Synthesis, characterization and molecular structure of Ru(II) complex with benzoylpyrazine carboxylic acid derivatives

Article abstract of DOI:10.1016/j.poly.2012.04.033

Two benzoylpyrazine ligands containing carboxyl and amide functions and their hydride-carbonyl complexes of ruthenium were synthesized and characterized by infrared, proton, carbon phosphorus nuclear magnetic resonance, electronic absorption and emission

Full text of DOI:10.1016/j.poly.2012.04.033

Polyhedron 41 (2012) 104–114
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and molecular structure of Ru(II) complex
with benzoylpyrazine carboxylic acid derivatives
a
b
c
b
J.G. Małecki a, , A. Maron , M. Serda , M. Dolezal , J. Polanski
⇑
´
´
a Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
b Department of Organic Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice, Poland
c Department of Pharmaceutical Chemistry and Drug Control, Charles University in Prague, Faculty of Pharmacy, 500-05 Hradec Králové, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Two benzoylpyrazine ligands containing carboxyl and amide functions and their hydride-carbonyl com-
plexes of ruthenium were synthesized and characterized by infrared, proton, carbon phosphorus nuclear
magnetic resonance, electronic absorption and emission spectroscopy and X-ray crystallography. The
experimental studies were completed by theoretical calculations. From the electronic spectrum of the
complex the Racah’s and nepheloauxetic parameters are calculated. The electronic structure of the com-
plexes, presented in particular by the density of states diagram, have been correlated with its ability to
fluoresce and used to analyze the UV–Vis spectra.
Received 30 March 2012
Accepted 25 April 2012
Available online 7 May 2012
Keywords:
Pyrazines
Ruthenium(II) hydride carbonyl complexes
X-ray structure
UV–Vis
Ó 2012 Elsevier Ltd. All rights reserved.
Luminescence
DFT
TD-DFT
1. Introduction
properties that are caused by a low lying unoccupied
p-molecular
orbital and by the ability to act as a bridging ligand.
Pyrazine is crucial biomolecule which possess excellent coordi-
nation properties as convenient N-donor ligand [1,2]. Moreover the
structure of pyrazine can be considered as a privileged structure
which occurs in many bioactive compounds [3,4]. For example pyr-
azinamide (PZA), an analogue of nicotinamide, is a unique common
used anti-tuberculosis prodrug which is activated to active form in
acid conditions. Dolezal et al. described [5,6] antifungal and anti-
mycobacterial properties of selected benzoylpyrazines and their
derivatives. Thus the investigation of pyrazine ruthenium com-
plexes could be interesting due to their potential applications in
drug development.
On the other hand the ruthenium hydride complexes containing
carbonyl and triarylphosphine ligands are interesting due to their
reactivity and efficiency as catalysts in wide spectrum of reactions
[7–12]. The studies on synthesis and characterization of ruthenium
complexes containing nitrogen heteroaromatic ligands have re-
ceived considerable recent attention, owing to their interesting
photophysical and photochemical properties. Pyrazine, its deriva-
tives as well as other 1,4-diazines, i.e. compounds with partial pyr-
azine structure (e.g. quinoxaline, phenazine, pteridine, flavin and
their derivatives), demonstrate unique physico-chemical
The azine ligands have energetically low lying p-antibonding
orbitals, which can accept electrons from filled metal d orbitals.
In consequence, they can exhibit charge transfer bands with inter-
esting spectroscopic properties in the visible region [13]. Ligands
containing pyrazine ring are widely studied and their
p-donor
properties are interesting. Its combination with other donor atoms
should in principle afford complexes with tunable spectroscopic
properties [14–16]. The hydride ligand – a powerful
r-donor – is
found to be very efficient at compensating the electron deficiency
at the metal central ion in complexes. The ‘‘trans effect’’ of HÀ li-
gand and the interaction between carbonyl and donor ligands in
trans positions to one another are stabilizing factors which explain
stability of these complexes [17], are interesting due to theirs
properties.
Here is reported an experimental and quantum chemical study
of ruthenium hydride carbonyl complex with pyrazine derivative
ligand. The quantum chemical study included a characterization
of the molecular and electronic structures of the complex by anal-
ysis of optimized molecular geometry, electronic populations by
using the natural bond orbitals scheme. The latter was used to
identify the nature of the interactions between the ligands and
the central ion. The calculated density of states showed the inter-
actions and influences the orbital composition in the frontier elec-
tronic structure. The time dependent density functional theory
⇑
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.2012.04.033

J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
105
(TD-DFT) was finally used to calculate the electronic absorption
spectra. Based on a molecular orbital scheme, these results allowed
the interpretation of the UV–Vis spectra obtained at an experimen-
tal level. The complex reported in this paper combine the interest
in ruthenium hydride carbonyl coordination compounds and com-
plexes containing nitrogen heterocyclic ligands [18–26].
UV–Vis (methanol, k [nm]): 360.2 (1.18), 312.2 (2.17), 273.8
(3.02), 214.6 (4.27). MP: 235 °C (lit [5], 235-236 °C).
2.3. Synthesis of the complexes
[RuHCl(CO)(PPh3)3] (0.2 mmol) and equimolar quantities of 5-
(4-hydroxybenzoyl)pyrazine-2-carboxylic acid ((4-OH)BPA) and
O
O
N
N
N
N
HO
HO
NH2
OH
O
O
5-(4-hydroxybenzoyl)pyrazine-2-carboxylic acid
(4OH)-BPA
5-(4-hydroxybenzoyl)pyrazine-2-carboxamide
(4OH)-BPAm
5-(4-hydroxybenzoyl)pyrazine-2-carboxamide ((4-OH)BPAM) in
CH3OH (80 cm3) were refluxed until the complex suspension dis-
solved and also 1 h longer. The reaction solution was filtered and
the single crystals were obtained by slow evaporation of solvent.
[RuH(CO)((4-OH)BPA)(PPh3)2]ÁCH3OHÁH2O (1): IR: 3565, 3495
2. Experimental
All free ligands were synthesized using modified method of
Dolezal et al. [5]. Briefly, a stirred mixture of the 4-hydroxybenzal-
dehyde (120 mmol), and pyrazine-2-carboxamide or pyrazine-2-
carbocyclic acid (40 mmol) in 50% H2SO4 (80 ml) and 99% AcOH
(80 ml) was cooled to À20 °C. To this mixture 80% tert-BuO2H
m
m
m
OH; 3054
as(COO); 1603
Ph(P–Ph); 1339
plane); 862 d(Ru–H); 744 d(C–C
m
PhH; 2923
m
CH(methanol); 1970; 1938
m
RuCO/RuH; 1626
plane); 1434
m
CN/C@C; 1573
m
as(COO); 1479 d(C–CH
in the
m
s(COO); 1284, 1274, 1171, 1092 d(pyz ring); 1013
(13.5 g, 120 mmol) and
a
solution of FeSO4Á7H2O (33.4 g,
d(CH
plane); 517, 496
120 mmol) in water were added simultaneously. The temperature
must not exceed 0 °C. The resulting mixture was stirred for addi-
tional 3 h, during which the temperature was allowed to rise to
room temperature. The reaction product (yellow crystals) was fil-
tered and crystallized from MeOH.
in the
out of the
m(COO–Ru–P)
.
1H NMR (400 MHz, CDCl3) d 8.39 (d, J = 2.9 Hz, pyz), 8.12–7.66
(m, PPh3), 7.61 (d, J = 2.1 Hz, Ph), 7.25–7.21 (m, PPh3), 7.01 (dd,
J = 11.2, 6.7 Hz, Ph), 3.98 (s, OH), 3.51 (s, CH3OH), 2.62–2.57 (m,
H2O), À9.57 (t, J = 19.3 Hz, Ru–H). 31P NMR (162 MHz, CDCl3) d:
The [RuHCl(CO)(PPh3)3] complex was synthesized according to
the literature method [27].
43.83 (s, PPh3). UV–Vis (methanol, k [nm] (loge)): 422 (1.16),
361 (1.39), 314 (2.37), 274 (4.76), 208 (4.28).
[RuH(CO)((4-OH)BPAM)(PPh3)2]Á2CH3OH (2): IR: 3547, 3415
OH NH; 3053 PhH; 2014; 1925 RuCO/RuH; 1652 CONH; 1598
CN/C@C; 1480 d(C–CH plane); 1433 Ph(P–Ph); 1275, 1171, 1091
2.1. Synthesis of 5-(4-hydroxybenzoyl)pyrazine-2-carboxylic acid
m
m
/
m
m
m
m
Yield = 14% IR: 3457, 3354 mOH
;
3057, 3000, 2947 mPhH
C@C; 1573 as(COO); 1488
s(COO); 1297 (-C(O)-); 1273,
plane); 940, 843 (pyz,Ph); 761
;
in the
d(pyz ring/NH); 1027 d(CH in the plane); 844 d(Ru–H); 865 d(C–C out of the plane)
.
1914water; 1698
m
COOH; 1640
mCN; 1602
m
m
m
c
1H NMR (400 MHz, CDCl3) d 9.77 (d, J = 101.9 Hz, pyz), 8.32, 8.18
(s, Ph), 7.88–7.24 (m, PPh3), 6.96 (s, Ph), 6.08 (d, J = 150.0 Hz, NH),
3.51 (s, OH), À9.80 (t, J = 18.3 Hz, Ru–H).
d(C–CH plane); 1451
mPh; 1357
m
in the
1165, 1038 dpyz ring); 1013 d(CH
in the
d(C(OH)@O); 621, 505
.
(C–C out of the plane)
31P NMR (162 MHz, CDCl3) d: 44.86 (s), 44.57 (s). UV–Vis (meth-
1H-NMR (d6-DMSO, 400 MHz): 10.66 (s, 1H, OH), 9.25 (m, 1H,
pyrazine), 9.14 (m, 1H, pyrazine), 7.93 (d, 2H, J = 7.2 Hz, ArH),
6.91 (d, 2H, J = 7.6 Hz, ArH).
anol, k [nm] (loge)): 457 (1.16), 374 (1.29), 311 (2.47), 276 (4.56),
214 (4.88).
13C-NMR (d6-DMSO, 100 MHz): 190.2, 165.1, 163.5, 152.9,
145.2, 144.9, 144.3, 134.0, 126.8, 115.9. UV–Vis (methanol, k
[nm]): 370.2 (1.20), 311.5 (2.21), 277.5 (3.20), 204.5 (4.38) MP:
195–196 °C.
2.4. Physical measurements
Infrared spectrum was recorded on a Perkin Elmer spectropho-
tometer in the spectral range 4000–450 cmÀ1 using KBr pellet.
Electronic spectrum was measured on a Lab Alliance UV–Vis
8500 spectrophotometer in the range of 600–180 nm in methanol
2.2. Synthesis of the 5-(4-hydroxybenzoyl)pyrazine-2-carboxamide
solution. 1
H
13C and 31P NMR spectra were obtained at room tem-
Yield: 12% IR: 3438
1634 CN; 1597 C@C; 1478 d(C–CH in the plane); 1448
1384, 1298
843 (pyz,Ph); 540, 508
m
OH/NH; 3192
m
PhH; 1922water; 1687 mCO–NH2
;
;
perature in CDCl3 or d6-DMSO using a Bruker 400 spectrometer.
Luminescence measurement was made in methanolic solution on
an F-2500 FL spectrophotometer at room temperature.
m
m
m
Ph, 1415 mCONH
m
(–C(O)–); 1278, 1168 dpyz ring); 1034 d(CH in the plane); 927,
c
.
(C–C out of the plane)
1H-NMR (d6-DMSO, 400 MHz):10.55 (s, 1H, OH), 9.23 (d, 1H,
J = 1.3 Hz, pyrazine), 9.06 (d, 1H, J = 1.3 Hz, pyrazine), 8.43 (bs,
1H, NH2), 7.99 bs 1H (NH2), 7.96-7.88 (m, 2H, ArH), 6.94–6.87
(m, 2H, ArH). 13C-NMR: (d6-DMSO, 100 MHz): 190.2, 164.9,
163.2, 152.6, 146.2, 143.8, 142.2, 134.0, 126.7, 115.6.
2.5. Computational methods
The calculations were carried out using GAUSSIAN09 [28] program.
Molecular geometry of the singlet ground state of the complex was

106
J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
fully optimized in the gas phase at the B3LYP/DZVP level of theory
[29,30]. For the compound a frequency calculation was carried
out, verifying that the optimized molecular structure obtained cor-
responds to energy minimum, thus only positive frequencies were
expected. The DZVP basis set [31] with f functions with exponents
1.94722036 and 0.748930908 was used to describe the ruthenium
atom and the basis 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 dependent density functional theory) method [32]
was employed to calculate the electronic absorption spectra of the
complexes in the solvent PCM (Polarizable Continuum Model) mod-
el. In this work 90 singlet excited states were calculated as vertical
transitions for the complexes. A natural bond orbital (NBO) analysis
was also performed for all the complexes using the NBO 5.0 package
[33] included in GAUSSIAN09. Natural bond orbitals are orbitals local-
ized on one or two atomic centers, that describe molecular bonding
in a manner similar to a Lewis electron pair structure, and they cor-
respond to an orthonormal set of localized orbitals of maximum
occupancy. NBO analysis provides the contribution of atomic orbi-
Lorentz, polarization and empirical absorption correction using
spherical harmonics implemented in SCALE3 ABSPACK scaling
algorithm [CrysAlis RED, Oxford Diffraction Ltd., Version
1.171.29.2] were applied. The structure was solved by the direct
method and subsequently completed by the difference Fourier
recycling. All the non-hydrogen atoms were refined anisotropically
using full-matrix, least-squares technique. All the hydrogen atoms
were found from difference Fourier synthesis after four cycles of
anisotropic refinement, and refined as ‘‘riding’’ on the adjacent car-
bon atom with individual isotropic temperature factor equal 1.2
times the value of equivalent temperature factor of the parent
atom. The OLEX2 [35] and SHELXS97, SHELXL97 [36] programs were
used for all the calculations. Details concerning crystal data and
refinement are gathered in Table 1.
3. Results and discussion
All free ligands were synthesized using modified method of
Dolezal et al. [5]. Briefly, a stirred mixture of the 4-hydroxybenzal-
dehyde (120 mmol), and pyrazine-2-carboxamide or pyrazine-2-
carbocyclic acid (40 mmol) in 50% H2SO4 (80 ml) and 99% AcOH
(80 ml) was cooled to À20 °C. To this mixture 80% tert-BuO2H
(13.5 g, 120 mmol) and a solution of FeSO4Á7H2O (33.4 g, 120 mmol)
in water were added simultaneously. The temperature must not ex-
ceed 0 °C. The resulting mixture was stirred for additional 3 h, dur-
ing which the temperature was allowed to rise to room
temperature. The reaction product (yellow crystals) was filtered
and crystallized from MeOH. The complexes were synthesized by
simply reactions between [RuHCl(CO)(PPh3)3] and equimolar quan-
tities of the ligands in refluxed methanolic solutions.
tals (s, p, d) to the NBO
r and p hybrid orbitals for bonded atom
pairs. In this scheme, three NBO hybrid orbitals were 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 interac-
tion with the ruthenium atom. The contribution of a group (ligands,
central ion) to a molecular orbital was calculated using Mulliken
population analysis. GAUSSSUM 2.2 [34] was used to calculate 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.
2.6. Crystal structure determination and refinement
3.1. Spectroscopic characterization of the ligands and complexes
X-ray intensity data were collected with graphite monochro-
mated Mo Ka radiation at temperature of 295.0(2) K, with x scan
mode using the Oxford Diffraction Gemini A Ultra diffractometer.
The structures of the 5-(4-hydroxybenzoyl)pyrazine-2-carbox-
ylic acid and amide derivative were confirmed by 2D-NMR tech-
niques (COSY, HMQC and NOESY experiments). In addition the
Table 1
Crystal data and structure refinement details of (4-OH)BPA, [RuH(CO)((4-OH)BPA)(PPh3)2]ÁCH3OHÁH2O (1), (4-OH)BPAm and [RuH(CO)((4-OH)BPAm)(PPh3)2]Á2CH3OH (2).
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C12H8N2O4Á2(H2O)
280.24
295.0(2)
C49H38N2O5P2Ru,CH4OÁH2O
C12H9N3O3ÁH2O
261.24
295.0(2)
C49H39N3O4P2RuÁ2(CH4O)
947.88
960.93
295.0(2)
triclinic
960.93
monoclinic
P21/n
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
6.7346(5)
7.2143(5)
13.9007(10)
86.321(6)
82.561(6)
66.713(7)
615.06(7)
2
11.2730(5)
13.1500(6)
15.0795(7)
90.857(4)
94.858(3)
95.041(4)
2218.17(18)
2
6.6417(4)
7.1466(5)
13.4848(9)
85.194(6)
76.503(5)
67.397(6)
574.57(7)
2
17.9948(16)
15.4596(8)
18.8528(16)
90
117.001(11)
90
4673.0(8)
4
1.366
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
Volume (Å3)
Z
DCalc (mg/m3)
1.513
0.123
292
1.419
0.481
976
1.510
0.116
272
Absorption coefficient (mmÀ1
F(000)
)
0.456
1984
Crystal dimensions (mm)
h range for data collection (°)
Index ranges
0.24 Â 0.06 Â 0.04
3.39–25.05
À8 6 h 6 8
À8 6 k 6 8
À16 6 l 6 16
8729
0.22 Â 0.06 Â 0.04
3.37–25.05
À13 6 h 6 13
À15 6 k 6 15
À17 6 l 6 17
20792
0.17 Â 0.10 Â 0.05
3.41–25.05
À7 6 h 6 7
À8 6 k 6 8
À16 6 l 6 16
4747
0.15 Â 0.11 Â 0.09
3.38–25.05
À20 6 h 6 21
À18 6 k 6 18
À22 6 l 6 19
25126
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit on F2
)
2165 (0.0542)
2165/0/189
0.979
7840 (0.0558)
7840/0/569
0.946
2029 (0.0209)
2029/0/216
1.068
2029 (0.0479)
8256/0/580
1.051
Final R indices [I > 2
r
(I)]
R1 = 0.0402
wR2 = 0.0844
R1 = 0.0759
wR2 = 0.0910
0.165 and À0.189
R1 = 0.0444
wR2 = 0.0810
R1 = 0.0763
wR2 = 0.0873
0.582 and À0.456
R1 = 0.0371
wR2 = 0.0882
R1 = 0.0500
wR2 = 0.0938
0.138 and À0.200
R1 = 0.0602
wR2 = 0.1529
R1 = 0.0922
wR2 = 0.1678
1.020 and À0.700
R indices (all data)
Largest diff. Peak and hole (eÅÀ3
)

J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
107
The 31P NMR spectra of the complexes show singlet at
43.83 ppm in the case of complex (1) and two close together sing-
lets at 44.86 and 44.57 ppm on the spectrum of complex (2). The
1H NMR spectra of the complexes show set of signals correspond-
ing to the PPh3 ligands and the aromatic protons of the ligands. The
OH and NH protons gave signals at 3.98, 3.51 and 6.08 ppm,
respectively. The signals at high field (À9.57 and 9.80 ppm) indi-
cate the presence of the hydride coordinated with the ruthenium.
The shifts of the signals are due to the shielding effect of the metal
and to the charge of the hydrogen atom. The signals are triplets due
to coupling with the two trans equivalent phosphorus atoms
(JHP ꢀ 19.3 and 18.3 Hz). The complexes display strong Ru–H and
C„O bands at 1970, 1938 cmÀ1 and 2014, 1925 cmÀ1. The consid-
erable difference in the Ru–H stretching band in the complexes
suggests stronger interaction of hydride ligand with ruthenium(II)
central ion in complex (2). The C@N and C@C stretching bands in
the free ligands have maxima at 1640, 1602 cmÀ1 and 1634,
1597 cmÀ1, respectively. In the complexes the C@N bands are
shifted by about 36 cmÀ1 which supports efficient back donation
from dpRu to antibonding p⁄ orbitals. The stretching modes of
pyz
carboxyl group in the complex (1) and amide in (2) are decreased
by 78 and 36 cmÀ1 compared with free ligands which indicate the
coordination of ruthenium central ions by the COOÀ and C(O)NH2
groups, respectively.
3.2. Molecular structure
ꢀ
The ligands crystallise in P1 space groups and the complexes in
ꢀ
triclinic P1 and monoclinic P21/n space groups, respectively. Fig. 1
presents the molecular structures of the ligands and complexes
and the selected bond distances and angles are collected in Table
2. The structures of the complexes can be considered as a distorted
octahedral. The angles between ligands are different than expected
for regular octahedron such as 82.5(9)° for C(1)–Ru(1)–H(1) and
79.8(9)° for P(2)–Ru(1)–H(1). The P(1)–Ru(1)–P(2) angles are lower
than 180° (166.16(3)° and 173.99(4)°). As one can see the angle be-
tween triphenylphosphine ligands in complex (1) more deviates
from the ideal angle and on the 31P NMR spectrum one signal is vis-
ible. In the structure of the complex electronic interaction (p–p
stacking) between PPh3 phenyl and pyrazine ring exists with the
plane-to-plane distance of 3.609 Å. The interaction may explain
the equivalence of the phosphorus in the solution of the complex.
In the complex (2) there is no such interaction and two 31P signals
are presented on the NMR spectrum. In the molecular structure of
the complexes the
p–p stacking interactions are visible. In the
complex (2) the phenyl ring of PPh3 ligand and the 4-hydroxy-
phenyl ring are T-shaped with distance 2.890 Å as is presented
on Fig. 2. In the crystal structures of the complexes intra- and in-
ter-molecular hydrogen bonds exist [37] collected in Table 3.
The Ru(1)–C(1) bond length in the complex (2) is longer by
0.03 Å than in complex (1) and accordingly C(1)–O(1) is shorter
by 0.011 Å in complex (2). In the structure of complex (1) the car-
bonyl ligand is in trans position to carboxyl group of the (4-HO)BPA
ligand. The electron-donor COOÀ group at Ru(II) ion delivers elec-
tron density via backbonding to the anti-bonding orbitals of the CO
and produces a decrease in the carbonyl bond length. Additionally
the decreasing of the CO vibration frequencies from 2014 to
1970 cmÀ1 in the complexes (1) and (2), respectively indicate the
differences in the acceptor properties of carboxylic acid and amide
ligands. In fact, by reducing the electron density on the metal the
Fig. 1. ORTEP drawing of (4-OH)BPA, (4-OH)BPAm ligands and [RuH(CO)((4-
OH)BPA)(PPh3)2], [RuH(CO)((4-OH)BPAm)(PPh3)2] complexes with 30% probability
thermal ellipsoids. Hydrogen atoms except H(1Ru) and solvent molecules in the
complexes structures are omitted for clarity.
carbonyl ligand it will receive the electron density via dp ?
p⁄
interaction, which would increase the bond order, in turn increas-
ing the vibration frequency of the CO bond. So it can be said that
the amide ligand behave as weaker donor with respect to the
carboxylic derivative. In the complexes considerable differences
are in the Ru–H bond lengths. Knowing about the limits of Fourier
values of proton conjugation constants in pyrazine ring (J = 1.3 Hz)
can be associated only with this regioisomers.

108
J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
Table 2
Selected bond lengths [Å] and angles [°] for [RuH(CO)((4-OH)BPA)(PPh3)2]ÁCH3OHÁH2O (1) and [RuH(CO)((4-OH)BPAm)(PPh3)2]Á2CH3OH (2) with the optimized geometry values.
(1)
(2)
Exp.
Calc.
Exp.
Calc.
Bond lengths (Å)
Ru(1)–C(1)
Ru(1)–N(1)
Ru(1)–O(2)/N(3)
Ru(1)–H(1)
Ru(1)–P(1)
Ru(1)–P(2)
C(1)–O(1)
1.812(4)
1.857
1.842(5)
2.147(4)
2.168(4)
1.26(4)
2.341(13)
2.351(13)
1.152(6)
1.864
2.162(2)
2.149(2)
1.61(3)
2.3741(9)
2.3489(9)
1.163(4)
2.232
2.161
1.62
2.435
2.433
1.164
2.190
2.207
1.64
2.427
2.427
1.165
C(13)–O(2)
[free ligand]
[1.205(2)]
1.271(4)
1.229
C(13)–O(3)
[free ligand]
C(13)–N(3)
[free ligand]
1.229(4) [1.302(2)]
1.297
1.262(6) [1.2282(18)]
1.288(6) [1.319(2)]
1.244
1.335
Angles (°)
O(2)/N(3)–Ru(1)–C(1)
N(1)–Ru(1)–C(1)
N(3)/O(2)–Ru(1)–N(1)
C(1)–Ru(1)–P(2)
O(2)/N(3)–Ru(1)–P(2)
N(1)–Ru(1)–P(2)
C(1)–Ru(1)–P(1)
O(2)/N(3)–Ru(1)–P(1)
P(1)–Ru(1)–N(1)
P(2)–Ru(1)–P(1)
C(1)–Ru(1)–H(1)
O(2)/N(3)–Ru(1)–H(1)
N(1)–Ru(1)–H(1)
P(2)–Ru(1)–H(1)
P(1)–Ru(1)–H(1)
Ru(1)–C(1)–O(1)
175.83(13)
101.03(13)
75.69(9)
92.06(11)
85.77(6)
95.82(7)
94.16(11)
88.73(6)
95.11(7)
166.16(3)
82.5(9)
100.6(9)
174.6(9)
79.8(9)
88.7(9)
178.1(3)
174.86
99.68
75.19
89.92
90.97
95.95
95.02
85.33
96.56
165.58
89.00
96.00
172.00
83.00
84.00
175.70
103.3(2)
177.5(2)
74.37(15)
90.10(17)
91.60(11)
90.88(11)
89.02(17)
94.39(11)
90.24(11)
173.99(4)
87(2)
169(2)
95(2)
87.0(19)
87.0(19)
179.0(5)
105.79
179.68
74.53
88.88
91.63
91.09
88.82
91.86
91.19
176.24
89.00
166.00
91.00
89.00
88.00
179.56
synthesis and the problems in recognizing artifacts in the immedi-
ate neighborhood of heavy atoms it is doubtful if a reliable position
for the hydrogen atom bound to the Ru-atom can be found in the
difference Fourier map avoiding the danger of mistaking the effects
of the series termination errors for a true atomic position. In the
studied complexes that is very possible taking into account the
bond lengths in complex (2) of 1.26(4) Å shorter than in (1) about
0.35 Å but the ruthenium-hydride distances are known [38,39]. In
the complex (2) the hydride ligand is in trans position to amide
nitrogen donor. As one can see from the data in Table 2 the
C–Namide bond length in the free ligand is reduced in complex by
about 0.031 Å and the amide C@O bond increases to 1.262(6) Å.
The electron-donor hydride ligand at Ru(II) ion delivers electron
density via backbonding to the anti-bonding orbitals of the amide
and produces a significant decrease of about 35 cmÀ1 in the vibra-
tion frequency of the coordinated amide compared to free ligand.
The electronic effects are supported by theoretically determined
charge values which indicate the more negative charge of Ru(II)
central ion (À0.83) in (2) than in complex (1) (À0.72). Additionally
the charges on the hydride ions are also different in the complexes
0.05 in (1) and 0.01 in complex (2).
ones and the differences in calculated and experimental spectra
mainly result from the negligence of intermolecular interactions
for the gas phase. From the data collected in Table 2, one may
see that the majority of differences between the experimental
and calculated geometries are found in the Ru–P distance
(ꢀ0.08 Å) and the maximum angle differences are visible in C(1)–
Ru(1)–H(1) 6.5°. The C„O bond length does not undergo impor-
tant change and slight increase of ꢀ0.013 Å is seen.
The NBO analyses were performed for the complexes which al-
lowed knowing the nature of the coordination between ruthenium
and the atoms of the ligands directly interacting with it. This
methodology also gave a better understanding of the optimized
molecular structures. In the analysis was found that the N,O- and
N,N-donor ligand does not show covalent bonding with ruthenium.
The Coulomb-type interaction between the ruthenium central ions
and pyrazine carboxylic acid and amide derivative ligands is
clearly visible in the calculated Wiberg bond indices whose values
are considerably lower than one. The Ru–Npyz and Ru–O bond indi-
ces for complex (1) are close to 0.38 and 0.41 and in the complex
(2) the ruthenium pyrazine nitrogen bond is slightly more covalent
(W = 0.48) and the Wiberg index for Ru–Namide is 0.42. The Ru–P
bond orders are also smaller than 1 (ꢀ0.7). For the carbonyl group
of the complex, 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 CꢁO bond orbitals
are polarized towards the oxygen end. The oxygen atom of the car-
bonyl ligand has one lone pair (LP) orbital. The charges of CO li-
gands can be easily calculated by summing the individual
charges on the carbon and oxygen atoms and have values 0.19 in
both complexes. The Wiberg indexes of the CO bonds in the com-
plexes are reduced by about 0.23 with respect to free CO
(WCO = 2.23) and the WRu–C in the complexes have values 1.34
3.3. Optimized geometries, hybrid and molecular orbitals description
The ground state 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. The calculated IR frequencies of the complexes
shown in Fig. 3 confirm calculated structures with experimental

J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
109
Fig. 2. The p-stacking interactions in the [RuH(CO)((4-OH)BPAm)(PPh3)2] (2) complex. The distances are in [A]. The position of the molecule #2 is generated by 1 À x,
1 À y, À z symmetry operation.
Table 3
dyz – 1.90; dx2
– 1.16; dz2 – 1.21. The d-electron populations of
Ày2
Hydrogen bonds for [RuH(CO)((4-OH)BPA)(PPh3)2]ÁCH3OHÁH2O (1) and [RuH(CO)((4-
7.59 for (1) and 7.62 for (2) correspond to the oxidation state
Ru(0), not to their formal oxidation state Ru(II). This is a supporting
argument for ligands to dRu electron transfer. The data suggest that
the donation from ligands to dRu orbitals plays a role in the elec-
tronic structure of the complexes, and in order to determine the
donation, the stabilization energies1 were calculated. The stabiliza-
tion energies calculated in NBO analyses have shown that the lone
pairs localized on the N(O/N)-donor atoms of ligands in the com-
plexes donate the charge to ruthenium, and the stabilization ener-
OH)BPAm)(PPh3)2]Á2CH3OH (2) (Å and o).
D–HÁ Á ÁA
(1)
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
<(DHA)
O(5)–H(5A)Á Á ÁO(6) #1
O(6)–H(6)Á Á ÁO(3) #2
O(7)–H(7A)Á Á ÁO(4) #3
O(7)–H(7B)Á Á ÁO(3) #4
C(45)–H(45)Á Á ÁO(7)
C(49)–H(49)Á Á ÁO(2)
0.82
0.73
0.85
0.85
0.93
0.93
1.79
2.06
2.11
1.99
2.57
2.51
2.581(4)
2.776(4)
2.953(4)
2.820(4)
3.358(6)
3.067(4)
161.1
167.0
172.4
166.7
142.5
118.8
gies
(DEij) are 131.97 and 112.23 kcal/mol for (1) and (2),
(2)
respectively. The back donations to pyrazine type ligands are equal
to 33.34 and 43.21 kcal/mol for complexes (1) and (2), respectively
O(4)–H(4)Á Á ÁO(6)
O(5)–H(5A)Á Á ÁO(3)
O(6)–H(6)Á Á ÁO(5) #5
C(8)–H(8)Á Á ÁN(2)
C(42)–H(42)Á Á ÁO(3) #6
0.82
0.82
0.82
0.93
0.93
1.85
1.82
1.88
2.36
2.58
2.640(7)
2.635(6)
2.696(8)
2.861(7)
3.383(8)
159.8
176.6
170.9
113.5
144.9
and the data point out the higher
derivative.
p-acceptor properties of amide
Analysis of the frontier molecular orbitals is useful for under-
standing the spectroscopic properties as electronic absorption
and emission spectra of organometallic complexes. The densities
of states (DOS) in terms of Mulliken population analysis were cal-
culated using the GAUSSSUM program and Fig. 4 presents the compo-
sition of the fragment orbitals contributing to the molecular
orbitals for the studied complex and the insets present the overlap
Symmetry transformations used to generate equivalent atoms: #1 1 À x, 1 À y, Àz;
#2 1 + x, y, z; #3 1 À x, 1 À y, 1 À z; #4 Àx, 1 À y, 1Àz; #5 x, À1 + y, z; #6 1/2 + x, 3/
2 À y, 1/2 + z.
and 1.32 in complexes (1) and (2), respectively. These weak values
are in agreement with the elongation of the C„O bond in com-
plexes and charge distribution in the terminal bonding carbonyl
group to ruthenium central ion. Moreover these points to rather
small differences in the properties of donor–acceptor of studied
pyrazine derivatives manifested as evidenced by the acceptance
of charge by a carbonyl ligand in the complexes. Additionally sim-
ilar values are in the ruthenium(II) complexes with pyrazine (1.31)
[26], pyrazine-2-carboxylic acid and pyrazine-2,3-dicarboxylic
acid ligands (WRu–C = 1.35) [40]. The similar values of Wiberg in-
dexes suggest almost the same donor–acceptor properties of the
pyrazine and its derivatives. The natural charges on the ruthenium
central ions are À0.72 for (1) and À0.83 for (2) and the occupancies
of the ruthenium d orbitals are as follows: (1) dxy – 1.84; dxz – 1.70;
partial density of states. As one can see the p-acceptor interaction
between carbonyl groups towards ruthenium(II) in complex (1) is
smaller compared with interaction in complex (2). To compare
the properties of the pyrazine and its derivatives as ligands on
the Fig. 5 are presented the OPDOS diagrams for ruthenium hy-
dride-carbonyl complexes with the ligands. As one can see the
interaction of accepting properties of pyrazine is smaller than its
carboxylic derivative (pyz-2-COOÀ) and the amide ligand (4-HO)B-
PAm is strongest p-acceptor from these ligands.
1
D
Eij (kcal/mol) associated with delocalization is estimated by the second-order
Eij = qi (F(i,j)2)/(ej
i) where qi is the donor orbital occupancy, ei, ej
perturbative as:
D
À
e
are diagonal elements (orbital energies) and F(i,j) is the off-diagonal NBO Fock or
dyz – 1.73; dx2
– 1.31; dz2 – 1.01 and (2) dxy – 1.68; dxz – 1.66;
Kohn–Sham matrix element.
Ày2

110
J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
Fig. 3. Experimental and calculated IR spectra of [RuH(CO)((4-OH)BPA)(PPh3)2] and [RuH(CO)((4-OH)BPAm)(PPh3)2] complexes.
The electronic structures of the complexes are similar. The
complex (2) with amide derivative ligand the HOMO and HOMOÀ1
HOMOs are localized on the d ruthenium orbital (53% in (1) and
33% in (2)) with contribution of pyrazine derivative ligands. In
the complexes dRu play significant role in HOMOÀ1 and HOMOÀ2
in the complex (1) and in the case of complex (2) in the HOMOÀ2
to HOMOÀ6 range. LUMO and LUMO+1 are localized on the pyra-
zine derivative ligands (97%) in both complexes as can be seen on
orbitals are shifted to higher energy and the ligand play dominant
role in the frontier occupied orbitals.
3.4. Experimental and theoretical electronic spectra
The UV–Vis spectra of the complexes are similar and in the
spectra the maxima close to 422, 361, 314 and 457, 374, 311 were
measured. Based on the pseudooctahedral geometry of the com-
plex and taking into account the d–d transitions assigned to
1A1 ? 1T1 and 1A1 ? 1T2 in octahedron (or 1A1 ? 1A2/B1/E in lower
symmetry fields), the ligand field parameters 10Dq can be esti-
mated to 23468 cmÀ1 and 21514 cmÀ1 for complexes (1) and (2),
the DOS diagrams in Fig. 4. The dz2 and dx2
orbitals of ruthenium
Ày2
are visible in LUMO+2 orbitals (17% and 18%) and in higher virtual
orbitals in the range of LUMO+16 to LUMO+19 with the contribu-
tion of p⁄ orbitals of carbonyl ligands. The difference in electronic
structures of the complexes manifest itself in the HOMO–LUMO
gaps 3.27 eV in (1) and 2.67 eV in complex (2). In the case of

J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
111
Fig. 4. The density-of-states diagrams with overlap density-of-states as inset diagram for [RuH(CO)((4-OH)BPA)(PPh3)2] and [RuH(CO)((4-OH)BPAm)(PPh3)2] complexes.
respectively. Adequately Racah’s parameters are B = 250 and
304 cmÀ1 and the nepheloauxetic parameters have values b55
calculated at 337.8 nm and 372.9 (HOMO ? L+2) in complexes (1)
and (2), respectively but this is no ‘‘clear’’ LF transition due to con-
tribution of ligands in HOMO and LUMO+2 molecular orbitals. The
=
0.35 and 0.42. The bands observed in the vicinity of 300 nm have
been attributed to intra- and interligand (pbC6H6 ? 3dphosphorus
intraligand transitions (
vicinity of 300 nm. The highest experimental band close to
p
(PPh3) ? p⁄(L)) were calculated in the
and
Transfer transitions (dRu
est experimental band close to 208, 214 nm may result from tran-
p
?
p
C@C) transitions with admixture of Metal-Ligand Charge
?
p⁄
and dRu
?
p⁄Ph). The high-
210 nm may result from transitions in the PPh3 and from
excitations in the pyrazine derivative ligands.
p ?
p⁄
N,O/N-ligand
sitions in the PPh3 ligands and from
N,O/N-heteroaromatic ligands.
p
?
p⁄ excitations in the
The emission characteristic of the complex (1) has been
examined in the methanol solution (with concentration of
5 Â 10À4 mol/dm3) at room temperature. The excitation at
301 nm gave fluorescence with maximum at 399 nm as presents
Fig. 6a. The red shifts of the emission maximum is typical to ruthe-
nium(II) complexes and the emission originating from the metal to
ligand charge transfer (MLCT) state, derived from the excitation
In Table 4, several calculated electronic transitions and their
assignments to the experimental absorption bands are gathered.
The assignment of the calculated orbital excitations to the experi-
mental bands was based on an overview of the composition and
relative energy to the orbitals HOMO and LUMO involved in the
electronic transitions. As can be seen most of the excitations have
Metal-to-Ligand Charge Transfer character. The d ? d transition was
involving a d
?
pligand transition. The assignment is supported
p
by the analysis of the frontier orbitals of the corresponding

112
J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
Fig. 5. The overlap partial density of states diagrams for interaction of ruthenium(II) central ions with pyrazine, pyrazine-2-carboxylic acid, (4-OH)BPA and (4-OH)BPAm
ligands.
Table 4
The calculated electronic transitions and their assignments to the experimental absorption bands.
The most important orbital excitations
Character
k (nm)
f
Experimental k (nm)
(1)
HOMO ? LUMO (98%)
H-1 ? LUMO (88%)
d ? p⁄(L)
d ? p⁄(L)
d ? p⁄(L); (L) ? p⁄(L)
p
460.5
413.9
362.6
337.8
320.9
315.9
304.6
299.8
289.1
270.9
268.6
264.1
260.6
0.0519
0.0001
0.2528
0.1262
0.0073
0.0032
0.0278
0.0362
0.0317
0.0282
0.051
422
361
H-3 ? LUMO (60%); H-2 ? LUMO (10%); HOMO ? L + 1 (18%)
HOMO ? L + 2 (61%); HOMO ? L + 3 (15%)
H-10 ? LUMO (19%); H-8 ? LUMO (36%); H-6 ? LUMO (14%); H-5 ? LUMO (14%)
H-2 ? LUMO (75%)
H-7 ? L + 1 (10%); H-1 ? L + 2 (20%)
H-2 ? L + 2 (16%); HOMO ? L + 4 (20%); HOMO ? L + 10 (10%)
H-18 ? LUMO (25%); H-7 ? L + 1 (29%)
HOMO ? L + 6 (87%)
d ? d/p⁄(L)
p
(PPh3) ? p⁄(L); (L) ? p⁄(L)
p
d ? p⁄(L)
314
274
p
(PPh3) ? p⁄(L); d ? d
d ? d; d ? p⁄(PPh3); d ? p⁄(L)
p
(L/PPh3) ? p⁄(L)
d ? p⁄(PPh3)
d ? p⁄(L/PPh3)
d ? p⁄(L/PPh3)
H-20 ? LUMO (21%); H-19 ? LUMO (10%); H-2 ? L + 4 (10%)
HOMO ? L + 7 (44%); HOMO ? L + 10 (15%)
H-4 ? L + 2 (49%)
0.0289
0.3641
p(L) ? d
(2)
HOMO ? LUMO (97%)
HOMO ? L + 1 (97%)
H-2 ? LUMO (94%)
HOMO ? L + 2 (80%)
H-2 ? L + 1 (81%)
H-17 ? LUMO (67%)
HOMO ? L + 5 (61%)
H-4 ? L + 1 (77%)
H-5 ? L + 2 (16%), H-2 ? L + 2 (53%)
HOMO ? L + 12 (58%)
H-21 ? LUMO (32%), HOMO ? L + 14 (33%)
d ? p⁄(L)
564.1
426.5
396.0
372.9
318.4
314.0
306.95
296.3
290.8
276.9
267.1
0.0265
0.0005
0.0171
0.0247
0.0339
0.0038
0.019
0.1597
0.1867
0.0017
0.1333
d ? p⁄(L)
457
374
311
d ? p⁄(L)
d ? d/p⁄(PPh3)
d ? p⁄(L)
p
(L) ? p⁄(L)
d ? p⁄(PPh3)
d/
d/
p
p
(PPh3) ? p⁄(L)
(PPh3) ? d/p⁄(PPh3)
d ? p⁄(PPh3)
276
p
(L) ? p⁄(L); d ? p⁄(PPh3)
L denotes (4-OH)BPA in (1) and (4-OH)BPAm in (2).
complex showing a contribution of ligands nature. Moreover in
the electronic structure of the complexes and much larger participa-
tions of ligand in molecular orbitals taking part in MLCT transitions.
these regions were calculated the transitions composite from Li-
gand-to-Ligand and Metal-to-Ligand Charge Transfer (pPPh3
?
p⁄
L
and d ? p⁄L; d ? p⁄(PPh3)). The emission properties of 5-(4-hydrox-
ybenzoyl)pyrazine-2-carboxylic acid is presented on the Fig. 6b.
The methanolic solution of the ligand excited at 282 nm presents
fluorescence with maximum at 330 nm.
4. Conclusion
Two new benzoylpyrazine carboxylic acid ligands and its
hydride-carbonyl complexes of ruthenium were synthesized and
characterized by infra red, proton and phosphorus nuclear mag-
netic resonance, electronic absorption and emission spectroscopy
and X-ray crystallography. In the crystal structure of the complexes
The methanol solution of complex (2) was excited in the range
between 270 and 600 nm and the emission was not observed. This
lack of fluorescence is probably associated with the differences in

J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
113
Fig. 6. Fluorescence spectra of [RuH(CO)((4-OH)BPA)(PPh3)2]ÁCH3OHÁH2O (1) complex (a) and 5-(4-hydroxybenzoyl)pyrazine-2-carboxylic acid (b) in methanolic solutions.
two types of non-covalent interactions between aromatic rings
(parallel-displaced and T-shaped) have been found.
Electronic structures of the complexes have been determined
using the density functional theory (DFT) method, and employed
for discussion of its properties. The NBO analyses point out the
and consequently dividing levels of dxy, dxz and dyz ruthenium orbi-
tals through ligand orbitals (HOMOÀ1 in complex (2) is localized
(89%) on the (4-OH)BPAm ligand).
Acknowledgements
higher
p-acceptor properties of amide derivative than carboxylic
acid (4-OH)BPA ligand. The differences in the donor–acceptor
properties of the amide and carboxylic ligands manifest itself in
the considerable difference in the Ru–H stretching band in the
complexes. The stronger COO donor is in trans to carbonyl ligand
in complex (1) and the weaker amide donor in complex (2) occu-
pies trans position to hydride. The electronic structures of these
complexes, presented in particular by the density of states dia-
grams, have been correlated with their ability to fluoresce and used
to analyze the UV–Vis spectra. The lack of luminescence in the case
of complex (2) is probably associated with the smaller participa-
tion of ruthenium in molecular orbitals involved in MLCT transi-
tions. The differences in frontier occupied molecular orbitals are
clearly visible on the DOS diagrams. The amide derivative unlike
carboxylic ligand causes the increase in the energy the HOMO’s
M. Serda was supported by a TWING fellowship and NCN grant
DEC-2011/01/N/NZ4/01166. The GAUSSIAN-09 calculations were
carried out in the Wrocław Centre for Networking and Supercom-
puting, WCSS, Wrocław, Poland, http://www.wcss.wroc.pl, under
calculational Grant No. 18.
Appendix A. Supplementary data
CCDC 856480, 855434, 857547 and 864845 contain the supple-
mentary crystallographic data for C12H8N2O4Á2(H2O), C49H38N2O5-
P2RuÁCH4OÁH2O, C12H9N3O3ÁH2O and C49H39N3O4P2RuÁ2(CH4O)
compounds, respectively. These data can be obtained free of charge
from http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the

114
J.G. Małecki et al. / Polyhedron 41 (2012) 104–114
[21] J.G. Małecki, R. Kruszyn´ ski, Z. Mazurak, Polyhedron 28 (2009) 3891.
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: deposit@ccdc.
cam.ac.uk.
´
[22] J.G. Małecki, R. Kruszynski, Z. Mazurak, J. Coord. Chem. 61 (2008) 2186.
[23] J.G. Małecki, R. Kruszyn´ ski, D. Tabak, J. Kusz, Polyhedron 26 (2007) 5120.
[24] J.G. Małecki, R. Kruszynski, Z. Mazurak, Polyhedron 26 (2007) 4201.
[25] J.G. Małecki, R. Kruszyn´ ski, Polyhedron 26 (2007) 2686.
[26] J.G. Małecki, R. Kruszyn´ ski, J. Coord. Chem 60 (2007) 2085.
[27] N. Ahmad, J.J. Levinson, S.D. Robinson, M.F. Uttely, Inorg. Synth. 15 (1974) 48.
[28] Gaussian 09, Revision A.1, M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria,
M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G.
Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A.
Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M.
Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L.
Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J. Dannenberg,
S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski, and
D.J. Fox, Gaussian, Inc., Wallingford CT, 2009.
References
[1] C.H. Londergan, J.C. Salsman, S. Ronco, C.P. Kubiak, Inorg. Chem. 42 (2003) 926.
[2] M.G. Sauaia, R.G. de Lima, A.C. Tedesco, R.S. da Silva, JACS 125 (2003) 14718.
[3] V. Opletalova, D.S. Kalinowski, M. Vejsova, J. Kunes, M. Pour, J. Jampilek, V.
Buchta, D.R. Richardson, Chem. Res. Toxicol. 21 (2008) 1878.
[4] R. Rajagopalan, W.L. Neumann, A.R. Poreddy, R.M. Fitch, J.N. Freskos, B.
Asmelash, K.R. Gaston, K.P. Galen, J. Shieh, R.B. Dorshow, J. Med. Chem. 54
(2011) 5048.
[5] M. Dolezal, J. Jampilek, Z. Osicka, J. Kunes, V. Buchta, P. Vichova, Farmaco 58
(2003) 1105.
[6] M. Dolezal, P. Cmedlova, L. Palek, J. Vinsova, J. Kunes, V. Buchta, J. Jampilek, K.
Kralova, Eur. J. Med. Chem. 43 (2008) 1105.
[7] L. Salvi, A. Salvini, F. Micoli, C. Bianchini, W. Oberhauser, J. Organomet. Chem.
692 (2007) 1442.
[29] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[8] C. Po Lau, S. Man Ng, G. Jia, Z. Lin, Coord. Chem. Rev. 251 (2007) 2223.
[9] C. Jun Yue, Y. Liu, R. He, J. Mol. Catal. A: Chem. 259 (2006) 17.
[10] F. Nipa Haque, A.J. Lough, R.H. Morris, Inorg. Chim. Acta 361 (2008) 3149.
[11] P. Buskens, D. Giunta, W. Leitner, Inorg. Chim. Acta 357 (2004) 1969.
[12] J. Bravo, J. Castro, S. Garcia-Fontana, M.C. Rodriguez-Martinez, G. Albertin, S.
Antoniutti, A. Manera, J. Organomet. Chem. 692 (2007) 5481.
[13] M. Chandra, A.N. Sahay, D.S. Pandey, M.C. Puerta, P. Valerga, J. Organomet.
Chem. 648 (2002) 39.
[14] A.K. Singh, P. Kumar, M. Yadav, D.S. Pandey, J. Organomet. Chem. 695 (2010)
567.
[15] M. Arias, J. Concepción, I. Crivelli, A. Delgadillo, R. Díaz, A. Francois, F. Gajardo,
R. López, A.M. Leiva, L. Loeb, Chem. Phys. 326 (2006) 54.
[16] W. Henry, W.R. Browne, K.L. Ronayne, N.M. O’Boyle, J.G. Vos, J.J. McGarvey, J.
Mol. Struct. 735–736 (2005) 123.
[30] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[31] K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theor. Chim. Acc. 97 (1997)
119.
[32] M.E. Casida, in: J.M. Seminario (Ed.), Recent Developments and Applications of
Modern Density Functional Theory, Theoretical and Computational Chemistry,
vol. 4, Elsevier, Amsterdam, 1996, p. 391.
[33] E. D. Glendening, A. E. Reed, J. E. Carpenter, and F. Weinhold, NBO (version 3.1).
[34] N.M. O’Boyle, A.L. Tenderholt, K.M. Langner, J. Comp. Chem. 29 (2008) 839.
[35] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Cryst. 42 (2009) 339.
[36] G.M. Sheldrick, Acta Crystallogr., Sect. A64 (2008) 112.
[37] G.R. Desiraju, T. Steiner, The Weak Hydrogen Bond in Structural Chemistry and
Biology, Oxford University Press, 1999.
[38] M. Trivedi, M. Chandra, D.S. Pandey, M.C. Puerta, P. Valerga, J. Organomet.
Chem. 689 (2004) 879.
[39] A. Romero, A. Vegas, A. Santos, J. Organomet. Chem. 310 (1986) C8.
[17] B.J. Coe, S.J. Glenwright, Coord. Chem. Rev. 203 (2000) 5.
´
[18] J.G. Małecki, A. Maron, Polyhedron 30 (2011) 1225.
[19] J.G. Małecki, Polyhedron 30 (2011) 79.
[20] J.G. Małecki, Polyhedron 29 (2010) 2489.
´
[40] J.G. Małecki, T. Gron, H. Duda, Polyhedron 31 (2012) 319.