Nickel and copper complexes based on tridentate nitrogen donor ligand 2,6-bis-(1-phenyliminoethyl) pyridine: Synthesis, spectral and structural characterization

Article abstract of DOI:10.1016/j.ica.2006.12.031

The reaction of CuCl₂ · 2H₂O with 2,6-bis(1-phenyliminoethyl)pyridine (referred hereafter as L) in 1:1 molar ratio in methanol or acetronitrile at room temperature afforded distorted trigonal-bipyramidal complex [Cu(κ³-L)C

Full text of DOI:10.1016/j.ica.2006.12.031

Inorganica Chimica Acta 360 (2007) 2492–2498
www.elsevier.com/locate/ica
Nickel and copper complexes based on tridentate nitrogen donor
ligand 2,6-bis-(1-phenyliminoethyl) pyridine: Synthesis, spectral
and structural characterization
a
a,
b,
*
Manoj Trivedi , Daya S. Pandey *, Qiang Xu
a
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, Uttar Pradesh, India
National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
b
Received 18 September 2006; received in revised form 30 November 2006; accepted 8 December 2006
Available online 4 January 2007
Abstract
The reaction of CuCl2 Æ 2H2O with 2,6-bis(1-phenyliminoethyl)pyridine (referred hereafter as L) in 1:1 molar ratio in methanol or ace-
tronitrile at room temperature afforded distorted trigonal-bipyramidal complex [Cu(j3-L)Cl2]. On the other hand, the reaction of
NiCl2 Æ 6H2O with 2 equivalents of L gave an octahedral complex [Ni(j3-L)2]2+, which was isolated as [Ni(j3-L)2][BF4]2 using NH4BF4.
The complexes have been characterized by elemental analyses, FAB-MS, IR, EPR and electronic spectral studies. Molecular structures of
both the [Cu(j3-L)Cl2] (1) and [Ni(j3-L)2](BF4)2 (2) have been determined by single crystal X-ray analyses. Weak interaction studies on 1
and 2 revealed stabilisation of the crystal packing by inter and intra-molecular C–Hꢀ ꢀ ꢀX (X = F, Cl, p) interactions. In complex 2 ortho
C–H bond from phenyl rings leads to unexpected C–Hꢀ ꢀ ꢀp interaction with nickel a,a0-diimine chelate ring. This provides structural sup-
port for metalloaromaticity in the chelate ring of complex 2.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Metal complexes; Bis-immine ligand; X-ray; C–Hꢀ ꢀ ꢀp interaction
1. Introduction
are either five-coordinate complexes with the formulations
[M(L)X2] or six-coordinate [M(L)2]2+, [M(j2-NO3)X(L)],
[M(j2-NO3)(NO3)(L)], [M(NO3)(en)(L)]+ (M = Ni, Cu,
Zn and Cd; X = halide; en = 1,2-diaminoethane) [3]. It
has also been shown that reactions of L with the group
VI and VII metal carbonyls or their derivatives give com-
plexes in which the potentially tridentate ligands act in a
bidentate chelating mode binding to metal centre via the
pyridyl and just one of the imino nitrogen atoms [4].
CHꢀ ꢀ ꢀp interactions are weakest hydrogen bonds that
operate between a soft acid and a soft base p system and
play significant roles in the various fields of chemistry
and biology [5]. The soft base p system which acts as a
CH acceptor comprises not only of an organic moiety such
as a double bond, triple bond or a delocalized aromatic
ring [6], but also of a metal chelate ring of suitable transi-
tion metal complexes [7]. Group of authors in their inter-
esting work have presented a remarkable effort towards
Bis-(iminoalkyl)pyridine metal complexes have drawn
much attention due to their interesting coordination
chemistry and applications in catalysis [1,2]. The donor
properties of the N,N,N donor ligands 2,6-diacetylpyri-
dine-bis(imines) derived by Schiff base condensation of
2,6-diacetylpyridine with aromatic amines is comparable
to that of terpyridine (terpy). It is well established that they
normally behave as planar, tridentate ligand towards vari-
ous kinetically labile metal ions such as Fe(II), Mn(II),
Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) halides, nitrates,
perchlorates, and tetrafluoroborate. The resulting products
*
Corresponding authors. Tel.: +91 9450960400 (D. S. Pandey); tel.: +81
72 751 9652 (Q. Xu).
E-mail addresses: dsprewa@yahoo.com (D.S. Pandey), q.xu@aist.
go.jp (Q. Xu).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.12.031

M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
2493
the definition of structural parameters for the interaction
between C–H polar bonds and the whole of a p(metal-che-
late ring) system [7]. The concept of ‘‘metalloaromaticity’’
was proposed a long time ago and it is well known that a
large variety of transition metal-chelate rings feature this
aromaticity [8]. Here we provide structural support for
nickel(II) complex in which nickel-diimine chelate ring acts
as a CH acceptor.
Because of interests in N,N,N donor ligands, we have
examined the reactivity of L with Cu(II) and Ni(II) salts
[9]. We describe herein the reproducible synthesis, spectral
and structural characterization of five-coordinate copper
complex [Cu(j3-L)Cl2] (1) and six-coordinate nickel com-
plex [Ni(j3-L)2](BF4)2 (2) containing 2,6-di-iminopyridyl
unit. We also report herein structural evidence for metallo-
aromaticity in the chelate ring of nickel complex 2.
consistent with the formulations of the respective com-
plexes. Infrared spectra in nujol displayed bands corre-
sponding to m(C@N) at ꢂ1585 cmꢁ1 and bands around
289–330 cmꢁ1 assignable to m(Cu–Cl). Bands at 1060–
1055 and 525–530 cmꢁ1 are assigned to the asymmetric
stretching B–F vibrations and B–F bending, respectively.
The absorption spectra of 1 and 2 in DMSO displayed
bands at ꢂ489 nm and an intense higher-energy band at
249–296 nm. The lowest-energy bands in the range of
489 nm can be assigned to metal to ligand charge transfer
transition MLCT ½MðIIÞ ! pꢃLꢄ. The intense band in the
region 249–296 nm has been assigned to L-centered intra-
ligand (p–p*) transitions.
Information regarding the immediate environment
about the metal centre in complex 1 was obtained from
ESR spectral studies. The X-band ESR spectra of 1 in
DMSO were recorded at liquid-nitrogen and room temper-
atures (Fig. 1). The spectrum at room temperature shows
one intense band in the high field while in frozen state it
shows four well resolved peaks. Three bands are at a higher
field and one is at a lower field than the relative to that of
TCNE. Complex 1 in the solid state afforded a broad spec-
trum. The copper complex exhibits the gi value of 2.274
and g^ 2.092. These values indicate that the ground state
of Cu(II) is predominant [10].
2. Results and discussion
2.1. Synthesis
The reactions of CuCl2 Æ 2H2O with L in methanol or
acetronitrile in equimolar ratio under stirring conditions
at room temperature gave neutral complex with the formu-
lations [Cu(j3-L)Cl2] (1). On the other hand, the reaction
of two equivalents of L with NiCl2 Æ 6H2O under analogous
conditions afforded the corresponding bis-(ligand) complex
cation [Ni(j3-L)2]2+ (2) which was isolated as the BFꢁ4 salt
by using NH4BF4. Synthesis of 2 has previously been
described by Schroder et al. following a quite different pro-
cedure but no structural data were reported [3b]. A simple
scheme showing the syntheses of the complexes is given
below.
2.3. Molecular structures
Molecular structures of 1 and 2 were determined by sin-
gle-crystal X-ray diffraction studies. The details about data
collection, solution and refinement are recorded in Table 1.
The molecular structures of complexes 1 and 2 with atom
numbering scheme are shown in Fig. 2 and the important
2+
N
N
N
N
N
N
CuCl2.2H2O
NiCl2.6H2O
Methanol
N
N
N
Methanol/CH3CN
Ni
N
N
N
Cu
Cl
Cl
[2]
[1]
2.2. Characterization
geometrical parameters are recorded in Table 2. Complex
1 crystallizes in the orthorhombic space group Pbca and
the crystallographic asymmetric unit contains two indepen-
dent molecules, which have almost identical geometry,
while 2 crystallizes in the monoclinic space group P21/n.
The molecular structure of 1 shows a distorted square-
bipyramidal geometry consisting of two axial imino N-
atoms N2 and N3, and two Cl-ions and a pyridyl N1-atom
as equatorial ligands (see Table 2). The Cu–N distances are
longer compared to the values reported in the literature
[1a,11], indicating that the ligand is more loosely bound
with the metal centre. The N–Cu–N angle is 154.8ꢁ and this
The complexes are air stable, non-hygroscopic shiny
crystalline solids, sparingly soluble in common organic sol-
vents, and insoluble in diethyl ether and petroleum ether.
The complexes were fully characterised by IR, UV–Vis,
FAB-MS and EPR spectroscopies. Analytical data of the
complexes (recorded in the experimental section) corrobo-
rated well their respective formulations. The FAB-MS
spectra of the complexes correspond to their respective
formulations. The positions of various peaks and overall
fragmentation patterns (recorded in the Section 4) are

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M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
Fig. 1. (a) EPR spectra of 1 at RT; (b) at LNT.
Table 1
Crystal data for 1 and 2
1
2
Empirical formula
Formula weight
C
447.83
21H19Cl2N3Cu
C42H38B4F8N6Ni
880.73
Colour and habit
yellow red needle
red needle
Crystal size (mm)
Crystal system, space group
0.50 · 0.30 · 0.20
0.30 · 0.25 · 0.20
orthorhombic, Pbca monoclinic, P21/n
˚
a (A)
15.6109(9)
20.1076(11)
24.8441(13)
90
7798.5(7)
15, 1.430
1.317
14.0472(16)
13.9261(16)
20.729(2)
97.064
4024.4(8)
4, 1.454
0.560
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z, Dc (g cmꢁ3
)
l (mmꢁ1
T (K)
)
373(2)
0.71073
293(2)
˚
k (Mo Ka) (A)
Number of reflections/unique 37246/9675
Number of refined parameters 221
0.71073
26468/9838
536
R factor [I > 2r(I)]
wR2 [I > 2r(I)]
R factor (all data)
wR2 (all data)
0.0582
0.1548
0.0835
0.1875
1.193
0.0703
0.1567
0.1417
0.2013
Goodness-of-fit
0.934
angle in the other symmetrically identical molecule is 155.5,
which is lower than the expected trans N–Cu–N angle. The
Cu–Cl distances are comparable to the values reported in
the literature [12].
Fig. 2. ORTEP views of 1 (top) and 2 (bottom) with thermal ellipsoids
shown at the 30% level; hydrogen atoms were omitted for clarity.
The molecular structure of 2 shows two molecules of L
coordinated to the nickel centre in a meridional manner.
The geometry around the NiII is distorted octahedral with
four imino N-atoms bound in an equatorial plane Ni–N3a
2.117(3), Ni–N2a 2.149(3), Ni–N2b 2.135(3), Ni–N3b
2.145(3) and the two pyridyl N-atoms occupying the axial
the four positions of the phenyl ring lying at distances of
˚
7.68 and 5.28 A from one another.
Crystal packing in 1 is stabilized by C–Hꢀ ꢀ ꢀCl type inter-
and intra-molecular hydrogen bonds, which lead to
straight chain motif in which the phenyl rings attached to
imino nitrogen are perpendicular to this chain (Fig. 3).
Contact distances between C–Hꢀ ꢀ ꢀCl are in the range of
˚
positions Ni–Npy1a 1.980(3), Ni–Npy1b 1.976(3) A. The
Ni–Nimine and Ni–Npy separations are comparable to
those in the closely related complexes [3b,1b,11]. The dihe-
dral angle between two pyridyl rings is 89.9ꢁ. The N–Ni–N
angles are markedly distorted from 90ꢁ with N1a–Ni–N3a,
77.32(13)ꢁ, N1a–Ni–N2a, 76.93(13)ꢁ, N1b–Ni–N1a, 166.71
(14)ꢁ, N1b–Ni–N2b, 77.37(13)ꢁ, N1b–Ni–N3b, 76.55(13)ꢁ.
In the solid-state structure, two of the phenyl rings (i.e.
centroids of the rings) of each tridentate ligand extend
away from the metal centre beyond the coordination
sphere of other coordinated ligands and are situated with
˚
2.64–2.92 A and angles are in the range of 153.6–160.6ꢁ.
Extra stabilization of the phenyl rings has been found in
both complexes 1 and 2 by intramolecular C–Hꢀ ꢀ ꢀp inter-
actions (Fig. 4). The inter-molecular C–Hꢀ ꢀ ꢀF weak inter-
actions that are present in complex 2 result in parallel
chain like structure, which expands the motif in the crystal
lattice through these interactions (Figs. 5a and 5b). Contact

M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
2495
Table 2
Selected bond lengths (A) and bond angles (ꢁ) for 1 and 2
3. Conclusions
˚
Complex 1
2
In this work, we have presented synthesis, spectral and
structural properties of the Cu(II) and Ni(II) complexes
derived from 2,6-bis-(1-phenyliminoethyl) pyridine. Weak
interaction studies on the nickel complex indicated the
occurrence of metalloaromaticity in this complex.
Cu–N1a
Cu–N3a
Cu–N2a
Cu–Cl2a
Cu–Cl1a
Cu–N1b
Cu–N3b
Cu–N2b
Cu–Cl1b
Cu–Cl2b
N3a–C16a
N2a–C10a
N2b–C10b
N3b–C16b
1.947(3)
2.084(3)
2.109(3)
2.226(11)
2.405(11)
1.961(3)
2.080(3)
2.115(3)
2.246(9)
2.402(9)
1.433(4)
1.442(4)
1.432(4)
1.425(4)
Ni–N1b
Ni–N1a
Ni–N3a
Ni–N2b
Ni–N2a
Ni–N3b
N3a–C2a
N2b–C8b
N2a–C8a
N2b–C16b
N3b–C2b
N2b–C16b
N2a–C16a
N3a–C10a
1.976(3)
1.980(3)
2.117(3)
2.135(3)
2.149(3)
2.145(3)
1.288(5)
1.287(5)
1.285(5)
1.436(5)
1.286(5)
1.436(5)
1.436(4)
1.436(5)
4. Experimental
4.1. Materials and physical measurements
All the synthetic manipulations were performed under
oxygen free nitrogen atmosphere. The solvents were dried
and distilled before use following the standard procedures.
Ammonium tetrafluoroborate (Aldrich), copper chloride
dihydrate, and nickel chloride hexahydrate were used
as received. 2,6-bis(1-phenyliminoethyl) pyridine was
prepared and purified following the literature procedure
[15].
Elemental analyses were performed at Sophisticated
Analytical Instrumental Facility, Central Drug Research
Institute, Lucknow. Infrared spectra and Electronic spectra
were obtained on a Perkin–Elmer 577 and Shimadzu UV-
1601 spectrometer, respectively. Electron paramagnetic res-
onance (EPR) spectra were recorded with a Varian E-line
Century Series EPR Spectrometer equipped with a dual
cavity and operating at X-band of 100 kHz modulation fre-
quency. Tetracyanoethylene was used as a field marker
(g = 2.00277). The FAB mass spectra were recorded on a
JEOL SX 102/DA 6000 mass spectrometer using Xenon
(6 kV, 10 mA) as the FAB gas. Accelerating voltage was
10 kV and the spectra were recorded at room temperature
with m-nitrobenzyl alcohol as the matrix.
N1a–Cu–N3a
N1a–Cu–N2a
N3a–Cu–N2a
N1a–Cu–Cl2a
N1b–Cu–N3b
N1b–Cu–N2b
N3b–Cu–N2b
77.71(11)
77.94(12)
154.82(11)
151.94(8)
77.92(11)
77.64(11)
155.51(11)
N1b–Ni–N3b
N1a–Ni–N3a
N1b–Ni–N2b
N1b–Ni–N1a
N1a–Ni–N2a
76.55(13)
77.32(13)
77.37(13)
166.71(14)
76.93(13)
˚
distances between C–Hꢀ ꢀ ꢀF are in the range of 2.38–2.62 A
and angles are in the range of 126–151ꢁ.
The most noteworthy structural feature of complex 2 is
that two ortho-H atoms from phenyl ring point towards
the centre of the corresponding nickel-a,a0diimine chelate
ring (Fig. 6). Comprehensive analysis was carried out with
the program PLATON, and relevant structural parameters
are listed in Table 3 [13]. The H-ring centroid (Hꢀ ꢀ ꢀCt) dis-
˚
tance is of 2.68–2.94 A, Cꢀ ꢀ ꢀCt distance is in the range of
˚
3.379–3.416 A, Hꢀ ꢀ ꢀring plane (Hꢀ ꢀ ꢀ^) distance is in the
˚
range of 2.66–2.88 A and the C–Hꢀ ꢀ ꢀCt angle is 111–
136.0ꢁ, still below the optimal value (180ꢁ) for the strongest
C–Hꢀ ꢀ ꢀp interactions, which may be due to the steric con-
straint in the molecule. The c angle is found to be 5.41–
11.58ꢁ and is within the range reported in the literature
[14]. This indicates that C–Hꢀ ꢀ ꢀp interactions occur
between ortho–CH bonds and the whole of an electroni-
cally delocalized nickel chelate ring in complex 2. On the
basis of the reported metalloaromaticity in aryl metal che-
late rings [7,8], this kind of C–Hꢀ ꢀ ꢀp (planar chelate ring)
interaction in complex 2 is thought to be structural support
for metalloaromaticity.
4.2. Synthesis
4.2.1. Cu[(j3-L)Cl2] (1)
To a suspension of CuCl2 Æ 2H2O (0.170 g, 1.0 mmol) in
20 mL of acetonitrile or methanol, L (0.313 g, 1.0 mmol)
was added and the resulting solution was stirred at room
temperature for 30 min. Slowly, the color of the solution
changes from green to yellow and yellow coloured precip-
itate separated out. The resulting precipitate was filtered
Fig. 3. C–Hꢀ ꢀ ꢀCl interactions lead to a straight chain motif in which the phenyl rings attached to imino nitrogen are perpendicular to this chain in 1.

2496
M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
Fig. 4. Intra-molecular C–Hꢀ ꢀ ꢀp interactions in (a) 1 and (b) 2.
Fig. 5a. Parallel chains structure made through C–H–F interactions in complex (side view).

M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
2497
Fig. 5b. Apical view of chains made through C–H–F interactions in complex 2.
4.2.2. [Ni(j3-L)2] (BF4)2 (2)
Complex 2 was prepared following the above procedure
from the reaction of NiCl2 Æ 6H2O (0.238 g, 1.0 mmol) in
methanol (10 mL) with L (0.626 g, 2.0 mmol). The color
of the solution changes from green to yellowish red. The
resulting solution was filtered to remove any solid residue.
The filtrate was concentrated under reduced pressure to
one fourth of its volume and a saturated solution of ammo-
nium tetrafluoroborate dissolved in methanol was added
and left for slow crystallization in the refrigerator at
ꢂ4 ꢁC. Slowly, a microcrystalline product was obtained,
which was separated by filtration and washed repeatedly
with diethyl ether and dried in vacuo. Dark red needle
shaped crystals suitable for X-ray diffraction studies were
grown by diffusion method from methanol-diethyl ether.
Yield: 0.354 g (80%). Anal. Calc. for C42H38N6B2F8Ni: C,
58.67; H, 4.42; N, 9.78. Found: C, 58.30; H, 4.12; N,
9.60%. FAB-MS m/z: 772(771), 5 [Ni(j3-L)2]+(BF4);
685(684), 50 [Ni(j3-L)2]2+; 372(371), 100 [Ni(j3-L)]2+
.
UV–Vis {DMSO, kmax nm (e/Mꢁ1cmꢁ1)}: 302 (24221),
489 (2103).
Fig. 6. The ortho C–H bond from the phenyl ring produces unexpected
C–Hꢀ ꢀ ꢀp interactions with the nickel-a,a0-diimine chelate ring in 2.
4.3. X-ray crystallographic study
Crystals suitable for single-crystal X-ray analyses for the
complexes [Cu(j3-L)Cl2] (1) and [Ni(j3-L)2](BF4)2 (2) were
grown at room temperature. Preliminary data on the space
group and unit cell dimensions as well as intensity data
were collected on Enraf-Nonius MACH3 diffractometer
using graphite monochromatized Mo Ka radiation. The
crystal orientation, cell refinement and intensity measure-
ments were made using the program CAD-4 PC. The struc-
ture was solved by direct methods and refined by using
MAXUS (1999) and SHELX-97 [16]. The non-hydrogen atoms
were refined anisotropically. All the hydrogen atoms were
geometrically fixed and allowed to refine using a riding
and washed with diethyl ether. It was dissolved in methanol
and layered with diethyl ether and left in a refrigerator for
slow crystallization. In a couple of days reddish yellow nee-
dle shaped diffraction quality crystals separated. These
were separated and washed with diethyl ether. Yield:
0.317 g (71%). Anal. Calc. for C21H19N3Cl2Cu: C, 56.37;
H, 4.25; N, 9.39. Found: C, 56.20; H, 4.10; N, 9.29%.
FAB-MS m/z: 447(445), 5 [Cu(j3-L)Cl2]; 411(411), 20
[Cu(j3-L)Cl]; 375(376) [Cu(j3-L)]; 313(314), 5 [(j3-L)].
UV–Vis {DMSO, kmax (nm) (e/Mꢁ1 cmꢁ1)}: 294(3502),
486(1432).
Table 3
Intramolecular ‘‘CHꢀ ꢀ ꢀp(chelate ring)’’ interaction parameters for 2
˚
˚
˚
CH-chelate ring
Hꢀ ꢀ ꢀCg (A)
Hꢀ ꢀ ꢀ(ring plane) (A)
Cꢀ ꢀ ꢀCg (A)
C–Hꢀ ꢀ ꢀCg (ꢁ)
136
r (ꢁ)
5.41
11.58
C11aH11aꢀ ꢀ ꢀ(NiN1bN3b)
C17aH17aꢀ ꢀ ꢀ(NiN1bN3b)
2.68
2.94
2.669
2.880
3.416
3.379
111

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M. Trivedi et al. / Inorganica Chimica Acta 360 (2007) 2492–2498
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model. The computer program PLATON was used for analyz-
ing the interaction and stacking distances [17].
Acknowledgements
[5] (a) M. Nishio, M. Hirota, Y. Umezawa, The CH/p Interaction,
Evidence, Nature and Consequences, Wiley VCH, New York,
1998;
Financial support from the council of Scientific and
Industrial Research, New Delhi, in the form of Scheme
[HRDG 01(1784)/EMR-II/2002] and help from National
Institute of Advanced Industrial Science and Technology
(AIST), Osaka, Japan, is gratefully acknowledged. We also
thank the Head, SAIF, Central Drug Research Institute,
Lucknow, for analytical and spectral facilities, and the Head,
Department of Chemistry, Faculty of Science, Banaras Hin-
du University, Varanasi, for extending laboratory facilities.
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Appendix A. Supplementary material
(i) K. Burley, G.A. Petsko, Science 229 (1985) 23;
(j) M. Nishio, Bio-org. Med. Chem. Lett. 9 (1999) 221.
[6] M.C.B. Colbert, J. Lewis, N.J. Long, P.R. Raithby, A.J.P. White,
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[7] (a) G.A. Bogdanovic, A.S. -De Bire, S.D. Zaric, Eur. J. Inorg. Chem.
(2002) 1599;
CCDC 602708 and 602709 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@
ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:
10.1016/j.ica.2006.12.031.
(b) Z.D. Tomic, V.M. Leovac, S.V. Pokorni, D. Zobel, S.D. Zaric,
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