New ruthenium(II) heteroleptic complexes containing the 4-(2-pyridyl)pyrimidine ligand with amine and amino acid substituents

Article abstract of DOI:10.1039/a904617h

New 4-(2-pyridyl)pyrimidines (L) have been synthesized in high yields by condensing enaminones with the appropriate carboxamidine or guanidine under basic conditions. These asymmetric bidentate diimine ligands coming from a one-step functionalization of amine and amino acid groups were complexed to ruthenium to obtain new heteroleptic complexes of type [Ru(bpy)₂(L)]²⁺. The ligands and complexes have been characterized by usual analytical methods, and the crystallographic study of one complex has been performed. Their spectroscopic and electrochemical properties have been investigated. ZINDO Calculations show that in the MLCT excited state the electron is mainly localized on the pyridylpyrimidine ligand. On the basis of electrochemical data, the first reduction potential of the complexes has been assigned to the redox couple involving this ligand.

Full text of DOI:10.1039/a904617h

View Article Online / Journal Homepage / Table of Contents for this issue
New ruthenium(II) heteroleptic complexes containing the 4-(2-
pyridyl)pyrimidine ligand with amine and amino acid substituents
a
a
a
a
Hassan Aït-Haddou,* Elena Bejan, Jean-Claude Daran, Gilbert G. A. Balavoine,
b
b
b
Florence Berruyer-Penaud, Lydia Bonazzola, Henda Smaoui-Chaabouni and
b
Edmond Amouyal*
a
Laboratoire de Chimie de Coordination, CNRS UPR 8241, 205 route de Narbonne,
1077 Toulouse Cedex, France. E-mail: aithad@lcc-toulouse.fr
Laboratoire de Physico-Chimie des Rayonnements, CNRS UMR 8610, Bat. 350,
Université Paris-Sud, 91405 Orsay, France. E-mail: edmond.amouyal@lpcr.u-psud.fr
3
b
Received 9th June 1999, Accepted 13th July 1999
New 4-(2-pyridyl)pyrimidines (L) have been synthesized in high yields by condensing enaminones with the appro-
priate carboxamidine or guanidine under basic conditions. These asymmetric bidentate diimine ligands coming from
a one-step functionalization of amine and amino acid groups were complexed to ruthenium to obtain new hetero-
2ϩ
leptic complexes of type [Ru(bpy) (L)] . The ligands and complexes have been characterized by usual analytical
2
methods, and the crystallographic study of one complex has been performed. Their spectroscopic and electro-
chemical properties have been investigated. ZINDO Calculations show that in the MLCT excited state the electron is
mainly localized on the pyridylpyrimidine ligand. On the basis of electrochemical data, the first reduction potential
of the complexes has been assigned to the redox couple involving this ligand.
6
ligands, we were interested by the synthesis of newly designed
Introduction
4
-(2-pyridyl)pyrimidine asymmetric ligands (L) and their
2ϩ
Polypyridine complexes of ruthenium() have stimulated con-
heteroleptic ruthenium() complexes of type [Ru(bpy) (L)]
2
siderable interest and activity as photosensitizers for photo-
chemical and photoelectrochemical conversion of solar energy.
(Scheme 1). On the other hand, it was interesting to introduce
amine and amino acid groups at position 2 of the pyrimidine
ring. Such substituents should increase the affinity of the
1
These complexes might also find application as components
2
7
of molecular electronics devices and as photoactive DNA
corresponding complexes to DNA. By the way, it should be
3
cleavage agents for phototherapeutic purposes. Symmetric
emphasized that we herein report a one-step functionalization
of an amino acid bearing an asymmetric bidentate diimine
which was subsequently and successfully complexed to
ruthenium. In this work the spectroscopic and electrochemical
properties of this novel series of substituted pyridylpyrimidine
ligands as well as the corresponding heteroleptic complexes
have been investigated. ZINDO Calculations have been per-
formed and support the assignment of electronic absorption
spectra.
polypyridine ligands such as 2,2Ј-bipyridine (bpy) have been
4
extensively utilized as chelating agents, but relatively little
attention has been directed towards complexes that possess
5
asymmetric bidentate diimine ligands. It is clear that the
replacement of one of the pyridine rings by other nitrogen-
containing heterocycles offers the possibility of tuning the
redox and photophysical properties of the complexes. As part
of our programme of designing new nitrogen bidentate
1
5
Scheme 1 Synthesis of the 4-(2-pyridyl)pyrimidines L –L [(a) 1.25 equivalents of (CH ) NCH(OCH ) at 100 ЊC, 16 h, 99%, (b) Guanidine or
3
2
3 2
2
ϩ
carboxamidine, 1 or 3 equivalents of sodium, EtOH, reflux] and the corresponding heteroleptic [Ru(bpy) (L)] complexes.
2
J. Chem. Soc., Dalton Trans., 1999, 3095–3101
3095

View Article Online
Experimental
General
a solution of Nα-Boc--Arg (0.77 g, 2.8 mmol; Boc =
COOC(CH ) ) in 10 mL of absolute EtOH. After 10 min of
3
3
stirring, 0.195 g (8.4 mmol, 3 equivalents) of sodium in 5 mL
of absolute EtOH was added and the reflux maintained for
2 h. The solution was cooled to room temperature and con-
centrated under vacuum. The residue was purified by column
chromatography on deactivated aluminium (methanol–diethyl
All reactions were carried out under an argon atmosphere.
Nuclear magnetic resonance spectra were recorded with
Bruker AM-250 (250 MHz) and AC-200 (200 MHz) spectro-
1
meters for H. Chemical shifts are reported in ppm and the
5
solvent was used as internal reference. These instruments were
ether, 97:3) to give 1.1 g of L as a yellow powder. Yield: 100%.
13
D
3
Ϫ1
Ϫ1
1
also used for C spectra. All melting points are uncorrected.
The CI and FAB mass spectra (m-nitrobenzyl alcohol matrix)
were recorded with a quadripolar Nermag R10-10H instru-
ment. Elemental analyses were performed by the “Service de
Microanalyse” of the LCC (Laboratoire de Chimie de Co-
ordination). Column chromatography purifications were per-
formed with Merck aluminium (deactivated with 8% water) or
with silica gel (35–70 mesh). The complex [Ru(bpy) Cl ]ؒ2H O,
[α]25 ϩ13.5 deg. cm g dm (c [g per 100 ml] 1.0, CH
3
OH). H
NMR (CDCl , 250 MHz): δ 8.6 (d, 1 H, J = 4.4), 8.27 (d, 1 H,
3
J = 5.2), 7.7 (dd, 1 H, J = 7.7, 1.5), 7.4 (d, 1 H, J = 4.67 Hz), 7.3
(m, 1 H), 6.5 (m, 3 H), 5.9 (m, 1 H), 4.1 (s, 1 H), 3.4 (m, 2 H), 1.7
1
3
(m, 4 H) and 1.3 (s, 9 H). C NMR (CDCl
161.7, 157.3, 156.0, 154.2, 149.1, 136.8, 125.0, 121.6, 106.0,
79.1, 52.0, 50.3, 30.3, 28.3 and 25.8. MS (CI, NH ): m/z = 388
: C, 58.9; H, 6.5; N, 18.08.
Found: C, 58.21; H, 6.35; N, 17.74%.
): δ 178.1, 163.9,
3
3
ϩ
(MH , 100%). Calc. for C19
H N O
25 5 4
2
2
2
2
-acetylpyridine and dimethylformamide dimethyl acetal
were purchased from Fluka, 2,2Ј-bipyridine (99.5%) from
Aldrich and [Ru(bpy) ]Cl ؒ6H O (99%) from Strem Chemicals.
Synthesis of [Ru(bpy) (L)][PF ] complexes
2
6 2
3
2
2
The guanidines and carboxamides were purchased from
1
2؉
[
Ru(bpy) (L )] . The complex cis-[Ru(bpy) Cl ]ؒ2H O (0.21
2 2 2 2
1
3
Aldrich. For the preparation of compounds 2, L and L see
ref. 6. Spectroscopic grade ethanol (Carlo Erba) was used
as supplied. For cyclic voltammetry, acetonitrile (Aldrich,
g, 0.4 mmol) was suspended in a mixture of ethanol and water
50 mL, 75:25) and heated under argon for 30 min. Ligand
(
1
L (0.075 g, 0.48 mmol, 1.2 equivalent) was added, and the
mixture refluxed for 16 h. The resulting solution was cooled to
room temperature and the ethanol removed under pressure.
After filtration, a saturated solution of ammonium hexa-
fluorophosphate was added dropwise to the filtrate to com-
plete precipitation. The precipitate was collected by filtration,
washed by water and diethyl ether, and dried to give 0.292 g of
the desired complex. TLC (alumina, acetone–water–saturated
spectrophotometric grade, 99.5%) was used as solvent and
Ϫ1
0
9
.1 mol l tetrabutylammonium tetrafluoroborate (Janssen,
9%) as supporting electrolyte.
Synthesis of the 4-(2-pyridyl)pyrimidine ligands
2
2
-Methyl-4-(2-pyridyl)pyrimidine L . A solution of aceta-
midinium chloride (2.14 g, 22.6 mmol) in absolute ethanol
75 ml) was added to a stirred solution of 2-[3-(dimethyl-
aqueous potassium nitrate, 90:10:1) showed the material to be
(
1
pure. Yield: 85%. H NMR (CD CN): δ 9.18 (1 H, d, J = 5.28),
3
amino)-1-oxoprop-2-en-1-yl]pyridine 2 (2.0 g, 11.3 mmol) in
boiling absolute EtOH (50 ml) and stirring was continued for
8
7
.9 (1 H, d, J = 8.06), 8.7 (5H, m), 8.55 (1 H, s), 8.3 (5 H, m),
.99 (1 H, d, J = 5.43), 7.97 (1 H, d, J = 5.44), 7.87 (1 H, d,
2
0 min. To this mixture was added Na (0.78 g, 33.9 mmol, 3
1
3
J = 5.33 Hz), 7.82 (2 H, m), 7.5 (4 H, m) and 7.2 (1 H, m).
C
equivalents) in absolute EtOH (50 ml) and the reaction mixture
refluxed for 16 h. The solution was allowed to cool to room
temperature and then concentrated under reduced pressure.
The residue was dissolved in dichloromethane followed by
removal of the precipitate by filtration. The filtrate was concen-
trated and the residue purified by column chromatography on
NMR (CD CN): δ 161.5, 159.24, 158.5, 153.7, 153.2, 152.8,
3
1
39.5, 130.9, 129.2, 129.1, 127.8, 125.9, 125.8 and 120.6. FAB
ϩ
ϩ
MS: m/z = 716 (100, M Ϫ PF ), 571 (47%, M Ϫ 2PF ). Calc.
6
6
for C H F N P Ru: C, 40.48; H, 2.69; N, 11.39. Found: C,
29
23 12
7
2
4
0.75; H, 2.54; N, 11.51%.
2
flash silica gel (ethyl acetate) to give 1.88 g of L as a white
2
2؉
[
Ru(bpy) (L )] . This complex was obtained by reaction of
2
1
microcrystalline powder. Yield: 97%. H NMR (CDCl , 250
3
0
.168 g (0.32 mmol) of cis-[Ru(bpy) Cl ]ؒ2H O with 1.2 equiv-
2
2
2
MHz): δ 8.7 (d, 1 H, J = 4.45), 8.63 (m, 1 H), 8.43 (d, 1 H,
2
1
2ϩ
alents of L using the procedure described for [Ru(bpy) (L )] .
2
J = 5.24), 8.1 (d, 1 H, J = 8.01), 7.8 (t, 1 H, J = 7.85 Hz), 7.35
The complex was purified as a hexafluorophosphate salt, 0.258
13
(
m, 1 H) and 2.8 (s, 3 H). C NMR (CDCl ): δ 167.87, 162.80,
1
3
g. Yield: 92%. H NMR (CD CN): δ 9.05 (2 H, m), 8.84 (4 H,
3
1
2
57.82, 154.01, 149.44, 136.98, 125.20, 121.61, 114.22 and
m), 8.72 (1 H, d, J = 7.85), 8.55 (1 H, d, J = 7.3), 8.25 (6 H,
m), 8.02 (1 H, d, J = 8.1), 7.96 (1 H, d, J = 5.54), 7.85 (1 H, d,
J = 7.36 Hz), 7.65 (5 H, m) and 2.35 (3H, s). C NMR
ϩ
6.08. MS (CI, NH ): m/z = 172 (MH , 100%). Calc. for
3
C H N : C, 70.16; H, 5.30; N, 24.54. Found: C, 70.41; H, 5.62;
13
10
9
3
N, 24.12%.
(
CD CN): δ 174.13, 165.41, 158.75, 157.94, 157.70, 157.45,
3
1
1
2
57.19, 154.32, 152.94, 152.56, 152.21, 139.05, 138.80, 138.60,
4
2
-Ethylamino-4-(2-pyridyl)pyrimidine L . This compound was
29.68, 128.76, 128.52, 127.35, 125.37, 125.16, 117.04 and
2
prepared in the same fashion as for L by condensation of 3.0 g
16.95 mmol) of 2 with 1.23 g (16.95 mmol) of ethyl guanidine
sulfate {[C H NHC(᎐NH)NH ] ؒH SO } in the presence of 3
equivalents of sodium in absolute EtOH. The desired product
was purified by column chromatography on silica gel (ethyl
acetate–n-pentane, 80:20) to give 3.12 g of L as a microcrystal-
line white powder. Yield: 92%. H NMR (CDCl , 250 MHz):
δ 8.64 (dd, 1 H, J = 6.33, 1.6), 8.38 (d, 1 H, J = 5.15), 8.34
d, 1 H, J = 8.0), 7.77 (ddd, 1H, J = 7.78, 6.0, 1.76), 7.31 (m,
H), 5.48 (m, 1 H), 3.5 (m, 2 H) and 1.23 (t, 3 H, J = 7.2 Hz).
C NMR (CDCl ): δ 163.0, 162.0, 158.5, 154.3, 148.8, 136.3,
24.4, 120.9, 106.0, 35.8 and 14.4. MS (CI, NH ): m/z = 201
MH , 100%). Calc. for C H N : C, 65.98; H, 6.04; N, 27.98.
ϩ
7.79. FAB MS: m/z = 730 (56.95, M Ϫ PF ) and 585 (100%,
6
(
ϩ
M Ϫ 2PF ). Calc. for C H F N P Ru: C, 41.20; H, 2.88; N,
11.21. Found: C, 40.85; H, 3.04; N, 11.35%.
6
30 25 12
7
2
2
5
2 2
2
4
3
2؉
[Ru(bpy) (L )] . This complex was obtained by reaction of
2
4
0.084 g (0.16 mmol) of cis-[Ru(bpy) Cl ]ؒ2H O with 1.2 equiv-
alents of L using the procedure described for [Ru(bpy) (L )] .
The complex was purified as a hexafluorophosphate salt, 0.126
g. Yield: 90%. H NMR (CD CN): δ 9.08 (1 H, dd, J = 7.22,
1.12), 8.9 (1 H, d, J = 8.18), 8.8 (1 H, d, J = 8.12), 8.65 (3 H, m),
8.55 (1 H, t, J = 7.95 Hz), 8.25 (5 H, m), 8.05 (2 H, m), 7.8 (3 H,
m) and 7.55 (5 H, m). C NMR (CD CN): δ 162.9, 160.9,
159.0, 158.8, 158.7, 158.2, 157.7, 155.1, 153.9, 153.7, 153.1,
151.9, 141.2, 140.0, 139.9, 139.7, 129.9, 129.6, 129.1, 128.6,
2
2
2
1
3
1
2ϩ
3
2
1
(
3
1
13
3
13
1
(
3
3
ϩ
11
12
4
Found: C, 66.21; H, 6.35; N, 27.64%.
1
28.1, 127.1, 126.5, 126.3, 125.9, 125.8, 125.6 and 125.1. FAB
ϩ
ϩ
2
-(4-tert-Butoxycarbonylamino-4-carboxybutylamino)-4-(2-
MS: m/z = 731 (56.95, M Ϫ PF ) and 585 (100%, M Ϫ 2PF ).
6
6
5
pyridyl)pyrimidine L . To a stirred solution of compound 2
0.5 g, 2.8 mmol) in 5 mL of boiling absolute EtOH was added
Calc. for C H F N P Ru ϩ 4H O: C, 36.76; H, 3.40; N,
29 24 12 8 2 2
11.82. Found: C, 36.39; H, 3.51; N, 12.11%.
(
3
096
J. Chem. Soc., Dalton Trans., 1999, 3095–3101

View Article Online
4
2؉
[
Ru(bpy) (L )] . This complex was obtained by reaction of
Flack’s enantiopole parameter, 0.50, its rather good standard
2
0
.150 g (0.286 mmol) of cis-[Ru(bpy) Cl ]ؒ2H O with 1.2
deviation (0.04), and the agreement between related distances
in two molecules, the occurrence of a racemic twin might be
considered. The structure was refined by least-squares pro-
2
2
2
4
equivalents of L using the procedure described for [Ru(bpy) -
2
1
2ϩ
(
L )] . The complex was purified as a hexafluorophosphate
1
2
salt, 0.219 g. Yield: 85%. HMR (CD CN): δ 8.75 (6 H, m), 8.45
cedures on F . The H atoms were introduced as a riding
3
(
1 H, d, J = 5.3), 8.2 (5 H, m), 8.0 (1 H, d, J = 5.58), 7.9 (1 H,
model and given isotropic thermal parameters 20% higher
than those of the carbon to which they are attached. Details
of data collection and refinement are given in Table 2.
Selected bond lengths and angles for the two molecules are
listed in Table 3.
d, J = 5.06), 7.65 (8 H, m), 5.25 (1 H, m, NH), 3.15 (2 H, m)
and 0.63 (3 H, t, J = 7.25 Hz). C NMR (CD CN): δ 165.8,
1
1
1
13
3
65.3, 161.3, 159.1, 158.8, 158.6, 158.5, 155.1, 153.2, 153.0,
52.7, 152.6, 130.0, 129.9, 129.4, 129.3, 129.2, 127.6, 126.5,
26.0, 125.9, 109.8, 38.0 and 13.1. FAB MS: m/z = 759
The calculations were carried out with the help of the
ϩ
ϩ
9
(
30.29, M Ϫ PF ) and 613 (73.53%, M Ϫ 2PF ). Calc. for
SHELXL 97 programs running on a PC. The drawing of the
6
6
10
C H F N P Ru: C, 41.21; H, 3.12; N, 12.40. Found: C, 41.28;
H, 3.25; N, 12.56%.
molecule was realized with the help of CAMERON.
CCDC reference number 186/1571.
3
1
28 12
7
2
See http://www.rsc.org/suppdata/dt/1999/3095/ for crystallo-
graphic files in .cif format.
5
2؉
[
Ru(bpy) (L )] . This complex was obtained by reaction of
2
0
.150 g (0.286 mmol) of cis-[Ru(bpy) Cl ]ؒ2H O with 1.2
2 2 2
5
equivalents of L using the procedure described for [Ru(bpy) -
(
ZINDO calculations
2
1
2ϩ
L )] . The complex was purified as a hexafluorophosphate
1
The optical absorption spectra of the ligands and of the [Ru-
salt, 0.219 g. Yield: 85%. H NMR(CD CN): δ 8.75 (6 H, m),
3
2
2ϩ
(
bpy) (L )] complex were calculated by using the ZINDO
2
11
8
(
(
.45 (1 H, m), 8.2 (5 H, m), 8.0 (2 H, m), 7.65 (8 H, m), 5.25
semiempirical program. This Intermediate Neglect of Differ-
ential Overlap (INDO) model, adapted for spectroscopy and
extended to second transition metal series, has been used for
1 H, m, NH), 4.1 (1 H, m), 3.15 (2 H, m), 1.8 (1 H, m), 1.51
13
1 H, m), 1.45 (9 H, s) and 1.05 (2 H, m). C NMR (CD CN):
3
δ 177.5, 165.9, 165.6, 161.5, 159.3, 158.9, 158.7, 158.6, 155.3,
12
some time for studying the spectroscopy of large complexes.
The SCF calculation is followed by a configuration interaction
CI) calculation; a Rumer diagram is used to generate the
1
1
1
55.0, 153.3, 153.0, 152.8, 152.6, 150.8, 140.5, 140.0, 139.7,
39.4, 139.2, 130.1, 129.6, 128.8, 128.3, 127.8, 126.9, 126.2,
(
25.8, 125.2, 124.8, 110.0, 80.2, 65.2, 45.0, 43.0, 26.4 and 25.9.
ϩ
CI matrix. The CI contains all singly excited configurations
generated by removing electrons from the ten highest occupied
MOs and placing them into the ten lowest unoccupied MOs.
The geometries of the cis and trans conformers of all the
ligands were optimized by using the AM1 method. Concerning
FAB MS: m/z = 946 (9.16, M Ϫ PF ) and 800 (13.79%,
M Ϫ 2PF ). Calc. for C H F N O P Ru ϩ 2H O: C, 41.57;
6
ϩ
6
39 41 12
9
4
2
2
H, 4.03; N, 11.19. Found: C, 41.68; H, 4.21; N, 11.26%.
Absorption spectroscopy and cyclic voltammetry
2
2ϩ
the complex [Ru(bpy) (L )] , the crystallographic data deter-
2
The UV-visible electronic absorption spectra were recorded
on a Perkin-Elmer Lambda 9 spectrophotometer. Cyclic voltam-
metry curves were recorded with a Wenking system (model
mined in this paper for N, C and Ru atoms were used for the
ZINDO calculation. Hydrogen atoms were placed at a distance
of 1.09 Å from their bonding partner.
8
1
1 potentiostat) using a platinum button (Solea Tacussel EDI
01T) as the working electrode and a platinum wire of 1 mm
Results and discussion
Ligands
diameter as the counter electrode. The working electrode was
carefully polished with diamond sprays (Struers) and rinsed
with ethanol before each potential run. Experiments were
performed at a scan rate of 0.2 V s on Ar-purged acetonitrile
solutions, containing 0.1 mol l tetrabutylammonium tetra-
fluoroborate as the supporting electrolyte. Concentrations of
1
respectively.
1
5
Synthesis. The synthesis of ligands L –L is outlined in
Scheme 1 (i). The enaminone 2 was obtained with quantit-
ative yield by reaction of 2-acetylpyridine 1 with 1.2 equivalents
of the dimethylformamide dimethyl acetal at 100 ЊC.
Ϫ1
6a
Ϫ1
13
Ϫ3
Ϫ4
Ϫ1
0
and 5 × 10 mol l were used for ligands and complexes
The condensation of 2 with the appropriate guanidine or
carboxamidine under basic conditions yielded the 4-(2-pyridyl)-
1
5
pyrimidine ligands L –L in good to excellent yields. The func-
2
2؉
؊
6
Structure determination of [Ru(bpy) (L )] , 2PF
5
2
tionalized amino acids with metal-binding sites such as L are
The data were collected on a Stoe IPDS (Imaging Plate Diffrac-
tion System) equipped with an Oxford Cryosystems cooler
device. Coverage of the unique set was over 96% complete to
at least 24.1Њ. Crystal decay was monitored by measuring
attractive building blocks for the construction of synthetic
14
peptides. Since only a few examples of functionalized amino
acids with bidentate metal-binding sites have been described,
it was interesting to use this straightforward procedure in the
preparation of new functionalized amino acids using the Nα-
Boc--Arg as the guanidine reagent. Thus, the reaction of 2
with 1 equivalent of Nα-Boc--Arg in hot absolute ethanol in
2
00 reflections per image. The final unit cell parameters were
obtained by the least-squares refinement of 5000 reflections.
Only statistical fluctuations were observed in the intensity
monitors over the course of the data collection. Owing to the
rather low µx value, 0.24 (µx is the product of the mid size
of the crystal and the absorption coefficient), no absorption
correction was considered.
5
the presence of 2 equivalents of sodium ethoxide yielded L
without loss of the tert-butoxycarbonyl group, in quantitative
15
yield.
1
3
On the basis of the systematic absences, the space group
Spectroscopy. Electronic absorption spectra of ligands L , L ,
4
5
(
P2 /c or P2 ) could not be unambiguously defined. Indeed if
L and L are shown in Fig. 1. The corresponding experimental
and calculated absorption maxima for all ligands are presented
in Table 1. The geometries of cis and trans conformers of bpy
have been determined at the MP2/6-31G**//HF/6-31G** level
1
1
the absences corresponding to the twofold screw axis 2 were
1
verified, the systematic absences related to the c glide plane
(
h0l, l = 2n ϩ 1) were not fully satisfied. The structure could be
8
16
solved by direct methods (SIR 92) in P2 /c but the refinement
by Howard. The trans conformer is predicted to be lower in
1
was unstable with large discrepancies between the anisotropic
thermal parameters. A much better refinement was obtained in
energy but the cis–trans interconversion barrier is only of 6 kJ
Ϫ1
mol . In organic solvents, dipole measurements indicate a
16
P2 with two molecules in the asymmetric unit. Although these
trans non-planar configuration. The calculated spectra are in
17
1
two molecules are closely related by a pseudo inversion centre,
no unusual parameter correlations were observed. Considering
good agreement with previous INDO/S CI calculations and
with experimental results if we assume that bpy is in the trans
J. Chem. Soc., Dalton Trans., 1999, 3095–3101
3097

View Article Online
Table 1 Experimental and calculated absorption maxima in ethanol
and redox potentials in acetonitrile for the different ligands at 298 K
Ϫ1
Ϫ1
λmax/nm (ε/l mol cm
)
calculated
Ered/V vs.
Ligand
bpy
a
b
experimental
SCE
273
2
2
284
283 (14480)
244 (sh) (9950)
236 (12240)
279 (12820)
Ϫ2.18
35
29
240
278
1
L
Ϫ1.78
Ϫ1.85
Ϫ1.90
2
42 (sh) (6880)
2
280
34
235 (7620)
280 (15240)
2
L
2
44 (sh) (7360)
2
296
35
237 (8710)
324 (7660)
3
L
2
2
296
2
89
35
286 (sh) (7280)
2
76 (9380)
241 (23010)
352 (sh) (2110)
338 (2430)
4
c
L
Ϫ1.98
Ϫ1.95
90
2
2
2
87 (sh) (2550)
73 (sh) (4760)
53 (13100)
2
37
242 (sh) (11390)
342 (3730)
5
L
2
2
2
88 (sh) (4440)
77 (sh) (7260)
53 (19830)
a
b
c
cis Conformer. trans Conformer. Calculation performed on NHCH
3
instead of NHCH CH .
2
3
conformation. The experimental and calculated absorption
1
2
spectra of L and L are similar to the bpy spectrum. From
ZINDO calculations we have attributed the absorption bands
3
4
to strong π → π* transitions. Absorption spectra of L , L
5
and L present a supplementary band at wavelengths above 320
4
5
nm. For L and L this band is very large and is characterized
by a molar absorption coefficient ε less intense than that of the
π–π* bands. It can be attributed to a n–π* transition implying a
lone pair of electrons located on one of the nitrogen atoms. For
3
L , the band at 324 nm is relatively fine and it seems difficult
with the present data to conclude about its nature (n–π* or
π–π* transition). The absence of any calculated absorption
band at a wavelength longer than 300 nm does not agree
with experimental data. A possible explanation would be the
presence of a species due to hydrogen-bonded interactions
with ethanol in the first solvation shell of 2-aminopyrimidine
18
compounds.
1
3
4
5
Redox properties. Peak potentials of the “free” ligands are
given in Table 1. We observed that L is easier to reduce than
Fig. 1 Absorption spectra of ligands L (a), L (b), L (c) and L (d),
1
Ϫ5
Ϫ1
in ethanol (10 mol l ).
bpy. In fact, the mesomeric donor effect of the nitrogen atom at
the 1 position of the pyrimidine induces an electronic depletion
around this nitrogen. This increases the electron attractor
19
boiling 75:25 solution of EtOH–water. After removal of
ethanol under reduced pressure and filtration of the aqueous
solution, the complexes were precipitated with an excess of
NH PF . They were obtained in excellent yield with high purity
1
3
4
power of L . The reduction potentials of ligands L , L and
5
1
L are similar and more negative than that of L . Indeed, the
lone pair of the nitrogen atom of the substituent at the 2
position to the pyrimidine increases the electron density via a
donor mesomeric effect making the reduction of the ligands
4
6
as their hexafluorophosphate salts and characterized by NMR
spectroscopy, mass spectrometry, electrochemistry and absorp-
tion spectroscopy. An X-ray structural analysis of [Ru(bpy) -
2
2
more difficult. The reduction potential of L is intermediate
2
2ϩ
(
L )] was carried out.
1
3
(
Ϫ1.85 V) between those of L and L . This is in line with the
well known inductive effect of a methyl group which is less
intense than the mesomeric effect.
2
2؉
؊
Structure of [Ru(bpy) (L )] , 2PF . The asymmetric unit
2
6
contains two cations and four anions. The two cations are
nearly identical; only one (molecule 1) is shown on Fig. 2 with
the atom labelling scheme. The ruthenium–nitrogen bond
lengths range from 2.022(7) to 2.137(6) (Table 3). The longest
is observed for the pyrimidine ring 2.137(6) Å [2.109(7) Å].
Similar lengthening were observed in related complexes with
Complexes
Synthesis. Ruthenium() complexes containing the novel
ligands were synthesized by utilizing [Ru(bpy) Cl ] as the source
2
2
of the metal fragment as shown in Scheme 1 (ii). The complex
6b,20
[
Ru(bpy) Cl ] reacted for 16 h with the respective ligands in a
α substituted bpy or related ligands.
As suggested by the
2
2
3
098
J. Chem. Soc., Dalton Trans., 1999, 3095–3101

View Article Online
2
Table 2 Crystallographic data for [Ru(bpy) (L )][PF ] recorded at
short contact between one H of the methyl substituent and the
2
6 2
1
60 K
nitrogen N(16), 2.563 Å [2.558 Å], this increase in bond length
might result from the steric interaction between this methyl
substituent on the pyrimidine ring and the bpy ring 5. It is
indeed this bpy ligand which exhibits the larger twisting
Empirical formula
C H F N P Ru
30 25 12 7 2
M
874.58
8
.4(4) [8.9(5)]Њ about the interannular C–C bond. The other
Shape (color)
Crystal system
Space group
Box (dark red)
Monoclinic
P21
12.2871(17)
10.5692(12)
25.100(4)
95.266(17)
3245.9(8)
4
bpy ligand displays an inter-ring angle of only 5.6(1) [5.6(2)]Њ,
whereas the two rings of the (pyridyl) pyrimidine are almost
planar, interplanar angle 1.2(5) [2.7(5)]Њ. However, an electronic
influence of the pyrimidine ring itself could not be ruled out.
a/Å
b/Å
c/Å
β/Њ
3
V/Å
Spectroscopy. The absorption data for all the complexes are
Z
R(int)
summarized in Table 4. The absorption spectra of [Ru(bpy) -
2
1
2ϩ
5
2ϩ
0.0285
(
L )] and [Ru(bpy) (L )] determined in ethanol solutions are
2
R
wR2
0.0348
0.0841
presented in Fig. 3. By comparison with the reference product,
2ϩ
i.e. [Ru(bpy) ] , the absorption band in the visible region has
3
Goodness of fit
1.024
been assigned to a metal-to-ligand charge transfer (MLCT)
2
Table 3 Selected interatomic distances [Å] and bond angles [Њ] for [Ru(bpy) (L )][PF ]
2
6
2
Molecule 1
Molecule 2
Ru(1)–N(11)
Ru(1)–N(12)
Ru(1)–N(13)
Ru(1)–N(14)
Ru(1)–N(15)
Ru(1)–N(16)
N(11)–C(111)
N(11)–C(115)
N(12)–C(121)
N(12)–C(125)
N(13)–C(131)
N(13)–C(135)
N(14)–C(141)
N(14)–C(145)
N(15)–C(151)
N(15)–C(155)
N(16)–C(161)
N(16)–C(165)
N(114)–C(113)
N(114)–C(115)
2.137(6)
2.060(4)
2.051(6)
2.022(7)
2.088(7)
2.051(5)
1.356(8)
1.372(10)
1.321(9)
1.369(10)
1.355(10)
1.354(9)
1.318(10)
1.375(9)
1.356(10)
1.315(10)
1.377(8)
1.333(8)
1.301(11)
1.353(10)
Ru(2)–N(21)
Ru(2)–N(22)
Ru(2)–N(23)
Ru(2)–N(24)
Ru(2)–N(25)
Ru(2)–N(26)
N(21)–C(211)
N(21)–C(215)
N(22)–C(221)
N(22)–C(225)
N(23)–C(231)
N(23)–C(235)
N(24)–C(241)
N(24)–C(245)
N(25)–C(251)
N(25)–C(255)
N(26)–C(261)
N(26)–C(265)
N(214)–C(213)
N(214)–C(215)
2.109(7)
2.050(5)
2.061(7)
2.054(8)
2.038(8)
2.060(5)
1.349(10)
1.337(11)
1.398(9)
1.328(10)
1.372(10)
1.344(9)
1.400(11)
1.308(10)
1.340(11)
1.396(11)
1.347(9)
1.362(8)
1.341(13)
1.331(13)
N(14)–Ru(1)–N(13)
N(14)–Ru(1)–N(16)
N(13)–Ru(1)–N(16)
N(14)–Ru(1)–N(12)
N(13)–Ru(1)–N(12)
N(16)–Ru(1)–N(12)
N(14)–Ru(1)–N(15)
N(13)–Ru(1)–N(15)
N(16)–Ru(1)–N(15)
N(12)–Ru(1)–N(15)
N(14)–Ru(1)–N(11)
N(13)–Ru(1)–N(11)
N(16)–Ru(1)–N(11)
N(12)–Ru(1)–N(11)
N(15)–Ru(1)–N(11)
C(111)–N(11)–C(115)
C(111)–N(11)–Ru(1)
C(115)–N(11)–Ru(1)
C(121)–N(12)–C(125)
C(121)–N(12)–Ru(1)
C(125)–N(12)–Ru(1)
C(135)–N(13)–C(131)
C(135)–N(13)–Ru(1)
C(131)–N(13)–Ru(1)
C(141)–N(14)–C(145)
C(141)–N(14)–Ru(1)
C(145)–N(14)–Ru(1)
C(155)–N(15)–C(151)
C(155)–N(15)–Ru(1)
C(151)–N(15)–Ru(1)
C(165)–N(16)–C(161)
C(165)–N(16)–Ru(1)
C(161)–N(16)–Ru(1)
C(113)–N(114)–C(115)
78.5(3)
84.8(3)
96.2(2)
93.9(3)
88.3(3)
174.91(19)
96.05(17)
173.4(3)
79.5(3)
95.8(3)
170.4(3)
96.4(2)
N(24)–Ru(2)–N(23)
N(24)–Ru(2)–N(26)
N(26)–Ru(2)–N(23)
N(22)–Ru(2)–N(24)
N(22)–Ru(2)–N(23)
N(22)–Ru(2)–N(26)
N(25)–Ru(2)–N(24)
N(25)–Ru(2)–N(23)
N(25)–Ru(2)–N(26)
N(25)–Ru(2)–N(22)
N(24)–Ru(2)–N(21)
N(23)–Ru(2)–N(21)
N(26)–Ru(2)–N(21)
N(22)–Ru(2)–N(21)
N(25)–Ru(2)–N(21)
C(215)–N(21)–C(211)
C(211)–N(21)–Ru(2)
C(215)–N(21)–Ru(2)
C(225)–N(22)–C(221)
C(221)–N(22)–Ru(2)
C(225)–N(22)–Ru(2)
C(235)–N(23)–C(231)
C(235)–N(23)–Ru(2)
C(231)–N(23)–Ru(2)
C(245)–N(24)–C(241)
C(241)–N(24)–Ru(2)
C(245)–N(24)–Ru(2)
C(251)–N(25)–C(255)
C(255)–N(25)–Ru(2)
C(251)–N(25)–Ru(2)
C(261)–N(26)–C(265)
C(265)–N(26)–Ru(2)
C(261)–N(26)–Ru(2)
C(215)–N(214)–C(213)
80.1(3)
87.7(3)
96.7(2)
92.3(3)
87.8(3)
175.5(2)
95.09(19)
173.1(3)
78.1(3)
97.4(3)
170.5(3)
96.3(2)
103.9(2)
77.8(2)
89.5(3)
101.5(2)
78.8(3)
89.1(3)
117.4(6)
113.1(4)
129.5(5)
117.2(5)
117.6(5)
125.1(5)
117.2(7)
126.5(5)
116.3(4)
118.4(6)
117.3(5)
123.8(5)
121.3(7)
124.6(6)
113.8(5)
118.4(5)
126.3(4)
115.2(4)
118.2(7)
114.4(7)
114.5(5)
131.1(6)
117.7(5)
115.8(5)
126.4(5)
119.2(7)
127.0(6)
113.8(5)
118.5(7)
113.7(5)
127.5(6)
116.2(8)
126.2(7)
117.5(6)
117.9(6)
125.3(4)
116.8(5)
117.2(8)
J. Chem. Soc., Dalton Trans., 1999, 3095–3101
3099

View Article Online
Ϫ5
Ϫ1
Table 4 Absorption parameters in ethanol solution for ruthenium() complexes (10 mol l
)
Ϫ1
Ϫ1
Complex
λmax/nm (ε/l mol cm )
2
ϩ
[
[
[
[
[
[
Ru(bpy)3]
450 (13700)
441 (7210)
442 (5140)
449 (6610)
447 (17290)
448 (10950)
287 (80290)
286 (52260)
286 (44940)
289 (31390)
288 (85500)
289 (61890)
245 (25620)
245 (15960)
243 (20870)
236 (13210)
244 (47300)
245 (29500)
1
2ϩ
2ϩ
2ϩ
2ϩ
2ϩ
Ru(bpy) (L )]
Ru(bpy) (L )]
Ru(bpy) (L )]
Ru(bpy) (L )]
482 (sh) (5310)
480 (sh) (3620)
2
2
2
3
2
4
483 (sh) (11250)
487 (sh) (7950)
2
5
Ru(bpy) (L )]
2
Table 5 Redox potentials in acetonitrile for ruthenium() complexes
E1/2/V vs. SCE
Reduction
Complex
Oxidation
∆E1/2/V
2
ϩ
[
[
[
[
[
[
Ru(bpy)3]
1.30
1.33
1.38
1.34
1.34
1.34
Ϫ1.30
Ϫ1.48
Ϫ1.40
Ϫ1.45
Ϫ1.43
Ϫ1.32
Ϫ1.42
Ϫ1.73
Ϫ1.70
Ϫ1.70
Ϫ1.67
Ϫ1.55
Ϫ1.65
2.60
2.34
2.50
2.45
2.42
2.44
1
2ϩ
2ϩ
2ϩ
2ϩ
2ϩ
Ru(bpy) (L )]
Ru(bpy) (L )]
Ru(bpy) (L )]
Ru(bpy) (L )]
Ϫ1.01
Ϫ1.12
Ϫ1.11
Ϫ1.08
Ϫ1.10
2
2
2
3
2
4
2
5
Ru(bpy) (L )]
2
1
2ϩ
Fig. 3 Absorption spectra of complexes [Ru(bpy) (L )] (full line)
2
5
2ϩ
Ϫ5
Ϫ1
and [Ru(bpy) (L )] (dotted line) in ethanol (10 mol l ).
2
Table 5. The voltammograms exhibit, in each case, one
reversible oxidation wave and three reversible reduction waves.
By comparison with the oxidation potential of the reference
complex, we attribute the potentials in the range ϩ1.33 to
2
2ϩ
Fig. 2 Molecular view of the cation [Ru(bpy) (L )] (molecule 1).
2
Ellipsoids represent 50% probability. Hydrogen atoms have been omit-
ted for clarity.
3ϩ
2ϩ
ϩ1.38 V vs. SCE to the redox couple Ru –Ru of the hetero-
21
transition. The ZINDO calculation performed on [Ru(bpy)2-
L )] suggests several bands (from 446 to 400 nm) in the visible
leptic complexes. These potentials are related to the energy of
2
2ϩ
(
23
the HOMO orbital of the metal. The potentials of the second
region which can be assigned to a metal-to-ligand charge trans-
fer associated with the promotion of a ruthenium d electron
into a π* orbital of bpy and (or) pyridylpyrimidine ligands.
In the concerned excited state the electron is mainly localized
on the pyridylpyrimidine ligand.
A more intense band appears in the region 280–320 nm
which can be associated with a π → π* ligand-centred (LC)
transition in agreement with the ZINDO calculation. More-
over the calculation results in this region lead to the attribution
of several bands to d → d* transitions (MC). A third absorp-
tion band appearing in the 230–260 nm region of the experi-
mental spectra can be assigned to MLCT transitions according
to ZINDO calculations.
and third reduction of the heteroleptic complexes are similar
to the corresponding potentials of the reference complex. This
indicates that these two reductions take place on the bpy
ligands of the heteroleptic complexes. The first reduction
potentials ranging from Ϫ1.01 to Ϫ1.12 V vs. SCE are less
2ϩ
negative than that of [Ru(bpy)3]
(Ϫ1.30 V vs. SCE).
Consequently, it is clear that the first reduction can only be
attributed to the redox couple involving the pyridylpyrimidine
ligand. The corresponding potential is related to the energy of
the π* (LUMO) ligand orbital. The successive reductions of the
heteroleptic complexes take place according to eqns. (1)–(3).
22
II
2ϩ
Ϫ
II
Ϫ
ϩ
[
Ru (bpy) (L)] ϩ e → [Ru (bpy) (L )]
(1)
2
2
Redox properties. The redox potentials of all the complexes
as determined by cyclic voltammetry in acetonitrile are in
II
Ϫ
ϩ
Ϫ
II
Ϫ
Ϫ
[Ru (bpy) (L )] ϩ e → [Ru (bpy)(bpy )(L )] (2)
2
3
100
J. Chem. Soc., Dalton Trans., 1999, 3095–3101

View Article Online
II
Ϫ
Ϫ
Ϫ
[
Ru (bpy)(bpy )(L )] ϩ e →
4 K. Kalyanasundaram, Coord. Chem. Rev, 1982, 46, 159; A. Juris,
II
Ϫ
Ϫ
Ϫ
Ϫ
V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A. Von
Zelewsky, Coord. Chem. Rev., 1988, 84, 85; E. C. Constable, Adv.
Inorg. Chem., 1989, 34, 1; Prog. Inorg. Chem., 1994, 42, 67.
[Ru (bpy )(bpy )(L )]
(3)
The comparison between the first reduction potential values
shows that the non-substituted ligand L in the complex is
easier to reduce than the substituted one (by about 100 mV).
Consequently, the π* antibonding orbital (LUMO) of L is that
of lowest energy. This result is in agreement with those obtained
for the “free” ligand. The ZINDO calculated levels of the
orbitals for the “free” ligands in their trans conformations
are correlated with the electrochemical data. The difference
5
6
7
Y. Kawanishi, N. Kitamura and S. Tazuke, Inorg. Chem., 1989, 28,
1
2
968; F. Casalboni, Q. G. Mulazzani, C. D. Clark, M. Z. Hoffman,
P. L. Orizondo, M. W. Perkovic and D. P. Rillema, Inorg. Chem.,
1997, 36, 2252.
1
(a) E. Bejan, H. Aït-Haddou, J.-C. Daran and G. G. A. Balavoine,
Synthesis, 1996, 1012; (b) E. Amouyal, F. Penaud-Berruyer,
D. Azhari, H. Aït-Haddou, C. Fontenas, E. Bejan, J.-C. Daran and
G. A. A. Balavoine, New J. Chem., 1998, 22, 373.
I. Sasaki, M. Imberdis, A. Gaudemer, B. Drahi, D. Azhari and
E. Amouyal, New J. Chem., 1994, 18, 759; D. Esposito, G. Del
Vecchio and G. Barone, J. Am. Chem. Soc., 1997, 119, 2606 and refs.
therein; R. H. Terbrueggen, T. W. Johann and J. K. Barton, Inorg.
Chem., 1998, 37, 6874.
A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, SIR 92, a program for auto-
matic solution of crystal structures by direct methods, J. Appl.
Crystallogr., 1994, 27, 435.
∆
E1/2 between the oxidation potential Eox and the first reduction
Ered1 of the heteroleptic complexes is correlated with the differ-
ence between the HOMO and LUMO energy, i.e. to the energy
at the maximum of the absorption band located in the visible
region. This result reinforces the attribution of this band mainly
to the transition S → MLCT(L). Thus, the optical and
redox orbitals are of similar nature, and the MLCT excited
state of the heteroleptic complexes [Ru(bpy) (L)] corresponds
essentially to the Ru→L transition.
8
1
0
2ϩ
9 G. M. Sheldrick, SHELXL 97, program for crystal structure
refinement, University of Göttingen, 1997.
0 D. J. Watkin, C. K. Prout and L. J. Pearce, CAMERON, Chemical
Crystallography Laboratory, University of Oxford, Oxford, 1996.
1 A. D. Bacon and M. C. Zerner, Theor. Chim. Acta, 1979, 53, 21.
2 W. P. Anderson, T. R. Cundari and M. C. Zerner, Int. J. Quantum
Chem., 1991, 39, 31.
13 R. F. Abdulla and R. V. Brinkmeyer, Tetrahedron , 1979, 35, 1675.
4 B. Imperiali and S.L. Fisher, J. Am. Chem. Soc., 1991, 113, 8527;
B. Imperiali, T. J. Prins and S. T. Fisher, J. Org. Chem., 1993, 58,
2
1
In summary, we have prepared, characterized and studied
the spectroscopic and electrochemical properties of 4-(2-
pyridyl)pyrimidine asymmetric ligands (L) and their hetero-
1
1
2
ϩ
leptic ruthenium() complexes [Ru(bpy) (L)] . The presence
2
of amine and/or amino acid functions on the 4-(2-pyridyl)-
pyrimidine ligand makes the corresponding complexes
interesting candidates for immobilization on solid supports
or incorporation into dendrimers. It is interesting that ligand L
which is a functionalized amino acid with metal-binding sites
provides new opportunities for the construction of synthetic
peptides. The synthesis of such new peptides containing L or
its corresponding complex [Ru(bpy) (L )] is currently under
investigation.
1
1
1
1
613; M. R. Ghadiri, C. Soares and C. Choi, J. Am. Chem. Soc.,
992, 114, 825; S. R. Wilson, A. Yasmin and Y. Wu, J. Org. Chem.,
992, 57, 6941; P. R. Cheng, S. L. Fisher and B. Imperiali, J. Am.
5
Chem. Soc., 1996, 118, 11349.
5
15 E. Bejan, H. Aït-Haddou, J.-C. Daran and G. G. A. Balavoine,
Eur. J. Org. Chem., 1998, 2907.
5
2ϩ
2
1
1
1
6 S. T. Howard, J. Am. Chem. Soc., 1996, 118, 10268.
7 S. J. Milder, Inorg. Chem., 1989, 28, 868.
8 J. N. Spencer, S. W. Barton, K. A. Smith, W. S. Wolbach, J. F. Powell,
M. R. Kirschenbaum and D. W. Firth, Can. J. Chem., 1982, 61, 194.
9 R. P. Thummel and F. Lefoulon, Inorg. Chem., 1987, 26, 675.
Acknowledgements
1
F. B.-P., L. B. and E. A. are indebted to Dr B. Levy for very
helpful discussions and valuable suggestions regarding the
theoretical calculations. Financial support from the Centre
National de la Recherche Scientifique and for a doctoral
fellowship (E. B.) from the “Ministère des Affaires Etrangères”
are gratefully acknowledged.
20 D. P. Rillema, D. G. Taghdiri, D. S. Jones, C. D. Keller, L. A. Worl,
T. J. Meyer and H. A. Levy, Inorg. Chem., 1987, 26, 578; H. Ichida,
S. Tachiyashiki and Y. Sasaki, Chem. Lett., Chem. Soc. Jpn.,
1
990, 63, 1299; E. Kimura, S. Wada, M. Shionoya, T. Takahashi and
Y. Iitaka, J. Chem. Soc., Chem. Commun., 1990, 397; R. Chotalia,
E. C. Constable, M. J. Hannon and D. A. Tocher, J. Chem. Soc.,
Dalton Trans., 1995, 3571; D. A. Bardwell, F. Barigelletti, R. L.
Cleary, L. Flamigni, M. Guardigli, J. C. Jeffery and M. D. Ward,
Inorg. Chem., 1995, 34, 2438.
References
2
1 G. Calzaferri and R. Rytz, J. Phys. Chem., 1995, 99, 12141; B. J.
Coe, D. W. Thompson, C. T. Culbertson, J. R. Schoonover and
T. J. Meyer, Inorg. Chem., 1995, 34, 3385.
1
E. Amouyal, Sol. Energy Mater. Sol. Cells, 1995, 38, 249; in
Homogeneous Photocatalysis, ed. M. Chanon, Wiley, Chichester,
2
2 R. P. Thummel, F. Lefoulon and J. D. Korp, Inorg. Chem., 1987, 26,
1
997, ch. 8, p. 263; A. Kay and M. Gratzel, Sol Energy Mater. Sol.
2
370.
Cells, 1996, 44, 99; R. Argazzi, C. A. Bignozzi, G. M. Hasselman
2
3 Y. Kawanishi, N. Kitamura, Y. Kim and S. Tazuke, Sci. Pap. Inst.
Phys. Chem. Res. (Jpn.), 1984, 78, 212; A. Vlcek, Chemtracts-Inorg.
Chem., 1991, 5, 2144.
and G. J. Meyer, Inorg. Chem., 1998, 37, 4533.
2
3
V. Balzani and F. Scandola, Supramolecular Photochemistry, Ellis
Horwood, New York, 1991; A. Hatzidimitriou, A. Gourdon, J.
Devillers, J. P. Launay, E. Mena and E. Amouyal, Inorg. Chem.,
1
996, 35, 2212.
J. K. Barton, A. T. Danishefksy and J. M. Goldberg, J. Am. Chem.
Soc., 1984, 106, 2172; J. Kelly, A. Tossi, D. McConnel and
C. OhUigin, Nucleic Acids Res., 1985, 13, 6017.
Paper 9/04617H
J. Chem. Soc., Dalton Trans., 1999, 3095–3101
3101