Synthesis, spectroscopic and structural characterization of new complex of ruthenium(II) with Hmtpo ligand

Article abstract of DOI:10.1016/j.poly.2009.12.007

The [(PPh₃)₂RuHCl(CO)(Hmtpo)] complex has been prepared and studied by IR, NMR, UV-VIS spectroscopy and X-ray crystallography. The complex was prepared in reactions of [RuHCl(CO)(PPh₃)₃] with 7-hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine in methanol. The electronic structure and UV-Vis spectrum of the obtained compound have been calculated using the TD-DFT method.

Full text of DOI:10.1016/j.poly.2009.12.007

Polyhedron 29 (2010) 1023–1028
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, spectroscopic and structural characterization of new complex
of ruthenium(II) with Hmtpo ligand
b
J.G. Małecki a, , R. Kruszynski
*
a Department of Inorganic and Coordination Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna Street, 40-006 Katowice, Poland
b
_
´
´
X-Ray Crystallography Laboratory, Institute of General and Ecological Chemistry, Technical University of Łódz, 116 Zeromski Street, 90-924 Łódz, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The [(PPh3)2RuHCl(CO)(Hmtpo)] complex has been prepared and studied by IR, NMR, UV–VIS spectros-
copy and X-ray crystallography. The complex was prepared in reactions of [RuHCl(CO)(PPh3)3] with
7-hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine in methanol. The electronic structure and UV–Vis
spectrum of the obtained compound have been calculated using the TD–DFT method.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 26 August 2009
Accepted 3 December 2009
Available online 11 December 2009
Keywords:
Ruthenium hydride carbonyl complexes
7-Hydroxy-5-methyl[1,2,4]triazolo[1,5-
a]pyrimidine
X-ray structure
UV–Vis
DFT
TD–DFT
1. Introduction
2. Experimental
In the chemistry of ruthenium, the coordination chemistry of
complexes containing N-heterocyclic derivatives is one of the
most studied aspects. The wide interest is this field originates
form very rich redox chemistry and photophysics of these com-
pounds. Even small changes in coordination environment
around ruthenium plays a key role in altering the redox proper-
ties of its complexes and thus complexation of ruthenium by
different ligands is very interesting and been widely studied
[1–7].
The ruthenium carbonyl and hydride complexes are very inter-
esting due to their catalytic and structural properties. On the other
hand the triazolopyrimidine derivatives are examples of purine
mimics and 7-hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine
(Hmtpo) is a good sample among these derivatives. The studied
compound merge the benefits of ruthenium coordination com-
pounds and complexes containing Hmtpo and carbonyl group, thus
their synthesis and determination of properties was undertaken. In
the paper, we present the synthesis, crystal, molecular and elec-
tronic structures and the spectroscopy characterization of the
new carbonyl ruthenium(II) complex.
2.1. Physical measurements
Infrared spectra were recorded on a Nicolet Magna 560 spectro-
photometer in the spectral range of 4000–400 cm1 with the sample
in the form of KBr pellet. Electronic spectra were measured on a
Lab Alliance UV–VIS 8500 spectrophotometer in the range of
800–200 nm in dichloromethane solution. Elemental analyses (C,
H, N) were performed on a Perkin–Elemer CHN-2400 analyzer.
The 1H NMR spectrum was obtained at room temperature in CDCl3
using INOVA 300 spectrometer.
All reagents used for the synthesis of the complex are commer-
cially available and were used without further purification. The
[RuHCl(CO)(PPh3)3] complex was synthesized using a literature
method [8].
2.2. Synthesis of [RuHCl(CO)(PPh3)2(Hmtpo)]
A suspension of [RuHCl(CO)(PPh3)3] (0.95 g; 1 Â 10–3 mol) and 7-
hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine (Hmtpo) (0.30 g;
2 Â 10–3 mol) in methanol (100 cm–3) was refluxed until the solid
dissolved, cooled and filtered. The crystals suitable for X-ray crystal
analysis were obtained by slow evaporation the reaction mixture.
Yield 79%.
* Corresponding author.
E-mail addresses: gmalecki@us.edu.pl (J.G. Małecki), rafal.kruszynski@p.lodz.pl
(R. Kruszynski).
Anal. Calc. for C44H40ClN4O2P2Ru: C, 61.79; H, 4.71; Cl, 4.15; N,
6.55; O, 3.74; P, 7.24; Ru, 11.82. Found: C, 62.01; H, 4.63; N, 6.66%.
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.007

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J.G. Małecki, R. Kruszynski / Polyhedron 29 (2010) 1023–1028
1H NMR (d, CDCl3): À10.74 (t, Ru–H); 7.05–7.71 (m, PPh3); 8.42
and refined as ‘‘riding” on the adjacent atom with individual isotro-
pic temperature factor equal 1.2 times the value of equivalent tem-
perature factor of the parent atom. The H(1R) atom has been
placed in calculated position (Ru–H distance 1.6 Å) according to
similar structures. SHELXS97, SHELXL97 [16] and SHELXTL [17] programs
have been used for all calculations. Atomic scattering factors had
values incorporated in the computer programs.
(Hmtpo); 6.92 (Hmtpo); 2.01 (Hmtpo). 31P NMR (d, CDCl3): 43.87
(s, PPh3).
UV–VIS (nm) in acetonitrile: 267.5; 209.0.
2.3. DFT calculations
GAUSSIAN-03 program [9] was used for the calculations. The geometry
optimization was carried out using the DFT method with the B3LYP
functional [10,11]. The electronic transitions were calculated with
the PCM model [12] in the acetonitrile solution as the solvent. The cal-
culation was performed using the DZVP basis set [13] with f functions
with exponents 1.94722036 and 0.748930908 on ruthenium atom,
and polarization functions for all other atoms: 6–31 g(2d,p) – chlorine,
6–31 g – carbon, nitrogen, oxygen, and 6–31 g(d,p) – hydrogen. Nat-
ural bond orbital (NBO) calculations were performed using the NBO
code [14] included in GAUSSIAN-03.
3. Results and discussion
The reactions of the ruthenium(II) carbonyl hydride complex
[RuHCl(CO)(PPh3)3] with 7-hydroxy-5-methyl[1,2,4]triazolo[1,5-
a]pyrimidine (Hmtpo) has been performed. Refluxing the [RuHCl(-
CO)(PPh3)3] complex with the ligand in methanol leads to
[(PPh3)2RuHCl(CO)(Hmtpo)] complex with good yields. Elemental
analysis of the compound is in a good agreement with their for-
mula. Infrared spectrum of the complex exhibit characteristic
**
2.4. Crystal structure determination and refinement
bands due to ligand rings vibrations. The mC@N band appears around
1611 cmÀ1. The mRu–H with mC@O band in this compound appears
around 1967 cm–1. More details are given in Table 2. The mCO and
mRu–H stretching vibration in the [RuHCl(CO)(PPh3)3] complex are
at 2020 and 1903 cmÀ1, respectively. The positions of the mCO and
mRu–H bands in the IR spectrum of the studied complex indicate a
decrease of the metal – carbonyl carbon interaction and an in-
crease of the Ru–H bond order.
A yellow prism of [(PPh3)2RuHCl(CO)(Hmtpo)] was mounted on
a KM–4–CCD automatic diffractometer equipped with CCD detec-
tor, and used for data collection. X-ray intensity data were col-
lected with graphite monochromated Mo
Ka
radiation
(k = 0.71073 Å) at temperature 291.0(3) K, with
x
scan mode.
The full Ewald sphere reflections were collected up to 2h = 50.0°.
The unit cell parameters have been determined basing on least-
squares refinement of the setting angles of 7026 strongest reflec-
tions. Details concerning crystal data and refinement are given in
Table 1. During the data reduction a decay correction coefficient
has been taken into account. Lorentz, polarization, and numerical
absorption [15] corrections have been applied. The structure has
been solved by direct methods. All the non-hydrogen atoms were
refined anisotropically using full-matrix, least-squares technique
on F2. The carbon bonded hydrogen atoms were found from differ-
ence Fourier synthesis after four cycles of anisotropic refinement,
The 1H NMR contains a triplet at À10.736 ppm, resulting from
hydrido ligand coordinated to ruthenium. The Hmtpo and triphen-
ylphosphine ligands have given the signals at 8.418, 6.921, 2,005
and 7.049–7.710 ppm, respectively. The singlet at 43.871 ppm in
the 31P NMR spectrum indicated both the triphenylphosphoine li-
gands in the studied complex are equivalent and are mutually trans
disposed.
Studied compound crystallize in monoclinic P21/c space group.
The molecular structure of the complex is shown in Fig. 1 (struc-
tural drawing is presented in Fig. 2). The selected bond lengths
and angles with the calculated values are listed in Table 3. The
ruthenium atom has a distorted octahedral environment with the
trans triphenylphosphine ligands (angle P–Ru–P 170.05(2)o). The
N donor atom of 7-hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimi-
dine is in trans positions to carbonyl (C(27)–Ru(1)–O(1)
175.94(9)o) and cis to hydride (N(1)–Ru(1)–H(1Ru) 85.7o) ligands.
The Ru–Cl distance (2.557(6) Å) is longer than the typical ruthe-
nium–chloride distance due to the trans effect of hydride ligand.
The Ru–P and Ru–N distances are normal and comparable with dis-
tances in other ruthenium complexes containing the heterocyclic
ligands.
Table 1
Crystal data and structure refinement details of [(PPh3)2RuHCl(CO)(Hmtpo)].
1
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C43H37ClN4O2P2Ru
840.23
293(2)
monoclinic
P21/c
Unit cell dimensions
a (Å)
b (Å)
c (Å)
b
18.0095(7)
20.3436(7)
10.9748(4)
102.388(4)
3927.3(3)
The two intermolecular hydrogen bond [18–20] linking the OH
group of 7-hydroxy-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine and
Volume (Å3)
Z
4
Calculated density (Mg/m3)
Absorption coefficient (mm–1
F (0 0 0)
1.431
0.591
1744
Table 2
The vibrational spectrum of studied compound.
)
Assignment
Crystal dimensions (mm)
h Range for data collection (°)
Index ranges
0.16 Â 0.16 Â 0.16
2.84–25.00
À21 6 h 6 20
À22 6 k 6 24
À13 6 l 6 10
6880
4919 (Rint = 0.0277)
4919/0/480
0.911
O–H str
3278
3058
1967
1611, 1521
1481
1434, 1027
1344
1090
Alkyl group C–H str
Ru–H str + C@O str
Phenyl ring C@C str + C@N str
Phenyl ring C–H bend
Alkyl group C–H bend
Phenyl ring C–H bend
All C–H bend
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0277
wR2 = 0.0658
R1 = 0.0470
wR2 = 0.0687
0.556 and À0.388
Phenyl ring C@C str
Phenyl ring C–H twist
Phenyl ring C@C str
Phenyl ring C–H twist
Skeleton deformation
899
848, 828
743
695
619
R indices (all data)
Largest difference in peak and hole (e Å–3
)

J.G. Małecki, R. Kruszynski / Polyhedron 29 (2010) 1023–1028
1025
Fig. 1. ORTEP drawing of [(PPh3)2RuHCl(CO)(Hmtpo)] with 50% probability thermal ellipsoids.
CO
Ru
Table 4
Cl
Hydrogen bonds in [(PPh3)2RuHCl(CO)(Hmtpo)]. Distances are in (Å) and angles are in
(°).
Ph3P
PPh3
N
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
2.48
2.33
2.51
d(DÁ Á ÁA)
3.377(4)
3.181(4)
3.125(3)
<(DHA)
H
C(5)–H(5)Á Á ÁO(2)#1
C(29)–H(29)Á Á ÁO(2)#2
C(39)–H(39)Á Á ÁO(1)#3
0.93
0.93
0.93
161.4
152.6
124.3
N
CH3
N
N
Symmetry operators used to generate equivalent atoms: #1 x, 5/2 À y, 1/2 + z; #2
2 À x, 2 À y, Àz; #3 x, y, À1 + z.
HO
phenyl from triphenylophosphine ligands and one between car-
bonyl and pyrimidine ligand are being observed (see Table 4).
Fig. 2. Structural drawing of [(PPh3)2RuHCl(CO)(Hmtpo)].
Table 3
Selected bond lengths (Å) and angles (°) for [(PPh3)2RuHCl(CO)(Hmtpo)].
3.1. Optimized geometries
Experimental
Calculated
The geometry of the studied complex has been optimized in sin-
glet states using the DFT method with the B3LYP functional. The
optimized geometric parameters of the singlet state of the complex
are gathered in Table 3. In general, the predicted bond lengths and
angles are in good agreement with the values based on the X-ray
crystal structure data, and the general trends observed in the
experimental data are well reproduced in the calculations. The
largest differences are observed in the Ru–H distance 0.22 Å. Max-
imum deviation between the calculated angles and the observed
ones is close to 9.95° (carbonyl–ruthenium–chloride).
Bond lengths (Å)
Ru(1)–C(43)
Ru(1)–Cl(1)
Ru(1)–N(1)
Ru(1)–P(2)
Ru(1)–P(1)
Ru(1)–H1(Ru)
C(43)–O(1)
1.818(3)
2.557(6)
2.177(19)
2.348(7)
2.376(6)
1.588
1.815
2.557
2.177
2.344
2.372
1.368
1.155
1.155(3)
Angles (°)
C(43)–Ru(1)–P(2)
C(43)–Ru(1)–N(1)
N(1)–Ru(1)–P(2)
C(43)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
P(2)–Ru(1)–P(1)
C(43)–Ru(1)–Cl(1)
N(1)–Ru(1)–Cl(1)
P(2)–Ru(1)–Cl(1)
P(1)–Ru(1)–Cl(1)
C(43)–Ru(1)–H(1Ru)
Cl(1)–Ru(1)–H(1Ru)
N(1)–Ru(1)–H(1Ru)
P(2)–Ru(1)–H(1Ru)
P(1)–Ru(1)–H(1Ru)
88.40(8)
175.94(9)
91.18(5)
93.80(8)
85.94(5)
170.05(2)
90.32(8)
93.73(5)
96.37(2)
93.33(2)
90.2
89.4
168.0
91.0
90.6
89.0
180.0
99.6
92.3
92.8
87.2
99.6
174.1
85.9
89.5
90.5
3.2. Electronic structure and NBO analysis
After geometry optimization the contributions from various
groups of the molecule in molecular orbitals were described. The
occupancies of the ruthenium d orbitals, obtained from NBO anal-
ysis, are as follows: dxy – 1.74; dxz – 1.93; dyz – 1.67; dZ – 1.29;
2
179.0
85.7
84.4
85.8
dx
– 1.07. The Homo orbital of studied compound is composed
2Ày2
of the dxz metal orbital with antibonding contribution of
p chlorine
orbital. The Lumo orbital is mainly localized on the Hmtpo ligand.
The Homo–Lumo gap is 4.18 eV in B3LYP functional and 3.61 eV in

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J.G. Małecki, R. Kruszynski / Polyhedron 29 (2010) 1023–1028
Generalized Gradient Approximation (GGA) term which is more
‘‘realistic”. The following orientation of the axes has been used
for determination of the MO characters: the z axis goes along
H(1Ru)–Re–Cl(1) linkage and x goes through the P(1)–Re–P(2)
bonds. More details of atomic contributions to the lowest unoccu-
pied and highest occupied molecular orbitals are given in Supple-
mentary Data in Table S1. Moreover the isodensity plots of the
several Homo and Lumo orbitals of studied complex are shown
in Fig. 3. Wiberg bond order for Ru–Cl and Ru–P are close to 0.59
(0.54)1 and 0.70 (0.45), respectively.
In the frontier region, neighboring orbitals are being often clo-
sely spaced. In such cases, consideration of only the Homo and
Lumo may not yield a realistic description of the frontier orbitals.
For this reason, the density-of-states (DOS) and overlap population
density-of-states (OPDOS) in terms of Mulliken population analysis
were calculated using the GAUSSSUM program [21]. They provide a
pictorial representation of MOs compositions and their contribu-
tions to chemical bonding. The DOS and OPDOS diagrams are
shown in Fig. 4. The DOS plots mainly present the composition of
the fragment orbitals contributing to the molecular orbitals. The
OPDOS can enable us to ascertain the bonding, non-bonding and
antibonding characteristics with respect to the particular frag-
ments. A positive value in OPDOS plots means a bonding interac-
tion; while a negative value represents antibonding interaction
and a value near zero indicates a non-bonding interaction.
As can be seen from the OPDOS plot in the Homo and HomoÀ1
molecular orbitals the chloride ligand has significant antibonding
character and bonding character in the HomoÀ4 and HomoÀ5.
The interactions of phosphine and Hmtpo ligands with Ru(II) d
orbitals have negative values in the frontier occupied molecular
orbitals (antibonding character of the interactions). The covalent
bond character of Ru–CO and Ru–H is displayed by positive values
of the interactions in OPDOS plot. Wiberg bond order for Ru–C is
close to 1.33 (1.37) and for Ru–H 0.79 (0.79). The lowest virtual
orbitals are mainly localized on the Hmtpo and phosphine ligands.
In the Lumo+1 the antibonding interaction of ruthenium d orbital
(29%) with PPh3 ligand is visible. The interactions between metal
and phosphine, Hmtpo ligands are antibonding in the frontier vir-
tual orbitals but in this energy region Ru and H ligand has bonding
interaction. In the Lumo orbitals composed with more Hmtpo con-
tributions the Ru(II) proportion is small (Lumo, Lumo+3, Lumo+5)
which indicates the ligand as a weak p-acceptor. Wiberg bond or-
der for Ru–N(7) is close to 0.37 (0.29) which indicate the stronger
ionic character of Ru–N bond comparing with other ruthenium li-
gand interaction in studied compound.
Basing on the NBO theory [22], occupancy and hybridization of
the calculated natural bond orbital between the ruthenium and the
hydrido ligand in the complex is 1.861 and 0.721(sd)Ru + 0.693(s)H,
respectively; occupancy of the antibonding orbital of Ru–H is
0.131. The occupancy and hybridization of Ru–CO bond is as follows:
1.938 (antibonding 0.142) and 0.586(sd2.52 Ru + 0.810(sp0.50)C.
)
The stabilization energy2 which has been calculated in this analysis
has shown that the lone pairs localized on the ruthenium atom in the
compound donate the charge to ruthenium carbonyl bond, and the sta-
bilization energy (DEij) is 105.79 kcal/mol. The interaction between anti-
bonding parts of Ru–C and Ru–H has the energy close to 80.89 kcal/mol.
The stabilization energy calculated in this analysis for the complex has
shown that the lone pairs localized on the chlorine and Hmtpo’s
1
In parenthesis are given values from Nalewajski-Mrozek bond-order analysis
(A. Michalak, R.L. DeKock, T. Ziegler, Bond Multiplicity in Transition-Metal
Complexes: Applications of Two-Electron Valence Indices, J. Phys. Chem.
A 112
Fig. 3. The contours of several Homo and Lumo molecular orbitals.
(2008) 7256.
2
D
Eij (kcal/mol) associated with delocalization is estimated by the second-order
perturbative as:
D
Eij = qi (F(i,j)2)/(ej
À
e
i) where qi is the donor orbital occupancy, ei
, ej
nitrogen ligands donate the charge to ruthenium d orbital, and the sta-
are diagonal elements (orbital energies) and F(i,j) is the off-diagonal NBO Fock or
Kohn-Sham matrix element.
bilization energy (DEij) is 218.33 and 79.03 kcal/mol, respectively.

J.G. Małecki, R. Kruszynski / Polyhedron 29 (2010) 1023–1028
1027
Fig. 5. Electrostatic potential (ESP) surface of [(PPh3)2RuHCl(CO)(Hmtpo)] complex.
ESP surface is shown both in space (with positive and negative regions shown in
blue and red, respectively) and mapped on electron densities (isovalue = 0.004) of
the molecule (ESP color scale is such that d+ ? dÀ in the direction red ? blue). (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
where blue indicates the strongest attraction and red indicates
the strongest repulsion. Regions of negative V(r) are usually associ-
ated with the lone pair of electronegative atoms. The negative po-
tential in the studied compound wraps the heteroaromatic
nitrogen, hydroxyl, carbonyl oxygen and chloride atoms.
The energy decomposition analysis of the studied complex
based on the work of Morokuma [23] and the extended transition
state (ETS) partitioning scheme of Ziegler [24] has been carried out
using ADF program (Release 2008) at the level of B3LYP/TZP has
been performed. The binding energy of the compound was calcu-
lated as the difference between the energy of complex with the
optimized geometry and the energies of the optimized ligand
Hmtpo and fragment [(PPh3)2RuHCl(CO)]. General theoretical
background on the bond energy decomposition scheme can be
found in the review paper [25]. In Table 5 are listed the result of
energy decomposition analysis calculated for the complex in gas
phase and more realistic in methanol solvent. As could be seen
the Coulomb (steric and orbital interaction) energy plays a impor-
tant role for the [(PPh3)3RuHCl(CO)]–Hmtpo binding.
Fig. 4. Partial density-of-states and overlap population density-of-states diagrams
for [(PPh3)2RuHCl(CO)(Hmtpo)] complex.
In studied complex, ruthenium is formally +2 but the calculated
natural charge on the ruthenium atom is À0.928. The charges of
hydride and chloride ligands are close to 0.04 and À0.516, respec-
tively. The charge on the carbon atom of the carbonyl ligand is po-
sitive (0.709), whereas the oxygen atom is negatively charged
(À0.491). The atomic charge calculations can give a feature for
the relocation of the electron density of the compounds. Because
the electron distribution is not apparent from the partial atomic
charges in Fig. 5 are given the plot of the electrostatic potentials
for the studied compound. The isoelectronic contours are plotted
at 0.005 a.u. (3.1 kcal/mol). The color code of these maps is in
the range of 0.05 a.u. (deepest red) to À0.005 a.u. (deepest blue),
3.3. Electronic spectra
Several transitions, with the oscillator strength above 0.01, have
been collected in Table S2 in Supplementary Data. In the studied
complex, 140 electronic transitions have been calculated using
the TDDFT method and they do not comprise all the experimental
Table 5
Energy decomposition analysis for complex [(PPh3)2RuHCl(CO)(Hmtpo)] in the [(PPh3)2RuHCl(CO)] fragment and the Hmtpo ligand (energies in kcal molÀ1).
Energy (kcal/mol)
[(PPh3)2RuHCl(CO)(Hmtpo)] gas phase
[(PPh3)2RuHCl(CO)(Hmtpo)] CH3OH solvent
D
D
D
D
D
D
Eelstat
Ekinetic
ECoulomb
EXC
Esolvation
E
À69.65
À60.60
À91.66
193.26
À48.79
À25.04
À32.83
À2985.63
2728.31
249.60
(steric+orbInt)
À77.37

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J.G. Małecki, R. Kruszynski / Polyhedron 29 (2010) 1023–1028
[7] A.H. Velders, A.G. Quiroga, J.G. Haasnoot, J. Reedijk, Eur. J. Inorg. Chem. (2003)
713. and references therein.
absorption bands. The UV–Vis spectra have been calculated up to
ꢀ215 nm, so considering that the solution spectra of PPh3 and
N-heterocyclic ligands exhibit intense absorption bands in about
210 nm region, some intraligand and interligand transitions are
expected to be found at higher energies in the calculations.
The experimental spectrum of studied complex exhibit broad
band with the maximum at 267.5 nm. Basing on the calculated
transitions the band is of Metal–Ligand Charge Transfer type with
the d ? d (Ligand Field) contribution. The intra- and interligand
transitions are calculated in the region of high energies and attrib-
uted to the experimental band with maximum at 209.0 nm. As it
was pointed out in the literature, the TDDFT method gives such
transitions at too small energies [26–34] and we may expect also
that this is the case in our calculations.
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