Study on molecular and electronic structures, and spectroscopic properties of azide ruthenium complexes with pyridine and β-picoline ligands

Article abstract of DOI:10.1016/j.poly.2011.08.043

The [Ru(N₃)₂(PPh₃)(py)₃] and [Ru(N₃)₂(PPh₃)₂(β-pic) ₂] complexes have been prepared and studied by IR, NMR, UV-Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of [RuCl₂(PPh₃)₃] with pyridine, β-picoline and NaN₃ in methanol solutions. The electronic structures of the obtained complexes have been calculated using the DFT/TD-DFT method. The trans effect of triphenylphosphine on the pyridine molecule has been studied using NBO and molecular orbital terms, and impact of the acceptor properties of the halide/pseudohalide co-ligands was indicated.

Full text of DOI:10.1016/j.poly.2011.08.043

Polyhedron 31 (2012) 44–50
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Study on molecular and electronic structures, and spectroscopic properties
of azide ruthenium complexes with pyridine and b-picoline ligands
⇑
´
J.G. Małecki , A. Maron
Department of Crystallography, Institute of Chemistry, University of Silesia, 9th Szkolna St., 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:
Received 4 July 2011
Accepted 10 August 2011
Available online 21 September 2011
The [Ru(N3)2(PPh3)(py)3] and [Ru(N3)2(PPh3)2(b-pic)2] complexes have been prepared and studied by IR,
NMR, UV–Vis spectroscopy and X-ray crystallography. The complexes were prepared in the reactions of
[RuCl2(PPh3)3] with pyridine, b-picoline and NaN3 in methanol solutions. The electronic structures of the
obtained complexes have been calculated using the DFT/TD-DFT method. The trans effect of triphenyl-
phosphine on the pyridine molecule has been studied using NBO and molecular orbital terms, and impact
of the acceptor properties of the halide/pseudohalide co-ligands was indicated.
Keywords:
Ruthenium azide complexes
Pyridine
Ó 2011 Elsevier Ltd. All rights reserved.
b-Picoline
X-ray structure
UV–Vis
DFT
TD-DFT
Luminescence
trans Effect
1. Introduction
Here, an experimental and quantum chemical study of ruthe-
nium azide complexes with pyridine and b-picoline ligands is re-
In the chemistry of ruthenium, the coordination chemistry of
complexes containing pyridine derivatives is one of the most fre-
quently studied aspects. The wide interest is this field originates
from the very rich redox chemistry and photophysics of these com-
pounds. Even small changes in the coordination environment
around the ruthenium atom plays a key role in altering the redox
properties of its complexes, and thus complexation of ruthenium
by various ligands is very interesting and widely studied [1–3].
These attributes of substituted pyridine-containing ruthenium
compounds lead to their application in conversion of solar energy
to electrical energy [4], in long-range electron transfer and energy
translocation [5], molecular electronic devices [6], supramolecular
self-assembly processes [7] and as DNA photoprobes [8,9]. The
molecular and electronic structures of pyridine and picoline ruthe-
nium(II) chloride and isothiocyanate complexes were studied ear-
lier [10–12]. Additionally, thiocyanate ligands tune the spectral
and redox properties of ruthenium(II) complexes by destabilizing
the metal t2g orbital. In general, azine ligands have energetically
ported. The quantum chemical study includes characterization of
the molecular and electronic structures of the complexes by anal-
ysis of their optimized molecular geometries, and their electronic
populations using the natural bond orbitals scheme. The latter
was used to identify the nature of the interactions between the li-
gands and the central ion. The calculated density of states showed
the interactions and influences of the orbital composition on the
frontier electronic structure. The time dependent density func-
tional theory (TD-DFT) was finally used to calculate the electronic
absorption spectra. Based on a molecular orbital scheme, these re-
sults allowed the interpretation of the UV–Vis spectra obtained at
the experimental level.
2. Experimental
All reagents used in the synthesis of the complexes are com-
mercially available and were used without further purification.
The [RuCl2(PPh3)3] complex was synthesised according to the liter-
ature method [13].
low p-antibonding orbitals, which can accept electrons from occu-
pied metal d orbitals. As a consequence, they can exhibit charge
transfer bands with interesting spectroscopic properties in the vis-
ible region.
2.1. Synthesis of the complexes [Ru(N3)2(PPh3)(py)3] (1) and
[Ru(N3)2(PPh3)2(b-pic)2] (2)
⇑
The complexes were synthesised in the reaction between
Corresponding author.
E-mail address: gmalecki@us.edu.pl (J.G. Małecki).
[RuCl2(PPh3)3] (0.2 g, 2 ꢀ 10ꢁ4 mol), NaN3 (0.02 g) and pyridine
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.043

´
45
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
or b-picoline (0.1 mL). A mixture of the compounds was refluxed in
[Ru(N3)2(PPh3)(py)3] (1): Yield 70%. IR (KBr, cmꢁ1): 3050 mArH
;
;
;
methanol (50 mL) for 3 h. After this time it was cooled and filtered.
Crystals suitable for X-ray crystal analysis were obtained by slow
evaporation of the reaction mixture.
2039
m
(N@N@N); 1635 mCN
,
m
C@C; 1479 d(C–CH in the plane); 1432 mP–Ph
1310
m
(N@N@N); 1089 d(C–CH
plane); 1027 d(C–H
in the
out of the plane)
748 d(C–C out of the plane); 696 d(NNN); 515 m(P–Ph). UV–Vis (methanol,
nm), (loge): 475.5 (1.31), 371.0 (2.04), 273.0 (sh), 211.0 (5.10).
1H NMR (d, CDCl3): 8.621 (HPy), 7.679 (HPy), 7.700, 7.569–7.496
(m, PPh3), 7.312 (HPy). 31P NMR (d, CDCl3): 29.621 (s, PPh3).
[Ru(N3)2(PPh3)2(b-pic)2] (2): Yield 68%. IR (KBr, cmꢁ1): 3059 mArH
,
Table 1
Crystal data and structure refinement details of the complexes [Ru(N3)2(PPh3)(py)3]
(1) and [Ru(N3)2(PPh3)2(b-pic)2] (2).
2920
(N@N@N); 1434
plane); 790 Pic-ring, 750 d(C–C out of the plane); 698 d(NNN); 510 m(P–Ph)
UV–Vis (methanol, nm), (log
m
CH; 2040
m
(NNN); 1639 mCN
,
m
C@C; 1479 d(C–CH in the plane); 1329
m
mP–Ph; 1089 d(C–CH
plane); 1028 d(C–H
in the
out of the
1
2
m
.
e): 470.0 (1.09), 362.0 (3.38), 270.1
Empirical formula
Formula weight
T (K)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
33H30N9PRu
C48H44N8P2Ru
895.92
295(2)
triclinic
P1
(sh), 213.0 (5.12). 1H NMR (d, CDCl3): 8.398 (HPic), 7.684–7.469
(m, PPh3), 7.539 (HPic), 7.212 (HPic), 2.344 (CH3(Pic)). 31P NMR (d,
CDCl3): 29.936 (s, PPh3).
684.70
295(2)
monoclinic
C2/c
ꢀ
34.498(6)
9.9413(5)
17.9742(8)
90
96.815(10)
90
6120.7(11)
8
1.486
9.7160(8)
11.3665(8)
11.6723(11)
103.932(7)
111.583(8)
103.946(7)
1083.1(2)
1
2.2. Physical measurements
b (Å)
c (Å)
Infrared spectra were recorded on a PerkinElmer FT-IR spectro-
photometer in the spectral range of 4000–450 cmꢁ1 using KBr pel-
lets. Electronic spectra were measured on a Lab Alliance UV–Vis
8500 spectrophotometer in the range of 600–180 nm in methanol
solution. The 1H and 31P NMR spectra were recorded at room tem-
perature in CDCl3 using a Bruker 400 spectrometer. Luminescence
measurements were made in methanolic solutions on an F-2500 FL
spectrophotometer at room temperature.
a
(°)
b (°)
c
(°)
V (Å3)
Z
Calculated density (mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.374
0.480
462
)
0.604
2800
Crystal dimensions (mm)
h range for data collection (°)
Index ranges
0.27 ꢀ 0.10 ꢀ 0.07 0.27 ꢀ 0.10 ꢀ 0.07
3.41–25.05
ꢁ40 6 h 6 40
ꢁ11 6 k 6 11
ꢁ20 6 l 6 21
27352
3.44–25.05
ꢁ11 6 h 6 11
ꢁ13 6 k 6 13
ꢁ13 6 l 6 13
13241
3817 (0.0315)
3817/0/269
1.058
R1 = 0.0513
wR2 = 0.0971
R1 = 0.0686
wR2 = 0.1015
2.3. DFT calculations
Reflections collected
The calculations were carried out using the GAUSSIAN09 [14] pro-
gram. The DFT/B3LYP [15,16] method was used for the geometry
optimization and electronic structure determination, and elec-
tronic spectra were calculated by the TD-DFT [17] method. The cal-
culations were performed using the DZVP basis set [18] with f
functions with exponents 1.94722036 and 0.748930908 on ruthe-
nium atom, and polarization functions for all other atoms: 6-31g⁄⁄
– carbon, nitrogen and hydrogen. The PCM solvent model was used
in the GAUSSIAN calculations with methanol as the solvent. The con-
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
)
5399 (0.0305)
5399/0/397
1.014
R1 = 0.0291
wR2 = 0.0635
R1 = 0.0397
wR2 = 0.0659
Final R indices [I > 2
r(I)]
R indices (all data)
Largest difference in peak and hole 0.570 and ꢁ0.378 0.739 and ꢁ0.546
(e Åꢁ3
)
Fig. 1. Experimental and calculated IR spectra of the [Ru(N3)2(PPh3)(py)3] complex.

´
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
46
tribution of a group to a molecular orbital was calculated using
Mulliken population analysis. GaussSum 2.2 [19] was used to cal-
culate group contributions to the molecular orbitals and to prepare
the partial density of states (DOS) and overlap population density
of states (OPDOS) spectra. The PDOS and OPDOS spectra were cre-
distances are normal and comparable with distances in other
ruthenium complexes containing N-heterocyclic ligands. In the
structure of complex 1, the Ru(1)–N(8) distance is elongated by
about 0.05 Å compared to the length of the other two ruthe-
nium–pyridine bonds. This bond elongation is a result of the im-
pact of the phosphine ligand in a trans position on the pyridine–
N(8) molecule.
ated by convoluting the molecular orbital information with
sian curves of unit height and FWHM of 0.3 eV.
Gaus-
The conformations of the complex molecules are stabilized by
intra- and intermolecular weak hydrogen bonds, details of which
are collected in Table 3. Additionally, in the structure of complex
2.4. Crystal structures determination and refinement
2, some weak electronic interactions (p–p stacking) between the
PPh3 phenyl and picoline rings are possible. The plane-to-plane
distance between the centroids, determined by C(7) to C(12) car-
Red crystals of [Ru(N3)2(PPh3)(py)3] (1) and [Ru(N3)2(PPh3)2
(b-pic)2] (2) were mounted in turn on a Gemini A Ultra Oxford Dif-
fraction automatic diffractometer equipped with a CCD detector,
and used for data collection. X-ray intensity data were collected
bons and the picoline ring is equal to 3.731(3) Å, indicating a
stacking interaction. The angle between the normal to the phenyl
and picoline planes is 18.4(3)°.
p–
p
with graphite monochromated Mo K
the temperature 295(2) K, with the
a
x
radiation (k = 0.71073 Å) at
scan mode. Ewald sphere
reflections were collected up to 2h = 50.10°. The unit cell parame-
ters were determined from least-squares refinement of the
11817 and 5907 strongest reflections for complexes 1 and 2,
respectively. The details concerning crystal data and refinement
are gathered in Table 1. Lorentz, polarization and empirical absorp-
tion correction using spherical harmonics implemented in SCALE3
ABSPACK scaling algorithm [20] were applied. The structures were
solved by the Patterson method and subsequently completed by
difference Fourier recycling. All the non-hydrogen atoms were re-
fined anisotropically using the full-matrix, least-squares tech-
nique. The hydrogen atoms were treated as ‘‘riding’’ on their
parent carbon atoms and assigned isotropic temperature factors
equal to 1.2 times the value of the equivalent temperature factor
of the parent atom. The OLEX2 [21] program was used for all the cal-
culations. The atomic scattering factors used were those incorpo-
rated in the computer programs.
3. Results and discussion
The reactions of the [RuCl2(PPh3)3] complex with an excess of
pyridine, b-picoline and sodium azide have been carried out.
Refluxing the starting ruthenium(II) complex with the ligands in
methanol leads to two new complexes with formula
[Ru(N3)2(PPh3)(py)3] (1) and [Ru(N3)2(PPh3)2(b-pic)2] (2) in good
yields. The IR spectra of the complexes show sharp and strong
absorption bands at 2040 cmꢁ1 assignable to the asymmetric
strꢁetching frequency of the terminal azide groups. The symmetric
N3 stretching frequency is observed at 1310 and 1329 cmꢁ1 for
complexes (1) and (2), respectively. The characteristic bands of
the C@C and C@N stretching modes of pyridine occur at 1635
and 1639 cmꢁ1 in complexes 1 and 2, respectively. The experimen-
tal and calculated infrared spectra of complex 1 are presented in
Fig. 1. The 31P{1H} NMR spectra of the complexes present a singlet
at 29.621 ppm for 1 and 29.936 ppm for 2. The singlet in the spec-
trum of complex 2 indicates a trans conformation of PPh3 ligands in
consistence with the crystallographic data. The 1H NMR spectra of
the complexes displayed sets of signals, reported in the experimen-
tal section, that are ascribed to the pyridine (b-picoline) and tri-
phenylphosphine ligands.
The complexes 1 and 2 crystallize in the monoclinic C2/c and
ꢀ
triclinic P1 space groups, respectively, and their molecular struc-
tures are shown in Fig. 2. Selected bond lengths and angles are
listed in Table 2. In the complexes, the ruthenium atoms have an
octahedral environment, and the maximum distortion from an
ideal octahedron is visible in complex 1 in the fact that the angle
between the azide ligands is 175.18(8)°. The azide N@N bond
lengths values fall in the range 1.151(3)–1.186(5) Å, similar to
the values observed earlier for azide complexes [22–25]. The azido
groups are slightly bent, with an angle near 176°. The Ru–N(py)
Fig. 2. Ortep drawings of the [Ru(N3)2(PPh3)(py)3] and [Ru(N3)2(PPh3)2(b-pic)2]
complexes with 50% probability displacement ellipsoids. Hydrogen atoms are
omitted for clarity.

´
47
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
Table 4
3.1. Optimized geometries, hybrid and molecular orbitals description
Selected natural atomic charges and Ru–L bond order in the complexes 1 and 2.
The ground state geometries of the studied complexes were
optimized in the singlet state using the DFT method with the
B3LYP functional. The optimizations were carried out for gas phase
molecules and in general the predicted bond lengths and angles are
1
2
Natural atomic charges
Ru
N(azide)
P
0.092
ꢁ0.193
ꢁ0.475
1.244
ꢁ0.487
1.259
N(8)/N(4)
N(7)
N(9)
ꢁ0.397
ꢁ0.407
ꢁ0.399
ꢁ0.387
Table 2
Selected bond lengths (Å) and angles (°) for the complexes [Ru(N3)2(PPh3)(py)3] (1)
and [Ru(N3)2(PPh3)2(b-pic)2] (2), with the optimized geometry values.
Bond orders
Ru–P
Ru–N(azide)
Ru–N(7)/(4)
Ru–N(8)
1
2
0.743
0.543
0.540
0.477
0.457
0.681
0.547
0.463
Exp
Calc
Exp
Calc
Bond lengths (Å)
Ru(1)–N(1)
Ru(1)–N(4)
Ru(1)–N(7)
Ru(1)–N(8)
Ru(1)–N(9)
Ru(1)–P(1)
N(1)–N(2)
2.108(2)
2.119(2)
2.173
2.174
2.103(4)
2.121(3)
2.168
2.172
Ru–N(9)
2.1047(19) 2.144
2.1681(19) 2.200
2.1155(19) 2.169
in agreement with the values based on the X-ray crystal structure
data, and the general trends observed in the experimental data are
reproduced well in the calculations. The calculated IR frequencies
of complex 1, shown in Fig. 1, confirm the accordance of the calcu-
lated structures with the experimental ones, and the differences
between the 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 (ꢂ0.09 Å) and the max-
imum angle differences do not exceed 8.2°.
2.3137(6)
1.170(3)
1.154(3)
1.183(3)
1.151(3)
2.411
1.207
1.165
1.207
1.165
2.3952(12) 2.484
1.186(5)
1.157(6)
1.206
1.165
N(2)–N(3)
N(4)–N(5)
N(5)–N(6)
Angles (°)
N(1)–Ru(1)–N(7)
N(7)–Ru(1)–N(9)
N(1)–Ru(1)–N(9)
N(7)–Ru(1)–N(4)
N(1)–Ru(1)–N(4)
N(9)–Ru(1)–N(4)
N(7)–Ru(1)–N(8)
N(1)–Ru(1)–N(8)
N(9)–Ru(1)–N(8)
N(4)–Ru(1)–N(8)
N(7)–Ru(1)–P(1)
N(1)–Ru(1)–P(1)
N(9)–Ru(1)–P(1)
N(4)–Ru(1)–P(1)
N(8)–Ru(1)–P(1)
N(1)–N(2)–N(3)
N(4)–N(5)–N(6)
Ru(1)–N(1)–N(2)
Ru(1)–N(4)–N(5)
89.31(8)
175.24(7)
89.94(8)
90.75(8)
175.18(8)
89.61(8)
87.85(7)
92.84(7)
87.50(7)
82.34(8)
94.03(6)
87.00(6)
90.63(5)
97.81(6)
178.12(5)
176.4(3)
176.2(3)
92.81
175.36
88.82
90.22
176.38
90.22
88.39
90.22
87.26
87.93
92.72
87.92
90.17
92.72
174.95
177.76
177.84
92.47(14)
93.35
The NBO analyses were performed for the complexes which al-
lowed the nature of the coordination between ruthenium and the
atoms of the ligands directly interacting with it to be learned. This
methodology also gave a better understanding of the optimized
molecular structures. In the analysis, it was found that the
90.22(11)
89.16(10)
176.4(5)
132.9(3)
90.22
ꢁ
N3 ligands exhibited covalent bonding with ruthenium. The
88.86
calculated Wiberg bond indices have values close to 0.54 and the
⁄
177.41
125.73
occupancies and hybridization are: 1.618BD (0.219BD
0.390(sp12.71d11.59 Ru + 0.921(sp9.54
(0.221BD⁄) and 0.397(sp13.43d12.49
) and
)
)
)
for complex 1, and 1.620BD
N3
129.12(18) 124.28
134.24(18) 126.13
Ru + 0.918(sp8.96
)
N3
for 2. The
data show that the Ru–N3 bonds are polarized towards the azide
ligands. The occupancy of the ruthenium azide bonds is below 2,
suggesting redistributions of electron density in the molecules.
The natural charges on the ruthenium central ions are close to zero
(0.09 for 1 and ꢁ0.19 for 2) and the occupancies of the ruthenium d
Dihedral angles (°)
P(1)–Ru(1)–N(1)–N(2)
N(7)/N(4)–Ru(1)–N(1)–
N(2)
N(8)/N(4A)–Ru(1)–N(1)–
N(2)
N(9)–Ru(1)–N(1)–N(2)
P(1)–Ru(1)–N(4)–N(5)
N(7)–Ru(1)–N(4)–N(5)
N(8)–Ru(1)–N(4)–N(5)
N(9)–Ru(1)–N(4)–N(5)
ꢁ178.0(2)
131.8(5)
42.6(5)
153.55
61.07
122.96
34.09
87.9(2)
0.1(2)
ꢁ137.4(5) ꢁ27.35
ꢁ145.91
orbitals are as follows:
1
dxy ꢁ 1.77; dxz ꢁ 1.90; dyz ꢁ 1.89;
ꢁ87.4(2)
ꢁ76.3(2)
17.8(2)
105.6(2)
ꢁ166.9(2)
ꢁ114.59
ꢁ117.75
ꢁ24.97
63.42
dx2
dx2
ꢁ 0:81; dz2 ꢁ 0:74 and 2 dxy ꢁ 1.42; dxz ꢁ 1.46; dyz ꢁ 1.41;
ꢁy2
ꢁy2
ꢁ 1:44; dz2 ꢁ 1:57. Table 4 presents the atomic charges and
Ru–L bond orders. The d-electron populations of 7.11 for 1 and
7.30 for 2 correspond to the oxidation state Ru(I), not to the formal
oxidation state Ru(II). This is a supporting argument for ligand to
dRu electron transfer. The data suggest that the donation from the
ligands to dRu orbitals plays a role in the electronic structure of
the complexes, and in order to determine the donation, the stabil-
ization energies1 were calculated. In these analyses, it has become
evident that the pyridine ligands donate charge to ruthenium and
150.74
Table 3
Hydrogen bonds for [Ru(N3)2(PPh3)(py)3] (1) and [Ru(N3)2(PPh3)2(b-pic)2] (2) (Å and
°).
D–Hꢃ ꢃ ꢃA
1
d(D–H)
d(Hꢃ ꢃ ꢃA)
d(Dꢃ ꢃ ꢃA)
\(DHA)
the stabilization energies (DEij) are 251.22 (72.49) kcal/mol and
203.90 kcal/mol for complexes 1 and 2, respectively. The back dona-
tions from ruthenium to N-donor ligands in complexes 1 and 2 have
values of 112.21 (34.17) and 75.84 kcal/mol, respectively. The values
of the interactions between ruthenium and the pyridine molecule in
the trans position to the PPh3 ligand in complex 1 are reported in the
C(1)–H(1)...N(5)
C(5)–H(5)...N(2)
C(11)–H(11)...N(1)
C(15)–H(15)...N(4)
C(23)–H(23)...N(4)
0.93
0.93
0.93
0.93
0.93
2.48
2.60
2.43
2.35
2.28
3.033(3)
3.326(3)
3.016(3)
2.974(3)
3.107(3)
118.4
135.3
121.2
123.9
147.8
2
C(1)–H(1)...N(1)
C(1)–H(1)...N(2)
C(5)–H(5)...N(1) #1
C(14)–H(14)...N(1)
0.93
0.93
0.93
0.93
2.57
2.51
2.39
2.52
3.118(6)
3.117(6)
2.958(6)
3.056(6)
118.1
123.3
119.5
116.9
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
ꢁ
e
are diagonal elements (orbital energies) and F(i,j) is the off-diagonal NBO Fock or
#1 ꢁx, 1 ꢁ y, ꢁz.
Kohn–Sham matrix element.

´
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
48
brackets. As one can see, the interactions are relatively weaker com-
pared to the other Ru–py bond. The weakening of the interactions
may also be seen in the Wiberg indices, which are decreased in com-
parison to the other ones (Ru–N(8) 0.424; Ru–N(7) 0.478; Ru–N(9)
0.457).
complexes causes the mapping, is reflected in their spectroscopic
properties, in particular with regard to the ability of fluorescence.
This effect may be associated with a strong
r-donor interaction
of the phosphine with the ruthenium central ion and a relatively
weak interaction of the pyridine acceptor. Accumulation of a par-
tial charge on the dx2
orbital of ruthenium offsets the
p-backdo-
ꢁy2
nation, and limits the
r-donation from pyridine. This trans
influence is shown in Fig. 3. The overlap partial density of states
diagram shows the weak acceptor properties of the pyridine ligand
compared with the strong accepting possibility of the PPh3 ligand.
Additionally, one can see the weak interaction between the phos-
phine and pyridine ligands affected by the dRu orbital. A similar ef-
fect occurs in the chloride complex, however the elongation of the
bond between ruthenium and pyridine in the trans position to the
PPh3 molecule is smaller (Ru–Nt 2.1527(14) Å) [11]. The differ-
ences in the strength of the trans effect in these complexes result
from the donor–acceptor properties of the chloride and azide li-
gands. In Fig. 3, the OPDOS diagram showing the interaction be-
tween the ruthenium(II) central ion with the chloride and azide
ligands is presented as the insert. Much stronger interaction prop-
erties of the chloride ligand allow a redistribution of the electron
density from the b1 term (d
interaction with the pyridine donor in the trans position to the
) of ruthenium and thus a stronger
x2ꢁy2
Fig. 4. Simplified molecular orbital diagrams for the complexes [Ru(N3)2(PPh3)
(py)3] (1) and [Ru(N3)2(PPh3)2(b-pic)2] (2).
PPh3 ligand.
In the studied complexes, the HOMO and HOMOꢁ1 molecular
orbitals are composed of d ruthenium and
p
azide orbitals. HOMOꢁ2
is localized on the ruthenium central ion in complex 1 and on the
azide ligands in 2, as is shown in Fig. 4. The HOMO, H and LUMO, L
abbreviations denote the Highest Occupied Molecular Orbital and
Lowest Unoccupied Molecular Orbital. In the frontier virtual molecu-
lar orbitals, dRu has a share in LUMO+10 and LUMO+13 in complex
1 and LUMO+1, LUMO+12 in 2. In LUMO+13 and LUMO+12, in
addition to the dx2
orbital of ruthenium, the azide, PPh3 and pyr-
ꢁy2
idine or picoline orbitals are visible. Fig. 5 presents the partial den-
sity of states of the complexes, which is a more realistic description
of the frontier orbitals than a simplified molecular diagram. As it
may be seen, the lowest unoccupied molecular orbitals in complex
1 are localized on the pyridine ligands in contrast to complex 2, in
which the picoline ligands do not play a significant role in the low-
er LUMO orbitals. This difference in the electronic structure of the
Fig. 5. The density of states (DOS) diagrams for the complexes [Ru(N3)2(PPh3)(py)3]
(1) and [Ru(N3)2(PPh3)2(b-pic)2] (2). Dotted line represents the chloride DOS from
the [RuCl2(PPh3)(py)3] complex.
Fig. 3. The overlap partial density of states (OPDOS) diagram for the interaction
between the ruthenium central ion and the ligands in complex 1.

´
49
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
3.2. Absorption and emission electronic spectra
trum, showed in Fig. 6, suggests that more than one state is in-
volved in the luminescence processes. The excitation at 439 nm
results in an emission with a maximum at a wavelength of
505 nm, at the same time a shoulder at 493 nm and a weak band
with maximum at 650 nm are observed.
The UV–Vis spectra of the complexes are very similar and they
present bands with maxima close to 470 and 370 nm which are as-
signed to 1A1 ? 1T1 and 1A1 ? 1T2 transitions based on the pseudo-
octahedral geometry of the molecules. The shoulders at 270 nm
and the intense bands with maxima at 211 and 213 nm are attrib-
4. Conclusions
uted to pbC6H6 ! 3dphosphorus
,
p
!
pꢄCAC and
p
!
pꢄC@ transitions.
N
The values of the ligand field parameter 10Dq, calculated on the
basis of the positions and molar extinction coefficients of elec-
tronic bands for the complexes, are equal to 22560 and
22498 cmꢁ1 for complexes 1 and 2, respectively. The Racah param-
eter B is equal to 360 cmꢁ1 for 1 and 433 cmꢁ1 for 2, and the nep-
heloauxetic parameter b55 is 0.50 and 0.60 for complexes (1) and
(2), respectively. The Racah parameters B are lower than 500, sug-
gesting that the first transition bands have d ? d character with a
Metal-Ligand Charge Transfer (MLCT) admixture. The absorption
electronic spectra of the complexes are calculated with use of the
TD-DFT method. In the energy range corresponding to the first
In this paper, an experimental and theoretical study of ruthe-
nium(II) azide complexes with pyridine and 3-methylpyridine li-
gands has been made. The crystal structure and IR, 1H, 31P NMR
and UV–Vis spectroscopic properties of the complexes were deter-
mined. Theoretical calculations were carried out to determine the
electronic structures of these complexes. A molecular orbital
description of the HOMOs and LUMOs showed that the complexes
can present an intramolecular charge transfer of metal to ligand
character. The differences in the frontier molecular orbitals of
these complexes determine their fluorescent properties. The trans
influence of the triphenylphosphine ligand, shown in the molecu-
lar structure of complex 1, has been studied by NBO and molecular
orbital terms. A significant impact of the acceptor properties of the
halide/pseudohalide co-ligands on the strength of the trans effect
induced by phosphine was indicated.
experimental
bands
transitions,
HOMO ? LUMO
(53%),
1 and
HOMO ? L+1 (41%), Hꢁ1 ? L+1 (76%) for complex
HOMO ? LUMO (99%), HOMO ? L+3 (96%) for 2 are calculated.
As the frontier HOMO is localized on the d ruthenium orbitals with
an admixture of p
N3ꢁ and the LUMOs are localized on the pyridine
or b-picoline ligands with a contribution of dRu, the MLCT transi-
tions are associated with these. The second transitions with max-
ima near 370 nm have HOMO ? L+5/6/7 and HOMO ? L+12
(74%) character, therefore these bands have MLCT character. In
the energy region corresponding to the shoulders at 270 nm, the
MLCT and LMCT (Ligand to Metal Charge Transfer) transitions are
calculated and the highest energy bands are assigned to LLCT (Li-
gand to Ligand Charge Transfer) transitions.
Appendix A. Supplementary data
CCDC 818252 and 818088 contain the supplementary crystallo-
graphic data for the complexes [Ru(N3)2(PPh3)(py)3] and
[Ru(N3)2(PPh3)2(b-pic)2]. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
The emission characteristics of the complexes have been exam-
ined in methanol solutions (with a concentration of 5 ꢀ 10ꢁ4 mol/
dm3) at room temperature. The excitations were executed at wave-
lengths corresponding to the maxima of the first electronic absorp-
tions. Emission was observed only in the case of the pyridine
complex 1, which is associated with differences in the electronic
structure of these complexes, particularly involving the ligands in
the lowest unoccupied molecular orbitals, that is clearly visible
in the DOS diagrams presented in Fig. 5. Therefore, an emission
originating from the lowest energy metal to ligand charge transfer
References
[1] X.-Y. Lu, H.-J. Xu, X.-T. Chen, Inorg. Chem. Commun. 12 (2009) 887.
[2] V. Dragutan, I. Dragutan, L. Delaude, A. Demonceau, Coord. Chem. Rev. 251
(2007) 765.
[3] J.B. Coe, J.S. Glenwright, Coord. Chem. Rev. 203 (2000) 5.
[4] E.A. Medlycott, G.S. Hanan, Coord. Chem. Rev. 250 (2006) 1763.
[5] J. Otsuki, T. Akasaka, K. Araki, Coord. Chem. Rev. 252 (2008) 32.
[6] F. Puntoriero, S. Campagna, A.-M. Stadler, J.-M. Lehn, Coord. Chem. Rev. 252
(2008) 2480.
(MLCT) state, derived from the excitation involving a dp
transition, is observed. The structure of the luminescence spec-
!
pꢄligand
[7] Yu. E. Alexeev, B.I. Kharisov, T.C.H. Garcia, A.D. Garnovskii, Coord. Chem. Rev.
254 (2010) 794.
[8] H.E. Toma, K. Araki, Coord. Chem. Rev. 196 (2000) 307.
[9] Li-Feng Tan, H. Chao, K.-Ch. Zhen, J.-J. Fei, F. Wang, Y.-F. Zhou, L.-N. Ji,
Polyhedron 26 (2007) 5458.
[10] J.G. Małecki, M. Jaworska, R. Kruszynski, R. Gil-Bortnowska, Polyhedron 24
(2005) 1445.
[11] R. Kruszynski, J.G. Małecki, Acta Crystallogr., Sect. E63 (2007) m3052.
[12] J.G. Małecki, Polyhedron 29 (2010) 1973.
[13] T.A. Stephenson, G. Wilkonson, J. Inorg. Nucl. Chem. 28 (1966) 945.
[14] 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, D.J. Fox, GAUSSIAN09, Revision A.1, Gaussian, Inc.,
Wallingford, CT, 2009.
[15] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[16] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785.
[17] 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.
[18] K. Eichkorn, F. Weigend, O. Treutler, R. Ahlrichs, Theor. Chim. Acc. 97 (1997)
119.
Fig. 6. Methanolic solution fluorescence of [Ru(N3)2(PPh3)(py)3] (1) excited at
439 nm.

´
J.G. Małecki, A. Maron / Polyhedron 31 (2012) 44–50
50
[19] N.M. O’Boyle, A.L. Tenderholt, K.M. Langner, J. Comput. Chem. 29 (2008) 839.
[20] CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.33.46.
[21] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Crystallogr. 42 (2009) 339.
[22] C.-H. Lin, T.-S. Kuo, H.-C. Tong, C.-Y. Chen Hsu, Y.-H. Lo, Acta Crystallogr., Sect.
E64 (2008) m1511.
[23] P. Govindaswamy, P.J. Carroll, Y.A. Mozharivskyj, M.R. Kollipara, J. Organomet.
Chem. 690 (2005) 885.
[24] Ch.-K. Chen, H.-Ch. Tong, Ch.-Y. Chen Hsu, Ch.-Y. Lee, Y.H. Fong, Y.-S. Chuang,
Y.-H. Lo, Y.-Ch. Lin, Y. Wang, Organometallics 28 (2009) 3358.
[25] Ch.-Ch. Huang, H.-G. Hen, Y.H. Lo, W.-R. Lai, Ch.-H. Lin, Acta Crystallogr., Sect.
E66 (2010) m864.