Synthesis and characterizations of hydride carbonyl ruthenium(II) complexes with (benzimidazol-2-yl)-pyridine ligand

Article abstract of DOI:10.1016/j.poly.2012.07.002

The hydride carbonyl ruthenium(II) [RuH(CO)(bzimpy)(PPh₃) ₂]Cl·CH₃OH (1) and [RuH(CO)(bzimpy)(PPh ₃)₂]·CH₃OH (2) complexes were synthesized and characterized by IR, ¹H, ³¹

Full text of DOI:10.1016/j.poly.2012.07.002

Polyhedron 44 (2012) 221–227
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Polyhedron
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Synthesis and characterizations of hydride carbonyl ruthenium(II) complexes
with (benzimidazol-2-yl)-pyridine ligand
⇑
´
J.G. Małecki , A. Maron
Department of Crystallography, Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40-006 Katowice, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The hydride carbonyl ruthenium(II) [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH (1) and [RuH(CO)(bzim-
py)(PPh3)2]ÁCH3OH (2) complexes were synthesized and characterized by IR, 1H, 31P NMR, UV–Vis spec-
troscopy and X-ray crystallography. In the complexes the 2,6-bis-(benzimidazol-2-yl)-pyridine functions
as bidentate ligand exists as protonated in (1) and deprotonated form in (2). The experimental studies
were complemented by quantum chemical calculations which were used to identify the nature of the
interactions between the ligands and the central ion and the orbital compositions in the frontier elec-
tronic structures. Based on a molecular orbital scheme, the calculated results allowed the interpretation
of the UV–Vis spectra obtained at an experimental level.
Received 3 June 2012
Accepted 1 July 2012
Available online 9 July 2012
Keywords:
Ruthenium hydridocarbonyl complexes
2,6-Bis-(benzimidazol-2-yl)-pyridine
X-ray
Ó 2012 Elsevier Ltd. All rights reserved.
Electronic structure
Absorption electronic spectra
DFT
TDDFT
1. Introduction
attention to the hydride carbonyl complexes of ruthenium(II) with
this ligand.
Ruthenium(II) complexes with ligands based on pyridine as well
as benzimidazole ring are one of the most interesting area of ruthe-
nium coordination chemistry [1–8]. 2,6-Bis-(benzimidazol-2-yl)-
pyridine (bzimpy) is an example of combination of these two kinds
of ligands and its coordination toward various transition metals is
widely studied in many papers and can be characterized as very di-
verse [9–16]. The special properties of this compound as a ligand is
associated with the fact that it contains both pyridine and benz-
imidazole rings and the differences between coordination behav-
iors of pyridine and benzimidazole are also responsible for unique
nature of bzimpy compared to the ligands including only one type
of these heteroaromatic rings such as terpy, bpy. The pyridine ring
Here, we present the synthesis, crystal, molecular and
electronic structures, and spectroscopy characterization of two
ruthenium(II) hydridocarbonyl complexes with 2,6-bis-(ben-
zimidazol-2-yl)-pyridine ligands. The electronic structures of the
complexes have been determined by density functional theory
(DFT) and employed for the discussion of bonding properties. The
time dependent density functional theory (TD-DFT) was finally
used to calculate the electronic absorption spectra. Based on a
molecular orbital scheme, the results allowed for the interpreta-
tion of the UV–Vis spectra obtained at an experimental level.
2. Experimental
as a good
centre better than the imidazole and its derivatives, which exhibit
moderate –donor properties [17].
p–acceptor tends to stabilize the ruthenium(II) acceptor
All reagents used for the synthesis of the complexes are com-
mercially available and have been used without further purifica-
tion. The [RuHCl(CO)(PPh3)3] complex was synthesized according
to the literature method [18].
p
Although 2,6-bis-(benzimidazol-2-yl)-pyridine is usually de-
scribed as tridendate ligand, in some cases it can create another
possibilities of coordination [9]. Additionally according to some
sources the coordination with central atom may increase the ease
of dissociation of the benzimidazole NH imino protons [11]. Taking
into account these factors, it is not surprising the widespread inter-
est of ruthenium(II) complexes with bzimpy and ligands derived
from bzimpy, but up to now it has not been paid too much
2.1. Synthesis of [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH (1) and
[RuH(CO)(bzimpy)(PPh3)2]ÁCH3OH (2)
The complexes (1) and (2) were synthesized in a reaction be-
tween [RuHCl(CO)(PPh3)3] (0.2 g, 2 Â 10À4 mol) and 2,6-bis-(ben-
zimidazol-2-yl)-pyridine (bzimpy) (0.068 g, 2.2 Â 10À4 mol) in
methanol solutions (100 cm3). In the case of complex (2) to the
reaction mixture the stoichiometric amount of NaN3 (0.22 mmol)
⇑
Corresponding author.
E-mail address: gmalecki@us.edu.pl (J.G. Małecki).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.07.002

´
222
J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
Table 1
was added. The mixture of the compounds was refluxed in metha-
nol by 4 h. After this time, it was cooled, filtered and left out to
slow evaporation.
Crystal data and structure refinement details of [RuH(CO)(bzimpyH)(PPh3)2]Cl.CH3OH
(1), [RuH(CO)(bzimpy)(PPh3)2].CH3OH (2) complexes.
1
2
Complex 1: Yield. IR (KBr): 3387
(Ru–H); 1943 (CO); 1603, 1588, 1567
Ph(P–Ph); 1092 d(C–CH in the plane); 743 d(C–C out of the plane);
m
OH; 3047
mArH; 2845 mCH; 2040
m
m
m
(C=N; C=C); 1474 d(C–CH
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
57H48ClN5O2P2Ru C57H47N5O2P2Ru
in the
1033.46
295.0(2)
triclinic
997.01
295.0(2)
plane); 1434
m
697 d
; 520 d(Ru-(H)CO). UV–Vis (methanol; loge): 374
(C–C in
(1.27), 332 t(he2.p4la6ne)) , 260 (sh), 208 (4.75). H NMR (400 MHz, CDCl3)
d: 9.11 (d, J = 79.3 Hz, py), 7.75–6.87 (m, Ph(Im)/NH/PPh3), 3.51 (s,
CH3OH), À13.19 (t, J = 19.5 Hz, H(Ru)).
triclinic
ꢀ
ꢀ
P1
P1
11.2286(5)
12.1197(6)
19.4523(9)
74.554(4)
74.374(4)
86.348(4)
2457.2(2)
2
11.2284(4)
11.9902(3)
19.1843(5)
108.170(2)
104.036(2)
93.391(2)
2355.15(12)
2
31P NMR (162 MHz, CDCl3) d: 43.70 (s, PPh3), 42.35 (s, PPh3).
b (Å)
c (Å)
Complex 2: Yield. IR (KBr): 3393
1600, 1567 (C=N; C=C); 1480 d(C–CH in the plane); 1434
d(C–CH in the plane); 737 d(C–C out of the plane); 694 d(C–C in the plane); 519
d(Ru-(H)CO). UV–Vis (methanol; log ): 340 (1.26), 291 (2.09), 269
m
OH; 3046
m
ArH, 1940 m(Ru–H/CO)
;
a
(°)
m
m
Ph(P–Ph); 1093
b (°)
c
(°)
V (Å3)
e
Z
(1.81), 208 (4.92). H NMR (400 MHz, CDCl3) d: 9.12 (s, py), 8.03–
Calculated density (Mg/m3)
Absorption coefficient (mmÀ1
F(000)
1.397
1.406
6.85 (m, Ph(Im)/NH/PPh3), 3.51 (s, CH3OH), À13.65 (t, J = 19.6 Hz,
)
0.487
0.451
H
(Ru)). 31P NMR (CDCl3) d: 43.57 (s, PPh3), 42.57 (s, PPh3).
1064
1028
Crystal dimensions (mm)
h range for data collection (°)
Index ranges
0.20 x 0.12 x 0.04 0.17 x 0.14 x 0.06
3.38–25.05
À13 ꢀ h ꢀ 13
À14 ꢀ k ꢀ 14
À23 ꢀ l ꢀ 23
20130
3.34–25.05
À13 ꢀ h ꢀ 13
À14 ꢀ k ꢀ 14
À22 ꢀ l ꢀ 22
26607
2.2. Physical measurements
Infrared spectra were recorded on a Perkin Elmer spectropho-
tometer in the spectral range 4000–450 cm1 using KBr pellets.
Electronic spectra were measured on a Lab Alliance UV–Vis 8500
spectrophotometer in the range of 600–180 nm in methanol solu-
tion. The 1H and 31P NMR spectra were obtained at room temper-
ature in CDCl3 using Bruker 400 MHz spectrometer.
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2
)
8700 (0.0514)
8700/0/619
1.060
8328 (0.0366)
8328/0/610
1.027
Final R indices [I > 2s(I)]
R1 = 0.0521
wR2 = 0.1161
R1 = 0.0832
wR2 = 0.1275
R1 = 0.0311
wR2 = 0.0762
R1 = 0.0408
wR2 = 0.0797
0.53/À0.36
R indices (all data)
Largest difference in peak and hole 0.79/À0.42
2.3. Computational methods
The calculations were carried out using Gaussian09 [19] pro-
gram. Molecular geometries of the singlet ground state of com-
plexes (1) and (2) were fully optimized in the gas phase at the
B3LYP/DZVP level of theory. [20,21] For each compound a fre-
quency calculation was carried out, verifying that the obtained
optimized molecular structure corresponds to an energy mini-
mum, thus only positive frequencies were expected. The DZVP ba-
sis set [22] with f functions with exponents 1.94722036 and
0.748930908 was used to describe the ruthenium atom and the ba-
sis set used for the lighter atoms (C, N, O, P, H) was 6–31G with a
set of ‘‘d’’ and ‘‘p’’ polarization functions. The TD-DFT (time depen-
dent density functional theory) method [23] was employed to cal-
culate the electronic absorption spectra of the complexes in the
solvent PCM (Polarizable Continuum Model) model. In this work
90 singlet excited states was calculated as vertical transitions for
the complexes. A natural bond orbital (NBO) analysis was also
made for all the complexes using the NBO 5.0 package [24] in-
cluded in Gaussian09. Natural bond orbitals are orbitals localized
on one or two atomic centers, that describe molecular bonding in
a manner similar to a Lewis electron pair structure, and they corre-
spond to an orthonormal set of localized orbitals of maximum
occupancy. NBO analysis provides the contribution of atomic orbi-
2.4. Crystal structures determination and refinement
The yellow crystals of [RuH(CO)(bzimpyH)(PPh3)2].CH3OH (1)
and [RuH(CO)(bzimpy)(PPh3)2]ÁCH3OH (2) were mounted in turn
on an Xcalibur, Atlas, Gemini Ultra Oxford Diffraction automatic
diffractometer equipped with a CCD detector, and used for data
collection. X-ray intensity data were collected with graphite mono-
chromated Mo
295.0(2) K, with
K
x
a
radiation (k = 0.71073 Å) at temperature
scan mode. Ewald sphere reflections were col-
lected up to 2h = 50.10. The unit cell parameters were determined
from least-squares refinement of the setting angles of 12205 stron-
gest reflections. Details concerning crystal data and refinement are
gathered in Table 1. Lorentz, polarization and empirical absorption
correction using spherical harmonics implemented in SCALE3 AB-
SPACK scaling algorithm [26] were applied. The structure was
solved by the Patterson method and subsequently completed by
the difference Fourier recycling. All the non-hydrogen atoms were
refined anisotropically using full-matrix, least-squares technique.
The Ru–H hydrogen atoms were found from difference Fourier syn-
thesis after four cycles of anisotropic refinement, and refined as
‘‘riding’’ on the adjacent carbon atom with individual isotropic
temperature factor equal 1.2 times the value of equivalent temper-
ature factor of the parent atom. The Olex2 [27] and SHELXS97,
tals (s, p, d) to the NBO
r and p hybrid orbitals for bonded atom
pairs. In this scheme, three NBO hybrid orbitals are defined, bond-
ing orbital (BD), lone pair (LP), and core (CR), which were analyzed
on the atoms directly bonded to or presenting some kind of inter-
action with the ruthenium atom. The contribution of a group (li-
gands, central ion) to a molecular orbital was calculated using
Mulliken population analysis. GaussSum 2.2 [25] was used to cal-
culate group contributions to the molecular orbitals and to prepare
the partial density of states (DOS) spectra. The DOS spectra were
created by convoluting the molecular orbital information with
Gaussian curves of unit height and FWHM (Full Width at Half
Maximum) of 0.3 eV.
S
HELXL97 [28] programs were used for all the calculations. Atomic
scattering factors were incorporated in the computer programs.
3. Results and discussion
3.1. Spectroscopic characterization of the complexes
The 1H NMR spectra of the complexes are similar and show a set
of signals corresponding to the PPh3 and bzimpy ligands given in
experimental section. The spectra are complicated due to set of

´
223
J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
benzimidazole and triphenylphosphine protons. The triplets at
3.51 ppm indicate methanol, which occurs as solvent in the struc-
tures of the complexes. On the 1H NMR spectra signals at high field
(À13.19 and À13.65 ppm) indicate the presence of the hydride
coordinated with the metal. The shifts of the signals are due to
the shielding effect of the metal and to the charge of the hydrogen
atom. The Ru–H signals are triplets due to coupling with the two
trans phosphorus atoms (JHP ꢁ 20 Hz). The 31P NMR spectra of the
complexes show two signals at 43.70, 42.35 ppm in complex (1)
and 43.57, 42.57 ppm on the spectrum of 2. The presence of mag-
netically unequivalent phosphorus atoms suggests the presence of
two triphenylphosphine groups not in perfect trans positions.
The IR spectrum of the cationic complex 1 displays strong CꢂO
band at 1943 cmÀ1 and the Ru–H stretching bands are displayed
at 2040 cmÀ1. On the spectrum of complexes 2 the Ru–CO and
Ru–H bands are combined with the maximum of broad band at
1940 cmÀ1. The mCO and mRu–H stretching bands in the parent
[RuHCl(CO)(PPh3)3] complex are at 1922 and 2020 cmÀ1 respec-
tively and the decreasing of carbonyl stretches are clearly visible
in the studied complexes. The decrease in the vibration frequency
of the CO bond, compared with starting ruthenium(II) complex, is
connected with delivering electron density via backbonding to
the anti-bonding orbitals of the CO by benzimidazole in trans posi-
tion to CO. The IR spectrum of complex 1 presents Fig. 1.
1 [2]
Fig.
2. ORTEP
drawings
of
[RuH(CO)(MeImCOO)(PPh3)2].CH3OH
and[RuH(CO)(BImCOO)(PPh3)2] (2) and complexes with 30% probability displace-
(1)
ment ellipsoids. Hydrogen atoms (except Ru–H) and solvent are omitted for clarity.
3.2. Molecular structures
Table 2
Crystals of the complexes suitable for single crystal X-ray anal-
yses were obtained by slow evaporation of the reaction mixtures.
The complexes crystallize in triclinic P1 space group as solvate
Selected bond lengths (Å) and angles (°) of [RuH(CO)(bzimpy)(PPh3)2]Cl.CH3OH (1)
and [RuH(CO)(bzimpy)(PPh3)2].CH3OH (2) complexes.
ꢀ
1
2
with one methanol molecule. Fig. 2 presents their molecular struc-
tures and the selected bond distances and angles are collected in
Table 2. The bond lengths are similar in both complexes and com-
parable with distances in other hydride–carbonyl ruthenium(II)
complexes with N-heteroaromatic ligands. Knowing about the lim-
its of Fourier synthesis and the problems in recognizing artifacts in
the immediate neighborhood of heavy atoms it is doubtful if a reli-
able position for the hydrogen atom bound to the Ru-atom can be
found in the difference Fourier map avoiding the danger of mistak-
ing the effects of the series termination errors for a true atomic po-
sition. In the studied complexes the Ru–H distances do not differ
significantly from the values for other ruthenium carbonyl hydride
complexes found in Cambridge Structural Database (CSD;
Exp
Calc
Exp
Calc
Bond lengths (Å)
Ru(1)–H(1)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–C(1)
C(1)–O(1)
1.47(4)
1.58
2.48
2.45
2.52
2.16
1.88
1.16
1.49(2)
1.59
2.47
2.43
2.47
2.14
1.88
1.16
2.3907(11)
2.3535(11)
2.365(3)
2.106(3)
1.838(4)
1.155(5)
2.3815(6)
2.3419(6)
2.3707(17)
2.1114(18)
1.841(2)
1.154(3)
Angles (°)
P(1)–Ru(1)–H(1)
P(2)–Ru(1)–H(1)
P(2)–Ru(1)–P(1)
P(2)–Ru(1)–N(2)
N(1)–Ru(1)–H(1)
N(1)–Ru(1)–P(1)
N(1)–Ru(1)–P(2)
N(1)–Ru(1)–N(2)
N(2)–Ru(1)–H(1)
N(2)–Ru(1)–P(1)
C(1)–Ru(1)–H(1)
C(1)–Ru(1)–P(1)
C(1)–Ru(1)–P(2)
C(1)–Ru(1)–N(1)
C(1)–Ru(1)–N(2)
Ru(1)–C(1)–O(1)
86.2(17)
86.5(17)
172.21(4)
93.81(8)
88.8(16)
86.55(9)
90.46(9)
74.80(12)
163.6(16)
92.34(8)
86.4(16)
93.81(13)
88.56(13)
175.14(15)
110.01(15)
173.4(4)
84.7
84.8
169.4
94.2
90.0
87.6
91.5
72.4
163.2
94.2
85.7
90.9
89.3
176.4
111.1
174.9
85.6(10)
83.9(10)
168.59(2)
95.84(4)
92.9(10)
86.02(5)
90.23(5)
74.95(6)
167.9(10)
93.59(4)
83.7(10)
94.41(7)
88.71(7)
176.62(8)
108.35(8)
174.17(19)
84.7
84.2
168.7
94.7
90.8
86.6
91.4
74.0
164.8
95.4
86.7
92.5
89.0
177.4
108.5
174.6
ConQuest v. 1.14; 2012). The structures of the complexes can be
considered as a distorted octahedral with the largest deviation
from the expected 90° bond angles coming from the bite angle of
2,6-bis-(benzimidazol-2-yl)-pyridine. It equals to 74.80(12)° and
74.95(6)° for N–Ru–N and 110.01(15)°, 108.35(8)° for C(1)–
Ru(1)–N(2) angles in complexes (1) and (2), respectively. The P–
Ru–P angles are lower than 180° vary in the 172.21(4)° to
168.59(2)° range which is confirmed by the presence of two signals
at 31P NMR spectra. As shown in Fig. 2, the CO groups are in the
trans positions to the benzimidazole ring and the hydride ligands
are in trans to pyridine ring in the complexes.
Fig. 1. The experimental and calculated IR spectra of [RuH(CO)(MeIm-
COO)(PPh3)2]ÁCH3OH complex.

´
J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
224
In the molecular structures of the complexes several inter- and
intra- molecular hydrogen bonds [29] exist what is collected in Ta-
ble 3. Additionally in the structure of the complexes some elec-
ally in the structures of the complexes some intermolecular
C–H. . . -ring interactions are visible. Fig. 4 presents the interac-
p
tions between C(4)–H(4). . .C(4)[Àx;Ày;1 À z] and C(36)–H(36). . .
tronic interactions (p–p stacking) between PPh3 phenyl and
H(16)[À1 + x;y;z] in the complexes 1 and 2, respectively. The C–
imidazole and pyridine rings from bzimpy are visible and Fig. 3
presents the alignment of centroids formed by imidazole, pyridine
and phosphine phenyl rings. The plane-to-plane distances between
the phosphine phenyl centroids, determined by C(37) to C(42) and
C(45) to C(50) carbons, and imidazole and pyridine rings of bzimpy
are equal to 3.80 Å and 3.55 Å with angles between the normal to
the centroids of 22.83° and 19.51° (shift distances 1.31 Å and
H. . .p-ring distances are 3.378 Å and 2.843 Å and the electrostatic
potentials surfaces presented on Fig. 4 allow these specifying as
some stacking interactions.
3.3. Optimized geometries, hybrid and molecular orbitals description
The ground states geometries of the complexes were optimized
in singlet states using the DFT method with the B3LYP functional.
The calculations were carried out for gas phase molecules and in
general, the predicted bond lengths and angles are in an agreement
with the values based on the X-ray crystal structure data, and the
general trends observed in the experimental data are reproduced
in the calculations (see Table 2). The calculated IR frequencies of
complexes 1, which are shown in Fig. 1, confirm calculated struc-
tures with experimental ones and the differences in calculated
and experimental spectra mainly result from the negligence of
intermolecular interactions for the gas phase. From the data col-
lected in Table 2, one may see that the major of differences be-
tween the experimental and calculated geometries are found in
the Ru–H and Ru–N(1) distance (ꢁ0.1 Å) and the differences be-
tween angles do not exceed 3°.
The NBO analyses, which allowed to know the nature of the
coordination between ruthenium and the atoms of the ligands di-
rectly interacting with it, were performed for the complexes. This
methodology also gave a better understanding of the optimized
molecular structures. In the analyses were found that the bzimpy
as N,N–donor ligands do not show covalent bonding with ruthe-
nium. The Coulomb-type interactions between the ruthenium cen-
tral ions and bzimpy ligands are clearly visible in the calculated
0.33 Å) in complex 1 indicating p–p stacking interactions. A similar
arrangement between aromatic rings occurs in the structure of the
complex 2, where the distances between phenyl rings and imidaz-
ole, pyridine centroids are 3.70 Å and 3.63 Å and angles between
the normal to the centroids equal to 18.65° and 20.23°. Addition-
Table 3
Hydrogen bonds for [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH (1) and [RuH(CO)(bzim-
py)(PPh3)2]ÁCH3OH (2) complexes (Å and °).
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
<(DHA)
1
O(2)–H(2). . .Cl(1)
N(3)–H(3A). . .Cl(1) #1
N(5)–H(5A). . .Cl(1)
C(22)–H(22). . .N(4)
0.82
0.86
0.86
0.93
2.27
2.21
2.33
2.40
3.076(7)
3.041(4)
3.136(4)
3.324(6)
168.0
162.1
156.4
170.7
2
O(2)–H(2). . .N(2) #2
N(5)–H(5A). . .O(2) #3
C(10)–H(10). . .N(2)
C(22)–H(22). . .N(4)
0.82
0.86
0.93
0.93
1.90
1.98
2.60
2.37
2.715(3)
2.757(3)
2.908(3)
3.296(4)
172.9
150.0
99.6
179.1
Symmetry transformations used to generate equivalent atoms: #1 Àx, Ày,1 À z; #2
1Àx,1 À y,1 À z; #3 1 + x,y,z.
Fig. 3. The p
-stacking interactions in the molecules of [RuH(CO)(MeImCOO)(PPh3)2].CH3OH (1) and [RuH(CO)(BImCOO)(PPh3)2] (2) complexes.

´
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J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
1
2
Fig. 4. The density of states (DOS) diagrams for the complexes 1 and 2.
Wiberg bond indices whose values are considerably lower than
one. The Ru–NIm and Ru–Npy bond indices are similar and close
to 0.41, 0.46 and 0.29, 0.32 in the complexes 1 and 2, respectively.
The Ru–P bond orders are also smaller than 1 (ꢁ0.7). For the car-
bonyl groups of the complexes, three natural bond orbitals were
detected for the C–O bond, and one for the Ru–C bond. The Ru–C
bond orbitals are polarized towards the carbon atom, and the C–
O bond orbitals are polarized towards the oxygen end. The oxygen
atom of the carbonyl ligand has one lone pair (LP) orbital. The
occupancies and hybridization of the Ru–H, Ru–C and CO bonds
are gathered in Table 4 (anti-bonding NBOs are given in round
brackets). The charge of CO ligands, calculated by summing the
individual charges on the carbon and oxygen atoms, have values
equal to 0.23 and 0.19 in complexes 1 and 2, respectively. The val-
ues show that there are some charge transfer between CO and the
Ru fragment. The Wiberg indexes of the CO bonds in the complexes
are reduced (by about 0.20) with respect to free CO (WCO = 2.23).
These values are in agreement with the elongation of the C–O bond
in complexes and charge distribution in the terminal bonding car-
bonyl group to ruthenium central ion. The bonding can be de-
scribed as the result of two electron transfers. First this binding
Table 4
The occupancies and hybridization of the calculated R–H, Ru–C and CꢂO natural bond
orbitals (NBOs) of [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH (1) and [RuH(CO)(bzim-
py)(PPh3)2]ÁCH3OH (2) complexes.
BD (2-center Occupancy Hybridization of NBO
bond)
Wiberg bond
indices
Ru–H
1.852
(0.103)
1.852
(0.111)
1
2
0.74(sp0.58d2.78
0.73(sp0.64d2.85
)
Ru + 0.681(s)H
Ru + 0.683(s)H
0.80
0.79
)
Ru–C
1
2
1.942
(0.154)
1.944
(0.160)
0.568(sp0.78d2.33
0.566(sp0.84d2.32
)
Ru + 0.823(sp0.49
Ru + 0.825(sp0.48
)
)
1.24
1.27
C
)
C
CꢂO
1
1.996
0.490(sp)C + 0.872(sp)O
0.508(sp15.87 C + 0.861(p10.34
0.544(sp2.69 C + 0.839(sp1.60
2.06
(0.205)
1.993
(0.168)
1.993
(0.045)
1.996
(0.221)
1.994
)
)
O
)
)
O
mode involves a
r-donation from the CO lone pair orbital to the
2
0.485(sp)C + 0.875(p)O
0.499(sp29.41 C + 0.866(sp18.30
0.548(sp2.42 C + 0.836(sp1.36
2.03
LUMO orbital of complex. On the other hand, the highest occupied
)
)
O
orbitals of the metallic fragment, mainly 4dRu orbitals, are involved
p
back-bonding from the metal to the CO p⁄ orbitals. The inter-
(0.193)
1.994
(0.032)
in a
)
)
O
actions are visible on the overlap density-of-states diagram pre-
sented in the Fig. 5. In the frontier HOMOs the bonding
interactions between carbonyl and ruthenium(II) central ions ap-
pear (dRu
? r-donation from CO to dRu plays role in
p⁄CO). The
the higher LUMOs. The ruthenium d orbitals occupancies in the
are also similar in the complexes and considerable lower than for-
mal +2 (À0.77). On the Fig. 5 the ruthenium–hydride ion interac-
tion shows strong bonding affect which is in accordance with
complexes are similar and as follow: dxy 1.36, dxz 1.40, dyz 1.63,
2
dx 2 1.75, dz2 1.54. The ruthenium(II) central ions natural charges
Ày

´
226
J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
Table 5
The calculated electronic transitions for [RuH(CO)(bzimpy)(PPh3)2]+ (1) and [RuH(-
CO)(bzimpy)(PPh3)2] (2) complexes.
(nm)
f
Transitions
Charter
1
414.7
380.4
374.4
365.0
349.2
0.0149
0.0495
0.0144
0.0311
0.1895
HOMO ? LUMO (90%)
H-1 ? LUMO (77%)
H-2 ? LUMO (65%)
HOMO ? L+1 (94%)
H-3 ? LUMO (55%);
H-2 ? LUMO (22%)
H-1 ? L+1 (55%)
H-4 ? LUMO (63%);
H-3 ? LUMO (22%)
H-6 ? LUMO (54%);
H-3 ? L+1 (30%)
HOMO ? L+6 (60%)
H-5 ? L+2 (41%);
HOMO ? L+6 (15%)
dRu/p bzimpy
dRu/p bzimpy
dRu/p bzimpy
?
?
?
p bzimpy
pbzimpy
pbzimpy
dRu
? pbzimpy
dRu/p bzimpy
?
pbzimpy
334.5
332.5
0.0274
0.0217
dRu
/
pbzimpy
?
?
pbzimpy
pbzimpy
dRu//p bzimpy
318.3
0.3554
dRu
/
p PPh3//p bzimpy
?
pbzimpy
263.6
262.5
0.0763
0.2066
dRu
dRu
/
/
pbzimpy
? pPPh3/bzimpy
p
PPh3 ? d/pbzimpy
2
390.5
372.0
364.3
358.6
355.5
0.0216
0.1480
0.0481
0.0291
0.1068
HOMO ? LUMO (95%)
H-1 ? LUMO (80%)
HOMO ? L+1 (89%)
H-2 ? LUMO (63%)
H-2 ? LUMO (11%);
H-2 ? L+2 (39%);
HOMO ? L+2 (24%)
H-3 ? LUMO (12%);
H-2 ? LUMO (12%);
H-2 ? L+1 (21%)
H-3 ? LUMO (65%);
H-2 ? L+1 (24%)
H-4 ? LUMO (77%)
H-5 ? LUMO (86%)
H-4 ? L+1 (67%)
H-2 ? L+6 (82%)
HOMO ? L+10 (38%);
HOMO ? L+11 (21%)
dRu/p bzimpy
p bzimpy pbzimpy
dRu/p bzimpy
dRu pbzimpy
dRu/p bzimpy
? p bzimpy
Fig. 5. The overlap partial density of states diagrams (OPDOS) for the 1 and 2
complexes.
?
?
p bzimpy
?
?
pbzimpy/PPh3
341.3
336.1
0.2679
0.0105
dRu/p bzimpy/CO
?
pbzimpy
dRu/p bzimpy/CO
?
?
pbzimpy
?
pbzimpy
pbzimpy
297.2
292.3
284.9
267.6
264.8
0.0997
0.0361
0.152
0.0103
0.0231
dRu/p bzimpy/CO
p bzimpy/PPh3
dRu/p bzimpy/CO
dRu pbzimpy
dRu/p bzimpy
?
pbzimpy
?
?
p PPh3
erty, which is related to the nature of the aromatic rings in the
2,6-bis-(benzimidazol-2-yl)-pyridine molecule.
Analysis of the frontier molecular orbitals is useful for under-
standing the spectroscopic properties such as electronic absorption
and emission spectra of organometallic complexes. The electronic
structure of complexes 1 and 2 are similar because of similar com-
position of their coordination sphere. The densities of states (DOS)
in terms of Mulliken population analysis were calculated using the
GaussSum program and Fig. 6 presents the composition of the frag-
ment orbitals contributing to the molecular orbitals for complexes
1 and 2. The HOMOs are mainly localized on the ruthenium atoms
with contribution from bzimpy ligand. The participations of dRu
orbitals in HOMO to HOMO–5 in the electronic structures of the
2
complexes are in the range from 74% to 35%. The dz ruthenium
2
Ày
2
orbital plays role in LUMO+2 and dx
orbitals participate in
LUMO+12 in the complexes. LUMO and LUMO+1 are localized on
the bzimpy ligands.
3.4. Experimental and theoretical electronic spectra
The UV–Vis spectra of the complexes 1 and 2 are similar and the
maxima close to 374, 332, 260 nm and 340, 291, 269 nm were
measured. Based on the calculated electronic structure of the
complexes the bzimpy ligands participations in the transitions
are expected. The electronic spectra of the complexes were calcu-
lated with the TDDFT method with methanol as solvent in the
Polarizable Continuum Model (PCM). As one can see from the data
collected in Table 5 the Charge Transfer transitions are dominant in
the electronic spectra of the complexes. These calculated transi-
tions up to ꢁ260 nm have Metal-to-Ligand Charge Transfer charac-
Fig. 6. The fluorescence spectra of the 1 and 2 complexes in the dichloromethane
solutions (c = 1 Â 10À3 mol/dm3).
calculated Wiberg indices (Table 4) showing covalent character of
Ru–H bond as well as with the bond distance shorter than 1.5 Å
(Table 2). Considering the interaction of bzimpy ligand with ruthe-
nium central ion, one can see that it shows strong acceptor prop-

´
227
J.G. Małecki, A. Maron / Polyhedron 44 (2012) 221–227
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sitions proceed between the frontier HOMOs and LUMOs (mainly
LUMO+1/+2). Due to the localization of LUMO, LUMO+1/+2 on the
bzimpy and share of this ligand in HOMOs involved in the transi-
tions, the Ligand-to-Ligand Charge Transfer character plays role in
the UV–Vis spectrum of the complexes.
Summarizing two new ruthenium(II) complexes with 2,6-bis-
(benzimidazol-2-yl)-pyridine functions as bidentate ligand were
synthesized and characterized by infra red, proton and phosphorus
nuclear magnetic resonance, electronic absorption spectroscopy
and X-ray crystallography. In the complexes the bzimpy ligand ex-
ists as protonated in [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH complex
and deprotonated form in [RuH(CO)(bzimpy)(PPh3)2]ÁCH3OH ob-
tained in the reaction in the presence of azide anion. In the crystal
structure of the complexes, some types of noncovalent interactions
between aromatic rings have been found. Electronic structures of
the complexes have been determined using the density functional
theory (DFT) method, and employed for discussion of its proper-
ties. The bzimpy ligands play significant role in their electronic
structure and have a dominant participation in the UV–Vis spectra.
The lack of luminescence of these complexes is probably related
with the mixed nature of the transitions in which the MLCT transi-
tions have significant share of the LLCT character.
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Acknowledgement
Calculations have been carried out in Wroclaw Centre for Net-
working and Supercomputing (http://www.wcss.wroc.pl).
Appendix A. Supplementary data
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CCDC 871977 and 871976 contains the supplementary crystal-
lographic data for [RuH(CO)(bzimpy)(PPh3)2]ClÁCH3OH and [RuH
(CO)(bzimpy)(PPh3)2]ÁCH3OH complexes. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
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Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk.
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