Photoswitchable organoplatinum(IV) complexes

Article abstract of DOI:10.1021/om4000314

Organoplatinum(IV) complexes, [PtBrMe₂(CH₂-4-C ₆H₄-N-N-Ph)(NN)], containing trans-azobenzene functional groups, have been prepared by trans oxidative addition of BrCH ₂-4-C₆H₄-N-

Full text of DOI:10.1021/om4000314

Article
pubs.acs.org/Organometallics
Photoswitchable Organoplatinum(IV) Complexes
Mohamed E. Moustafa, Matthew S. McCready, and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
S
* Supporting Information
ABSTRACT: Organoplatinum(IV) complexes, [PtBrMe2(CH2-4-C6H4-NN-
Ph)(NN)], containing trans-azobenzene functional groups, have been prepared
by trans oxidative addition of BrCH2-4-C6H4-NN-Ph to the corresponding
platinum(II) complexes [PtMe2(NN)], with NN = 2,2′-bipyridine, 1,10-
phenanthroline, 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine, 1,4-di-2-pyridyl-
5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine. The complexes undergo efficient
and almost quantitative trans−cis isomerization on irradiation of dilute solutions
at 365 nm, as monitored by UV−visible spectroscopy, and somewhat less complete
1
photolysis in concentrated solution, as monitored by H NMR spectroscopy. The
cis isomers undergo slow thermal isomerization back to the trans isomers, thus proving the photoswitching property of the
complexes.
versus rearrangement to the cis isomer. As the concentration of
cis isomer builds up, the reverse photoisomerization may occur,
and this will often lead to a wavelength-dependent photo-
chemical steady state between the isomers. The thermal
conversion of cis isomer back to the more stable trans isomer
typically takes several hours at room temperature.5,6
INTRODUCTION
■
The synthesis of photoresponsive materials has attracted much
interest for potential applications in optical switching and
optoelectronics.1,2 The incorporation of a transition metal into
such materials can provide a photoswitching property to
complement the magnetic, electrochemical, catalytic, or bio-
logical properties of the metal center.3 Among the well-known
photoswitchable groups, azobenzene has been the most widely
used. The popularity of the azobenzene group is due to the
high efficiency of its reversible light-induced trans−cis isomer-
ization, the significant structural change which occurs on
isomerization with consequent changes in chemical and
physical properties, and the high thermal and photochemical
stability which allows many switching cycles to occur without
any decomposition.4 A typical case for switching in azobenzene
derivatives is illustrated, in simplified form, in Figure 1. The
Photoswitchable organometallic complexes are rare,7,8 and
the first organoplatinum derivatives were reported only
recently.9 The complexes contained an azobenzene substituent
in a bipyridine ligand, and both platinum(II) and platinum(IV)
complexes were studied (Scheme 1). By using UV light at 365
nm, the trans to cis isomerization reached a steady state
containing 20−40% of the cis isomer. These relatively low
conversions were attributed to conjugation of the diimine and
azobenzene groups and overlap and mixing of the n−π*
transitions associated primarily with the azobenzene groups
with Pt 5d−π* or halogen n−π* transitions associated mainly
with the diimine ligand, which gave additional routes from the
cis isomer back to the more stable trans isomer.9 The present
paper describes photoswitchable organoplatinum(IV) com-
plexes in which the azobenzene is a substituent of an
alkylplatinum group and which give higher conversion to the
cis isomer.
t
trans−cis photoisomerization begins by excitation to the S1
level, and the efficiency of the reaction depends initially on the
relative ease of nonradiative decay back to the ground state S0
t
RESULTS AND DISCUSSION
■
Synthesis and Characterization of [PtMe2(LL)] (2a−d).
The new complexes are shown in Scheme 2. The trans oxidative
addition of organic compounds with bromomethyl substituents
has given a wide range of functional organoplatinum
complexes,10 and it is now shown that the reaction of 4-
bromomethylazobenzene to complexes [PtMe2(NN)]11 (1,
NN = bipy; 2, NN = phen; 3, NN = bebipy; 4, NN = 6-dppd)
gave the corresponding organoplatinum(IV) complexes
Figure 1. Excitation and relaxation routes of trans and cis azobenzene
isomers. Φtc and Φct are the quantum yields of photoisomerization for
trans to cis and cis to trans, respectively, and γ0 is the thermal relaxation
rate.
Received: January 15, 2013
Published: April 30, 2013
© 2013 American Chemical Society
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The structures of the complexes 5−8 were confirmed
crystallographically and are shown in Figures 2−5. A summary
Scheme 1. Photoswitchable Organoplatinum Complexes
Figure 2. Structure of complex 5.
Scheme 2. Synthesis of the Complexes 5−8
Figure 3. Structures of the nonequivalent molecules in 6·0.5CH2Cl2.
Figure 4. Structure of complex 7.
[PtBrMe2(CH2-4-C6H4NNPh)(NN)] (5−8) (Scheme 2).
The selective formation of the products of trans oxidative
addition was shown initially by the H NMR spectra and
confirmed in each case by a structure determination. For
example, the 1H NMR spectrum of 5 showed a single
methylplatinum resonance at δ 1.52, with coupling constant
2JPtH = 70 Hz, and a single resonance for the PtCH2 protons at
δ 2.93 (2JPtH = 97 Hz). The product of cis oxidative addition
would have only C1 symmetry and so would give a more
complex spectrum.10
and comparison of selected bond parameters is given in Table
1. Each complex has octahedral stereochemistry at platinum-
(IV), with the expected stereochemistry formed by trans
oxidative addition. In all cases, the Pt−CH2 bond is slightly
longer than the Pt−CH3 bonds. The trans-azobenzene groups
are distorted to a minor extent from planarity, as measured by
the maximum values of the torsion angles CCNN = −17°,
measuring the twist of the C6H4 group from the CNN plane for
one of the molecules of 8, and NNCC = 16°, measuring the
1
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Scheme 3. Photoswitching of the Azobenzene Group
Figure 5. View of one of the two independent molecules in the
complex 8·0.5CH2Cl2. There is some disorder of the cyclooctene
group, which is not shown for clarity.
twist of the C6H5 group from the NNC plane for one of the
molecules of 6. The maximum twist of the CNNC atoms was
only 5° (Table 1). For all of the molecules except 7 the
azobenzene group lay roughly above one of the pyridyl groups,
with the corresponding torsion angle N−Pt−C−C in the range
−7 to +15° (a positive value indicates a twist from the eclipsed
conformation away from the adjacent Pt−Me group and toward
the other nitrogen donor). However, the torsion angle N−Pt−
C−C = −29° for complex 7 (Table 1, Figure 4). In all cases, the
angle Pt−C−C was slightly higher than the ideal tetrahedral
angle, suggesting that π stacking of the azobenzene and pyridyl
groups is not strong, and the conformation of the benzylic
group in the solid state is likely to be determined by
intermolecular packing forces.
1
Figure 6. H NMR spectra in the aromatic region of complex 6: (a)
before irradiation (trans form 6 only); (b) after irradiation with
monochromatic light at 365 nm for 60 min (both trans 6 and cis 6*
isomers present).
1
°C, as monitored by H NMR spectroscopy. Similar results
were obtained for the other complexes, though the ratio of
isomers at the stationary state varied. For example, the ratio
7:7* = 25:75 after irradiation for 1 h.
The UV−visible absorption spectra of the complexes 5 and 6
in dichloromethane, and the changes on photolysis, are shown
in Figure 7. Complex 5 exhibits major absorption bands at λmax
363 nm, ascribed to the strong π−π* transition of the
azobenzene moiety, and at λmax 443 nm, attributed to the weak
n−π* transition. As shown in Figure 7a, upon irradiation with
UV light at 365 nm, a decrease in the π−π* band was observed,
with the appearance of a new band at 285 nm due to formation
of the cis isomer. There was an isosbestic point at 310 nm
during this step, which was complete in about 13 min of
irradiation at 365 nm. A slow further reaction then occurred
with growth of a band at 393 nm, attributed to a MLCT band,
5d−*, of [PtBrMe(bipy)].13 The initial conversion of 5 to 5*
Photoisomerization Studies. The photoswitching of the
azobenzene group in the complexes (Scheme 3) was monitored
12
1
by both H NMR and UV−visible spectroscopy. Figure 6
1
shows changes in the H NMR spectra when a solution of
complex 6 in CD2Cl2 was irradiated with monochromic light at
365 nm in methylene chloride-d6 at room temperature. The
aromatic resonances for the azobenzene protons show the
characteristic shift to lower δ for the cis isomer 6* 12b and grow
with irradiation time. After photolysis for 1 h, the solution
contained the trans and cis isomers in the ratio 6:6* = 40:60.
The thermal back-reaction was complete in about 2 days at 20
Table 1. Selected Bond Parameters for Complexes 5−8
a
b
a
b
5
6(1)
6(2)
7
8(1)
8(2)
Pt−Me/Å
2.049(5)
2.050(5)
2.086(5)
2.156(4)
2.165(4)
2.5959(6)
1.264(6)
112.8(3)
176.0(4)
13.1(4)
2.085(8)
2.053(8)
2.121(8)
2.161(6)
2.175(6)
2.577(1)
1.243(9)
114.4(6)
178.0(5)
12.6(7)
2.063(8)
2.075(8)
2.108(9)
2.169(6)
2.173(7)
2.598(1)
1.14(1)
114.7(6)
179.0(7)
4.5(6)
2.045(6)
2.051(6)
2.105(6)
2.160(5)
2.169(4)
2.5870(6)
1.271(7)
113.9(4)
175.6(5)
−6.6(5)
−5.6(6)
−28.6(4)
2.043(6)
2.071(6)
2.092(6)
2.150(4)
2.151(4)
2.5749(6)
1.249(7)
116.3(4)
179.7(5)
2.7(6)
2.062(6)
2.060(5)
2.100(6)
2.144(4)
2.150(4)
2.5735(7)
1.239(7)
114.3(4)
178.2(6)
−17.1(7)
5.9(6)
Pt−CH2/Å
Pt−N/Å
Pt−Br/Å
NN/Å
Pt−C−C/deg
C−NN−C/deg
C−C−NN/deg
NN−C−C/deg
N−Pt−C−C/deg
15.5(4)
9.3(6)
16.4(8)
14.7(5)
−1.7(5)
2.1(5)
6.0(3)
10.2(5)
−6.8(5)
a
b
Parameters for the Pt(1) molecule. Parameters for the Pt(2) molecule.
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Figure 8 shows the recovery of intensity of the visible
absorption at 360 nm as a function of time during the thermal
Figure 8. Absorbance (A) at 360 nm versus time for the reaction of 6*
to give 6 in toluene at 55 °C.
isomerization of complex 6* back to the more stable isomer 6
when carried out in toluene at 55 °C. The reaction followed
first-order kinetics. Rate constants were obtained by simulation
of the intensity−ime curves and gave k1 = [4.51(8)] × 10−5 s−1
at 55 °C, [6.0(1)] × 10−5 s−1 at 60 °C, [1.05(5)] × 10−4 s−1 at
70 °C, and [1.92(6)] × 10−4 s−1 at 80 °C, from which the
activation parameters ΔH⧧ = 53(2) kJ mol−1 and ΔS⧧
=
−168(5) J K−1 mol−1 were determined. These rates are similar
to those found for cis to trans isomerization of several organic
azobenzene derivatives, which may occur by rotation or
inversion mechanisms.15
Figure 7. Changes in UV−visible spectra on photolysis at 365 nm: (a)
complex 5; (b) complex 6.
CONCLUSIONS
■
In the first photoswitchable organoplatinum complexes A and B
(Scheme 1) the azobenzene unit was conjugated to the diimine
ligand, and so there was mixing of the corresponding π and π*
molecular orbitals.9 In turn, this led to overlap and mixing of
the absorption bands primarily due to n−π* or π−π*
transitions of the azobenzene group with d−π* or π−π*
transitions of the platinum−diimine groups, and so there was
easy reversible interconversion of trans and cis isomers. Thus,
high conversion of trans to cis isomers was not possible. In the
new compounds 5−8, the single methylene bridge between the
azobenzene group and the platinum atom appears to be
sufficient to prevent significant communication between the
azobenzene and diimine groups. Figure 9 shows the DFT
calculated structures for the complexes 5 and 5* and the first
π* level of the azobenzene group in each case. The first π* level
of the bipy ligand is slightly lower in energy, but there is no
appreciable mixing of the orbitals of the azobenzene and bipy
groups. This lack of orbital overlap of the azobenzene and
diimine groups also leads to a shift in the absorption maximum
for the π−π* transition of the trans isomer from about 340 nm
in A and B to about 360 nm in 5−8, much closer to the
wavelength of the irradiation light at 365 nm.9 The result is that
the photoswitching is very efficient in the new complexes and
the reverse cis to trans photoisomerisation is not competitive.
The cis isomer 5* is calculated to be 50 kJ mol−1 less stable
than 5, and thermal isomerization of 5* back to 5 does occur
slowly, following first-order kinetics. We have attempted to
grow single crystals of the cis isomers, but without success.
Although the photoswitching is very efficient, the organo-
platinum complexes do undergo slow photodecomposition, and
this will limit the usefulness of these and similar compounds
because the number of photoswitching/thermal reversion
cycles will be limited.
was essentially quantitative under these conditions, and the
reaction could be reversed thermally, as monitored by the
complete recovery of the absorption band of 5 at 363 nm. The
complexes 6−8 behaved in a similar way, giving rapid
conversion to the cis isomers followed, on extended photolysis,
by slow photodecomposition of the cis isomer. Spectral changes
for complex 6 are shown in Figure 7b.
The quantum yields for the trans to photoisomerization of
the ligand and complexes were determined in toluene solution,
with irradiation at 365 nm (excitation into the π−π* absorption
band), by comparison to azobenzene standard (Φ = 0.11).14
The data are given in Table 2. It can be seen that the quantum
Table 2. Quantum Yields for trans−cis Isomerization of the
Compounds in Comparison to That of Azobenzene14
compd
aobenzene
ε/M−1 m−1
λmax/nm
Φtrans−cis
22300
24218
25022
27866
23450
29639
319
328
365
368
368
369
0.11
0.10
0.12
0.11
0.13
0.09
BrCH2-4-C6H4NNPh
5, NN = bipy
6, NN = phen
7, NN = bebipy
8, NN = 6-dppd
yields fall in the narrow range 0.09−0.13, all being close to the
value of 0.11 for azobenzene itself. This supports the hypothesis
that the azobenzene unit is insulated from platinum by the
saturated CH2 bridge and that the isomerization occurs in the
same way for all the compounds in Table 2.14 Deactivation of
the excited state by coupling to the platinum−iimine transitions
does not occur to a significant extent.9
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NMR in dichloromethane-d2: δ 1.67 (s, 6H, 2JPtH = 70 Hz, PtMe), 2.97
(s, 2H, 2JPtH = 97 Hz, PtCH2), 6.13 (d, 2H, 3JHH = 8 Hz, 3JPtH = 19 Hz,
3
Ho), 6.86 (d, 2H, JHH = 8 Hz, Hm), 7.49−7.55 (m, 3H, Hm′,p′), 7.77
3
3
(d, 2H, JHH = 9 Hz, Ho′), 7.80 (m, 2H, JHH = 6,9 Hz, H3), 7.90 (s,
2H, H5), 8.44 (d, 2H, 3JHH = 9 Hz, H4), 9.04 (d, 2H, 3JHH = 6 Hz, 3JPtH
= 18 Hz, H2). HRMS (ESI): m/z 600.1729 [M+ − Br]. Anal. Calcd for
C27H25BrN4Pt: C, 47.65; H, 3.70; N, 8.22. Found: C, 47.65; H, 3.69;
N, 8.19.
[PtBrMe2(CH2-4-C6H4NNPh)(bebipy)] (7). This was prepared
in a way similar to that for 5 and isolated as a yellow solid. Yield: 88%.
1H NMR in acetone-d6: δ = 1.34 (t, 6H, 3JHH = 7 Hz, CH3CH2), 1.57
(s, 6H, 2JPtH = 71 Hz, PtMe), 2.93 (s, 2H, 2JPtH = 97 Hz, PtCH2), 4.39
3
3
3
(q, 4H, JHH = 7 Hz, CH3CH2), 6.57 (d, 2H, JHH = 8 Hz, JPtH = 19
Hz, Ho), 7.20 (d, 2H, JHH = 8 Hz, Hm), 7.52−7.55 (m, 3H, Hm′,p′),
3
7.80 (d, 2H, 3JHH = 9 Hz, Ho′), 8.16 (d, 2H, 3JHH = 6 Hz, H5), 8.95 (s,
2H, H3), 9.02 (d, 2H, 3JHH = 6 Hz, 3JPtH = 19 Hz, H6). HRMS (ESI):
m/z 720.2152 [M+ − Br]. Anal. Calcd for C31H33BrN4O4Pt: C, 46.51;
H, 4.15; N, 7.00. Found: C, 45.51; H, 4.10; N, 6.70.
[PtBrMe2(CH2-4-C6H4NNPh)(6-dppd)] (8). This was prepared
in a way similar to that for 5 and isolated as a yellow solid. Yield: 77%.
1H NMR in dichloromethane-d2: δ 1.43 (s, 3H, 2JPtH = 70 Hz, PtMe),
2
1.78 (s, 3H, JPtH = 71 Hz, PtMe), 1.58 (m, 2H, CH2), 1.67 (m, 2H,
3
CH2), 2.09 (s, 2H, JPtH = 92 Hz, PtCH2), 2.89 (m, 2H, CH2), 2.96
(m, 2H, CH2), 3.10 (m, 2H, CH2), 3.21 (m, 2H, CH2), 6.53 (d, 2H,
3
3
3JHH = 8 Hz, JPtH = 19 Hz, Ho), 7.22 (d, 2H, JHH = 8 Hz, Hm), 7.54
Figure 9. Calculated structures for (a) complex 5 and (b) complex 5*
and lowest energy π* MO of the azobenzene group for (c) complex 5
and (d) complex 5*.
(m, 3H, Hm′,p′), 7.60 (m, 1H, H4′), 7.78 (d, 2H, JHH = 7 Hz, Ho′),
3
7.90 (m, 1H, H4), 8.16 (m, 2H, H3,3′), 8.36 (m, 2H, H5,5′), 8.75 (d,
1H, JHH = 7 Hz, H6′), 9.13 (d, 1H, JHH = 7 Hz, JPtH = 22 Hz, H6).
Anal. Calcd for C35H37BrN6Pt: C, 51.47; H, 4.57; N, 10.29. Found: C,
51.70; H, 4.76; N, 9.81.
3
3
3
EXPERIMENTAL SECTION
All reactions were performed under a nitrogen atmosphere. H NMR
spectra were recorded by using a Varian Mercury 400 and Inova 400
spectrometer, and data are reported with respect to the labeling system
of Chart 1. UV−vis spectra were measured using a Varian Cary 300
■
1
Photoswitching Studies. For UV−visible monitoring, a sample of
the complex was dissolved in CH2Cl2 or toluene and irradiated in a
quartz cuvette at room temperature with UV light at 365 nm, followed
immediately by recording the absorption spectrum. For 1H NMR
monitoring, a sample in CD2Cl2 or (CD3)2CO in an NMR tube was
irradiated at room temperature at 365 nm, followed by recording the
spectrum.
Chart 1. NMR Labeling
NMR in CD2Cl2 for cis Isomer 6*. δ(1H): 1.65 (s, 6H, 2JPtH = 70 Hz,
PtMe), 2.76 (s, 2H, 2JPtH = 96 Hz, PtCH2), 5.80 (d, 2H, 3JHH = 8 Hz,
Hm), 5.91 (d, 2H, 3JHH = 8 Hz, 3JPtH = 19 Hz, Ho), 6.60 (d, 2H, 3JHH
=
8 Hz, Ho′), 7.06 (t, 1H, JHH = 8 Hz, Hp′), 7.20 (t, 1H, JHH = 8 Hz,
3
3
Hm′), 7.78 (m, 2H, H3), 7.95 (s, 2H, H5), 8.48 (m, 2H, 3JHH = 6,8 Hz,
H4), 8.95 (d, 2H, JHH = 6 Hz, JPtH = 18 Hz, H2).
3
3
NMR in CD2Cl2 for cis Isomer 7*. δ(1H): 1.30 (t, 6H, 3JHH = 7 Hz,
2
2
CH3CH2), 1.52 (s, 6H, JPtH = 71 Hz, PtMe), 2.73 (s, 2H, JPtH = 97
Hz, PtCH2), 4.36 (q, 4H, 3JHH = 7 Hz, CH3CH2), 6.17 (d, 2H, 3JHH
=
6 Hz, 3JPtH = 19 Hz, Ho), 6.25 (d, 2H, 3JHH = 8 Hz, Hm), 6.55 (d, 2H,
3JHH = 8 Hz, Ho′), 6.55 (t, 1H, 3JHH = 8 Hz, Hp′), 7.31 (t, 2H, 3JHH = 8
Hz, Hm′), 8.18 (d, 2H, 3JHH = 7 Hz, H5), 8.92 (s, 2H, H3), 8.97 (d, 2H,
3
3JHH = 6 Hz, JPtH = 19 Hz, H6).
Bio spectrophotometer. Mass spectra were recorded using an
electrospray PE-Sciex mass spectrometer (ESI-MS). 4-Bromomethy-
lazobenzene was prepared by reaction of 4-methylazobenzene with N-
bromosuccinimide.16 The dimethylplatinum(II) complexes 1−4 were
prepared by the literature methods.11,17
Quantum Yield Determinations. A solution of the trans isomer
of each compound in toluene was irradiated with 365 nm light, and the
absorbance at the π−π* band maximum was recorded every 20 s. The
trans to cis photoisomerization rate ν was obtained from the slope of
the graph of concentration of trans isomer against irradiation time.
Azobenzene was used as a standard.14
Kinetic Studies. A sample of the complex in toluene solution in a
quartz cuvet was irradiated with UV light at 365 nm until the
photostationary state was reached. Then the sample was placed in the
thermostated cell block of the UV−visible spectrometer and the
absorbance at the maximum absorption wavelength of the trans isomer
at 360−366 nm was recorded at intervals of 3 s until no further change
in absorbance was observed (typically for 90 min). First-order rate
constants were obtained by simulation of the absorbance−time data
using Dynafit software.
[PtBrMe2(CH2-4-C6H4NNPh)(bipy)] (5). To a stirred solution
of [PtMe2(bipy)] (2; 0.09 mmol) in dry acetone (15 mL) was added
bromomethylazobenzene (0.025 g, 0.09 mmol). After 1 h, the yellow
solid which precipitated was separated by filtration, washed with
1
pentane (3 × 2 mL), and dried under high vacuum. Yield: 85%. H
NMR in dichloromethane-d2: δ 1.52 (s, 6H, 2JPtH = 70 Hz, PtMe), 2.93
(s, 2H, 2JPtH = 97 Hz, PtCH2), 6.45 (d, 2H, 3JHH = 8 Hz, 4JPtH = 19 Hz,
Ho), 7.20 (d, 2H, 3JHH = 8 Hz, Hm), 7.42−7.53 (m, 5H, Ho′,m′,p′), 7.81
3
3
(d, 2H, JHH = 7 Hz, H3), 7.96 (m, 2H, JHH = 6, 7 Hz, H5), 8.06 (t,
2H, JHH = 7 Hz, H4), 8.72 (d, 2H, JHH = 6 Hz, JPtH = 19 Hz, H6).
HRMS (ESI): m/z 576.1290 [M+ − Br]. Anal. Calcd for
C25H25BrN4Pt: C, 45.74; H, 3.84; N, 8.53. Found: C, 45.97; N,
8.15; H, 3.81.
3
3
3
X-ray Structure Determinations. Single crystals were grown
from acetone/n-pentane at ambient temperature. A suitable crystal of
each compound was coated in Paratone oil and mounted on a glass
fiber loop. X-ray data were collected at 150 K with ω and φ scans using
[PtBrMe2(CH2-4-C6H4NNPh)(phen)] (6). This was prepared in
a way similar to that for 5 and isolated as a yellow solid. Yield: 84%. 1H
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a Bruker Smart Apex II diffractometer using graphite-monochromated
Mo Kα radiation (λ = 0.71073 Å) and Bruker SMART software.18a
Unit cell parameters were calculated and refined from the full data set.
Cell refinement and data reduction were performed using the Bruker
APEX2 and SAINT programs, respectively.18b Reflections were scaled
and corrected for absorption effects using SADABS.18c All structures
were solved by either Patterson or direct methods with SHELXS and
refined by full-matrix least-squares techniques against F2 using
SHELXL.18d All non-hydrogen atoms were refined anisotropically.
The hydrogen atoms were placed in calculated positions and refined
using the riding model. The data are given as Supporting Information
in Table S1 and in the CID files.
DFT Calculations. DFT calculations were carried out by using the
Amsterdam Density Functional program based on the BLYP
functional, with first-order scalar relativistic corrections and double-ζ
basis set.19 All ground state structures were confirmed to be energy
minima by analysis of force constants for normal vibrations.19
J. Chem. 1973, 57, 3097−3101. (e) Camp, R. N.; Epstein, I. R.; Steel,
C. J. Am. Chem. Soc. 1977, 99, 2453−2459.
(7) (a) Segorra-Maset, M. D.; van Leeuwen, P. W. N. M.; Freixa, Z.
Eur. J. Inorg. Chem. 2010, 2075−2078. (b) Einaga, Y.; Mikami, R.;
Akitsu, T.; Li, G. M. Thin Solid Films 2005, 493, 230−236. (c) Yutaka,
T.; Mori, I.; Kurihara, M.; Mizutani, J.; Tamai, N.; Kawai, T.; Irie, M.;
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ASSOCIATED CONTENT
■
S
* Supporting Information
Table S1, giving crystal and refinement data for the complexes
and CIF files giving X-ray data for the complexes. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for R.J.P.: pudd@uwo.ca.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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We thank the NSERC (Canada) for financial support.
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