Spectroscopic and electrochemical properties of dichlorodiimine complexes of Au(III) and Pt(II) with 1,4-diazine derivatives of o-phenanthroline

Article abstract of DOI:10.1134/S1070363206060016

A series of dichlorodiimine complexes [M(N∧N)Cl₂] ^z of Au(III) and Pt(II) with 1,4-derivatives of o-phenanthroline [(N∧N) = o-phenanthroline (phen), dipyrido[f,h]quinoxaline (dpq), dipyrido[a,c]phenazine (dppz), 6,7-dicyanodipyrido[f,h]quinoxaline (dicnq)] were prepared and characterized by ¹H NMR, electronic absorption, and emission spectroscopy and by cyclic voltammetry. In all the complexes, the ³(π-π*)-type transition is the spin-forbidden transition of the lowest energy, responsible for the luminescence. The longest wave bands in the absorption spectra of the Au(III) and Pd(II) complexes were assigned in accordance with the results of the electrochemical studies to the ¹(d*)-and ¹(d*)-type transitions, respectively. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S1070363206060016

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 6, pp. 843 848.
Pleiades Publishing, Inc., 2006.
Original Russian Text M.A. Ivanov, M.V. Puzyk, K.P. Balashev, 2006, published in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 6, pp. 881 886.
Spectroscopic and Electrochemical Properties
of Dichlorodiimine Complexes of Au(III) and Pt(II)
with 1,4-Diazine Derivatives of o-Phenanthroline
M. A. Ivanov, M. V. Puzyk, and K. P. Balashev
Hertsen Russian State Pedagogical University,
nab. r. Moiki, 48, St. Petersburg, 191186 Russia
e-mail: michelivanov@yandex.ru
Received May 27, 2005
z
Abstract A series of dichlorodiimine complexes [M(N^N)Cl ] of Au(III) and Pt(II) with 1,4-derivatives
2
of o-phenanthroline [(N^N) = o-phenanthroline (phen), dipyrido[f,h]quinoxaline (dpq), dipyrido[a,c]phenazine
1
(
dppz), 6,7-dicyanodipyrido[f,h]quinoxaline (dicnq)] were prepared and characterized by H NMR, electronic
3
absorption, and emission spectroscopy and by cyclic voltammetry. In all the complexes, the (
*)-type
transition is the spin-forbidden transition of the lowest energy, responsible for the luminescence. The longest
wave bands in the absorption spectra of the Au(III) and Pd(II) complexes were assigned in accordance with
the results of the electrochemical studies to the 1
(
d*)- and 1(d *)-type transitions, respectively.
DOI: 10.1134/S1070363206060016
Coordination-unsaturated complexes of platinum
metals with heterocyclic ligands are characterized,
on the one hand, by long-lived electronically excited
states and reversible outer-sphere electron transfer
processes and, on the other hand, by the capability to
form metal complex systems organized on the molec-
ular level. These features make such complexes prom-
ising as structural components of artificial photosys-
tems with directional transport of charge and energy
The electronic structure of dipyrido-substituted
1,4-diazines is determined by their two heterocyclic
fragments: phenanthroline and diazine. In agreement
with the results of quantum-chemical calculations of
dppz [8], comparison of the spectroscopic and electro-
chemical characteristics (Tables 1, 2) of dipyrido-
substituted 1,4-diazines with those of o-phenanthro-
line and dibenzo-substituted 1,4-diazines shows that
the electronic interaction between the phenanthroline
and diazine moieties of the (N^N) ligands is weak.
[1 3]. Most of the data concerning the effect of the
ligands and metal center on the optical and electro-
chemical properties of the complexes were obtained
for octahedral polypyridine complexes of Ru(II),
Os(II), Rh(III), and Ir(III), whereas the square-planar
complexes of Au(III) and Pt(II), whose intercalation
with nucleic acids [4 7] alters the optical and electro-
chemical properties of the complexes, were studied
insufficiently.
The chemical shifts of the H and H protons in the
phenanthroline moiety of the dipyrido-substituted lig-
ands only slightly depend on the structure of diazine
substituents and are close to those in o-phenanthroline
(
< 0.2 0.1 ppm).
The optical and electrochemical properties of the
(N^N) ligands are determined by the photo- and elec-
trostimulated processes involving low-lying * orbi-
tals mainly localized on the phenanthroline ( p*hen)
In this study we examined the spectroscopic and
electrochemical properties of dichlorodiimine com-
and diazine ( * ) moieties. The voltammograms of
diaz
z
plexes [M(N^N)Cl2] [M = Au(III), Pt(II)] with
the reduction of o-phenanthroline and its 1,4-diazine
derivatives exhibit one-electron waves with virtually
equal half-wave potentials (E 2.53 0.03 V) (phen,
dppz) or current peak potentials (dpq, dicnq), assigned
1
,4-diazine derivatives of o-phenanthroline [(N^N) =
o-phenanthroline (phen), dipyrido[f,h]quinoxaline
dpq), dipyrido[a,c]phenazine (dppz), 6,7-dicyanodi-
(
pyrido[f,h]quinoxaline (dicnq)] in comparison with
the properties of the free diimines (N^N) and dibenzo-
substituted 1,4-diazines {dibenzo[f,h]quinoxaline
to the electron transfer to the
*
redox orbitals.
phen
At the same time, diazine derivatives of o-phenanthro-
line are characterized by additional anodically shifted
reversible one-electron reduction waves with the half-
wave potentials close to those of the one-electron
(
dbq), dibenzo[a,c]phenazine (dbpz), 6,7-dicyanodi-
benzo[f,h]quinoxaline (dicbq)}.
843

844
IVANOV et al.
reduction waves of the corresponding dibenzo deriva-
tives of 1,4-diazines. This fact allows this reduction
wave to be assigned to the electron transfer to the
lowest energy *diaz redox orbitals of the ligands. The
-acceptor benzo (dppz) and cyano (dicnq) substitu-
ents decrease the energy of the redox orbitals
and cause an anodic shift of the first reduction wave
of the ligands in the series dicnq > dppz > dpq.
*
diaz
N
N
N
N
N
N
N
N
N
N
N
N
N
N
CN
CN
phen
dpq
dppz
dicnq
N
N
N
N
CN
CN
N
N
dbq
dbpz
dicbq
3
1
1
The electronic absorption and luminescence spectra
of the ligands confirm the conclusion that the elec-
tronic interaction between the phenanthroline and di-
azine moieties of the (N^N) ligands is weak. First, the
[ (30.0 0.9) 10 l mol cm ] of the high-energy
1
spin-allowed optical transitions of the (
*) type
localized on the phenanthroline moiety of the (N^N)
ligands vary insignificantly. Second, the location of
the long-wave ( > 300 nm) absorption bands of the
3
1
energy [ max (37.1 0.6) 10 cm ] and efficiency
1
Table 1. Proton chemical shifts , ppm [(CD ) SO, relative to (CH ) Si] (J , Hz) in the H NMR spectra of dibenzo-
3
2
3 4
HH
and dipyrido-substituted 1,4-diazines, o-phenanthroline, and diimine complexes of Au(III) and Pt(II)
Compound
phen
H /H
9.08 (J
J
9.24 (J
J
9.14 (J
J
9.36 (J
J
H
H
H
H
4.3,
1.9)
3.8,
1.9)
4.2,
1.5)
4.4,
1.9)
7.71 (J
4.3,
8.6)
3.8,
8.1)
4.3,
8.1)
4.4,
8.43 (J
8.6,
1.9)
8.1,
1.9)
8.1,
1.5)
8.1,
1.9)
7.81
9.17
J
J
dpq
7.96 (J
9.45 (J
J
9.44 (J
J
9.41 (J
J
9.13 (J
J
dppz
dicnq
dbq
7.86 (J
8.27 (J
6.7,
3.7)
7.99 (J
6.7,
3.7)
J
8.04 (J
J
J
J
8.1)
7.87 (J
7.7)/ 7.82 (J
7.7)
7.6)
7.6)
9.04
8
.83 (J
dbpz
7.91 (J
7.6)/ 7.83 (J
7.6)
8.0)
9.32 (J
7.6)
8.36 (J
6.7,
3.3)
8.00 (J
6.7,
3.3)
,
J
J
8
.80 (J
8.05 (J
.92 (J
9.68 (J
7.6)
8.2)/ 7.93 (J
8.2)
dicbq
9.08 (J
9.03 (J
8.2)
8.1)
,
8
[Pt(phen)Cl2]
5.0)
8.16 (J
5.0,
8.1)
8.28
J
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES
845
Table 1. (Contd.)
Compound
H /H
9.30 (J
H
H
H
H
[
[
[
[
[
[
[
Pt(dpq)Cl2]
Pt(dppz)Cl2]
Pt(dicnq)Cl2]
4.9)
4.9)
4.1)
5.6)
5.4)
5.8)
5.8)
8.09 (J
4.9,
8.4)
4.9,
8.5)
4.1,
8.0)
5.6,
8.4)
5.4,
7.3)
5.8,
8.0)
5.8,
8.0)
9.59 (J
8.4)
8.5)
8.0)
8.4)
7.3)
8.0)
8.0)
9.23
J
9.37 (J
9.29 (J
9.82 (J
9.79 (J
9.82 (J
9.91 (J
8.33 (J
9.90 (J
9.87 (J
9.29 (J
10.02 (J
10.18 (J
9.99 (J
8.46 m
8.15 m
J
8.01 (J
J
Au(phen)Cl ]Cl a
8.45 (J
8.49
9.35
2
J
b
Au(dpq)Cl ]Cl
8.50 (J
2
J
b
Au(dppz)Cl ]Cl
8.54 (J
8.58 (J
8.0,
3.6)
8.26 (J
8.0,
3.6)
2
J
8.59 (J
J
J
J
b
Au(dicnq)Cl ]Cl
2
a
b
CD OD.
CD CN.
3
3
Table 2. Optical and electrochemical properties of dibenzo- and dipyrido-substituted 1,4-diazines, p-phenanthroline, and
diimine complexes of Au(III) and Pt(II)
Absorption,a 298 K
Luminescence,b 77 K
Electroreductionc
Compound
3
1
1
3
1
,
nm ( 10 , l mol cm ) assignment , nm ( vib 10 , cm ) assignment E1/2, V assignment
1
*)phen 459, 488, 521 (1.30) 3(
*)phen 428, 444, 454,
phen
dpq
226 (15.8), 262 (10.0)
232 (13.6), 252 (19.8),
(
(
*)phen
*)diaz
*)diaz
2.51
2.00
*
1
*
diaz
4
64 sh, 474,
3
3
02 sh (5.1), 323 sh (2.3), 1(
*)diaz 489 sh, 506 sh)
(0.84, 1.34)
3(
2.53
*
phen
40 sh (1.8)
1
1
dppz
240 (19.6), 268 (33.4),
(
(
*)phen 507 sh, 545, 559 sh,
1.61
2.49
*
diaz
2
3
93 sh (11.6), 358 (7.4),
77 (7.3)
*)diaz 589, 640 (0.46, 1.37) 3(
*
phen
1
1
dicnq
264 (40.5),
05 (24.9), 347 (8.5), 365
6.8)
305 (12.0), 338 (9.5), 353 1(
8.7)
306 (9.3), 374 (14.0), 392 1(
(
(
*)phen 466, 478, 499, 509, 533,
*)diaz 549 sh (0.47, 1.35)
1.09
2.57
*
diaz
3
(
3(
3(
3(
3(
*)diaz
*)diaz
*)diaz
*)diaz
*)phen
*
phen
dbqc
*)diaz 444, 459, 469, 492
(0.74, 1.20)
*)diaz 551, 563, 594 (0.39,
1.31)
2.12
1.57
1.03
*
diaz
(
dbpzc
dicbqc
*
diaz
(
14.9)
318 (14.4), 368 (6.7)
1(
*)diaz 469, 489 sh, 500,
*
diaz
5
29 (0.87, 1.32)
[
Au(phen)Cl ]+ 225 (32.7), 276 (24.4),
1
(
*)phen 463, 497, 532, 588 sh 3(
0.01d d*
Au
2
1
3
18 (4.6)
254 (39.5), 274 (39.5),
28 (7.4), 387 (4.4)
( phen d*) (1.37)
(
(d
(
(
( phen d*)
(
(
(d
1
1
1
2.8)e
3(d d*)
*)diaz
0.97d d*
Pt(phen)Cl2
*)phen 611 (
1/2
Pt
3
*
)
phen
[
Au(dpq)Cl ]+ 228 (41.6), 252 (37.4),
*)phen 437, 464, 478, (0.63, 3(
*)diaz 1.33)
0.48d d*
2
Au
2
99 sh (12.3), 324 sh (7.4), 339 1
1
(
5.4), 370 (1.5)
231 (30.0), 252 (42.6), 277
16.9), 322 sh (6.7), 339 (5.7),
91 (2.2)
1
1
1
*)phen 431 sh, 457, 477, 514, 3(
*)diaz 548 (0.92, 1.32)
Pt(dpq)Cl2
*)diaz
2.01
*
diaz
(
3
*
)
phen
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

846
IVANOV et al.
Table 2. (Contd.)
Absorption,a 298 K
Luminescence,b 77 K
Electroreductionc
Compound
3
1
1
3
1
,
nm ( 10 , l mol cm ) assignment , nm ( vib 10 , cm ) assignment E1/2, V assignment
1
3(
0.46d d*
Au
[
Au(dppz)Cl ]+ 227 (46.3), 283 (32.1),
(
(
(
(
(d
(
(
*)phen 546, 557, 588 (0.36,
*)diaz 1.31)
*)diaz
*)diaz
2
1
1
1
1
1
1
3
57 (8.7), 375 (7.6)
240 (13.0), 270 (23.6),
49 (4.4), 358 (4.9), 378
4.8), 410 (1.8)
Au(dicnq)Cl ]+ 227 (48.3), 265 (34.8),
Pt(dppz)Cl2
*)phen 552, 594, 645 (1.31) 3(
*)diaz
1.37
*
diaz
3
(
*
)
phen
[
*)phen 472, 485, 513, 546
*)diaz (0.57, 1.70)
3(
*)diaz
0.61d d*
2
Au
3
(
07 (21.2), 344 (8.6), 365
6.8)
264 (30.5), 290 (24.1),
84 (4.2)
1
1
1
3(
Pt(dicnq)Cl2
(
(
(
*)phen 451, 489, 510, 531
*)diaz
0.96
*
diaz
3
*) / (1.67)
diaz
f
d
*
)
phen
a
b
c
d
CH CN.
Dimethylformamide toluene, 1 : 1.
Dimethylformamide.
Current peak potential at a potential sweep rate
f
3
1
e
of 50 mV s
.
Polycrystal;
is the luminescence band width at half-height. Overlap of two bands.
/2
1
1
dipyrido- and dibenzo-substituted 1,4-diazines and the
shape of their vibronically structured low-temperature
num satellites and their apparent absence in the H
NMR spectra.
(
T 77 K) luminescence spectra caused by the spin-
3
The voltammograms of the reduction of the Pt(II)
complexes with dipyrido-substituted 1,4-diazines are
characterized by the presence of one-electron reversi-
ble waves suggesting a ligand-centered character of
the redox process (electron transfer to the * redox
orbitals localized on the diazine moiety). Comparison
of the electrochemical parameters of the electroreduc-
tion of the Pt(II) complexes and free ligands (Table 2)
shows that the position of the reduction wave assigned
to the electron transfer to the * redox orbital of the
diazine moiety is essentially the same. The voltammo-
grams of the oxidation of the platinum complexes are
characterized by the chemical and electrochemical ir-
forbidden optical transitions of the (
lized on the diazine moiety are similar.
*) type loca-
In accordance with the coordination mode, the
complexation of dipyrido-substituted 1,4-diazines
leads to a decrease in the electron density mainly on
the phenanthroline moiety, which is reflected in the
positive coordination-induced chemical shifts (CIS =
lig) of the H , H , and H protons, whereas
comp
the electron density on the diazine moiety, remote
from the coordination center, changes to a considera-
bly lesser extent (Table 1). A decrease in CIS for the
Pt(II) complexes in the series phen > dppz > dpq >
dicnq is consistent with the decrease in the basicity of
the imine nitrogen atoms of the ligands; it indicates
that the efficiency of the donor acceptor interaction
reversibility, suggesting the metal-centered d nature
Pt
of the highest occupied molecular redox orbital in
the complexes. The oxidation current peak potential
of the Pt(II) complexes is essentially independent of
(N^N) Pt(II) decreases in this series. A regular in-
crease in the efficiency of the donor acceptor interac-
tion of the ligands with Au(III), compared to Pt(II),
levels off the effect of substituents in the diazine
moiety on CIS of the H protons ( CIS 0.55 0.02).
the structure of the diazine ligands: E 0.29 0.02 V.
p
The voltammograms of the reduction and oxidation of
the Au(III) complexes are characterized by chemical
and electrochemical irreversibility, with the current
peak potentials essentially independent of the structure
1
A characteristic feature of the H NMR spectra of
red
ox
of the diazine ligands (Ep
.08 V), which is indicative of a metal-centered
0.58 0.09, Ep 0.54
the Pt(II) complexes with dipyrido-substituted 1,4-di-
0
azines is the absence of the characteristic platinum
satellites originating form the coupling of the 195Pt
nature of both the highest occupied and the lowest
unoccupied molecular redox orbitals.
nucleus with ligand protons. This is caused by the
strong anisotropy of the electric field gradient on Pt
in the square-planar surrounding and by the related
factor of second-kind scalar relaxation of the protons
coupled with 1 Pt [9]. The short relaxation time of
the diazine ligands leads to broadening of the plati-
Comparison of the electronic absorption spectra of
the Pt(II) and Au(III) complexes (Fig. 1) with those of
the ligands (Table 2) shows that, along with the intra-
95
1
ligand optical transitions of the (
*) type localized
on the phenanthroline and diazine moieties of the lig-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES
847
4
2
1
2
3
2
1
4
3
0
4
00
600
, nm
300
400
, nm
Fig. 2. Luminescence spectra: (1) [Au(dpq)Cl ]Cl,
2
(
2) [Au(dicnq)Cl ]Cl, and (3) [Au(dppz)Cl ]Cl.
2 2
8
tween the phenanthroline and diazine moieties of the
1
4
2
0
ligands, the intraligand absorption bands of the (
*)
5
type localized on the diazine moiety are not noticeably
shifted in the complexes relative to the free ligands.
7
1
The vibronically structured ( 1300 cm ) low-
temperature luminescence spectra of the complexes
6
(
Fig. 2) and free diazine ligands (Table 2), assigned to
3
spin-forbidden optical transitions of the
(
*)
type localized on the diazine moiety, are not noticea-
bly affected by the complexation either, which con-
firms the conclusion that the electronic interaction of
the diazine moiety with the phenanthroline moiety and
coordination center is weak.
300
400 , nm
Fig. 1. Absorption spectra: (1) [Pt(dpq)Cl ],
2
(
(
(
2) [Pt(dicnq)Cl ], (3) [Pt(dppz)Cl ], (4) [Pt(phen)Cl ],
The lack of the luminescence of the Au(III) and
Pt(II) complexes in solution and in the polycrystalline
state at room temperature suggests occurrence of
efficient thermally activated nonradiative energy
decay, apparently through population of the higher
2
2
2
5)
[Au(dpq)Cl ]Cl,
(6)
[Au(dicnq)Cl ]Cl,
2
2
7) [Au(dppz)Cl ]Cl, and (8) [Au(phen)Cl ]Cl.
2
2
ands, the complexation gives rise to new low-energy
charge-transfer transitions assigned, in accordance
with the results of the electrochemical studies, to the
spin-allowed metal-to-ligand charge transfer transi-
tions of the (d phen) type for the Pt(II) complexes
and ligand-to-metal charge-transfer transitions of the
3
lying state of the (d d*) type.
EXPERIMENTAL
1
1
The H NMR spectra were recorded on a Bruker
1
( phen d*) type for the Au(III) complexes. In agree-
DPX-300 Avance spectrometer at 298 K. The elec-
tronic absorption spectra were measured on an SF-
2000 spectrometer at 298 K in acetonitrile. The lumi-
nescence characteristics were obtained at 77 K in
frozen glass-forming DMF toluene mixtures (1 : 1)
on a previously described [10] KSVU-1 installation
with pulse photoexcitation (LGI-21 nitrogen laser,
ment with the NMR data, a decrease in the efficiency
of the (N^N) M donor acceptor interaction in the
order phen > dppz > dpq > dicnq results in a regular
short-wave shift of the metal-to-ligand charge-transfer
bands of the Pt(II) complexes and long-wave shifts of
both the ligand-to-metal charge-transfer bands of the
Au(III) and intraligand (
1
*)-type intraligand bands
337 nm,
efficiency was determined relative to fluorescein
0.85) [11].
10 ns). The luminescence quantum
pulse
localized on the phenanthroline moiety. At the same
time, because of the weak electronic interaction be-
(
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 6 2006

848
IVANOV et al.
Dipyrido and dibenzo derivatives of 1,4-diazines
2002, vols. 233 234, p. 341.
were prepared by a standard procedure [12 14] in-
volving oxidation of o-phenanthroline and phenanth-
rene to 1,10-phenanthroline-5,6-dione and 9,10-phen-
anthroquinone, respectively, followed by the conden-
sation with appropriate diamines: ethylenediamine
4
5
. Messori, L., Abbate, F., Marcon, G., Orioli, P., Fon-
tani, M., Mini, E., Mazzai, T., Cartti, S., O’Con-
nell, T., and Zanello, P., J. Med. Chem., 2000, vol. 43,
no. 19, p. 3541.
. Abbate, F., Orioli, P., Bruni, B., Marcon, G., and
Messori, L., Inorg. Chim. Acta, 2000, vol. 311, no. 1,
p. 1.
(
dpq, dbq), o-phenylenediamine (dppz, dpbz), and
diaminomaleonitrile (dicnq, dicbq).
The synthesis of Pt(phen)Cl [15], Pt(dppz)Cl [16],
6. Che, C.-M., Yang, M., Wong, K.-H., Chan, H.-L., and
2
2
and [Au(phen)Cl ]ClO [7] was described previously;
Lam, W., Chem. Eur. J., 1999, vol. 5, no. 11, p. 3350.
2
4
Pt(dpq)Cl and Pt(dicnq)Cl were prepared in 70%
yield by a procedure similar to that in [16].
2
2
7. Ivanov, M.A., Puzyk, M.V., and Balashev, K.P., Russ.
J. Gen. Chen., 2003, vol. 73, no. 11, p. 1821.
Complexes [Au(N^N)Cl ]Cl (general procedure).
A 10% excess of diimine ligand in acetonitrile was
8. Fees, J., Kaim, W., Moscherosch, M., Matheis, W.,
Klima, J., Krejcik, M., and Zalis, S., Inorg. Chem.,
1993, vol. 32, no. 2, p. 166.
2
added to aqueous solution of H[AuCl ], which led
4
to precipitation of light yellow dichlorodiimine
complexes. The suspension was stirred for 30 min,
and the precipitate was filtered off, washed with ace-
tonitrile and ether, and vacuum-dried. Yield 60%.
9
. Skvortsov, A.N., Zh. Obshch. Khim., 2000, vol. 70,
no. 7, p. 1092.
1
0. Vasil’ev, V.V., Balashev, K.P., and Shagisultano-
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