip, yellow
triclinic
C15.50H22.50F12N5.50O3P2PtS3
chip, orange
monoclinic
P21/n
14.6565(13)
18.0367(16)
21.869(2)
90
102.668(3)
90
5640.5(9)
8
C20H24F12N6P2PtS3
plate, red
monoclinic
P21/c
17.138(2)
11.312(2)
15.474(2)
90
92.703(6)
90
2996.5(8)
4
C18.5H20.5F6N4.5O7.5PdS5
chip, purple-red
orthorhombic
Pnma
chip, orange
triclinic
P1
ꢀ
P-1
11.1724(10)
11.7395(15)
11.9971(5)
100.622(18)
116.842(12)
100.220(18)
1317.6(2)
2
10.4688(5)
11.9727(9)
13.1470(15)
72.99(3)
74.54(2)
72.16(2)
16.053(2)
28.872(3)
11.9293(11)
90
90
90
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
1471.4(2)
2
5529.0(9)
8
Z
T (K)
183(2)
873.62
2.202
5.786
168(2)
914.68
2.065
5.187
163(2)
915.10
2.155
5.422
168(2)
929.66
2.061
5.099
173(2)
806.59
1.938
1.141
Fwt. (g molꢀ1
)
)
Dcalc (mg mꢀ3
l
(mmꢀ1
)
Reflections collected
11121
10759
39725
21280
33490
Unique reflections
Maximum, minimum transmission
Data, restraints, parameters
4613 (Rint = 0.0543)
0.6875, 0.5435
4613/0/363
0.0429, 0.0984
0.0480, 0.1011
1.109
5185 (Rint = 0.1038)
0.3590, 0.1220
5185/0/391
0.1041, 0.2471
0.1452, 0.3005
1.04
10143 (Rint = 0.0434)
0.3561, 0.2456
10143/0/761
0.0426, 0.0925
0.0616, 0.1052
1.095
5370 (Rint = 0.0876)
0.7750, 0.2467
5370/0/339
0.0567, 0.1363
0.0683, 0.1489
1.140
5027 (Rint = 0.0516)
0.7448, 0.2125
5027/0/405
0.0533, 0.1261
0.0645, 0.1358
1.092
R1, wR2 (I > 2r(I))
R1, wR2 (all data)a,b
Goodness-of-fit (F2)
Largest difference in peak, hole(e Åꢀ3
)
1.265, ꢀ1.517
7.200, ꢀ2.722
2.164, ꢀ1.261
2.764, ꢀ2.436
1.166, ꢀ1.054
aR1
bwR2 = {
=
R
||Fo| ꢀ |Fc||/
R
|Fo| for observed data (I > 2
r
(I).
2
R
[w(Fo ꢀ Fc2)2]/
R
[w(Fo2)2]}1/2 for all data.
Scheme 2. Two major synthetic schemes used in this report.
and the degree of distortion from an ideal square pyramidal struc-
ture is reflected by the parameter (see Table 2) [33]. The square
s
plane is comprised of a cis arrangement of the two nitrogen donors
of the diimine and two sulfur donors from the 9S3 with the third
9S3 sulfur showing a long distance axial interaction to complete
the elongated square pyramidal structure. In all complexes, the
metal ion is raised above the mean square equatorial plane and di-
rected towards the axial sulfur. These data are summarized in Ta-
ble 2. The two tap complexes show the largest degree of distortion.
Similarly, these two structures also show the largest deviation in
angles between the mean square planes for the diimine ring sys-
tem and the square planar coordination sphere. Conversely, the
two Me2-phen ligand complexes show the smallest degree of dis-
tortion. The equatorial Pt–S bond lengths fall in the range of
2.25–2.28 Å with the axial distances ranging from 2.8 to 3.0 Å.
Fig. 1. Thermal ellipsoid perspective (50% probability) of cation in [Pt(9S3)(5,6-
Me2-phen)](PF6)2 (1). H atoms omitted for clarity.

94
G.J. Grant et al. / Polyhedron 31 (2012) 89–97
Fig. 5. Thermal ellipsoid perspective (50% probability) of cation in Pd(9S3)(ta-
p)](OTf)2ꢂCH3NO2ꢂH2O (7). H atoms omitted for clarity.
two methyl substituents on the phen ring show the longest dis-
tances (5,6-Me2-phen = 2.937(2) Å; 4,7-Me2-phen = 3.002(6) Å).
Better donating substituents like methyl groups result in a more
electron rich Pt(II) center and a longer metal–sulfur axial distance.
In contrast, better electron-withdrawing diimines like tap result in
a more electron-poor metal center and shorter axial distances. As
we have observed previously, complexes with shorter Pt–S equato-
rial bonds typically have longer Pt–S axial distances and vice versa
[18]. The same general trend is seen in Table 2.
Fig. 2. Thermal ellipsoid perspective (50% probability) of cation in [Pt(9S3)(4,7-
Me2-phen)](PF6)2ꢂCH3NO2 (2). H atoms omitted for clarity.
It should be noted that the complexes with both bpm and tap
form exclusively mononuclear complexes with {Pt(9S3)} moieties,
illustrating the lack of these potential linker ligands to form metal-
losupramolecular complexes. Despite several attempts, we have
not been able to use tap as a linker to form a multinuclear complex
with either platinum(II) or palladium(II) despite our prior experi-
ence in forming a molecular square containing Pt 9S3 corners
linked by 4,40-bipyridine [34]. The formation of a metallosupramo-
lecular complex with a tap linker would involve a 2:1 metal:tap
stoichiometry as opposed to the 1:1 ratio for the formation of
the mononuclear complex. This is reflected in the stoichiometry
of the Pd(II) tap reaction while both ratios were explored with
the Pt(II) complex. We mention that the related two-ring diimine
system, 2,20-bipyrazine (bpz) has been shown by the Lippert group
readily to form squares and triangles with Pt(II) and Pd(II) ethy-
lenediamine corners [25,26]. The inability of tap to form similar
complexes may be due to the capping 9S3 ligand, which functions
as an electron-withdrawing ligand compared to ethylenediamine,
and/or a consequence of the sterics of the rigid three-ring tap li-
gand. Metallosupramolecular complexes with tap as a linker in
the Cambridge Structural Database is limited to only a single report
of a Ag(I) molecular triangle [35]. Nevertheless, both the Pt(II) and
Pd(II) 9S3 complexes with tap do possess distinctive electronic
properties as evidenced in their spectroscopic and electrochemical
data (see below).
Fig. 3. Thermal ellipsoid perspective (50% probability) of cation in [Pt(9S3)(2,20-
bpm)](PF6)2ꢂ1.5CH3NO2 (4). H atoms omitted for clarity.
In an earlier paper, we identified three common intermolecular
p–p
stacking motifs observed in [M(9S3)(L)]n+ complexes (M = Pt(II)
or Pd(II), L = diimine or cyclometallating ligand) which are illus-
trated in the Experimental Supplementary Information [22]. Inter-
molecular
the structures for Compounds 1 (5,6-Me2-phen), 2 (4,7-Me2-phen)
and 5 (tap). However, we do not observe stacking in the other
two structures 4 (bpm) and 7 (Pd tap complex). All three structures
in this report exhibit -stacking motif C (see Fig. 6) which is charac-
terized by isolated -dimeric stacking between neighboring parallel
p–p stacking of parallel diimine ligands is observed in
p
Fig. 4. Thermal ellipsoid perspective (50% probability) of cation in
Pt(9S3)(tap)](PF6)2ꢂ2CH3CN (5). H atoms omitted for clarity.
p
p
diimine groups with the 9S3 orientations pointing either in–in or
out–out. The three show out–out dimers, but what distinguishes
them is the distance between the phenanthroline planes. This dis-
tance in 1 is 3.48 and 3.39 Å in 2 (both Me2-phen complexes), but
the distance between planes in 5 (tap) is 3.70 Å. The difference in
the stacking distance is due to the more electron rich aromatic rings
The axial metal–sulfur distance is quite sensitive to the donor
properties of the diimine ligand, and thereby serves as an excellent
structural probe for donor effects of any ancillary ligand [13]. The
shortest axial sulfur distances are seen in the two tap complexes
(Pt = 2.882(2) Å, Pd = 2.831(1) Å) with a slightly longer distance
observed for the bpm ligand complex. In contrast, complexes with

G.J. Grant et al. / Polyhedron 31 (2012) 89–97
95
Table 2
Structural parameters. selected bond lengths (Å),a angles (°),a
s p–p stacking motifs [22] and other parameters for [Pt(9S3)(5,6-Me2-phen](PF6)2 (1), [Pt(9S3)(4,7-
parameters,b
Me2-phen](PF6)2ꢂCH3NO2 (2), [Pt(9S3)(2,20-bpm)](PF6)2ꢂ1.5 CH3NO2 (4), [Pt(9S3)(tap)](PF6)2ꢂ2CH3CN (5), and [Pd(9S3)(tap)](OTf)2ꢂCH3NO2ꢂH2O (7).
1
2
4c
5
7
M–Seq
2.267(2) Å
2.271(2) Å
2.253(5) Å
2.253(5) Å
2.261(2) Å
2.266(2) Å
2.260(2)
2.268(2)
2.927(2)
2.897(2)
2.032(6)
2.046(6)
2.052(6)
2.066(6)
89.24(7)
88.86(7)
78.94(2)
79.24(2)
0.060
2.264(2)
2.276(2)
2.275(1)
2.276(1)
M–Sax
M–N
2.937(2)
3.002(6)
2.882(2)
2.831(1)
2.058(6)
2.068(6)
NR
NR
2.064(8)
2.065(7)
2.073(4)
2.080(4)
Seq–M–Seq
88.95(7)
80.6(2)
0.070
88.90(2)
NR
89.19(8)
80.7(3)
0.010
88.42(5)
80.69(2)
0.10
N–M–N
s
NR
0.050
0.10 Å
0.10 Å
3.71°
Distance between metal and square planed
0.061 Å
4.97°
NR
0.18 Å
10.41°
0.16 Å
9.87°
Angles between square plane and diimine ligande
NR
3.71°
None
p–
p
stacking motiff
Out–out dimer
3.48 Å
Out–out dimer
3.39 Å
Out–out dimer
3.72 Å
None
a
b
c
d
e
f
Estimated standard deviations are given in parentheses.
See Ref. [22].
Two crystallographically independent complex cations are observed.
Displacement of metal ion above S2N2 mean least-squares plane, in Å.
Angle between mean least-squares planes for square plane (PtS2N2 coordination sphere) and diimine ligand plane.
See Ref. [22].
rings (1.3°), but at a distance of 3.59 Å, longer than the two di-
methyl-phen structures [19].
3.3. Spectroscopy and electrochemistry
Resonances for all hydrogens in the appropriate ratios and split-
tings are observed in the proton NMR spectra of the six complexes.
The ortho hydrogens of the pyridine rings in the Pt(II) complexes
3
are highly discernible by a distinctive JPt–H coupling at approxi-
mately 35 Hz and are typically the most deshielded resonances
4
in the proton NMR spectra. We also observe a smaller JPt–H cou-
pling exclusively in the tap complex. For all complexes, the 12
methylene protons of the 9S3 region disperse into a widely sepa-
rated set of six protons, consistent with an AA0BB0 pattern (see
Experimental Supplementary Information). The 13C NMR spectra
show the correct number of peaks and chemicals shifts corre-
sponding to their respective aromatic, methyl, and 9S3 methylene
resonances. Subsequent 13C DEPT experiments confirm carbon
connectivity for all complexes. As expected, the 9S3 ligand is flux-
ional in solution resulting in a single resonance for its six methy-
lene carbons near 34–35 ppm [18]. The 13C NMR chemical shifts
for the 9S3 singlets in all complexes are presented in Table 3. We
note that there is some correlation between these chemical shifts
and the donor properties of the diimine ligand. The better elec-
tron-withdrawing tap ligand shows more deshielded 9S3 reso-
nances in both its Pt(II) and Pd(II) complexes while more
shielded resonances are seen with electron-donating substituents.
The 195Pt NMR chemical shifts for the six Pt(II) complexes are also
presented in Table 3. In order to minimize solvent, anion, and tem-
perature effects, all 195Pt NMR spectra were obtained on hexa-
fluorophosphate salts in CD3NO2 at a temperature of 25 °C. The
chemical shift values generally cluster around ꢀ3290 ppm. How-
ever, the tap complex again shows the effects of the electron-with-
drawing ligand, and its resonance is shifted downfield nearly 100
to ꢀ3198 ppm. The 5-NO2-phen complex is also shifted downfield,
but not to the same degree (ꢀ3255 ppm).
Fig. 6. Intermolecular
p–p stacking interactions between cations to form out–out
dimers in [Pt(9S3)(5,6-Me2-phen)](PF6)2 (top) and [Pt(9S3)(tap)](PF6)2 (bottom).
stacking distances between parallel diimine planes are 3.48 and 3.72 Å,
respectively.
p–
p
associated with the electron-releasing methyl group substituents
on the phen ligands as opposed to the electron-withdrawing non-
coordinated nitrogen atoms located within the tap ring system. In
support of this hypothesis, we note that the reported 5-NO2-phen
complex also displays out–out dimers with nearly parallel phen

96
G.J. Grant et al. / Polyhedron 31 (2012) 89–97
Table 3
Selected electronic spectroscopic data, 13C and 195Pt NMR chemical shifts and CV potentials.
ꢃ
ꢃ
UV–Visa
13C NMR, 9S3b (ppm)
195Pt NMR (ppm)
d
d
Complex
Eox
Ered
[Pt(9S3)(5,6-Me2-phen)](PF6)2
[Pt(9S3)(4,7-Me2-phen)](PF6)2
[Pt(9S3)(4,7-Ph2-phen)](PF6)2
[Pt(9S3)(bpm)](PF6)2
[Pt(9S3)(tap)](PF6)2
[Pt(9S3)(5-NO2-phen)](PF6)2
[Pd(9S3)(tap)](PF6)2
400 (3200)
383 (3900)
401 (3100)
426 (1700)
464 (1600)
412 (2200)c
410 (1100)
34.53
34.49
34.19
34.67
35.20
34.63
36.27
ꢀ3286
ꢀ3298
ꢀ3288
ꢀ3277
ꢀ3198
ꢀ3255
NA
+1.13
+1.09
ꢀ1.29
ꢀ1.24
not measured
+0.98
none observed
not reported
none observed
not measured
ꢀ1.00
ꢀ0.95
not reported
ꢀ0.59, ꢀ0.78, ꢀ1.20, ꢀ1.40
a
b
c
MLCT band only, measured in nm with extinction coefficients (Mꢀ1 cmꢀ1) in parentheses.
9S3 resonance only.
Ref. [19].
d
Measured in V vs. Fc/Fc+ couple in MeCN solvent.
In the case of the Pt(II) 9S3 complexes with diimine ligands,
transfer bands, and less negative reduction potentials. The report
illustrates how the electronic properties of the complex can be
tuned by the nature of the substituents on the phen ligand.
the electronic spectra are dominated by two features – a metal-
to-ligand charge transfer (MLCT) band near 400 nm and more in-
tense
p–
p⁄ ligand-centered transitions around 300 nm [17,18].
The MLCT band data are presented in Table 3. Note the degree
of red shift observed in the tap complex, again consistent with
its ability to function as an electron-withdrawing ligand. The
maroon color of the [Pt(9S3)(tap)]2+ complex contrasts the orange
to yellow color observed for the remaining platinum complexes.
An interesting feature in the electronic spectra of the Pd(II) 9S3
Acknowledgments
Acknowledgment is made to the donors of the American Chem-
ical Society Petroleum Research Fund for partial support of this re-
search. This research was also generously supported by funding
from the Grote Chemistry Fund at UTC, the Research Corporation,
and the National Science Foundation RUI Program. We also thank
two UTC undergraduate researchers, Mr. Stephen Ledford for his
work with compound 1 and Mr. Rishi Naik for his work with com-
pound 5.
complex with tap is the presence of
a d–d transition near
560 nm which results in its distinctive purple color. Cyclic vol-
tammetric data obtained on the complexes in MeCN are pre-
sented in Table 3. Three of the Pt(II) complexes (both Me2-phen
complexes and bpm) show an irreversible oxidation. The oxida-
tions occur at more positive voltages than the related bipy com-
Appendix A. Supplementary data
plexes, consistent with the relative
p acidity of the two types of
ring systems [18]. Neither the Pt(II) nor the Pd(II) 9S3 tap com-
plexes show oxidative behavior within the potential window,
likely due to the electron-withdrawing characteristics of this li-
gand, and these data are consistent with the position of their
MLCT bands. The dimethyl-phen complexes have shorter solution
lifetimes (turning into a brown oil), possibly due to an oxidation
to Pt(IV). In contrast, irreversible reduction waves are observed in
all of the complexes studied, typically at voltages less negative by
0.2 V than the corresponding bipy complexes [18]. The ease of
reduction of the Pt(II) complexes generally follows the donor abil-
ities of the ligand with the tap complex being the easiest to re-
duce, but the 5,6-Me2-phen complex being the hardest.
CCDC 829065, 829066, 829067, 829068, and 829069 contain
the supplementary crystallographic data for 1, 2, 4, 5, and 7,
respectively. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2011.08.030.
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