Synthesis and characterisation of a series of mononuclear ruthenium(II) carbonyl complexes of heterocycle-based asymmetric bidentate ligands

Article abstract of DOI:10.1016/j.ica.2005.03.050

In this contribution, the synthesis and characterisation of a series of complexes of the type [Ru(L-L′)(CO)₂Cl₂] are reported, where L-L′ are the chelating ligands L1-L8, 2-(4H-[1,2,4] triazol-3′-yl)-pyridine (L1); 2-(4H-[1,2,4]triazol-3′-yl)-pyrazine; (L2); 2-(1-methyl-4H-[1,2,4]-triazol-3-yl)pyridine (L3); 2-(5-pyridin-2-yl-4H- [1,2,4]-triazole-3-yl)phenol (L4); 3-(5-methylphenyl)-pyridin-2-yl-1,2,4- triazole (L5); 3-(4-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L6); 3-(4-methoxyphenyl)-pyridin-2-yl-1,2,4-triazole (L7); 3,6-bis[(4-methoxyphenyl) iminomethyl]pyridazine (L8). L1-L7 are triazole-based ligands, which provide two distinct bidentate coordinate modes (via N2 or N4 of the triazole) whereas L8 is pyridazine-based and contains two identical bidentate binding pockets. The products obtained are analysed using infrared and NMR spectroscopy. The X-ray and molecular structures of the complexes with the ligands L2, L6, L7 and L8 are reported. These structures are the first to be reported for triazole based ruthenium chloro and ruthenium pyridazine imine complexes. The data show that the triazole ring in L2, L6 and L7 is coordinated via the N2 atom, and that the pyridazine-based ligand L8 uses only one binding pocket hence accommodating only one ruthenium(II) centre. For all compounds the cis(CO)transCl conformation is obtained. The results obtained are compared with those obtained for other similar compounds.

Full text of DOI:10.1016/j.ica.2005.03.050

Inorganica Chimica Acta 359 (2006) 736–744
www.elsevier.com/locate/ica
Synthesis and characterisation of a series of
mononuclear ruthenium(II) carbonyl complexes of
heterocycle-based asymmetric bidentate ligands
Declan Mulhern , Yanhua Lan , Sally Brooker ,b, John F. Gallagher , Helmar Gorls ,
a
b
c
d
*
¨
d
Sven Rau , Johannes G. Vos
a,
*
a
National Centre for Sensor Research, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
b
Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand
c
National Institute for Cellular Biotechnology, School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
d
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-University, 07743 Jena, Germany
Received 21 December 2004; accepted 26 March 2005
Available online 23 May 2005
Ruthenium and Osmium Chemistry Topical Issue.
Abstract
In this contribution, the synthesis and characterisation of a series of complexes of the type [Ru(L–L0)(CO)2Cl2] are reported,
where L–L0 are the chelating ligands L1–L8, 2-(4H-[1,2,4]triazol-30-yl)-pyridine (L1); 2-(4H-[1,2,4]triazol-30-yl)-pyrazine; (L2); 2-
(1-methyl-4H-[1,2,4]-triazol-3-yl)pyridine (L3); 2-(5-pyridin-2-yl-4H-[1,2,4]-triazole-3-yl)phenol (L4); 3-(5-methylphenyl)-pyridin-
2-yl-1,2,4-triazole (L5); 3-(4-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L6); 3-(4-methoxyphenyl)-pyridin-2-yl-1,2,4-triazole (L7);
3,6-bis[(4-methoxyphenyl)iminomethyl]pyridazine (L8). L1–L7 are triazole-based ligands, which provide two distinct bidentate
coordinate modes (via N2 or N4 of the triazole) whereas L8 is pyridazine-based and contains two identical bidentate binding pock-
ets. The products obtained are analysed using infrared and NMR spectroscopy. The X-ray and molecular structures of the com-
plexes with the ligands L2, L6, L7 and L8 are reported. These structures are the first to be reported for triazole based
ruthenium chloro and ruthenium pyridazine imine complexes. The data show that the triazole ring in L2, L6 and L7 is coordinated
via the N2 atom, and that the pyridazine-based ligand L8 uses only one binding pocket hence accommodating only one ruthe-
nium(II) centre. For all compounds the cis(CO)transCl conformation is obtained. The results obtained are compared with those
obtained for other similar compounds.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Carbonyl; Isomers; X-ray
1. Introduction
clear metal complexes of metals from the 1st, 2nd
and 3rd row transition metals. Many of the com-
pounds based on first row transition metals show
interesting magnetic properties, while in ruthenium
and osmium polypyridyl complexes the photophysical
properties of both mononuclear and dinuclear com-
pounds have been studied in detail [3]. Of particular
interest in these latter studies are complexes based
on pyridyl- and pyrazyltriazole type ligands. These
There is at present a considerable interest in transi-
tion metal complexes based on triazole containing
complexes [1,2]. Ligands based on this moiety are
ideal building blocks for the preparation of multinu-
*
Corresponding author. Tel.: +353 1 7005307; fax: +353 1 7005503.
E-mail addresses: sbrooker@alkali.otago.ac.nz (S. Brooker), Sven.
Rau@uni-jena.de (S. Rau), han.vos@dcu.ie (J.G. Vos).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.03.050

D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
737
H
studies have shown that both the coordination mode
H
N
N
N
of the triazole ring and its protonation are important
parameters, which control, the photophysical and
electrochemical properties of the compounds. It is ob-
served that in compounds of the type [Ru(bpy)2(L–
L0)]+ [4] the coordination mode of the ligands is
dependent on the substitution pattern at the ring.
For unsubstituted triazole ligands such as L1 and
L2, a 50:50 mixture of the N2 and N4 isomers is ob-
tained (see Fig. 1), while in the presence of a methyl
or an other substituent at the C5 position only the
sterically favoured N2 coordination is obtained [5].
However, for the analogous Rh(III) complexes
[Rh(bpy)2(L–L0)]2+ only one isomer, most likely the
N2 bound isomer is obtained. It seems likely that in
the latter type of compound electronic rather than ste-
ric considerations determine the binding mode of the
ligands [6]. In the present contribution, we
report on the reaction of a number of pyridyl and
pyrazyltriazole type ligands L1–L7: 2-(4H-[1,2,4]tria-
zol-30-yl)-pyridine (L1); 2-(4H-[1,2,4]triazol-30-yl)-pyra-
zine (L2); 2-(1-methyl-4H-[1,2,4]-triazol-3-yl)pyridine
(L3); 2-(5-pyridin-2-yl-4H-[1,2,4]-triazole-3-yl)phenol (L4);
3-(5-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L5); 3-
(4-methylphenyl)-pyridin-2-yl-1,2,4-triazole (L6); 3-(4-
methoxyphenyl)-pyridin-2-yl-1,2,4-triazole (L7) with
the precursor [RuII(CO)2Cl2]n. Of main interest in
these studies is the manner in which the triazole ring
is coordinated in the absence of any steric hindrance.
The reaction with the related pyridazine-based ligand
3,6-bis[(4-methoxyphenyl)iminomethyl]pyridazine (L8)
is also reported as this ligand [7] and related ligands
[2b] have also been proven to generate complexes with
a range of interesting structures and properties. For li-
gand structures see Fig. 2.
N
N
N
N
N
N
N
N
N
N
L1
L3
L2
L4
N
H
N
N
OH
N
Me
Me
H
N
H
Me
N
N
N
N
N
N
N
N
N
N
L5
L7
OMe
L6
H
N
N
MeO
N
N
N
N
OMe
N
L8
Fig. 2. Ligand structures.
and for the reduction of CO2 [9]. There are well-defined
synthetic methods for the preparation on these com-
pounds [10–13]. In a typical experiment, 1 mmol of
[RuII(CO)2Cl2]n was refluxed with 1.3 mmol of L1–L7
in MeOH (40 mL) for 2 h. The appearance of a precip-
itate meant that it was filtered hot and washed with
MeOH and dried in vacuo: if a precipitate did not ap-
pear, the solution was reduced to 5 mL, filtered, and 2
drops conc. HCl added. The solution was then placed
in a freezer overnight and the resulting precipitate of
[Ru(Lx)(CO)2Cl2] filtered. Satisfactory elemental analy-
ses were obtained for all compounds. Crystals of these
triazole-based complexes suitable for X-ray diffraction
studies were obtained by dissolving [Ru(CO)2Cl2]n
and L in separate aliquots of boiling MeOH, filtered,
mixed and allowed to stand overnight. The resultant
crystals were collected by filtration, washed with cold
MeOH and dried under vacuum. Elemental analysis
shows that for all of these compounds the triazole ring
is protonated. This is contrary to the results obtained
for the [Ru(bpy)2(L–L0)]+ type compounds, where
deprotonation of the triazole ring takes place spontane-
ously upon coordination [4]. Crystals of the analogous
pyridazine-based complex [RuII(L8)(CO)2Cl2] were
successfully grown by allowing a dilute 1:1 solution
of L8 and [RuII(CO)2Cl2]n in MeOH to react slowly
at room temperature. Attempts to occupy both binding
sites of L8 with metal centres, by adding either a
second equivalent of [RuII(CO)2Cl2]n, or an equivalent
of [CuI(CH3CN)4]PF6, failed. The crystals were analyt-
ically pure.
2. Results and discussion
2.1. Synthesis
For the last number of years there has been a
considerable interest in the synthesis and properties
of complexes of the type [RuII(L–L)(CO)2Cl2] and
[RuII(L–L)2(CO)2]2+. The compounds have been pro-
posed as intermediates for the synthesis of heteroleptic
ruthenium polypyridyl complexes [8] and several have
shown promising behaviour as water-gas-shift reagents
2.1.1. Spectroscopic characterisation
The spectroscopic data are listed in the experimental
part. 1H NMR spectra show only one set of signals indi-
cating the formation of only one main product. The
NMR data do however not allow for the determination
of the particular isomer obtained. The infrared spectra
show the presence of two CO stretching vibrations,
which indicates that the CO ligands are in a cis arrange-
ment. Since the chloro atoms can be trans or cis one may
N4
R
N2
N1
R
N
N
N1 N2
N4
M
M
N2 isomer
N4 isomer
Fig. 1. N2 and N4 isomers of pyridyltriazoles.

738
D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
expect to find four isomers two with a cis(CO)transCl
arrangement with either the triazole ring coordinated
via the N2 or the N4 atom of the triazole ring and
two equivalent cis(CO)cisCl isomers. It has been shown
before [9c,14] that the carbonyl stretching frequencies
for these types of isomers are not significantly different
therefore X-ray analysis was carried out (see Table 1).
In contrast to the large volume of literature relating
to first row transition metal complexes of triazole or
pyrazine containing ligands, relatively little attention
has been given to the structures of ruthenium com-
plexes of such ligands. To date, no structurally charac-
terised triazole-based ruthenium chloro complexes and
only six structurally characterised pyrazine-based
ruthenium(II) dichloro complexes (CSD codes BAM-
KIK, BAMKOQ, BAMKUW, MOLWEP, XOHTOD
and XOHTUJ) [15] have been reported (CSD search
version 5.25 [16]). The Ru–Npyrazine distance observed
for those six complexes lies in the range 2.043–
2.1.2. Single crystal X-ray analysis
The molecular structures of four of these eight mono-
nuclear compounds [Ru(Lx)(CO)2Cl2], specifically the
complexes of ligands L2, L6, L7 and L8, were investi-
gated by X-ray crystallography (Fig. 3, Table 2). The
single ruthenium(II) ion in each of these structures is
in a slightly distorted octahedral environment, in which
the donor atoms are provided by two nitrogen atoms
from the heterocycle-based asymmetric bidentate ligand
Lx, two carbon atoms from the two carbonyl groups
and two chloride ions. In all four complexes the CO
co-ligands are mutually cis, as anticipated from the
infrared spectroscopy, and the chloride co-ligands are
mutually trans. The major features of the three tria-
zole-based compounds are that the triazole ring is pro-
tonated and that the N2 atom of the triazole ring is
coordinated to the metal centre. In all three of these
compounds the proton is placed on the N4 atom. In
the case of the pyridazine-based compound [Ru(L8)-
(CO)2Cl2], only one of the two otherwise identical biden-
tate binding pockets accommodates a ruthenium(II) ion.
˚
˚
2.151 A with an average Ru–Npyrazine of 2.101 A [15].
In the mononuclear ruthenium(II) complexes of our
triazole and pyrazine-containing ligands, L2, L6 and
L7, the Ru–Npyrazine distances [2.150(3), 2.163(2) and
˚
2.143(2) A, respectively], are at the high end of this
range or in the case of [RuII(L6)(CO)2(Cl)2] it is
slightly longer than the previous maximum value. Con-
sistent with this the Ru–Ntriazole bond lengths are
shorter than the Ru–Npyrazine bond lengths, by 0.05,
˚
0.05 and 0.03 A for the complexes of L2, L6 and L7,
respectively. The Ru–Cl distance observed for the six
˚
literature complexes lies in the range 2.340–2.401 A
˚
and the average Ru–Cl distance is 2.379 A [15] The
Ru–Cl bond lengths observed in the three triazole com-
plexes fall within this range. These are the first triazole
based ruthenium chloro complexes to be structurally
characterised.
Table 1
Crystallographic data for [Ru(L)(CO)2Cl2]
[Ru(L2)(CO)2Cl2]
[Ru(L6)(CO)2Cl2]
[Ru(L7)(CO)2Cl2]
[Ru(L8)(CO)2Cl2]
Chemical formula
Fw
C8H5Cl2N5O2Ru
407.18
yellow
C16H15Cl2N5O3Ru
497.30
yellow
C15H11Cl2N5O3Ru
481.26
yellow
C22H18Cl2N4O4Ru
574.37
red
Colour
Crystal system
Temperature (K)
Crystal size (mm)
Unit cell dimensions
triclinic
183(2)
monoclinic
296(2)
monoclinic
294(2)
triclinic
168(2)
0.03 · 0.03 · 0.02
0.48 · 0.18 · 0.16
0.45 · 0.20 · 0.08
0.35 · 0.11 · 0.06
˚
a (A)
6.4153 (4)
10.6347 (6)
11.3683 (8)
71.016 (2)
80.825 (3)
83.878 (3)
722.78 (8)
1.871
11.0433 (6)
10.6963 (6)
16.7567 (10)
90
14.2089 (11)
9.5634 (5)
14.5834 (9)
90
9.303(3)
10.354(3)
13.072(4)
70.746(4)
72.006(4)
80.088
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
97.842 (4)
90
115.618 (5)
90
3
˚
V (A )
1960.83 (19)
1.685
992
1786.9 (2)
1.789
952
1127.2(6)
1.692
576
Dcalc (g cmꢀ3
F(000)
)
400
Z
2
P-1
4
P21/C
1.098
4
P2/n
2
P-1
Space group
Absorption coefficient l (mmꢀ1
Absorption correction T (minimum, maximum)
)
1.467
1.202
0.970
0.621, 0.844
1.9–26.0
3858
0.614, 0.910
2.1–28.0
4314
0.91, 1.00
2.09–26.48
14761
2h limits (ꢁ)
2.9–27.5
3273
199
Number of reflections
Number of parameters
R (F)
254
0.029
240
0.032
300
0.029
0.088
R1 (4 sig) = 0.0266
wR2 (all) = 0.0577
0.957
Rw (F)
Goodness-of-fit
Residual electron density
0.075
1.05
0.077
1.04
1.02
0.87/ꢀ0.76
0.55/ꢀ0.29
0.58/ꢀ0.40
0.36/ꢀ0.44

D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
739
Fig. 3. Molecular structure and atom numbering for; top to bottom (a) [Ru(L2)(CO)2Cl2], (b) [Ru(L6)(CO)2Cl2], (c) [Ru(L7)(CO)2Cl2] and
(d) [Ru(L8)(CO)2Cl2] (50% thermal ellipsoids).
To date, eleven pyridazine-containing ruthenium
complexes [17] have been structurally characterised
(CSD search version 5.25 [16]), only three [17b,17d]
of which are ruthenium(II) (CSD codes GIDBIE,
GIDBOK and LEJWOM). Of these, two complexes
(GIDBIE and GIDBOK) are of the [RuIIL(CO)2Cl2]
type which is of interest here. Bruno and co-workers
[12b] reported the structures of these two isomeric
complexes in which L = 3,6-bis(2-pyridyl)pyridazine
and the chloro ligands are mutually cis- or trans-.
Both structures are of a high precision in terms of
the average C–C esdꢀs. In the cis(CO)/cisCl derivative
GIDBOK, the Ru–Cl bond lengths are 2.405 and
served in the crystal structure. In the more symmetri-
cal cis(CO)/transCl derivative GIDBIE, which has the
same relative arrangements of the CO and the Cl li-
gands as is observed in the four complexes described
˚
here, the Ru–Cl bond lengths are 2.392 and 2.398 A
(mutually trans to each other) with typical Ru–CO
˚
distances of 1.882 and 1.885 A. The Ru–Npyridazine
˚
˚
bond length is 2.085 A and the Ru–Npyridine 2.122 A
(both trans to CO). No strong intermolecular hydro-
gen bonding is observed.
To the best of our knowledge [RuII(L8)(CO)2(Cl)2]
is the first structurally characterised pyridazine imine
ruthenium complex. The Ru–Npyridazine bond length
[2.092(2) A] in [Ru (L8)(CO)2(Cl)2] is similar to that
observed in GIDBIE. However, the Ru–Npyridazine
bond length is somewhat shorter, and the Ru–Nimine
II
˚
˚
2.431 A (trans to N and CO, respectively) and the
˚
Ru–CO distances of 1.890 and 1.897 A are typical.
˚
The Ru–Npyridazine bond length of 2.050 A is shorter
˚
than the Ru-Npyridine bond length of 2.111 A (trans
˚
bond length [2.176(2) A] is somewhat longer, than the
to Cl and CO, respectively). The longer Ru–Cl and
Ru–N bond lengths are trans to the two carbonyl
ligands. In this system the longer Ru–Cl bond is also
involved in three intermolecular contacts a C–Hꢁ ꢁ ꢁCl
and involving three aromatic C–H groups: however,
no strong intermolecular hydrogen bonding is ob-
Ru–Ntriazole and Ru–Npyrazine bond lengths in the three
˚
triazole-based complexes [2.106(3)–2.163(2) A]. The
Ru–C and Ru–Cl distances in [RuII(L8)(CO)2(Cl)2]
are very similar to those observed in GIDBIE and
the complexes of the triazole-based ligands L2, L6
and L7.

740
D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
Table 2
Selected bond lengths and angles for compounds [Ru(L)(CO)2Cl2]
[Ru(L2)(CO)2Cl2]
[Ru(L6)(CO)2Cl2]
[Ru(L7)(CO)2Cl2]
[Ru(L8)(CO)2Cl2]
˚
Bond distances (A)
Ru–Cl(1)
Ru–Cl(2)
2.3999(10)
2.3749(10)
1.875(4)
1.882(4)
2.106(3)
2.150(3)
1.140(5)
1.130(5)
2.3869(8)
2.3803(9)
1.862(3)
1.871(3)
2.115(2)
2.163(2)
1.126(4)
1.135(4)
2.4064(8)
2.3818(9)
1.876(3)
1.888(3)
2.109(2)
2.143(2)
1.127(4)
1.125(3)
2.4058(9)
2.3882(10)
1.886(3)
1.873(3)
2.092(2)
2.176(2)
1.132(3)
1.122(3)
Ru–C(1A)
Ru–C(2A)
Ru–N(2)
Ru–N(16)
C(1A)–O(1A)
C(2A)–O(2A)
Bond angles (ꢁ)
Cl(1)–Ru–Cl(2)
Cl(1)–Ru–C(1A)
Cl(1)–Ru–C(2A)
Cl(1)–Ru–N(16)
Cl(1)–Ru–N(2)
Cl(2)–Ru–C(1A)
Cl(2)–Ru–C(2A)
Cl(2)–Ru–N(16)
Cl(2)–Ru–N(2)
C(1A)–Ru–C(2A)
C(1A)–Ru–N(16)
C(1A)–Ru–N(2)
C(2A)–Ru–N(16)
C(2A)–Ru–N(2)
N(16)–Ru–N(2)
175.12(4)
91.95(13)
91.74(13)
89.10(8)
175.81(3)
91.45(11)
90.88(11)
89.30(6)
174.44(2)
92.11(12)
93.51(10)
88.57(6)
176.62 (3)
92.44(8)
94.02(9)
87.39(6)
88.37(6)
88.97(8)
89.12(9)
89.29(6)
90.21(6)
87.53(11)
102.84(9)
179.06(10)
169.48(9)
92.90(10)
76.71(8)
89.33(9)
86.07(7)
87.24(7)
92.02(13)
91.09(13)
87.67(8)
92.59(11)
90.35(11)
89.22(6)
90.66(12)
91.38(10)
86.36(6)
86.39(9)
89.91(18)
89.10(8)
89.77(7)
89.33(7)
88.48(13)
95.19(11)
171.02(11)
176.32(10)
100.18(11)
76.17(8)
88.46(13)
95.82(11)
171.89(11)
175.18(11)
99.65(10)
76.09(8)
173.03(15)
173.94(14)
96.90(15)
77.11(12)
The triazole compounds reported in this contribution
show extensive intermolecular interactions through
hydrogen bonding networks, whereas the related
non-triazole compounds in the literature [9,12] do not.
For example, in the two isomers of [RuII(bipy)(CO)2-
(Cl)2] reported by Haukka and co-workers[9c], there
are no strong intermolecular hydrogen bonds. For the
cis(CO)/cisCl-arrangement [9c] the Ru–Cl, Ru–N and
˚
Ru–C bond lengths are 2.411(4)/2.439(3) A, 2.090(8)/
˚
2.117(8) A and 1.899(11)/1.938(10) A while in the cis-
˚
(CO)/transCl-derivative the data are as follows
˚
2.391(5)/2.390(5) A, 2.102(9)/2.112(12) A and 1.817(8)/
˚
˚
1.835(17) A, respectively. However, the relatively large
esdꢀs mean that an in depth discussion is inappropriate.
In the ruthenium complex of L2 different hydrogen
bond interactions can be identified. As can be seen from
Fig. 3 a methanol molecule is H-bond donor to N16 of
˚
the pyrazine ring (N–O distance 2.844 A). The C–H
bond of the triazole of a different complex serves a H-
bond donor to the oxygen of the methanol molecule
Fig. 4. H-bond interactions between methanol and [Ru(L2)(CO)2Cl2].
˚
(C–O distance 2.704 A). This leads to the formation of
a dinuclear subunit, Fig. 4. In addition to these rela-
tively strong H-bonds a different set evolves around
the chloro ligands of each ruthenium centre, Fig. 4.
The N3–H bond of one ruthenium complex serves as
H-bond donor to the chloro ligand of a second ruthe-
serves in turn as H-bond donor to the chloro ligand of
˚
the first complex. This H-bond is 3.503 A and a C–H–
Cl angle of 136.8ꢁ indicates that the bonding is not very
strong. This solid-state interaction leads to the forma-
tion of a three dimensional chain of H-bond bridged
ruthenium complexes (see Fig. 5).
˚
nium complex, the distance of 3.468 A and the N–H–
Cl angle of 139.4ꢁ indicate a relatively weak interaction.
The C14–H bond of the second ruthenium complex
In the L6 derivative, a methanol molecule crystallises
with the ruthenium complex and links the L6 derivatives

D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
741
In the L7 derivative, dimers are formed through the
formation of centrosymmetric C–Hꢁ ꢁ ꢁCl interactions
as depicted in the PLATON packing diagram (Fig. 7):
further aggregation is achieved through pyridazinylC–
Hꢁ ꢁ ꢁOMe and methoxyC–Hꢁ ꢁ ꢁO@C interactions. The cen-
trosymmetric N3–H3ꢁ ꢁ ꢁCl1* interaction has an N3ꢁ ꢁ ꢁ
˚
Cl1* distance of 3.196(3) A (with symmetry operation
* = 1 ꢀ x, ꢀy, ꢀz). The C14-H14ꢁ ꢁ ꢁO27# interaction
#
˚
has a C14ꢁ ꢁ ꢁO27 distance of 3.208(3) A and the C27–
H27Bꢁ ꢁ ꢁO1A& contact has a C27ꢁ ꢁ ꢁO1A distance of
˚
3.455(4) A where the symmetry operations are # =
x ꢀ 1, y, z and & = 1 + x, 1 + y, z.
The crystal structure of [RuII(L8)(CO)2Cl2], confirms
the predictions based on the microanalysis and NMR re-
sults that only one of the two binding pockets of L8 is
occupied. As seen above, the L8 ligand is bidentate
and the two CO groups are cis to one another whilst
the chloride anions are mutually trans. The ligand itself
is quite flat as is indicated by the small intersection an-
gles between the mean plane of the central pyridazine
ring and those of each of the terminal benzene rings
[C12 ring 22.7(1); C22 ring 7.5(2)ꢁ]: the bigger twist
out of plane is observed for the phenyl ring which is
associated with the occupied binding pocket, presum-
ably due to steric effects. In the related GIDBIE crystal
structure, the ligand is also almost flat with dihedral an-
gles of only 4.9(1)ꢁ and 13.0(1)ꢁ between the central pyr-
idazine ring and the two terminal pyridine rings[12b]. In
the case of GIDBIE, the pyridine ring involved in chela-
tion to the ruthenium atom is less twisted [4.9(1)ꢁ] away
from the central pyridazine plane than the one which is
not involved in coordination [13.0(1)ꢁ]. There are no
strong intermolecular hydrogen bonds in the structure
of [RuII(L8)(CO)2Cl2].
Fig. 5. Intermolecular hydrogen bonding in [Ru(L2)(CO)2Cl2].
into chains along the b-axis. The N3–H triazole forms a
hydrogen bond with the methanol O–H which in turn
hydrogen bonds to the pyrazine N13 atom (not involved
in bonding to the Ru). The N3ꢁ ꢁ ꢁO1S distance is
ꢁ
˚
˚
2.679(3) A and the O1Sꢁ ꢁ ꢁ N13 is 2.969(3) A, (where ꢁ
is the symmetry operation x, 1 + y, z). There are two
other contacts of note namely C12–H12ꢁ ꢁ ꢁCl1i and
C14–H14ꢁ ꢁ ꢁCl2ii, where the symmetry operators are
i and ii are ꢀx, y ꢀ 1/2, ꢀz + 1/2 and 1 ꢀ x, y ꢀ 1/2,
1/2 ꢀ z. The interactions are depicted in Fig. 6, a
PLATON packing diagram showing the aggregation of
the 1:1 complex along the b-axis together with the flank-
ing C–Hꢁ ꢁ ꢁCl interactions.
3. Conclusions
One of the most important features of this work is
that for all triazole-based complexes only one structural
isomer was isolated and that in the pyrazinetriazole
based complexes the triazole ring is coordinated via
the N2 atom. Although we do not have direct evidence
for this we propose that for the pyridine triazole based
complexes the same coordination mode is obtained. As
pointed out in the introduction metal complexes of the
type [Ru(bpy)2(L–L0)]n+, where L–L0 is L1 or L2, two
isomers were obtained in a 1:1 ratio, while in the pres-
ence of substituents different ratios were obtained. It is
evident that for this class of compound steric consider-
ation are the main factors, which determine the nature
of the coordination isomer obtained. On the other hand
for the analogous Rh(III) compounds only one isomer
was obtained for all types of L–L0 and in these com-
plexes the coordination mode is most likely via N2. This
suggest that there electronic factors, i.e., the fact that
Fig. 6. Intermolecular interactions found in [Ru(L6)(CO)2Cl2].

742
D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
Fig. 7. Intermolecular interactions observed in [Ru(L7)(CO)2Cl2].
there is a larger electron density present on the N2 than
on the N4 atom determines the coordination mode of
the ring in these electron deficient complexes. It appears
that also for the compounds reported here electronic
factors are important. With the absence of large co-
ligands such as 2,20-bipyridyl the coordination mode
of the triazole ligands used in this study is not expected
to be driven by steric considerations and therefore the
formation of both N2 and N4 bound isomers would
be expected. It seems clear that because of the presence
of the strongly electron accepting CO ligands the coor-
dination of the more electron rich N2 atom of the ring
is favoured. Finally, one of the reasons for the prepara-
tion of these complexes was to investigate their potential
as intermediates for the preparation of tris heteroleptic
complexes. Unfortunately all compounds obtained
turned out to be unreactive under a wide range of
conditions.
tions were performed using w-scans (4 reflections for
L6 and 3 reflections for L7, with 5ꢁ increments from
0ꢁ to 360ꢁ) and data were processed using the XSCANS
software [19]. Data for the L8 complex were collected
on a Bruker SMART area detector diffractometer: a
SADABS absorption correction was performed.
All four structures were solved by direct methods
(SHELXS [20]) and refined by full-matrix least-squares
techniques against F 2o (SHELXL-97 [21]). For compound
[Ru(L2)(CO)2Cl2] the hydrogen atoms of the imin-group
N4 and for the C–H-groups of C1, C2 and C3 were lo-
cated by difference Fourier synthesis and refined isotrop-
ically. All other hydrogen atoms were included at
calculated positions with fixed thermal parameters. All
non-hydrogen atoms were refined anisotropically. XP
(SIEMENS Analytical X-ray Instruments, Inc.) was
used for structure representations for the L2 and L8
compounds. For L6 and L7 compounds the triazole
H3 atom was refined with isotropic parameters and also
the methanol H1S hydroxyl H atom in the L6 derivative:
the ORTEP and PLATON programs were used for the molec-
ular graphics in the L6 and L7 derivatives [22,23]. The
data have been deposited on the Cambridge Structural
Database.
4. Experimental
4.1. Instrumentation
1H and 1H COSY spectra were recorded on a Bruker
AC400 (400 MHz) instrument. Peak positions are rela-
tive to residual solvent peaks. Infrared Spectra were re-
corded on a Perkin Elmer 2000 FTIR.
4.2. Synthesis
All solvents were Analar grade and used without fur-
ther purification. The ligands L1–L8 were available
from earlier studies.
4.1.1. Crystal structure determinations of [Ru(L)(CO)2
Cl2] where L = L2, L6, L7 and L8
All X-ray data was collected using graphite-mono-
chromated Mo Ka radiation. The intensity data for
the L2 compound were collected on a Nonius Kap-
paCCD diffractometer. Data were corrected for Lorentz
and polarization effects, but not for absorption: details
are listed in Table 2 [18]. Intensity data for the L6 and
L7 derivatives were collected on a Siemens P4 4-circle
diffractometer at room temperature: absorption correc-
4.3. Preparation of metal complexes
4.3.1. [Ru(CO)2Cl2]n [24]
[RuCl3] Æ xH2O (5.0 g, 20.5 mmol) and paraformalde-
hyde (1.5 g) were added to a 90% solution of formic
acid. The solution was heated at reflux for 5 h. The
colour of the solution changed from red to dark green
to orange. When the orange colour was obtained the

D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
743
reaction was cooled in an ice bath and stored in the free-
m(CO) 2072, 2019 cmꢀ1
C15H12Cl2N4O4Ru: Anal. Calc. C, 37.20; H, 2.50; N,
11.57. Found: C, 37.43; H, 2.36; N, 11.10%.
.
Elemental analysis for
zer overnight (ꢀ4 ꢁC). The solvent was removed by ro-
tary evaporation to leave a yellow solid. This was
washed with hexane and dried in vacuo. Yield 4.6 g,
20.2 mmol, 98%. IR (KBr): 2074 and 2020 cmꢀ1
.
4.3.6. [Ru(L5)(CO)2Cl2] Æ H2O
[Ru(CO)2Cl2]n (0.19 g, 0.83 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L5
(0.2 g, 0.85 mmol in 10 mL) was added and the solution
heated at reflux for 2 h. The solution was reduced to
5 mL, 2 drops conc. HCl added and cooled at ꢀ4 ꢁC
overnight. The resultant yellow precipitate was filtered,
washed with cold MeOH (5 mL) and dried in vacuo.
Yield 0.21 g, 0.46 mmol, 56%. 1H NMR (d6-DMSO,
298 K) d 9.03 (d), 8.27 (d), 8.23 (t), 7.81 (s), 7.78 (d),
7.67 (t), 7.37 (t), 7.27 (d), 2.28 (s) ppm. IR (CHCl3)
4.3.2. [Ru(L1)(CO)2Cl2] Æ H2O
[Ru(CO)2Cl2]n (0.31 g, 1.4 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L1
(0.20 g, 1.4 mmol in 10 mL) was added and the solu-
tion heated at reflux for 2.5 h. The solution was re-
duced to 5 mL, 2 drops conc. HCl added and
cooled at ꢀ4 ꢁC overnight. The resultant feathery yel-
low precipitate was filtered, washed with cold MeOH
(5 mL) and dried in vacuo. Yield 0.13 g, 0.36 mmol,
26%. 1H NMR (d6-DMSO, 298 K) d 9.91 (s), 9.17
(d), 8.41 (d), 8.34 (t), 7.85 (t) ppm. IR (CHCl3)(CO)
2075, 2000 cmꢀ1. Elemental analysis for C9H8Cl2-
N4O3Ru: Anal. Calc. C, 27.56; H, 2.06; N, 14.29.
Found: C, 27.88; H, 1.80; N, 14.29%.
m(CO) 2078, 2021 cmꢀ1
. Elemental analysis for
C16H14Cl2N4O3Ru: Anal. Calc. C, 39.85; H, 2.93; N,
11.62. Found: C, 40.13; H, 2.99; N, 11.51%.
4.3.7. [Ru(L6)(CO)2Cl2] Æ MeOH
[Ru(CO)2Cl2]n (0.19 g, 0.83 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L6
(0.2 g, 0.85 mmol in 10 mL) was added and the solution
heated at reflux for 2 h. After cooling, 1 mL conc. HCl
was added and the solution stored at ꢀ4 ꢁC overnight.
The resultant yellow precipitate was filtered, washed
with cold MeOH (5 mL) and dried in vacuo. Yield
4.3.3. [Ru(L2)(CO)2Cl2] Æ MeOH
[Ru(CO)2Cl2]n (0.30 g, 1.3 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L2
(0.20 g, 1.35 mmol in 10 mL) was added and the solu-
tion heated at reflux for 1.5 h. The resultant red pre-
cipitate was filtered hot, washed with MeOH
(10 mL) and dried in vacuo. Yield 0.20 g, 0.52 mmol,
40%. 1H NMR (d6-DMSO, 298 K) d 10.01 (s), 9.71
(d), 9.34 (dd), 9.10 (d) ppm. IR (CHCl3) m(CO) 2072,
2011 cmꢀ1. Elemental analysis for C9H9Cl2N5O3Ru:
Anal. Calc. C, 26.55; H, 2.23; N, 17.20. Found: C,
26.42; H, 2.09; N, 16.94%.
1
0.09 g, 0.20 mmol, 24%. H NMR (d6-DMSO, 298 K)
d 9.48 (s), 9.22 (d), 8.93 (d), 7.96 (d), 7.35 (d), 3.07 (s)
ppm. IR (CHCl3) m(CO) 2074, 2012 cmꢀ1. Elemental
analysis for C16H15Cl2N5O3Ru: Anal. Calc. C, 38.64;
H, 3.04; N, 14.08. Found: C, 38.41; H, 3.06; N, 13.79%.
4.3.8. [Ru(L7)(CO)2Cl2] Æ MeOH
4.3.4. [Ru(L3)(CO)2Cl2]
[Ru(CO)2Cl2]n (0.20 g, 0.88 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L7
(0.23 g, 0.90 mmol in 10 mL) was added and the solu-
tion heated at reflux for 2 h. HCl was added and the
solution stored at ꢀ4 ꢁC overnight. The resultant yellow
precipitate was filtered, washed with cold MeOH (5 mL)
[Ru(CO)2Cl2]n (0.23 g, 1.0 mmol) was dissolved in hot
MeOH (30 mL). A methanolic solution of L3 (0.20 g,
1.3 mmol in 10 mL) was added and the solution heated
at reflux for 1 h. The resultant feathery yellow precipi-
tate was filtered hot, washed with MeOH (10 mL) and
1
1
dried in vacuo. Yield 0.23 g, 0.6 mmol, 59%. H NMR
and dried in vacuo. Yield 0.13 g, 0.28 mmol, 32%. H
(d6-DMSO, 298 K) d 9.72 (s), 9.05 (d), 8.22 (t), 8.21
(d), 7.73 (t), 4.03 (s) ppm. IR (CHCl3) m(CO) 2072,
2012 cmꢀ1. Elemental analysis for C10H8Cl2N4O2 Ru:
Anal. Calc. C, 30.94; H, 2.08; N, 14.43. Found: C,
30.94; H ,1.96; N, 14.18%.
NMR (d6-DMSO, 298 K) d 9.52 (s), 9.32 (d), 9.01 (d),
8.14 (d, 2H), 7.16 (d, 2H), 3.95 (s, 3H) ppm. IR (CHCl3)
m(CO) 2077, 2020 cmꢀ1. Elemental analysis for C16H15-
Cl2N5O4Ru: Anal. Calc. C, 37.44; H, 2.95; N, 13.64.
Found: C, 37.32; H, 2.80; N, 13.39%.
4.3.5. [Ru(L4)(CO)2Cl2] Æ H2O
4.3.9. [Ru(L8)(CO)2Cl2]
[Ru(CO)2Cl2]n (0.19 g, 0.83 mmol) was dissolved in
hot MeOH (30 mL). A methanolic solution of L4
(0.20 g, 0.83 mmol in 10 mL) was added and the solu-
tion heated at reflux for 3 h. The resultant precipitate
was filtered hot, washed with MeOH (5 mL) and dried
in vacuo. Yield 0.12 g, 0.25 mmol, 31%. H NMR (d6-
DMSO, 298 K) d 9.18 (d), 8.53 (d), 8.39 (t), 8.02 (d),
7.81 (t), 7.44 (t), 7.12 (d), 7.04 (t) ppm. IR (CHCl3)
L87 (104 mg, 0.3 mmol) was dissolved in 30 mL of
MeOH/CHCl3 (2:1) with a little heating. [Ru(CO)2Cl2]n
(160 mg, 0.7 mmol) was dissolved in 15 mL MeOH and
added in one portion. The solution was allowed reflux
for 3 h, cooled and the resulting precipitate filtered.
The precipitate was washed with hot MeOH
(2 · 10 mL) and finally CHCl3 (3 · 5 mL). Yield
90 mg, 0.16 mmol, (53%). 1H NMR (d6-DMSO,
1

744
D. Mulhern et al. / Inorganica Chimica Acta 359 (2006) 736–744
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m(CO) 2066, 1999 cmꢀ1. Elemental analysis for C22H18-
Cl2N4O4Ru: Anal. Calc. C, 46.00; H, 3.16; N, 9.75.
Found: C, 45.76; H, 3.07; N, 9.62%.
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5. Supplementary data
Crystallographic data for the crystal structure anal-
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lographic Data Centre, CCDC no. (FO637,2), for
[Ru(L2)(CO)2Cl2], CCDC no. 238930 for [Ru(L6)-
(CO)2Cl2], CCDC no. 238931 for [Ru(L7)(CO)2Cl2]
and CCDC no. 230603 for [Ru(L8)(CO)2Cl2]. 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).
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We thank Dr. J. Wikaira and Prof. W.T. Robinson
(University of Canterbury, New Zealand) for the X-
ray data collection on [Ru(L8)(CO)2Cl2]. The Electricity
Supply Board (Ireland), the University of Otago, New
Zealand (including a postgraduate scholarship to Y.L.
and a bridging grant) and the Marsden Fund (Royal
Society of New Zealand) are thanked for supporting this
work.
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