Structures, redox and spectroscopic properties of PdII and PtII complexes containing an azo functionality

Article abstract of DOI:10.1002/ejic.200900007

The complexes [PdCl₂(pap)] (1) and [PtCl₂(pap)] (2; pap = 2-phenylazopyridine) were synthesized, by treating PdCl2 or K ₂PtCl₄, respectively, with pap and characterized by ¹HNMR spectroscopy and eleme

Full text of DOI:10.1002/ejic.200900007

FULL PAPER
DOI: 10.1002/ejic.200900007
Structures, Redox and Spectroscopic Properties of PdII and PtII Complexes
Containing an Azo Functionality
Sayak Roy,[a] Ingo Hartenbach,[a] and Biprajit Sarkar*[a]
Keywords: Platinum / Palladium / Azo compounds / EPR spectroscopy / Cyclic voltammetry
The complexes [PdCl2(pap)] (1) and [PtCl2(pap)] (2; pap =
2-phenylazopyridine) were synthesized by treating PdCl2 or
K2PtCl4, respectively, with pap and characterized by 1H NMR
spectroscopy and elemental analysis. Both these complexes,
together with the previously reported complex [(az)Pd(µ-Cl)2-
Pd(az)] (3; az = azobenzene), were also characterized by X-
ray crystallography. The structures of 1, 2, and 3 show a
slightly elongated N–N azo double bond due to back-do-
nation from the metal centers and a twisting of the uncoordi-
nated part of the ligands with respect to the rest of the mole-
cule. Cyclic voltammetry of 1, 2, 3, and the related complex
[(az)Pt(µ-Cl)2Pt(az)] (4) shows reduction processes which are
reversible for 1 and 2 but irreversible for 3 and 4. The first
reduction of 1 and 2 leads to radical complexes, and EPR
spectroscopy shows the spin to be predominantly located on
the azo part of the complexes. The radical complex 2·– shows
an unprecedented 195Pt hyperfine coupling constant and g
anisotropy for such PtII radical species. The UV/Vis spec-
troscopy results for all the complexes are also discussed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
with metal complexes of such ligands showing fascinating
properties such as photoinduced isomerization and switch-
ing.[14–17] Although complexes of PtCl2 and PdCl2 have
been studied with a variety of nitrogen- containing π-ac-
ceptor ligands,[18,19] there are very few reports of such com-
plexes with ligands containing an azo group.[15,16,20] The li-
gand 2-phenylazopyridine (pap) has often been used in co-
ordination chemistry.[21–23] Azobenzene (az) has been used
for C–H bond activation with metal complexes[12,24] and
has been shown to be useful for properties such as switch-
ing.[17] Herein we report the synthesis of two complexes
containing pap, namely [PdCl2(pap)] (1) and [PtCl2(pap)]
(2). The crystal structures of these two complexes are dis-
cussed together with the structure of the synthetically
known, but hitherto crystallographically uncharacterized,
complex [(az)Pd(µ-Cl)2Pd(az)] (3). The electrochemical
properties of these complexes together with that of [(az)-
Pt(µ-Cl)2Pt(az)] (4), as well as their EPR and UV/Vis spec-
troscopic properties, are discussed below.
Introduction
Complexes of cis-dichloroplatinum with nitrogen co-li-
gands have been studied for a number of reasons. One
major incentive continues to be the use of certain of these
complexes in tumor therapy.[1] Another important aspect
of such complexes is their one-electron-transfer reactivity.
Reversible reduction in such complexes is usually ligand-
centered and leads to radical-anion intermediates which
often show well observable 195Pt hyperfine coupling in their
EPR spectra due to sizeable metal–ligand interactions.[2–6]
Luminescence in the solid state or in solution is another
fascinating field of research related to such platinum com-
plexes. Such luminescence, which usually occurs from
metal-to-ligand charge transfer (MLCT) or intraligand
πǞπ* excited states, has instigated several structure-spec-
troscopic correlation studies to clarify their behavior.[7,8] In
yet another field of research, PtII complexes have found use
as catalysts and catalyst precursors for C–H bond acti-
vation.[9–11] Indeed, one of the first studies of C–H bond
activation by transition metal complexes was reported for
complexes of PtII and PdII with azobenzene.[12] In recent
years, complexes of cis-dichloropalladium(II) have found
use as catalysts and pre-catalysts in a variety of organic
transformations.[13] Azo ligands, on the other hand, con-
tinue to play an important role in coordination chemistry,
Synthesis and Structures
The complexes 1 and 2 (Scheme 1) were obtained in a
straightforward manner by treating PdCl2 or K2PtCl4,
respectively, with pap. Complex 2 could also be obtained
by treating pap with PtCl2(dmso)2. This route required a
much shorter reaction time than the first route. Both com-
plexes were characterized by 1H NMR spectroscopy and
elemental analysis.
[a] Institut für Anorganische Chemie, Universität Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany
Fax: +49-711-6856-4165
E-mail: sarkar@iac.uni-stuttgart.de
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S. Roy, I. Hartenbach, B. Sarkar
FULL PAPER
N1–C6 distances [1.449(19) and 1.444(11) Å for 1 and 2,
respectively] for both complexes. Averaging out of bond
lengths inside a chelate ring after metalation is a typical
feature of metal complexes containing azo ligands.[14] The
M–N1 and M–N3 distances are almost the same in both 1
and 2, thereby suggesting equally strong bonding between
the metal centers and the pyridine and azo nitrogen atoms.
The pyridyl/azo/MCl2 section of both molecules is essen-
tially planar and adopts a dihedral angle with the phenyl
part with values of 42.2° and 37.1° for 1 and 2, respectively
(Figure 3). The phenyl ring twists with respect to the rest
of the molecule in order to minimize the steric repulsion
between a C–H group of the phenyl ring and the M–Cl
bond.[20]
Scheme 1.
Both complexes could be crystallized by slow evapora-
tion of a nitromethane solution at ambient temperature.
Complex 1 crystallizes in the C2/c space group and complex
2 in the I2/a space group. Crystal data and details of the
structure determination are listed in Table 6. Selected bond
lengths and angles are given in Tables 1 and 2.
Table 1. Comparison of selected interatomic distances [Å] in one
of the three molecules of 1 and 2 and in 3.
Bond lengths
1
2
3
N1–N2
M–N1
M–N3
N1–C6
N2–C5
M–C1
M–Cl
1.268(16)
2.017(12)
2.032(13)
1.449(19)
1.270(11)
1.977(9)
1.946(9)
1.444(11)
1.289(9)
2.027(6)
–
–
–
1.410(18)
1.385(13)
–
–
–
–
–
–
–
–
1.963(9)
Figure 1. ORTEP view of 1. The unit cell is constituted of three
independent but very similar molecules. Thermal ellipsoids enclose
50% of the electron density.
2.466(2)
1.389(10)
1.433(10)
N2–C6
N1–C7
Table 2. Selected bond angles [°] in one of the three molecules of 1
and 2 and in 3.
Bond angles
1
2
3
N3–M–N1
N3–M–Cl2
Cl1–M–Cl2
N1–M–Cl1
N1–M–C1
C1–M–Cl
Cl–M–Cl
N1–M–Cl
ω
78.8(5)
93.8(4)
90.1(2)
97.5(4)
77.7(4)
95.0(3)
89.5(1)
97.8(3)
–
–
–
–
–
–
–
–
–
–
–
–
78.7(3)
94.7(2)
85.3(2)
101.2(2)
40.5[a]
42.2[a]
37.1[a]
Figure 2. ORTEP view of 2. The unit cell is constituted of three
independent but very similar molecules. Thermal ellipsoids enclose
50% of the electron density.
[a] Dihedral angle between the planes of the free phenyl ring and
the coordinated part of the ligand.
The metal centers in complexes 1 and 2 (Figures 1 and
2, respectively) adopt an almost square-planar geometry.
The N1–M–N3 angles [78.8(5)° for 1 and 77.7(4)° for 2] are
slightly narrower in both complexes than the other angles
around the metal centers. This is in keeping with the shorter
M–N1 and M–N3 distances compared to the other dis-
tances at the metal centers. The N1–N2 azo bond [1.268(16)
and 1.270(11) Å for 1 and 2, respectively] is slightly longer
than previously reported N–N double-bonds in azo com-
Figure 3. Wireframe view of 1 showing the twisting of the free
phenyl part of pap with respect to the rest of the molecule.
Although the synthesis of complex 3 was reported in
plexes (1.25 Å).[14,25] This is due to back-donation from the 1965,[12] and this was the first PdII complex to show C–H
PdII or PtII centers into the empty π* orbital of pap. Such bond activation, to the best of our knowledge there has
an elongation has previously been observed for other metal been no report of its crystal structure to date in the litera-
complexes containing such azo ligands.[20] In agreement ture. The structures of some related complexes with substi-
with this back-donation, the N2–C5 distances [1.410(18) tuted azobenzenes have, however, been reported.[26] Com-
and 1.385 Å for 1 and 2, respectively] are shorter than the plex 3 was crystallized by slow diffusion of n-hexane into a
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PdII and PtII Complexes Containing an Azo Functionality
dichloromethane solution of the complex at ambient tem- 2.[6] The reduction processes for 1 take place at a less nega-
¯
perature. The complex crystallizes in the P1 space group. tive potential than those for 2 (–0.59 and –1.39 V for 1 and
Crystal data and details of the structure determination are –0.79 and –1.74 V for 2). This suggests that the [PdCl2] frag-
listed in Table 6. Selected bond lengths and angles are given ment has a better σ-acceptor capacity than [PtCl2] in these
in Tables 1 and 2. As in the case of 1 and 2, the geometry complexes. The separation between the two reversible re-
around the PdII centers in 3 is square planar (Figure 4). The duction processes in 2 is 0.95 V. This points to a large
N1–N2 azo bond [1.289(9) Å] is longer than a normal azo thermodynamic stability for the one-electron reduced radi-
N–N double bond[14] due to back-donation from the PdII cal complex 2·–, as exemplified by the comproportionation
center, and this back donation from the metal center means constant, Kc, of 1016 (Scheme 2). A separation of around
that the N2–C6 bond [1.389(10) Å] is shorter than the N1– 1 V between the two reduction processes is a typical phe-
C7 bond [1.433(10) Å]. The Pd–ClЈ distance [2.466(2) Å] is nomenon for azo complexes.[14] In contrast to 2, the pre-
longer than the Pd–Cl distance ]2.337(2) Å]. This is because viously reported complex [PtCl2(abpy)] (abpy = 2,2Ј-azobis-
of the stronger trans effect exerted by the σ-bonded phenyl pyridine) shows a complex reduction chemistry, with an
ring compared to the nitrogen atom on the azo group.[26] irreversible first reduction leading to dimerization of the
The coordinated phenyl/azo/PdII parts are essentially complex.[20] This difference is probably related to the more
planar, with a dihedral angle between this part and the un- robust Pt–Cl bond in 2 and also the lack of a second coor-
coordinated phenyl ring of 40.5°. The twisting of the phenyl dination site in pap as compared to abpy.
ring occurs for the same reasons discussed above for 1 and
2.
Figure 5. Cyclic voltammogram of 1 (top) at 253 K and 2 (bottom)
at 298 K in CH2Cl2/0.1  Bu4NPF6. Scan rate: 100 mV/s. Ferro-
cene/ferrocenium was used as an internal standard.
Figure 4. ORTEP view of 3. Thermal ellipsoids enclose 50% of the
electron density.
Cyclic Voltammetry
Complexes 1 and 2 show two well-separated one-electron
reduction processes, as can be seen from their cyclic voltam-
Scheme 2.
mograms in CH2Cl2/0.1  Bu4NPF6 (Figure 5). No oxi-
Complexes 3 and 4 show two irreversible reduction pro-
dation processes were observed within the dichloromethane cesses, neither of which becomes reversible at either lower
solvent window. Whereas the reduction processes are chem- temperatures or higher scan rates. Metal-chloride bonds
ically and electrochemically reversible for 2 at 298 K, com- with bridging chlorides are expected to be more labile on
plex 1 shows only irreversible reduction processes at that reduction than metal-chloride bonds with terminal chlo-
temperature. On cooling to 253 K, however, the first re- rides, which explains the irreversibility of the reduction pro-
duction process becomes reversible, although the second re- cesses of 3 and 4 as compared to 1 and 2. The reduction
duction of 1 remains irreversible even at lower tempera- potentials for 3 are anodically shifted compared to those
tures. The lability of metal-halide bonds on reduction is for 4 (–0.98 V for 3 and –1.38 V for 4 for the first reduction
much more pronounced for 4d metals than for 5d met- process). This is the same phenomenon as observed for 1
als.[27,28] Such lability can sometimes be desirable for certain and 2 above. On comparing the reduction potentials of 1
kinds of catalytic activation.[29,30] The reduction potentials vs. 3 and 2 vs. 4 (Table 3), it can be seen that the complexes
for both complexes are anodically shifted compared to that with pap are reduced at a less negative potential than the
of the free ligand. Such large anodic shifts illustrate the su- complexes with azobenzene. This can be explained by the
perb σ-acceptor ability of the [MCl2] fragments in 1 and fact that pap is a better π-acceptor ligand than az. The dif-
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S. Roy, I. Hartenbach, B. Sarkar
FULL PAPER
ference between the reduction processes for complexes 3 sition centered on the azo ligands. All the transitions for 1
and 4 is also around 1 V, as expected for complexes with are shifted to lower energies than for 3. The same is true
azo ligands (see above). No oxidation processes were ob- on comparing 2 to 4. This can be justified by invoking the
served for either 3 or 4 within the dichloromethane solvent better π-acceptor capability of pap compared to az. On re-
window.
duction of 2 to 2·–, the main bands in the visible region
appear at 592 and 480 nm. These can be tentatively as-
signed to intra-ligand transitions within the pap radical
anion and to MLCT transitions. There is very little absorp-
tion left in the visible region on further reduction to 22–, as
would be expected for a doubly reduced pap ligand bound
to [PtIICl2].
Table 3. Redox potentials of the complexes.[a]
Complex
E1/2 (∆Ep)[b]
E1/2 (∆Ep)[b]
1
2
3
4
–0.56 (65)[c]
–0.79 (70)
–0.98[d]
–1.39[c,d]
–1.74 (80)
–1.86[d]
–1.36[d]
–1.95[d]
[a] Electrochemical potentials in V from cyclic voltammetry in
CH2Cl2/0.1  Bu4NPF6 at 298 K. Scan rate: 100 mV/s. Ferrocene/
ferrocenium was used as internal standard. [b] ∆Ep: difference be-
tween peak potentials in mV. [c] Measurements at 253 K. [d] Cath-
odic peak potential for irreversible reduction.
EPR Spectroscopy
The radical anions 1·– and 2·– can be generated in situ
and this has allowed us to study these intermediates in fluid
and glassy frozen solutions by EPR spectroscopy. The data
obtained from EPR spectroscopic experiments and com-
puter simulations are listed in Table 5 along with data for
other related complexes. The dichloroplatinum(II) radical
species 2·– (Figure 7) shows a much larger g anisotropy and
larger 195Pt (I = 1/2) hyperfine coupling than [PtCl2-
(bpy)]·–[3] and [PtCl2(bpym)]·–, which have very similar val-
ues.[6] The azo-based ligand pap has a much lower lying π*
orbital than bpy and bpym. The SOMO in the case of 2·–
thus has a larger metal contribution as compared to
[Pt(bpy)Cl2]·– and [Pt(bpym)Cl2]·–, which explains the larger
∆g and a values for 2·–. Despite the large g anisotropy and
195Pt hyperfine coupling constant for 2·–, which are unprec-
edented for such radical anions, this radical anion is not a
PtI species. The reduction still predominantly takes place
at the azo ligand, with larger metal contributions than in
[PtCl2(bpy)]·– and [PtCl2(bpym)]·–. The aPt value of 8.5 mT
for 2·– represents only a fraction (6.9ϫ10–3) of the isotropic
UV/Vis Spectroscopy
Despite the presence of a low-lying π* orbital, as evi-
denced by the strongly shifted reduction potentials, particu-
larly for 1 and 2, the complexes show absorption bands at
comparatively higher energies. This can be rationalized by
the strong stabilization of the predominantly [MCl2]-cen-
tered HOMOs in these complexes. All the complexes show
two main features in their absorption spectrum (Figure 6
and Table 4). The long wavelength band (e.g. 512 nm for 2)
is tentatively assigned to a mixture of metal-to-ligand
charge transfer (MLCT) with some contribution from ha-
lide-to-ligand (XLCT) charge transfer.[6] The next highest
energy transition (e.g. 392 for 2) is most likely a πǞπ* tran-
hyperfine coupling constant for platinum (a0
=
1228 mT).[31] No coupling to the ligand nuclei could be re-
solved and hence these must have much smaller values than
Table 5. X-band EPR data fo the electrochemically generated first
reduced form of the complexes.
1·–
2·–
[PtCl2(bpy)]·–[a] [PtCl2(bpym)]·–[a]
[b]
g1
g2
g3
2.007
2.007
1.983
0.024
2.003
n.o.
2.086
2.007
1.930
0.156
2.002
8.5
2.038
2.009
1.935
0.103
1.998
5.6
2.034
2.005
1.938
0.096
1.993
5.0
Figure 6. UV/Vis spectra of 1 (---), 2 (-·-·), 3 (Ϫ), and 4 (···) in
CH2Cl2.
∆g[c]
[d]
gis[oe]
a1
Table 4. UV/Vis data for the complexes in CH2Cl2.
a2
n.o.
11.2
9.5
6.9
a3
aiso
Ref.
n.o.
0.7
Ͻ5.0
8.5
–
Ͻ3.0
Complex
λ (ε)[a]
[e]
5.4
4.6
[3]
[6]
1
243 sh, 397 (29500), 490 (2100)
this work this work
2
279 (7800), 392 (11400), 415 sh, 512 (2300)
273 (13100), 302 (13800), 345 sh, 367 (15600), 380
sh, 425 sh, 480 (4100), 592 (1600)
266 (18200), 290 sh, 355 (10900), 490 sh
240 sh, 329 (27900), 382sh, 450 (5900)
250 (12600), 330 (9000), 391 sh, 485 sh
[a] Measurements in dmf. n.o.: not observed. [b] From measure-
ments in glassy frozen solution in CH2Cl2/0.1  Bu4NPF6 at 110 K.
[c] ∆g = g1 – g3. [d] From measurements in CH2Cl2/0.1  Bu4NPF6
at 298 K. [e] Metal hyperfine coupling constant in mT as obtained
from computer simulation. Line width used for simulating low-tem-
perature spectrum of 2·–: 2.2 and 4.5 mT. Lineshape: lorentzian/
gaussian, 1/1 (see text for details). For 1·– additionally aN = 0.9 mT
was also determined.
2·–
22–
3
4
[a] Wavelength in nm; molar extinction coefficient in –1 cm–1. sh:
shoulder.
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PdII and PtII Complexes Containing an Azo Functionality
the 195Pt hyperfine coupling constants. The dichloropalladi- constant and g anisotropy in comparison to other related
um(II) radical species 1·– has a much smaller g anisotropy PtII radical anions. The utility of such complexes, and of
than 2·–. This is the effect of the much smaller spin-orbit related complexes with other azo ligands, in catalytic ethyl-
coupling constant values of PdII.[31] The solution EPR spec- ene poly- and oligomerization is currently under investiga-
trum for 1·– (Figure 8) could be simulated well by consider- tion.
ing the coupling of the unpaired electron to one Pd nucleus
(I = 5/2) with a hyperfine coupling constant of 0.7 mT and
an additional coupling to one 14N (I = 1) center with values
Experimental Section
of 0.9 mT. This is the nitrogen from the azo group which is
Instrumentation: 1H NMR spectra were recorded at 250.13 MHz
bound to the Pd center. Even though coupling to the other
with a Bruker AC250 instrument. EPR spectra in the X band were
recorded with a Bruker System EMX connected to an ER 4131 VT
variable temperature accessory. EPR simulations were performed
nitrogen atom of the azo group is expected, this will be
smaller than the coupling to the coordinated azo-nitrogen
atom. This most likely lies within the linewidth of the spec-
trum and hence is not resolved.
using the Simfonia software of Bruker. The EPR spectra were simu-
lated by considering the natural abundance of the various isotopes
involved. For EPR measurements, the paramagnetic species were
generated directly inside the EPR tube using a two-electrode cell.
UV/Vis/NIR absorption spectra were recorded with a Shimadzu
UV 3101 PC spectrophotometer. Cyclic voltammetry was carried
out in 0.1  Bu4NPF6 solution using a three-electrode configura-
tion (glassy carbon working electrode, Pt counter electrode, Ag wire
as pseudo-reference) and a PAR 273 potentiostat and function gen-
erator. The ferrocene/ferrocenium (Fc/Fc+) couple served as in-
ternal reference. Elemental analysis was performed with a Perkin–
Elmer Analyser 240.
General Considerations: The ligand pap was synthesized under nor-
mal atmospheric conditions using reagent-grade solvents. For the
metal complexes, all manipulations were carried out using Schlenk
techniques under argon. The solvents used for metal complex syn-
thesis were dried and distilled under argon and degassed by com-
mon techniques prior to use. Azobenzene was purchased from
Sigma–Aldrich. The precursor PdCl2 was purchased from Acros
and K2PtCl4 from ABCR. The ligand pap and complexes 3 and 4
were synthesized according to literature procedures.[12,22]
Figure 7. X-band EPR spectrum of electrochemically generated 2·–
in CH2Cl2/0.1  Bu4NPF6 at 110 K. Frequency: 9.4876 GHz;
power: 6.343 mW; modulation amplitude: 0.3 G.
Synthesis of [PdCl2(pap)] (1):[32] A mixture of palladium(II) dichlo-
ride (50 mg, 0.28 mmol) and pap (51 mg, 0.28 mmol) was stirred in
ethanol for 4 h at room temperature. A bright yellow precipitate
formed during this time. This solid was filtered off, washed with
methanol, and dried in vacuo. Yield 75 mg (74%) 1H NMR
(CDCl3): δ = 7.51 (m, 2 H), 7.63 (m, 1 H), 7.82 (m, 1 H), 8.01 (d,
2 H), 8.34 (m, 1 H), 8.44 (m, 1 H), 9.35 (d, J = 4 Hz, 1 H) ppm.
IR (solid): νN=N = 1603 cm–1. C11H9Cl2N3Pd (360.51): calcd. C
36.65, H 2.52, N 11.66; found C 36.35, H 2.55, N 11.51.
Figure 8. X-band EPR spectrum of electrochemically generated 1·–
in CH2Cl2/0.1  Bu4NPF6 at 253 K. Frequency: 9.4718 GHz;
power: 6.339 mW; modulation amplitude: 0.2 G.
Synthesis of [PtCl2(pap)] (2).[33] Route A: A mixture of potassium
tetrachloroplatinate (50 mg, 0.12 mmol) and pap (20 mg,
0.12 mmol) was dissolved in a mixture of water and dioxane (1:1)
and allowed to stand for 7 d. A dark crystalline solid precipitated.
This solid was filtered off, washed two or three times with dioxane
and dried in vacuo. Yield 32 mg (60%).
Conclusions
Route B: A mixture of PtCl2(dmso)2 (174 mg, 0.412 mmol) and pap
(75 mg, 0.412 mmol) was heated to reflux in 40 mL of nitrometh-
ane for 5 h. The solution turned dark brown during this time. After
removal of the solvent, the crude product was recrystallized from a
mixture of nitromethane and diethyl ether. The product was finally
Using the ligand pap we have been able to synthesize and
fully characterize the complexes 1 and 2. The structural
data of 1 and 2, together with that of the previously re-
ported complex 3, show a slightly elongated N–N azo
double bond and twisting of the non-coordinated part of
the ligands around the rest of the molecule. Whereas the
reduction of 3 and 4 proceeds irreversibly even at lower
temperatures, the first reduction of 1 or 2 leads to stable
radical intermediates where the spin is predominantly lo-
cated on the azo part of the complexes. The EPR spectrum
1
filtered off and washed with diethyl ether. Yield 102 mg (56%). H
NMR ([D6]acetone): δ = 7.63 (m, 3 H), 7.92 (m, 2 H), 8.30 (m, 1
H), 8.69 (td, J = 7.7, 1.6 Hz, 1 H), 8.83 (m, 1 H) ppm. IR (solid):
νN=N = 1606 cm–1. C11H9Cl2N3Pt (449.20): calcd. C 29.41, H 2.05,
N 9.04; found C 29.49, H 2.05, N 9.04.
Crystal Structure Determination: Single crystals were grown by slow
of 2·– shows an unusually large 195Pt hyperfine coupling evaporation of a nitromethane solution at ambient temperature (for
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1 and 2) or by layering a dichloromethane solution of the complex
with n-hexane at ambient temperature (for 3). A suitable crystal
was selected under a layer of viscous hydrocarbon oil, attached to
a glass fiber, and instantly placed in a low-temperature N2 stream.
The selected single crystals were measured using Mo-Kα radiation
(λ = 0.71073 Å) at 173 K. Calculations were performed with the
SHELXTL PC 5.03 and SHELXL-97[34,35] program system in-
stalled on a local PC. The structures were solved by direct methods
2
and refined on Fo by full-matrix least-squares refinement. Aniso-
tropic thermal parameters were included for all non-hydrogen
atoms. Further details can be found in Table 6. CCDC-714302 (for
1), -714303 (for 2), and -714301 (for 3) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.uk/data_request.cif.
Table 6. Crystal data and details of the structure determination for
complexes 1–3.
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1992, 31, 222.
1
2
3
Empirical formula C11H9Cl2N3Pd C11H9Cl2N3Pt C24H18Cl2N4Pd2
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
55.460(3)
9.3386(7)
13.9813(11)
90
98.733(5)
90
7157.2(9)
2.007
360.51
8
monoclinic
C2/c
100(1)
71.073
1.981
14.1202(5)
9.3784(4)
55.0598(16)
90
95.444(3)
90
7258.4(5)
2.466
449.20
8
monoclinic
I2/a
150(2)
71.073
12.018
29152
3.9515(3)
10.9806(8)
12.9995(11)
71.546(5)
89.888(5)
84.149(5)
531.98(7)
2.017
646.14
2
triclinic
P1
100(1)
71.073
1.963
4682
2560, 0.0933
Cell volume [Å3]
ρ(calcd.) [gcm–3]
Mr [gmol–1]
Z
Crystal system
Space group
T [K]
Radiation, λ [pm]
Abs. coeff. [cm–1]
Reflections
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1917.
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S. Zalis, V. K. Jain, W. Kaim, Inorg. Chem. 2004, 43, 5973.
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Chem. 2008, 47, 10446.
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G. K. Lahiri, W. Kaim, J. Am. Chem. Soc. 2008, 130, 3532.
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Acta Crystallogr., Sect. C 1991, 47, 966.
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568.
¯
11690
Unique reflections, 4713, 0.087
16171, 0.1433
Rint
Parameters
R values
248
463
145
R1 = 0.0763
wR2 = 0.1441
1.128
R1 = 0.0735
wR2 = 0.1275
0.948
R1 = 0.0661
wR2 = 0.1384
1.044
Goodness of fit
Largest electron
density difference/
hole [eÅ–3]
1.101/–1.027
4.06/–2.32
1.934/–2.147
Acknowledgments
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J. Electroanal. Chem. 1993, 352, 213.
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Chakravorty, Polyhedron 1994, 13, 999.
B. S. is indebted to the Landesstiftung Baden-Württemberg for the
financial support of this research project through the Elite Pro-
gramme for Postdocs. Ralph Huebner is kindly acknowledged for
carrying out the UV/Vis spectroelectrochemical measurements.
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Received: January 4, 2009
Published Online: April 8, 2009
2558
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2553–2558