Synthesis, X-ray structures, spectroscopic and electrochemical properties of ruthenium(II) complexes containing 2,2'-bipyrimidine

Article abstract of DOI:10.1016/S0020-1693(00)00123-7

Ruthenium polypyridyl complexes containing 2,2'-bipyrimidine, [Ru(bpy)₂bpm](PF₆)₂ (I) and [Ru(phen)₂bpm](PF₆)₂ (II), were synthesized with high yield and purity. An extensive characterization was carried out using ESMS, UV-Vis, ¹H and ¹³C NMR, electrochemistry and X-ray single crystal diffraction analysis. The experimental results show that the spectroscopic and electrochemical properties of I and II are similar to those of their parent complexes [Ru(bpy)₃](PF₆)₂ and [Ru(phen)₃](PF₆)₂. This indicates that both I and II can be used as building blocks for the construction of molecular devices. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00123-7

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 305 (2000) 127–134
Synthesis, X-ray structures, spectroscopic and electrochemical
properties of ruthenium(II) complexes containing 2,2%-bipyrimidine
Zhiqin Ji, Songping D. Huang* 1, Ana R. Guadalupe* 2
Department of Chemistry, PO Box 23346, Uni6ersity of Puerto Rico, San Juan, PR 00931-3346, Puerto Rico
Received 15 September 1999; accepted 15 March 2000
Abstract
Ruthenium polypyridyl complexes containing 2,2%-bipyrimidine, [Ru(bpy)2bpm](PF6)2 (I) and [Ru(phen)2bpm](PF6)2 (II), were
1
synthesized with high yield and purity. An extensive characterization was carried out using ESMS, UV–Vis, H and 13C NMR,
electrochemistry and X-ray single crystal diffraction analysis. The experimental results show that the spectroscopic and
electrochemical properties of I and II are similar to those of their parent complexes [Ru(bpy)3](PF6)2 and [Ru(phen)3](PF6)2. This
indicates that both I and II can be used as building blocks for the construction of molecular devices. © 2000 Elsevier Science S.A.
All rights reserved.
Keywords: Crystal structures; Electrochemistry; Ruthenium complexes; Polypyridyl complexes
1. Introduction
integrated systems by judicial selection of mononuclear
building blocks and bridging ligands [21]. Our goal is to
construct Ru(II)–Rh(III) dyads and triads for pho-
toelectrochemical regeneration of nicotinamide adenine
dinucleotide (reduced form, NADH). One of the most
important steps in our approach is to obtain highly
pure and well-characterized building block complexes.
In this paper, we report the synthesis, purification,
structural and spectroscopic characterization of
[Ru(bpy)2bpm](PF6)2 (I) and [Ru(phen)2bpm](PF6)2 (II)
(where bpy=2,2%-bipyridine, phen=1,10-phenanthrol-
ine and bpm=2,2%-bipyrimidine).
Research in ruthenium polypyridyl complexes spans
from photochemistry to photophysics, photocatalysis
and electrochemistry. Because of their chemical stabil-
ity, facile electron transfer, strong luminescence emis-
sion and relatively long-lived excited states [1], such
compounds have potential applications in many areas
including non-radioactive DNA probes or therapeutic
agents [2–9], photoelectrocatalysis [10] and molecular
recognition [11–13], to name just a few. For the last 30
years, increased research attention has been placed on
the synthesis, photochemistry, photophysics and elec-
trochemistry of polypyridyl-based polynuclear metal
complexes [14–20]. This is mainly prompted by at-
tempts to design and construct multicomponent systems
as artificial photochemical molecular devices. Ligand-
bridged polymetallic complexes are particularly suitable
for the study of photoinduced energy and electron
transfer processes [14c,16–18]. Our group is interested
in synthesizing structurally organized and functionally
2. Experimental
2.1. Materials
RuCl3·3H2O, 2,2%-bipyridine (bpy, 99%), 1,10-
phenanthroline (phen, 99%), Ru(bpy)3Cl3·6H2O (98%)
and Ru(phen)3Cl3·6H2O (98%) were purchased from
Aldrich Chemical, Co. 2,2%-Bipyrimidine (bpm, 96%)
was obtained from Lancaster Synthesis. Tetra-n-buty-
lammonium perchlorate (TBAP) from GSF Chemical,
Inc. was purified by recrystallization in ethyl acetate.
Acetonitrile (ACN) from Burdick Jackson was dried
1 *Corresponding author. Present address: Department of Chem-
istry, Kent State University, Kent, OH 44242, USA. Tel.: +1-330-
672 2230; fax: +1-330-672 3816; e-mail: shuang1@kent.edu
2 *Corresponding author.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00123-7

128
Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
,
with 4-A molecular sieves. [Ru(bpy)3](PF6)2 and
[Ru(phen)3](PF6)2 were obtained by dissolving the cor-
responding chloride salt in methanol followed by pre-
cipitating with KPF6. Other chemicals for the
preparations were at least reagent grade and used
without further purification.
The crystals were collected and washed with water (20
ml), ethanol (20 ml), and finally ether. The compound
was dried under vacuum. A green–black product was
obtained in 69% yield.
2.3.1.3. [Ru(phen)2bpm](PF6)2. In a typical preparation,
Ru(phen)2Cl2·2H2O (600 mg, 1 mmol) was suspended
in 30 ml of degassed ethanol–water and refluxed un-
der nitrogen for 3 h to form a brown–red solution.
237 mg (1.5 mmol) of bpm was added and the reflux
continued for 3 h. The color of solution turned red–
orange. Afterwards, the complex was precipitated by
the addition of a saturated aqueous solution of KPF6
and collected by vacuum filtration. This material was
dissolved in 20 ml of acetone, filtered, and reprecipi-
tated by addition of 150 ml of anhydrous ether. The
yield of the crude product was 87%. The complex was
purified by column chromatography (50 cm×2.5 cm)
packed with neutral aluminum oxide using 1:1
CH2Cl2–acetonitrile as the eluent. An orange band
eluted first followed by a green band. A brown band
on the top of column never eluted. The orange band
was dried and the solid was dissolved in a minimum
acetone followed by precipitation with ether. A pure
orange powder was obtained. The yield of recovery
was 60%.
2.2. Instrumentation
Electron spray mass spectra (ESMS) were obtained
with a VG Quattro II spectrometer (Fisons Instru-
ments). UV–Vis spectra were recorded using
Hewlett–Packard 8452A diode array spectrophotome-
ter. NMR spectra were determined with a Bruker
Avance DRX-500. Electrochemical measurements
were carried out in a BAS-100B/W electroanalyzer.
Single-crystal X-ray diffraction data were collected on
a Bruker SMART CCD diffractometer with graphite
a
,
monochromated Mo Ka radiation (u=0.71069 A) op-
erating at 50 kV and 35 mA.
2.3. Procedures
2.3.1. Synthesis of complexes
2.3.1.1. cis-Ru(bpy)2Cl2. This compound was prepared
by a published method [22] with a modified purifica-
tion procedure. Commercial RuCl3·3H2O (2.61 g, 10
mmol), 2.2%-bipyridine (3.12 g, 20 mmol) and LiCl
(4.2 g, 100 mmol) were added in 25 ml degassed
DMF, and refluxed for 8 h with stirring. After the
solution was cooled to room temperature (r.t.), a mix-
ture of 200 ml 1:1 acetone–water was added. A
green–black microcrystalline solid was obtained by
filtration. The solid was added into 200 ml water and
stirred for 10 h at r.t. followed by filtration. The
product was then washed three times with 25-ml por-
tions of water and ether. The yield was 80% based on
the ruthenium salt.
2.3.1.4. [Ru(bpy)2bpm](PF6)2. This complex was syn-
thesized and purified by the same procedure described
above. The yields of the crude product and recovery
were 85.8 and 62%, respectively.
2.3.2. Characterization
The ESMS spectra were collected with 4.8 ml h−1
acetonitrile as the mobile phase. The samples were
dissolved in acetonitrile and a 30 ml solution was in-
jected into the electron spray ion source. The extrac-
tion cone voltage was 10 V. The mass spectrometer
scanned from m/z 0 to 2000. The UV–Vis spectra
1
were recorded in acetonitrile solution. 1D H and 13C
2.3.1.2. cis-Ru(phen)2Cl2. RuCl3·3H2O (3.92 g, 15
mmol), 1,10-phenanthroline monohydrate (5.95 g, 30
mmol) and LiCl (4.2 g,100 mmol) were refluxed in
degassed DMF (50 ml) for 8 h under stirring. The
reaction mixture was cooled to r.t. and poured into
250 ml of 10% of LiCl aqueous solution, stirred for
30 min and filtered to obtain a brown–black solid.
The solid was washed three times with 25-ml portions
of water and ether. The crude product was recrystal-
lized by suspending it in 300 ml of 1:1 water–ethanol
and refluxing the mixture until all solids had dissolved
to form a deep brown–red solution. This solution was
filtered while hot and evaporated down in the pres-
ence of lithium chloride (20 g) to remove all the alco-
hol. After 4 h at r.t., the cis-Ru(phen)2Cl2 complex
recrystallized leaving a yellow–green mother liquor.
NMR spectra and 2D 1H–13C and 1H–1H COSY
were measured in CH3CN-d3 solution and the residual
signal of the solvent was used as an internal standard.
Chemical shifts and coupling constants were obtained
from 1D NMR analysis. Signal assignments were
confirmed by 2D NMR analysis. Electrochemical
measurements were carried out in a one-compartment
cell with a glassy carbon, an Ag/AgCl and a Pt wire
as the working, reference and auxiliary electrodes, re-
spectively. All electrochemical experiments were car-
ried out in acetonitrile and 0.1 M TBAP. IR drop
compensations were carried out in all cyclic voltam-
metry experiments. Diffusion coefficients (D0) were
measured by chronocoulometry with the following
conditions:
mV, and pulse width=250 ms.
E E
initial=E0%−200 mV, final=E0%+200

Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
129
2.3.3. X-ray data collection, structure solution and
refinement
A single crystal of either I or II was selected from the
reaction product and mounted on a thin glass fiber
using epoxy cement. The data were collected at r.t.
using a narrow frame method with scan widths of 0.3°
in ꢀ and exposure times of 20 s. A hemisphere of
intensity data were collected in 1081 frames with the
crystal-to-detector distance of 50.4 mm, which corre-
sponds to a maximum 2q value of 54.1°. Frames were
integrated with the Bruker SAINT program [23]. A
semi-empirical absorption correction based upon simu-
lated „-scans was applied to the data set. Both struc-
tures were solved by a combination of direct methods
and difference Fourier methods, and refined with full-
matrix least-squares techniques. The calculations were
performed using the TEXSAN crystallographic software
package of Molecular Structure Corporation [24]. All
the non-hydrogen atoms were refined anisotropically.
The positions of the hydrogen atoms were calculated,
but not refined. Details of the data collection, structure
solution and refinement are given in Table 1. Final
atomic coordinates for the two structures are given in
the supporting information. The selected bond dis-
tances and bond angles for I and II are summarized in
Table 2.
Table 1
Data for crystal structure analysis of I and II
Compound
[Ru(bpy)2bpm]
[Ru(phen)2bpm]
(PF6)2 (I)
(PF6)2 (II)
Formula
C28H22F12N8P2Ru C32H22F12N8P2Ru
,
a (A)
37.256(2)
11.0605(7)
17.502(1)
90
113.317(1)
90
11.9428(9)
12.859(1)
14.649(1)
85.846(1)
79.742(1)
77.749(1)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Z
8
3
,
V (A )
6623.1(7)
C2/c (no. 15)
1.728
0.673
0.44×0.19×0.17
23
2161.8(3)
(
Space group
P1 (no. 2)
Dcalc. (g cm−3
)
1.397
v (Mo Ka) (mm−1
Crystal size (mm)
Temperature (°C)
)
0.520
0.22×0.09×0.07
25
No. of unique data
No. of data used
| Cut off
13 416
3127
I\3.00|(I)
0.893
1.00
83
8173
4054
I\3.00|(I)
0.902
1.00
3. Results and discussion
Tmin./max.
3.1. Synthesis and characterization
Absorption correction
No. of atoms per
asymmetric unit
(including H)
87
The synthesis of I was reported in the earlier publica-
tions. Dose et al. [25b] obtained 11% I and the dimer
with a ratio of Ru(bpy)2Cl2: bpm equal to 1:1. Rillema
et al. [26] reported a procedure that involved the substi-
tution of acetone for chlorine with AgPF6 in acetone,
then reacting with two- to four-fold excess of bridging
ligand. With the procedure presented here, both I and
II can be readily prepared via the ligand substitution
reaction between bpm and the corresponding starting
materials cis-Ru(bpy)2Cl2 or cis-Ru(phen)2Cl2. With a
proper stoichiometry (RuL2Cl2: bpm=1:1.5), the
monosubstituted compounds are highly favored. Com-
plex I was obtained with high yield and purity. On the
other hand, to the best of our knowledge, the synthesis
of complex II has not been reported in the literature. It
should be noted that both I and II are chiral molecules,
the compounds were obtained as racemates with this
presented procedure. But the enantiomerically pure
compounds could be obtained by chiral resolution.
Although UV–Vis and some electrochemical data of I
were reported [25–35], some other important features
including MS spectra, single crystal X-ray structures,
NMR spectra and the electrochemical diffusion coeffi-
cient have not been published.
Max./min. peaks in final 0.87/−0.60
1.33/−0.78
−3
,
difference map (e A
Final R/Rw (%)
)
0.052/0.065
0.071/0.106
2.08
Goodness-of-fit
1.52
Table 2
,
Selected bond distances (A) and bond angles (°) for I and II
Compound I
RuꢀN(1)
RuꢀN(3)
RuꢀN(5)
N(3)ꢀC(11)
N(7)ꢀC(27)
C(11)ꢀC(12)
2.041(6)
2.066(7)
2.061(6)
1.35(1)
1.328(9)
1.36(1)
RuꢀN(2)
RuꢀN(4)
RuꢀN(6)
N(4)ꢀC(20)
N(8)ꢀC(28)
C(12)ꢀC(13)
2.064(6)
2.064(7)
2.062(6)
1.36(1)
1.33(1)
1.39(2)
N(1)ꢀRuꢀN(2)
N(5)ꢀRuꢀN(6)
N(1)ꢀRuꢀN(6)
78.8(3)
78.6(3)
174.8(3)
N(3)ꢀRuꢀN(4)
N(1)ꢀRuꢀN(3)
79.1(3)
86.7(2)
Compound II
RuꢀN(1)
RuꢀN(3)
2.086(9)
2.065(9)
2.072(9)
1.38(2)
1.32(2)
1.38(2)
RuꢀN(2)
RuꢀN(4)
RuꢀN(6)
N(4)ꢀC(24)
N(8)ꢀC(28)
C(14)ꢀC(15)
2.069(9)
2.04(1)
2.068(9)
1.37(2)
1.32(2)
1.39(2)
RuꢀN(5)
N(3)ꢀC(13)
N(7)ꢀC(27)
C(13)ꢀC(14)
Electrospray mass spectrometry (ESMS) has recently
been shown to be a powerful tool for measuring the
molecular masses of non-volatile and thermally un-
stable compounds. The soft ionization of ESMS yields
N(1)ꢀRuꢀN(2)
N(5)ꢀRuꢀN(6)
N(1)ꢀRuꢀN(6)
79.9(4)
78.5(4)
174.3(4)
N(3)ꢀRuꢀN(4)
N(1)ꢀRuꢀN(3)
78.3(4)
94.4(4)

130
Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
Table 3
Electrochemical and spectroscopic characterization of ruthenium complexes a
Complex
ESMS
Electrochemical parameters
Expected
molecular weight
m/z (assignment)
D09s×105
(cm2 s−1
Ru-based redox
Ligand-based redox
)
E0%(DEp) (mV)
E0%(DEp) (mV)
[Ru(bpy)2bpm](PF6)2
[Ru(phen)2bpm](PF6)2
861.5
909.6
717.2
2.3190.13
1436(58)
−971(74)
−1414(74)
−1644(59)
([M−PF6−])
286.1
([M−2PF6− 2+
]
)
765.32
2.0390.05
1433(60)
−992(61)
−1402(81)
−1638(93)
([M−PF6−])
310.1
([M−2PF6− 2+
]
)
[Ru(bpy)3](PF6)2
[Ru(phen)3](PF6)2
2.1090.05
2.1990.07
1316(59)
1322(60)
−1295(58)
−1481(60)
−1730(59)
a E0% (mV)=(Epc+Epa)/2, where Epc and Epa are the peak cathodic and peak anodic potentials, respectively. DEp (mV)=ꢀEpa−Epcꢀ. D0 values
were measured by chronocoulometry using the following conditions: Ei=E0%−200 mV, Ef=E0%+200 mV and pulse width=250 ms. s is the
standard deviation of the measurements.
a simple mass pattern that allows determination of
molecular mass accurately [36]. ESMS data for both
complex I and II recorded at low cone voltage (10 V)
ppm. Two sets of protons in the phen ring (i.e. protons
a, b, c and a%, b%, c%) were observed due to the relative
degree of the diamagnetic anisotropy effect from adja-
cent aromatic rings as shown in Scheme 1. From the
X-ray structure analysis (vide infra), it can be seen that
protons a, b and c are close to the bridging ligand bpm,
while a%, b% and c% are close to the another phen ring.
Since phen has three aromatic rings while bpm has only
two, a stronger shielding effect on protons a%, b% and c%
is expected. Therefore, protons a, b and c were assigned
to the downfield signals while a%, b% and c% are assigned
to the upfield signals. The 13C NMR signal assignments
are given in Table 3. The signals of [MꢀPF6− +
]
and
[Mꢀ2PF6− 2+
]
were observed, no other fragments were
detected under our experimental conditions. The mea-
sured molecular weights were consistent with expected
values. The UV–Vis spectra of the complexes are
shown in Fig. 1. The spectrum of the complex,
[Ru(bpy)2bpm]2+ (curve a), is very similar to that of
[Ru(bpy)3]2+(curve b). According to literature, the ad-
sorption at 422 nm is assigned to MLCT [25–27], the
strong absorptions at 246 and 286 nm are assigned to
ligand-centered p–p transitions [26,27]. The spectrum
of [Ru(phen)2bpm]2+(curve c), is similar to that of its
parent compound [Ru(phen)3]2+(curve d). The strong
absorptions in the UV region are also ligand-centered
p–p transitions as expected from the ligand absorp-
tions. The absorption in the visible region is a MLCT
transition as observed in ruthenium polypyridyl com-
plexes [1].
1
were based on the H-13COSY spectra. The same argu-
ment was used in the assignment of the NMR spectrum
NMR data are given in Table 4. The assignments of
signals were based on the 2D COSY spectra (Figs. 2
and 3). For example, in the complex II (see Fig. 2), the
protons in the bpm ring (H4, H5 and H6) could be
easily recognized by their coupling constants, while the
H4 and H6 assignments were made in comparison with
the NMR data of the free ligand bpm. In the free
ligand bpm, H4 and H6 have an identical chemical shift
of 8.94 ppm. However, in the metal complex, two
different signals for H4 and H6 were observed, i.e. H6
is shifted upfield to 7.96 ppm because this proton is
closer to the coordination center, while H4 is far away
from the coordination center and is less affected. Ac-
cordingly, its chemical shift changed slightly to 9.06
Fig. 1. UV–Vis spectra of the ruthenium complexes in acetonitrile
(5×10−4 M): (a) [Ru(bpy)2bpm](PF6)2; (b) [Ru(bpy)3](PF6)2; (c)
[Ru(phen)2bpm](PF6)2 (d) [Ru(phen)3](PF6)2.

Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
131
Table 4
NMR data of the ligands and complex I and II
Compound
1H (ppm)
13C (ppm)
2,2%-Bipyridine (CH3CN-d6)
8.64 (d, Ha, J=4.1, 2H)
8.40 (d, Hd, J=7.9, 2H)
7.85 (dt, Hc, J=7.9, 1.4, 2H)
7.35 (dd, Hb, J=7.9, 4.1, 2H)
156.9 (Ce), 150.2 (Ca)
138.0 (Cc), 124.9 (Cb)
121.6 (Cd)
1,10-Phenathroline (CH3CN-d6)
9.05 (dd, Ha, J=4.2,1.4, 2H)
8.27 (dd, Hc, J=8.0,1.4, 2H)
7.77 (s, Hf, 2H)
150.8 (Ca), 146.9 (Ce)
136.9 (Cc), 129.7 (Cd)
127.5 (Cf), 124.1 (Cb)
7.61 (dd, Hb, J=8.0, 4.2, 2H)
2,2%-Bipyrimidine (CH3CN-d3)
8.94 (d, 4H, H6, H4, J=4.8)
7.50 (t, 2H, H5, J=4.8)
164.1 (C2), 158.9 (C6, C4)
124.4 (C5)
[Ru(phen)2bpm](PF6)2 (CH3CN-d3)
bpm ring:
9.06 (dd, H4, J=4.8, 1.9, 2H)
7.96 (dd,H6, J=5.6,1.9, 2H)
7.39 (t, H5, J=5.2, 2H)
164.4 (C2), 161.1 (C6)
159.0 (C4), 124.9 (C5)
phen ring:
8.69 (dd, Hc, J=8.2, 0.8, 2H)
8.56 (dd, Hc%, J=8.2, 0.8, 2H)
8.35 (dd, Ha, J=5.2, 0.8,2H)
7.86 (dd, Ha%, J=5.2, 0.8,2H)
7.82 (dd, Hb, J=5.2, 8.2, 2H)
7.56 (dd, Hb%, J=5.2, 8.2, 2H)
8.24 (ABq Hf%, Hf, J=8.9, 4H)
154.6 (Ca), 153.9 (Ca%),
148.6 (Ce), 148.4 (Ce%),
138.3 (Cc), 138.1 (Cc%),
132.1 (Cd), 132.0 (Cd%),
129.1 (Cf, Cf%%),
127.1 (Cb), 126.9 (Cb%)
[Ru(bpy)2bpm](PF6)2 (CH3CN-d3)
bpm ring:
9.08 (dd, H4, J=4.8, 1.9, 2H)
8.02 (dd, H6, J=5.6, 1.9, 2H)
7.50 (dd, H5, J=5.6, 4.8, 2H)
164.1 (C2), 160.5 (C6)
159.1 (C4), 125.3 (C5)
bpy ring:
8.49 (dd, Hd, Hd%, J=8.2, 4H)
8.08 (dd, Hc, J=8.2, 7.1, 2H)
8.06 (dd, Hc%, J=8.2, 7.1, 2H)
7.86, (d, Ha, J=5.6, 2H)
157.9 (Ce), 157.7 (Ce%),
153.3 (Ca), 152.8 (Ca%),
139.3 (Cc), 139.2 (Cc%),
128.8 (Cb), 128.7 (Cb%),
125.4 (Cd), 125.1 (Cd%)
7.68 (d, Ha%, J=5.6, 2H)
7.42 (ddd, Hb, J=7.1, 5.6, 1.1, 2H)
7.40 (ddd, Hb%, J=7.1, 5.6, 1.1, 2H)
of [Ru(bpy)2bpm]2+ (Fig. 3). However, only Ha and
Ha% were resolved clearly while Hc and Hc%, Hd and
Hd% overlapped. This could be explained considering
that both bpy and bpm have two aromatic rings; conse-
quently, a slight difference in the shielding effect is
expected.
versus ln 6 were linear with a slope of 0.5. These results
indicate that the Ru(III)/Ru(II) redox process of the
four complexes is a reversible, one-electron transfer and
diffusion-controlled redox process. The fact that the E0%
of I and II shifted to the more positive potentials
compared to their parent complexes suggests that the
p-acceptor ability of the bpm ligand is stronger than
bpy and phen. The ligand-based redox of all complexes
occurred at negative potentials. The first redox with E0%
of −971 and −992 mV for both I and II, respectively,
is assigned to the reduction of bpm ligand. The assign-
ment of ligand reduction is consistent with prior publi-
cation [28a,b]. It is also supported by our two
observations. First, the reduction potentials of the free
ligands bpm, bpy and phen are −1837, −2187 and
−2045 mV, respectively. This indicates that bpm is
easier to reduce than bpy and phen. Second, the redox
at −971 and −992 mV were observed in both I and
II, respectively, but not in their parent complexes
3.2. Electrochemistry
The redox formal potential (E0%), peak potential sepa-
ration (DEp) and diffusion coefficient (D0) for the com-
plexes I, II, and their parent complexes [Ru(bpy)3]2+
and [Ru(phen)3]2+ are given in Table 3. The cyclic
voltammetry data showed that all the complexes had a
Ru-centered redox process at positive potentials, which
are similar to other ruthenium polypyridyl complexes
[1] and consistent with published results [1,25b,26,27].
The E0% and DEp (59–62 mV) values were independent
of the sweep rate from 50 to 1000 mV s−1. Plots of ln ip

132
Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
[Ru(bpy)3]2+ and [Ru(phen)3]2+. The diffusion coeffi-
cients (D0) were measured by chronocoulometry and
calculated from the slope of the Anson plot [37]. The
D0 values of all four complexes are very similar as
expected for a homogeneous solution.
3.3. X-ray structures
The crystal lattice of both I and II is made up of well
separated PF6− anions and [Ru(bpy)2bpm]2+ or
[Ru(phen)2bpm]2+ cations. In the unit cell of II, one of
Fig. 3. 1H–1H COSY spectrum and assignments of
[Ru(bpy)2bpm](PF6)2 in CH3CN-d3. (b) 1H-13C COSY spectrum and
assignments of [Ru(bpy)2bpm](PF6)2 in CH3CN-d3.
the PF6− anions is disordered over two different sites
for each atom in the anion. The structure refinement of
II was thus based on a model including such a disor-
dered anion, and converged at R=0.071 and Rw=
0.106. Otherwise, the PF6− anions appear to have the
normal structure, and warrant no further comment.
Both [Ru(bpy)2bpm]2+ and [Ru(phen)2bpm]2+ cations
are situated in general positions with no crystallograph-
ically imposed symmetry. Each complex cation features
distorted octahedral coordination around the Ru atom.
Fig. 4 gives ORTEP representations of both complex
cations. The six RuꢀN bond distances in the
Fig. 2. 1H–1H COSY spectrum and assignments of
[Ru(phen)2bpm](PF6)2 in CH3CN-d3. (b)1H–13C COSY spectrum and
assignments of [Ru(phen)2bpm](PF6)2 in CH3CN-d3.

Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
133
[Ru(bpy)2bpm]2+ cation are rather uniform, i.e. ex-
,
cept the shorter RuꢀN1 at 2.041(6) A, five other
RuꢀN bond distances are close to each other and
,
average 2.063(3) A. However, the NꢀRuꢀN bond an-
gles in this structure are all deviated from either 90
or 180°. The N7 and N8 atoms in the structure were
unambiguously assigned based on the typical CꢀN
,
bond distance of approximately 1.33 A as compared
with the typical CꢀC bond distance of approximately
,
1.37 A. On the other hand, both the bond distances
and bond angles in the [Ru(phen)2bpm]2+ cation are
comparable to those found in the [Ru(bpy)2bpm]2+
cation, but they have a greater disparity. For exam-
ple, the RuꢀN bond distances range from 2.04(1) to
,
2.086(9) A, and the NꢀRuꢀN bond angles fluctuate
from 78.3(4) to 96.6(4)° or from 170.7(4) to 174.3(4)°.
This may reflect the different coordination properties
of the N donors in the phen and bpm rings.
4. Conclusions
Two polypyridyl-based ruthenium complexes con-
taining the bridging ligand 2,2%-bipyrimidine have
been synthesized by ligand substitution reactions with
high yield and purity. The X-ray structures, thorough
NMR examination and diffusion coefficients of com-
plex I and II are reported for the first time. The
comparison of I and II have been done. Complex I
and II have very similar properties including MLCT
transitions, reversible metal and ligand-centered redox
characteristics, and diffusion coefficients. Thus, it is
possible to utilize these two ruthenium complexes as
building blocks to construct functional molecular
devices. The work on the Ru(II)ꢀRh(III) dyads
and triads containing the [Ru(bpy)2bpm]2+ or
[Ru(phen)2bpm]2+ species for the photoelectrochemi-
Fig. 4. (a) ORTEP representation of the [Ru(bpy)2bpm]2+ cation. (b)
ORTEP representation of the [Ru(phen)2bpm]2+ cation.
cal NADH regeneration is in progress and will be
published in due course.
5. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 144163 (complex I) and
144164 (complex II). Copies of this information may be
obtained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Scheme 1. Structures of the ligands and their ruthenium complexes.

134
Z. Ji et al. / Inorganica Chimica Acta 305 (2000) 127–134
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(grant no. FC0291ER75674). We also thank Mr Jose´
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