Zinc(II) and cadmium(II) complexes based on 4-(3,5-diphenyl-1H-pyrazol-1- yl)-6-(piperidin-1-yl)pyrimidine (L): Synthesis, structure, luminescence. Double lone pair-π interactions in the structure of ZnL2Cl2

Article abstract of DOI:10.1016/j.ica.2011.03.007

A series of zinc(II) and cadmium(II) complexes with 4-(3,5-diphenyl-1H- pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L), ZnLCl₂, CdLCl ₂, ZnL₂Cl₂, CdL₂Cl₂, CdL₂Cl₂·0.5Me₂CO·1.5H ₂O and CdL₂Cl₂·0.5CHCl ₃·0.5H₂O, have been synthesized. The compounds ZnLCl₂ and CdLCl₂ were obtained in a M:L = 1:1 molar ratio in EtOH solutions, while ZnL₂Cl₂ and CdL ₂Cl₂ were isolated in a M:L = 1:3 molar ratio in EtOH/Me₂CO mixtures. Surprisingly, attempts to crystallize CdLCl ₂ from EtOH/Me₂CO mixture afforded single crystals of a compound, having 1:2 metal-to-ligand stoichiometry, CdL₂Cl ₂·0.5Me₂CO·1.5H₂O, instead of a complex with 1:1 stoichiometry. At the same time, crystallization of CdL ₂Cl₂ from Me₂CO/CHCl₃ mixture afforded CdL₂Cl₂·0.5CHCl₃·0. 5H₂O single crystals. According to X-ray crystal structure data, ZnLCl₂, ZnL₂Cl₂, CdL₂Cl ₂·0.5Me₂CO·1.5H₂O and CdL ₂Cl₂·0.5CHCl₃·0.5H₂O complexes have molecular mononuclear structures. The molecules of L adopt bidentate chelating binding mode being coordinated to the metal ions through N² atom of the pyrazole and N³ atom of the pyrimidine rings. The coordination core of zinc atom in ZnLCl₂ complex is a distorted ZnN₂Cl₂ tetrahedron. The coordination cores of metal atoms in the structures of ZnL₂Cl₂, CdL ₂Cl₂·0.5Me₂CO·1.5H₂O and CdL₂Cl₂·0.5CHCl₃·0.5H ₂O are the distorted cis-MN₄Cl₂ (M = Zn, Cd) octahedra. In the structure of ZnL₂Cl₂ double lone pair(N(piperidine))-π(pyrimidine) interactions were observed. The photoluminescent properties of L, ZnLCl₂, CdLCl₂, ZnL ₂Cl₂ and CdL₂Cl₂ were studied in the solid state under the same experimental conditions. These compounds were found to display bright blue luminescence. Highest relative intensity of emission was detected for ZnL₂Cl₂.

Full text of DOI:10.1016/j.ica.2011.03.007

Inorganica Chimica Acta 371 (2011) 88–94
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Zinc(II) and cadmium(II) complexes based on 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-
(piperidin-1-yl)pyrimidine (L): Synthesis, structure, luminescence. Double lone
pair–p interactions in the structure of ZnL2Cl2
Mark B. Bushuev a,b, , Katerina A. Vinogradova a,b, Viktor P. Krivopalov c, Elena B. Nikolaenkova c,
Natalia V. Pervukhina a, Dmitrii Yu. Naumov a, Marianna I. Rakhmanova a, Evgenii M. Uskov a,
Lilia A. Sheludyakova a,b, Aleksei V. Alekseev a, Stanislav V. Larionov a
⇑
a Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Akad. Lavrentiev Ave., Novosibirsk 630090, Russia
b Novosibirsk State University, 2, Pirogova Str., Novosibirsk 630090, Russia
c N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Akad. Lavrentiev Ave., Novosibirsk 630090, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of zinc(II) and cadmium(II) complexes with 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-
yl)pyrimidine (L), ZnLCl2, CdLCl2, ZnL2Cl2, CdL2Cl2, CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O and CdL2Cl2ꢀ0.5CHCl3ꢀ
0.5H2O, have been synthesized. The compounds ZnLCl2 and CdLCl2 were obtained in a M:L = 1:1 molar
ratio in EtOH solutions, while ZnL2Cl2 and CdL2Cl2 were isolated in a M:L = 1:3 molar ratio in EtOH/Me2CO
mixtures. Surprisingly, attempts to crystallize CdLCl2 from EtOH/Me2CO mixture afforded single crystals
of a compound, having 1:2 metal-to-ligand stoichiometry, CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O, instead of a com-
plex with 1:1 stoichiometry. At the same time, crystallization of CdL2Cl2 from Me2CO/CHCl3 mixture
afforded CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O single crystals. According to X-ray crystal structure data, ZnLCl2,
ZnL2Cl2, CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O and CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O complexes have molecular mononuclear
structures. The molecules of L adopt bidentate chelating binding mode being coordinated to the metal
ions through N2 atom of the pyrazole and N3 atom of the pyrimidine rings. The coordination core of zinc
atom in ZnLCl2 complex is a distorted ZnN2Cl2 tetrahedron. The coordination cores of metal atoms in the
structures of ZnL2Cl2, CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O and CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O are the distorted cis-
Received 29 December 2010
Received in revised form 28 February 2011
Accepted 3 March 2011
Available online 10 March 2011
Keywords:
Zinc(II)
Cadmium(II)
Pyrazolylpyrimidines
Synthesis
Non-covalent (lone pair–
p, C–HꢀꢀꢀN
and C–HꢀꢀꢀCl) interactions
Luminescence
MN4Cl2 (M = Zn, Cd) octahedra. In the structure of ZnL2Cl2 double lone pair(N(piperidine))–p(pyrimidine)
interactions were observed. The photoluminescent properties of L, ZnLCl2, CdLCl2, ZnL2Cl2 and CdL2Cl2
were studied in the solid state under the same experimental conditions. These compounds were found
to display bright blue luminescence. Highest relative intensity of emission was detected for ZnL2Cl2.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Some of metal complexes with 4-pyrazolylpyrimidine ligands
manifest luminescence [3m,3p–r].
Pyrazolylpyrimidines are reported in the literature as the com-
pounds manifesting various kinds of biological activity [1]. They
can act as the ligands binding metal ions [2]. Depending on the
structure of the ligand, nature of metal ion, synthetic conditions,
etc., the ligands containing 4-pyrazolylpyrimidine core form
mono-, di- or oligo-nuclear complexes with metals [3]. Together
with the structural diversity of these complexes, they demonstrate
magnetic and catalytic activity [3b,3c,3g]. In addition, they were
used for the design of supramolecular self-assemblies [3a,3e,3f].
Earlier we reported two copper(II) coordination compounds
based on a new chelating pyrazolylpyrimidine ligand, 4-(3,5-di-
phenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L, Scheme
1). It was observed that the combination of a lone pair donor and
an acceptor within a single complex molecule/ion produces double
lone pair–
tions, namely bonding interactions between a lone pair donor
and an electron-deficient ring, are regarded as a new supramo-
p (lp–p) interactions [4]. These non-covalent interac-
p
lecular bond [5]. These interactions play a pivotal role in various
biological systems and were observed in the biomolecules [6].
In recent years, the design of luminescent compounds as a base
for the development of organic light-emitting diodes (OLED) and
sensors have attracted widespread attention [7]. One of the main
groups of luminescent compounds are the complexes of metals
having d10 electronic configuration, zinc(II) and cadmium(II), based
⇑
Corresponding author at: Nikolaev Institute of Inorganic Chemistry, Siberian
Branch of Russian Academy of Sciences, 3, Akad. Lavrentiev Ave., Novosibirsk
630090, Russia.
E-mail address: bushuev@niic.nsc.ru (M.B. Bushuev).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.007

M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
89
(dec.). Anal. Calc. for C24H23N5Cl2Zn: C, 55.6; H, 4.5; N, 13.5; Zn,
12.6. Found: C, 55.6; H, 4.6; N, 13.5; Zn, 12.9%.
Single crystals suitable for X-ray analysis were obtained by slow
crystallization of ZnLCl2 from mixture EtOH/CH2Cl2 (1:1).
2
N
N
N
2.3. Synthesis of CdLCl2 (2)
3
N
N
MCl
2
:L=1:1
MCl
2
:L=1:3
EtOH, Me
2
CO
EtOH
A hot solution of L (0.3 mmol, 114 mg) in EtOH (9 ml) was
(L)
added to
a
hot stirred solution of CdCl2ꢀ2.5H2O (0.3 mmol,
ML
2
Cl
2
MLCl
2
69 mg) in EtOH (3 ml). A white precipitate was formed immedi-
ately. In ca. 1 h reaction mixture was cooled, the precipitate was
filtered off, washed with EtOH and dried in ambient air. Yield:
188 mg (87%). m.p. 320 °C (dec.). Anal. Calc. for C24H23N5CdCl2: C,
51.0; H, 4.1; N, 12.4; Cd, 19.9. Found: C, 50.0; H, 3.9; N, 12.2; Cd,
20.2%.
M=Zn (1)
M=Cd (2)
M=Zn (3)
M=Cd (4)
(2), EtOH,
(4), CHCl
Me2
3
,
Me
2
CO
CO
. 0.5Me
2
CO . 1.5H
O
2
CdL
2
Cl
2
. 0.5CHCl
3
. 0.5H
O
2
CdL
2
Cl
2
2.4. Synthesis of ZnL2Cl2 (3)
(5)
(6)
Scheme 1. Synthesis of the complexes.
A hot solution of ZnCl2 (0.1 mmol, 14 mg) in EtOH (10 ml) was
added to a hot stirred solution of L (0.3 mmol, 114 mg) in the mix-
ture of EtOH (5 ml) and Me2CO (1 ml). The hot resulting colorless
reaction mixture was stirred for 1 h. When the volume of the reac-
tion mixture became 10 ml, a white precipitate was formed. The
reaction mixture was concentrated up to 1–2 ml. The precipitate
was filtered off, washed with hot EtOH and dried in ambient air.
Yield: 50 mg (57%). m.p. 210 °C (dec.). Anal. Calc. for
on the ligands with extended
p-system [8]. Depending on the
width of the band in the luminescence spectra these complexes
manifest blue or white (relatively rare) emission [9]. The emissions
observed in the complexes were assigned mainly to intra-ligand
transitions [10].
In this context here we report the synthesis, crystal structure
studies and luminescent properties of a series of zinc(II) and cad-
mium(II) chloride complexes with L. They are, to the best of our
knowledge, the first examples of zinc(II) and cadmium(II) com-
plexes with 4-pyrazolylpyrimidines. To study the effect of metal-
to-ligand stoichiometry on the luminescence properties of the
complexes, we attempted to prepare complexes having 1:1 and
1:2 metal-to-ligand stoichiometry. Finally, taking into account pre-
viously reported data [4], we were also endeavored to answer the
C48H46N10Cl2Zn: C, 64.1; H, 5.2; N, 15.6; Zn, 7.3. Found: C, 63.8;
H, 5.3; N, 15.5; Zn, 7.6%.
Single crystals suitable for X-ray analysis were obtained from
the solution containing ZnCl2 (0.01 mmol, 1.3 mg) and
L
(0.03 mmol, 11.4 mg) dissolved in 2 ml of EtOH/Me2CO (1:1)
mixture.
2.5. Synthesis of CdL2Cl2 (4)
question whether double lp–
found in [CuL2Cl2] and [CuL2Cl]2[Cu2Cl6], will be observed in the
zinc(II) and cadmium(II) complexes based on L.
p interactions, that we previously
A hot solution of CdCl2ꢀ2.5H2O (0.1 mmol, 20 mg) in EtOH (2 ml)
was added to a hot stirred solution of L (0.3 mmol, 114 mg) in the
mixture of EtOH (5 ml) and Me2CO (1 ml). White precipitate was
formed immediately. Reaction mixture was stirred with heating
for 1.5 h. Precipitate was filtered off, washed with hot EtOH and
dried in ambient air. Yield: 94 mg (98%). m.p. 210 °C (dec.). Anal.
Calc. for C48H46N10CdCl2: C, 60.9; H, 4.9; N, 14.8. Found: C, 60.6;
H, 5.2; N, 14.8%.
2. Experimental
2.1. General
4-(3,5-Diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine
(L) was prepared according to the reported procedure [4]. All other
reagents and solvents were commercially available and were used
without additional purification. The zinc and cadmium content
was determined by complexonometric titration, the samples were
mineralized in a 1:1 mixture of concentrated H2SO4 and HClO4. Ele-
mental analysis (C, H, N) was performed with a Carlo–Erba analyzer
using standard technique. IR absorption spectra were recorded on a
Scimitar FTS 2000 spectrophotometer at 375–4000 cmꢁ1 and on a
VERTEX-80 spectrophotometer at 100–600 cmꢁ1. Luminescence
spectra were recorded on a fluorescence spectrophotometer Cary
Eclipse (Varian). The X-ray powder diffraction data were obtained
2.6. Synthesis of CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O (5)
The complex CdLCl2 (a small tip of a spatula) was dissolved in
the mixture EtOH/Me2CO (1:2), colorless crystals appeared in a
month. They were used in X-ray diffraction analysis and their com-
position was identified as CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O.
2.7. Synthesis of CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O (6)
The complex CdL2Cl2 (a small tip of a spatula) was dissolved in
the mixture Me2CO/CHCl3 (2:1), colorless crystals appeared in a
month. They were used in X-ray diffraction analysis and their com-
position was identified as CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O.
with a DRON-3M automated diffractometer (R = 192 mm, Cu Ka-
radiation, Ni-filter, scintillation point detector with amplitude dis-
crimination) at the room temperature.
2.8. X-ray crystallographic study
2.2. Synthesis of ZnLCl2 (1)
Single crystal data for 1, 3, 5 and 6 were collected at 150 K with
A hot solution of L (0.2 mmol, 76 mg) in EtOH (3 ml) was added
to a hot stirred solution of ZnCl2 (0.2 mmol, 27 mg) in EtOH (2 ml).
In ca. 1 h resulting colorless solution was cooled and a white pre-
cipitate was formed. The precipitate was filtered off, washed with
EtOH and dried in ambient air. Yield: 72 mg (69%). m.p. 298 °C
Mo Ka radiation (k = 0.71073 Å) using a Bruker Nonius X8Apex
CCD diffractometer equipped with graphite monochromator. The
SMART software was used for data collection and also for indexing
the reflections and determining the unit cell parameters; the
collected data were integrated using SAINT software [11]. The struc-

90
M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
Table 1
Crystal data and structure refinement for compounds 1, 3, 5 and 6.
Compound
1
3
5
6
Empirical formula
Formula weight
Crystal system
Space group
C
24H23Cl2N5Zn
C48H46Cl2N10Zn
899.22
monoclinic
C2/c
C49.50H51CdCl2N10O2
1001.30
monoclinic
P21/n
C48.50H47.50CdCl3.5N10O0.5
1014.94
monoclinic
517.74
triclinic
P21/n
P1
a (Å)
b (Å)
c (Å)
9.863(1)
15.810(1)
15.810(1)
16.0854(6)
15.6026(8)
17.9943(9)
11.6994(5)
17.9487(7)
23.4173(11)
11.9380(4)
17.5345(7)
24.2630(10)
a
(°)
100.22(3)
b (°)
101.61(2)
105.308(1)
102.294(1)
99.551(2)
c
(°)
106.13(2)
2305.3
V (Å3)
4355.9(4)
4804.6(4)
5008.5(3)
Z
4
4
4
4
T (K)
150(2)
1.492
1.319
0.15 ꢂ 0.12 ꢂ 0.08
2.14–26.37
ꢁ12 6 h 6 12
ꢁ12 6 k 6 19
ꢁ20 6 l 6 19
16 624
150(2)
1.371
0.734
150(2)
1.381
0.616
150(2)
1.346
0.667
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
Crystal size (mm3)
0.32 ꢂ 0.28 ꢂ 0.12
0.32 ꢂ 0.12 ꢂ 0.06
0.42 ꢂ 0.06 ꢂ 0.02
Theta range for data collection (°)
Index ranges
2.00–26.37
2.14–25.68
2.05–26.37
ꢁ11 6 h 6 19
ꢁ19 6 k 6 19
ꢁ22 6 l 6 22
14 896
ꢁ14 6 h 6 14
ꢁ14 6 k 6 21
ꢁ28 6 l 6 28
31 139
ꢁ12 6 h 6 14
ꢁ20 6 k 6 21
ꢁ30 6 l 6 27
35 569
Reflections collected
Independent reflections (Rint
Completeness to theta
Absorption correction
)
9143 (0.0385)
97.1% (25.00°)
SADABS
4357 (0.0326)
98.2% (25.00°)
SADABS
9092 (0.0508)
99.7% (25.00°)
SADABS
10 218 (0.0381)
99.9% (25.00°)
SADABS
Maximum and minimum transmission
Refinement method
0.9018 and 0.8266
full-matrix least-squares on
F2
0.9171 and 0.7990
full-matrix least-squares on
F2
0.9640 and 0.8273
full-matrix least-squares on
F2
0.9868 and 0.7670
full-matrix least-squares on
F2
Data/restraints/parameters
9143/0/577
0.987
4357/0/276
1.058
9092/3/601
1.040
10 218/0/586
1.009
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0565, wR2 = 0.1376
R1 = 0.0927, wR2 = 0.1504
1.994 and ꢁ0.550
R1 = 0.0364, wR2 = 0.0885
R1 = 0.0522, wR2 = 0.0930
0.850 and ꢁ0.355
R1 = 0.0443, wR2 = 0.1123
R1 = 0.0770, wR2 = 0.1224
1.398 and ꢁ0.524
R1 = 0.0542, wR2 = 0.1558
R1 = 0.0999, wR2 = 0.1743
0.964 and ꢁ0260
Largest difference in peak and hole
(e Åꢁ3
)
tures were solved by direct methods and refined by full-matrix
least-squares calculations using SHELXTL software [12]. All the non-
H atoms were refined in the anisotropic approximation. The
crystallographic parameters of the compounds studied are given
in Table 1.
mixed EtOH/Me2CO solutions gives crystals of a compound with
1:2 metal-to-ligand stoichiometry, CdL2Cl2ꢀ0.5Me2COꢀ1.5H2O, in-
stead of the expected 1:1 complex. Crystallization of CdLCl2 from
EtOH instead of EtOH/Me2CO mixture provides only a cotton-
wool-like product. Attempts to obtain single crystals of CdL2Cl2
by slow concentration of the solution of 4 in Me2CO/CHCl3 mixture
afforded CdL2Cl2ꢀ0.5CHCl3ꢀ0.5H2O crystals. Note that the com-
plexes 5 and 6 have pseudo-octahedral cis-CdN4Cl2 coordination
core (see below). Since the compounds 4–6 have the same metal-
to-ligand molar ratio, i.e. 1:2, it seems to be reasonable that the
complex 4 also has similar distorted octahedral structure.
We used X-ray powder diffraction to check the identity of the
compounds obtained. These data reveal that (i) the powder sam-
ples of ZnLCl2 and ZnL2Cl2 correspond to their single crystals, (ii)
the complexes ML2Cl2 (M = Zn, Cd) are individual compounds and
are not the mixtures of corresponding MLCl2 complexes with
non-reacted L ligand. In addition, according to X-ray powder dif-
fraction data the compounds 1 and 2 are not isostructural ones
as well as 3 and 4.
3. Results and discussion
3.1. Synthetic aspects
The complex compounds 1–4 were synthesized by the reaction
of zinc(II) and cadmium(II) chlorides with L in EtOH or EtOH/
Me2CO solutions on heating. Taking into account possible biden-
tate chelating function of L as well as potential formation of the
molecular mono- and bis-chelates, MLCl2 and ML2Cl2 (M = Zn, Cd),
the syntheses were performed under various metal-to-ligand mo-
lar ratios. The reactions performed in a 1:1 metal-to-ligand molar
ratio produced complexes having the same stoichiometry, MLCl2
(M = Zn, Cd). X-ray diffraction data (see below) revealed that
ZnLCl2 has molecular mononuclear structure with the distorted
tetrahedral ZnN2Cl2 coordination core. To obtain complexes with
the 1:2 metal-to-ligand stoichiometry, ML2Cl2 (M = Zn, Cd),
M:L = 1:2 and 1:3 molar ratios were applied. Only the latter instead
of stoichiometric one afforded ML2Cl2 (M = Zn, Cd) complexes. The
M:L = 1:2 molar ratio in EtOH is unsuitable for the synthesis of
ML2Cl2 compounds since it provides only the samples with compo-
sitions corresponding to impure MLCl2 complexes. Noteworthy,
despite of noticeably smaller ionic radius of Zn2+ relatively to
Cd2+ together with the use of bulky L ligand we were able to obtain
zinc(II) complex compound having 1:2 metal-to-ligand stoichiom-
etry and pseudo-octahedral ZnN4Cl2 coordination core (structural
details see below). Interestingly, crystallization of CdLCl2 from
Thus, the following transformations were performed (Scheme 1):
The complexes 1–4 are stable in air. They are soluble in organic
solvents, i.e. EtOH, MeCN, CHCl3, Me2CO and their mixtures.
3.2. Crystal structures of 1, 3, 5 and 6
3.2.1. General remarks
The structures of 1, 3, 5 and 6 are molecular mononuclear. The
(hetero)aromatic rings are nearly planar in all reported com-
pounds, the piperidino-group adopts chair conformation. The bond
distances as well as valence angles in L molecules coordinated by
zinc and cadmium atoms in the structure of the complexes are very
close to those of free L molecules [4]. They are also in a good agree-
ment with the data [13]. The molecules of L are coordinated to me-

M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
91
tal ions through N2(pyrazole) and N3(pyrimidine) atoms adopting
thus bidentate chelating coordination mode. As a result of the li-
gand coordination, the MCN3 (M = Zn, Cd) chelate rings are closed.
In the structures of 1, 3, 5 and 6 the pyrazole and pyrimidine rings
of coordinated L molecules are not coplanar, the N(11)–N(12)–
C(14)–N(13) (or N(21)–N(22)–C(24)–N(23)) dihedral angles vary
from 13.8° up to 29.7° (Table 2). This observation results certainly
from the steric factors, namely, from the coordination of bulky L
molecules to the metal ions. Note, that the complex 1 is tetrahedral
compound, while the complexes 3, 5 and 6 are octahedral ones
with two bidentate chelating ligands. This results in the formation
of enantiomeric forms of the complex molecules [ZnLCl2] (for 1)
and [ML2Cl2] (M = Zn, Cd) for 3, 5 and 6, which present in the crys-
tals of these compounds (racemic mixture).
3.2.2. Crystal structure of 1
The unit cell of 1 contains two crystallographically independent
Zn atoms. The geometry around each zinc atom is distorted tetra-
hedral and formed by two chlorine atoms and two nitrogen atoms
of L molecule (Fig. 1). The ZnCN3 chelate rings are practically
planar (zinc atoms Zn(1) and Zn(2) deviate from the mean chelate
planes by 0.0082 and 0.0271 Å for two crystallographically inde-
pendent molecules) and practically symmetrical regarding to the
Zn–N distances. In the crystal packing it should outline the
presence of intermolecular contacts C–HꢀꢀꢀN and C–HꢀꢀꢀCl
(N(14)ꢀꢀꢀC(17)0 = 3.318 Å, Cl(21)ꢀꢀꢀC(22)0 = 3.632 Å, Cl(21)ꢀꢀꢀC(162)0 =
Table 2
3.830 Å,
Cl(11)ꢀꢀꢀC(264)0 = 3.732 Å,
Cl(12)ꢀꢀꢀC(234)0 = 3.795 Å,
Selected bond lengths (Å) and angles (°) for compounds 1, 3, 5 and 6.
Cl(22)ꢀꢀꢀC(136)0 = 3.605 Å).
Compound 1
Zn(1)–N(11)
Zn(1)–N(13)
Zn(1)–Cl(11)
Zn(1)–Cl(12)
Zn(2)–N(21)
2.093(3)
2.044(3)
2.209(1)
2.213(1)
2.060(3)
2.049(3)
2.217(1)
2.210(1)
79.5(1)
N(13)–Zn(1)–Cl(12)
N(11)–Zn(1)–Cl(12)
Cl(11)–Zn(1)–Cl(12)
N(21)–Zn(2)–N(23)
N(23)–Zn(2)–Cl(22)
N(21)–Zn(2)–Cl(22)
N(23)–Zn(2)–Cl(21)
N(21)–Zn(2)–Cl(21)
Cl(22)–Zn(2)–Cl(21)
N(11)–N(12)–C(14)–
N(13)
111.6(1)
111.7(1)
116.1(1)
79.4(1)
115.5(1)
115.2(1)
111.8(1)
110.5(1)
118.1(1)
26.1(1)
3.2.3. Crystal structure of 3
The geometry around zinc atom is highly distorted octahedral
one formed by two chlorine atoms occupying cis-positions and four
nitrogen atoms bearing from two L molecules (Fig. 2). The ZnCN3
chelate ring is non-planar (zinc atom deviates from the mean che-
late plane by 0.1076 Å). Length of the Zn–N3(pyrimidine) bond is in
agreement with these for the complex 1, however, the Zn–N2(pyr-
azole) bond length is markedly longer. This makes the chelate rings
highly unsymmetrical regarding to the Zn–N distances. In fact, the
Zn–N2(pyrazole) distance is rather long (2.643 Å, Table 2) to be
‘‘conventional’’ Zn–N coordination bond [14]. At the same time it
should be mentioned that the coordination of L molecules pro-
duces syn-disposition of N3(pyrimidine) and N2(pyrazole) donor
atoms (NB: in the free L molecule repulsion of the lone pairs of
N3(pyrimidine) and N2(pyrazole) atoms produces their anti-dispo-
sition, the corresponding dihedral angle N(11)–N(12)–C(14)–N(13)
is 141.3° [4]). This clearly demonstrates that the binding mode of L
molecules can be regarded as a bidentate chelating one instead of
monodentate. In the crystal structure the complex shows H-bond-
ing interactions involving coordinated chlorine atoms and the phe-
nyl as well as pyrimidine hydrogen atoms: Cl(1)ꢀꢀꢀC(135)0 =
3.545 Å, Cl(1)ꢀꢀꢀC(161)0 = 3.697 Å. Noticeable feature of the crystal
Zn(2)–N(23)
Zn(2)–Cl(21)
Zn(2)–Cl(22)
N(11)–Zn(1)–N(13)
N(13)–Zn(1)–Cl(11)
114.6(1)
N(11)–Zn(1)–Cl(11)
118.0(1)
N(21)–N(22)–C(24)–
N(23)
13.8(1)
Compound 3
Zn(1)–N(13)
Zn(1)–N(13) #1
Zn(1)–N(11)
Zn(1)–N(11) #1
Zn(1)–Cl(1)
Zn(1)–Cl(1) #1
N(13)–Zn(1)–N(13)#1
N(13)–Zn(1)–Cl(1)#1
N(13)#1–Zn(1)–
Cl(1)#1
2.059(2)
2.059(2)
2.643(2)
2.643(2)
2.3022(6)
2.3022(6)
144.9(1)
101.5(1)
100.3(1)
Cl(1)#1–Zn(1)–Cl(1)
N(11)–Zn(1)–N(13)
N(11)–Zn(1)–Cl(1)
N(11)–Zn(1)–N(11)#1
N(11)–Zn(1)–Cl(1)#1
N(13)#1–Zn(1)–N(11)
N(11)#1–Zn(1)–N(13)
N(11)#1–Zn(1)–Cl(1)
N(11)#1–Zn(1)–N(13)#1
102.5(1)
68.5(1)
90.5(1)
77.8(1)
165.1(1)
84.1(1)
84.1(1)
165.1(1)
68.5(1)
N(13)–Zn(1)–Cl(1)
N(13)#1–Zn(1)–Cl(1)
100.3(1)
101.5(1)
N(11)#1–Zn(1)–Cl(1)#1
N(11)–N(12)–C(14)–
N(13)
90.5(1)
25.5(1)
structure is the formation of double lp(N(piperidine))–p(pyrimi-
dine) interaction between the pyrimidine rings and nitrogen atoms
of the piperidino-group of neighboring molecules of 3. The distance
Compound 5
Cd(1)–N(11)
Cd(1)–N(13)
Cd(1)–N(21)
Cd(1)–N(23)
Cd(1)–Cl(1)
Cd(1)–Cl(2)
N(23)–Cd(1)–N(13)
N(23)–Cd(1)–Cl(1)
N(13)–Cd(1)–Cl(1)
N(23)–Cd(1)–Cl(2)
N(13)–Cd(1)–Cl(2)
2.555(3)
2.281(3)
2.602(3)
2.272(3)
2.529(1)
2.541(1)
155.1(1)
96.4(1)
Cl(1)–Cd(1)–Cl(2)
N(23)–Cd(1)–N(11)
N(13)–Cd(1)–N(11)
Cl(1)–Cd(1)–N(11)
Cl(2)–Cd(1)–N(11)
N(23)–Cd(1)–N(21)
N(13)–Cd(1)–N(21)
Cl(1)–Cd(1)–N(21)
Cl(2)–Cd(1)–N(21)
N(11)–Cd(1)–N(21)
N(11)–N(12)–C(14)–
N(13)
101.0(1)
94.3(1)
66.3(1)
93.9(1)
156.3(1)
67.1(1)
93.4(1)
161.8(1)
90.3(1)
80.4(1)
19.2(1)
100.2(1)
102.1(1)
92.8(1)
N(21)–N(22)–C(24)–
N(23)
29.7(1)
Compound 6
Cd(1)–N(11)
Cd(1)–N(13)
Cd(1)–N(21)
Cd(1)–N(23)
Cd(1)–Cl(1)
Cd(1)–Cl(2)
N(23)–Cd(1)–N(13)
N(23)–Cd(1)–Cl(2)
N(13)–Cd(1)–Cl(2)
N(23)–Cd(1)–Cl(1)
N(13)–Cd(1)–Cl(1)
2.624(3)
2.279(3)
2.644(4)
2.276(3)
2.536(1)
2.515(1)
154.28(13) N(13)–Cd(1)–N(21)
94.87(10)
101.10(9)
Cl(2)–Cd(1)–Cl(1)
N(23)–Cd(1)–N(11)
N(13)–Cd(1)–N(11)
Cl(2)–Cd(1)–N(11)
Cl(1)–Cd(1)–N(11)
N(23)–Cd(1)–N(21)
102.03(5)
93.31(11)
65.37(11)
95.47(8)
154.65(7)
66.12(12)
94.25(11)
159.27(9)
90.85(9)
78.28(11)
19.9(1)
Cl(2)–Cd(1)–N(21)
Cl(1)–Cd(1)–N(21)
103.21(10) N(11)–Cd(1)–N(21)
93.09(9)
N(11)–N(12)–C(14)–
N(13)
N(21)–N(22)–C(24)–
N(23)
27.7(1)
Symmetry transformations used to generate equivalent atoms: #1 ꢁx + 1, y, ꢁz + 1/2
Fig. 1. Molecular structure of 1.

92
M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
Fig. 2. Structure of 3 and double lone pair(N(piperidine))–p(pyrimidine) interactions.
between the centroid of pyrimidine ring and N(15) atom is 3.257 Å,
the angle between the N(piperidine), the ring centroid and the aro-
matic plane is 93.19 1.0°. These interactions result in the forma-
tion of zigzag chains along ac direction.
ero)aromatic rings in IR-spectra of the complexes shifted with re-
spect to their positions in the spectrum of L. The far-IR spectra of
the complexes exhibit the bands of the stretching vibrations of
the M–N (M = Zn, Cd) bonds. This suggests coordination of the het-
erocyclic rings of L molecule. The low-frequency region of the spec-
tra of the complexes 1–4 contains also bands which can be
assigned to the stretching vibrations of the bonds M–Cl (M = Zn,
Cd) indicating the coordination of chlorine atoms in discussed
complexes.
3.2.4. Crystal structures of 5 and 6
The coordination polyhedron of a cadmium atom in both struc-
tures is a distorted octahedron formed by two chlorine atoms occu-
pying cis-positions and four nitrogen atoms bearing from two L
molecules. Molecular structures are similar, a molecule of [CdL2Cl2]
in the structure of 5 is shown as an example (Fig. 3). The CdCN3
chelate rings are non-planar (deviations of cadmium atom from
the mean chelate planes involving different coordinated L mole-
cules are ꢁ0.0929 and ꢁ0.0655 Å for 5; these for 6 are ꢁ0.1059
and ꢁ0.0807 Å). Both structures are stabilized through C–HꢀꢀꢀCl
and O–HꢀꢀꢀCl hydrogen bonds (distances in the structure of 5:
Cl(1)ꢀꢀꢀC(135)0 = 3.793 Å, Cl(2)ꢀꢀꢀC(265)0 = 3.659 Å, Cl(1)ꢀꢀꢀO(1W)0 =
3.191 Å; those in the structure of 6: C–HꢀꢀꢀCl and O–HꢀꢀꢀCl
(Cl(1)ꢀꢀꢀC(265)0 = 3.704 Å, Cl(1)ꢀꢀꢀC(1S)0 = 3.818 Å, Cl(2)ꢀꢀꢀC(161)0 =
3.664 Å, Cl(2)ꢀꢀꢀO(1W) = 3.200 Å).
3.4. Photoluminescence
The compound L and complexes 1–4 manifest bright blue lumi-
nescence in the solid state, the excitation and emission spectra of
are displayed in Figs. S1–S5 (see Supplementary material). The
excitation maximum for free ligand is about 325 nm, correspond-
ing maxima for 1–4 are located at ca 340–344 nm. The emission
spectra of the compounds were recorded upon excitation at
320 nm (for L, 1–4) and 350 nm (for 1–4). The intensity of emission
of the complexes somewhat increases upon excitation at 350 nm.
The maxima of emission are observed at 402 nm (for L), 417 nm
(for 1), 414 nm (for 2), 401 nm (for 3) and 391 nm (for 4). Thus,
the Stokes shift for the complexes MLCl2 is higher than for ML2Cl2.
To compare the relative intensities of the emission, the mea-
surements were carried out under the same experimental condi-
tions (V = 450 V, kexc = 320 nm) at room temperature (Fig. 4).
3.3. IR-spectra
Table S1 (see Supplementary material) and Table 3 contains IR
spectroscopic data for L (extracted from [4]) and compounds 1 –
4. The bands of stretching-deformation vibrations of the (het-
Fig. 3. Structure of [CdL2Cl2] in 5.

M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
93
Table 3
The main vibration frequencies in far-IR spectra (cmꢁ1) of the complexes.
Appendix A. Supplementary material
Compound
m
(M–N)
m
(M–Cl)
CCDC 802635, 802636, 802637 and 802638 contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.03.007.
ZnLCl2
CdLCl2
ZnL2Cl2
CdL2Cl2
267
232
332, 316 (sh.)
291, 276 (sh.)
332, 315
283, 275, 267
253 (sh.), 240, 232 (sh.)
293, 281
References
500
400
300
200
100
0
[1] (a) M. Ikeda, K. Maruyama, Y. Nobuhara, T. Yamada, S. Okabe, Chem. Pharm.
Bull. 44 (1996) 1700;
(b) M. Ikeda, K. Maruyama, Y. Nobuhara, T. Yamada, S. Okabe, Chem. Pharm.
Bull. 45 (1997) 549;
(c) S.F. Sneddon, J.L. Kane, B.H. Hirth, F. Vinick, S. Qiao, S.R. Nahill, PCT Int. Appl.
WO 2001087849, 2001.;
(d) M.M. Staveski, S.F. Sneddon, C. Yee, A. Janjigian, PCT Int. Appl. WO
2001056974, 2001;
(e) V. Sedereviciute, V. Garaliene, P. Vainilavicius, A. Hetzheim, Pharmazie 53
(1998) 233;
(f) A. Ejima, M. Sugimori, I. Mitsui, PCT Int. Appl. WO 9610024, 1996;
(g) Y. Oshima, T. Akimoto, W. Tsukada, T. Yamasaki, K. Yamaguchi, H. Kojima,
Chem. Pharm. Bull. 17 (1969) 1492;
(h) J.M. Quintela, C. Peinador, M.J. Moreira, A. Alfonso, L.M. Botana, R. Riguera,
Eur. J. Med. Chem. 36 (2001) 321.
1 - ZnLCl
2
2 - CdLCl
2
3
4
3 - ZnL Cl
2 2
4 - CdL Cl
2
2
λ
=320 nm
exc
L
[2] (a) F. Gomez de la Torre, A. de la Hoz, F.A. Jalon, B.R. Manzano, A.M. Rodriguez,
J. Elguero, M. Martinez-Ripoll, Inorg. Chem. 39 (2000) 1152;
(b) J. Elguero, A. Guerrero, F. Gomez de la Torre, A. de la Hoz, F.A. Jalon, B.R.
Manzano, A. Rodriguez, New J. Chem. 25 (2001) 1050. and references therein;
(c) E. Escriva, J. Garcia-Lozano, J. Martinez-Lillo, H. Nunez, J. Server-Carrio, L.
Soto, R. Carrasco, J. Cano, Inorg. Chem. 42 (2003) 8328. and references therein;
(d) N.O. Druzhkov, I.A. Teplova, V.N. Glushakova, N.A. Skorodumova, G.A.
Abakumov, B. Zhao, E. Berluche, D.N. Schulz, L.S. Baugh, C.A. Ballinger, K.R.
Squire, J.A.M. Canich, M.P. Bubnov, PCT Int. Appl. WO 2004007509, 2004.;
(e) L. Soto, J. Garcia, E. Escriva, J.-P. Legros, J.-P. Tuchagues, F. Dahan, A. Fuertes,
Inorg. Chem. 28 (1989) 3378;
1
2
400
500
Wavelength, nm
Fig. 4. The emission spectra of the compounds.
(f) M. Benetó, L. Soto, J. García-Lozano, E. Escrivá, J.-P. Legros, F. Dahan, J. Chem.
Soc., Dalton Trans. (1991) 1057;
(g) L.S. Tuero, J. Garcia-Lozano, E.E. Monto, M.B. Borja, F. Dahan, J.-P.
Tuchagues, J.-P. Legros, J. Chem. Soc., Dalton Trans. (1991) 2619;
(h) J. García-Lozano, J. Server-Carrió, E. Escrivà, J.-V. Folgado, C. Molla, L.
Lezama, Polyhedron 16 (1997) 939;
From the data obtained for this series of compounds, the following
generalizations can be made. Within the pairs of compounds hav-
ing the same metal-to-ligand stoichiometry, MLCl2 (M = Zn, Cd)
and ML2Cl2 (M = Zn, Cd), (i) maximum of emission for zinc com-
pounds shifts toward higher wavelengths relatively to this of cor-
responding cadmium analogs and (ii) the relative intensities for
zinc complexes are higher than those of cadmium. Finally, relative
intensity of emission for ML2Cl2 complexes is higher than this for
MLCl2. The emissions observed can be attributed mainly to intra-li-
gand transitions.
(i) S. Trofimenko, Prog. Inorg. Chem. 34 (1986) 115.
[3] (a) E.V. Peresypkina, M.B. Bushuev, A.V. Virovets, V.P. Krivopalov, L.G.
Lavrenova, S.V. Larionov, Acta Crystallogr., Sect. B 61 (2005) 164;
(b) M.B. Bushuev, V.P. Krivopalov, E.V. Peresypkina, A.V. Virovets, Yu.G.
Shvedenkov, L.A. Sheludyakova, N.V. Semikolenova, V.A. Zakharov, S.V.
Larionov, Russ. J. Coord. Chem. 35 (2009) 597;
(c) M.B. Bushuev, V.P. Krivopalov, N.V. Semikolenova, Yu.G. Shvedenkov, L.A.
Sheludyakova, G.G. Moskalenko, L.G. Lavrenova, V.A. Zakharov, S.V. Larionov,
Russ. J. Coord. Chem. 33 (2007) 601;
(d) R. Uson, L.A. Oro, M. Esteban, D. Carmona, R.M. Claramunt, J. Elguero,
Polyhedron 3 (1984) 213;
4. Conclusion
(e) B.R. Manzano, F.A. Jalon, I.M. Ortiz, M.L. Soriano, F.G. de la Torre, J. Elguero,
M.A. Maestro, K. Mereiter, T.D.W. Claridge, Inorg. Chem. 47 (2008) 413;
(f) M.I. Ortiz, M.L. Soriano, M.P. Carranza, F.A. Jalón, J.W. Steed, K. Mereiter,
A.M. Rodríguez, D. Quiñonero, P.M. Deyà, B.R. Manzano, Inorg. Chem. 49 (2010)
8828;
(g) T. Ishida, K. Yanagi, T. Nogami, Inorg. Chem. 44 (2005) 7307;
(h) K.T. Prasad, B. Therrien, S. Geib, K.M. Rao, J. Organomet. Chem. 695 (2010)
495;
(i) S. Gupta, S. Pal, A.K. Barik, S. Roy, A. Hazra, T.N. Mandal, R.J. Butcher, S.K. Kar,
Polyhedron 28 (2009) 711;
(j) A. Gelling, D.R. Noble, K.G. Orrell, A.G. Osborne, V. Šik, J. Chem. Soc., Dalton
Trans. (1996) 3065;
(k) P.J. Steel, E.C. Constable, J. Chem. Soc., Dalton Trans. (1990) 1389;
(l) G.B. Caygill, P.J. Steel, J. Organomet. Chem. 395 (1990) 375;
(m) E. Brunet, O. Juanes, R. Sedano, J.C. Rodríguez-Ubis, Tetrahedron Lett. 48
(2007) 1091;
(n) A.V. Ivashchenko, A.I. Vasil’ev, O.N. Garicheva, E.S. Zaitseva, Koord. Khim. 7
(1981) 1236;
(o) A.V. Ivashchenko, O.N. Garicheva, A.P. Bogdanov, A.P. Malyshkin, Koord.
Khim. 9 (1983) 1089;
(p) J. Li, Z. Wang, E. Turner, PCT Int. Appl. WO 2009111299 A2, 2009.;
(q) S. Sugita, Jpn. Kokai Tokkyo Koho JP 2007123392 A, 17 May 2007.;
(r) N. Yasukawa, S. Otsu, T. Oshiyama, E. Katoh, PCT Int. Appl. WO 2007029466
A1, 2007.
In summary, we have synthesized a series of zinc(II) and cad-
mium(II) chlorido complexes based on a bidentate chelating L li-
gand. The M:L = 1:1 molar ratio gives complexes of the same
stoichiometry, MLCl2 (M = Zn, Cd). The ML2Cl2 (M = Zn, Cd) com-
pounds can be obtained from a M:L = 1:3 molar ratio. According
to X-ray data, ZnLCl2 and ZnL2Cl2 complexes are molecular com-
pounds with distorted tetrahedral (ZnN2Cl2) or octahedral (cis-
ZnN4Cl2) coordination cores, respectively. Attempts to crystallize
CdLCl2 and CdL2Cl2 afforded compounds of CdL2Cl2ꢀnSolv1ꢀmSolv2
(Solv1 = Me2CO, CHCl3; Solv2 = H2O) composition, with pseudo-
octahedral cis-CdN4Cl2 coordination core in both cases. In the
structure of ZnL2Cl2 complex, double lone pair(N(piperidine))–
p(pyrimidine) interactions were observed. The compounds L,
ZnLCl2, CdLCl2, ZnL2Cl2 and CdL2Cl2 were found to exhibit bright
blue luminescence. Relative intensity of emission for ML2Cl2 com-
plexes is higher than this for MLCl2.
[4] M.B. Bushuev, V.P. Krivopalov, N.V. Pervukhina, D.Yu. Naumov, G.G.
Moskalenko, K.A. Vinogradova, L.A. Sheludyakova, S.V. Larionov, Inorg. Chim.
Acta 363 (2010) 1547.
[5] (a) M. Egli, S. Sarkhel, Acc. Chem. Res. 40 (2007) 197;
(b) T.J. Mooibroek, P. Gamez, J. Reedijk, Cryst. Eng. Comm. 10 (2008) 1501;
Acknowledgement
The work was supported by Russian Foundation for Basic Re-
search (Grant 11-03-00221-a).

94
M.B. Bushuev et al. / Inorganica Chimica Acta 371 (2011) 88–94
(c) A. Das, S.R. Choudhury, B. Dey, S.K. Yalamanchili, M. Helliwell, P. Gamez, S.
[9] (a) D.S. Liu, Y. Sui, C.C. Huang, T.H. Pan, X.H. Huang, J.Z. Chen, X.Z. You, Inorg.
Chem. Commun. 13 (2010) 762;
Mukhopadhyay, C. Estarellas, A. Frontera, J. Phys. Chem. B 114 (2010) 4998;
(d) D. Sun, G.-G. Luo, N. Zhang, R.B. Huang, Acta Crystallogr., Sect. E 66 (2010)
M406;
(b) S. Gao, J.W. Liu, L.H. Huo, Y.M. Xu, H. Zhao, Inorg. Chem. Commun. 8 (2005)
361;
(e) M. Barcelo-Oliver, C. Estarellas, A. Garcia-Raso, A. Terron, A. Frontera, D.
Quinonero, E. Molins, P.M. Deya, Cryst. Eng. Comm. 12 (2010) 362;
(f) C. Biswas, M.G.B. Drew, D. Escudero, A. Frontera, A. Ghosh, Eur. J. Inorg.
Chem. (2009) 2238;
(c) B. Liu, Y.-C. Qiu, G. Peng, L. Ma, L.-M. Jin, J.-B. Cai, H. Deng, Inorg. Chem.
Commun. 12 (2009) 1200;
(d) R.-Q. Fan, H. Chen, P. Wang, Y.-L. Yang, Y.-B. Yin, W. Hasi, J. Coord. Chem. 63
(2010) 1514;
(g) J. Sun, X.D. Tong, Acta. Crystallogr., Sect. E 66 (2010) M70;
(h) T. Korenaga, T. Shoji, K. Onoue, T. Sakai, Chem. Commun. (2009) 4678;
(i) C.-Q. Wan, X. Li, C.-Y. Wang, X. Qiu, J. Mol. Struct. 930 (2009) 32;
(j) P. de Hoog, A. Robertazzi, I. Mutikainen, U. Turpeinen, P. Gamez, J. Reedijk,
Eur. J. Inorg. Chem. (2009) 2684;
(e) M.G. Babashkina, D.A. Safin, M. Bolte, A. Klein, Polyhedron 29 (2010) 1515;
(f) A.D. Garnovskii, A.S. Burlov, A.V. Metelitsa, I.G. Borodkina, K.A. Lysenko, S.O.
Bezuglyi, E.D. Garnovskaya, E.V. Sennikova, G.S. Borodkin, D.A. Garnovskii,
Russ. J. Gen. Chem. 80 (2010) 292;
(g) S. Huh, S. Jung, Y. Kim, S.-J. Kim, S. Park, Dalton Trans. 39 (2010) 1261;
(h) S.V. Larionov, Z.A. Savel’eva, R.F. Klevtsova, L.A. Glinskaya, E.M. Uskov, S.A.
Popov, A.V. Tkachev, J. Struct. Chem. 51 (2010) 519;
(i) Z.A. Savel’eva, S.A. Popov, R.F. Klevtsova, L.A. Glinskaya, E.M. Uskov, A.V.
Tkachev, S.V. Larionov, Russ. Chem. Bull. (2009) 1837;
(j) N.J. Williams, W. Gan, J.H. Reibenspies, R.D. Hancock, Inorg. Chem. 48 (2009)
1407;
(k) G. Yu, S.W. Yin, Y.Q. Liu, Z.G. Shuai, D.B. Zhu, J. Am. Chem. Soc. 125 (2003)
14816.
(k) S.-Q. Zang, J. Han, T.C.W. Mak, Organometallics 28 (2009) 2677.
[6] (a) M. Egli, R.V. Gessner, Proc. Natl. Acad. Sci. USA 92 (1995) 180;
(b) D. Bancroft, L.D. Williams, A. Rich, M. Egli, Biochemistry 33 (1994) 1073;
(c) S. Sarkhel, A. Rich, M. Egli, J. Am. Chem. Soc. 125 (2003) 8998;
(d) A. Jain, V. Ramanathan, R. Sankararamakrishnan, Protein Sci. 18 (2009) 595.
[7] (a) V. Balzani, G. Bergamini, S. Campagna, F. Puntoriero, Top. Curr. Chem. 280
(2007) 1;
(b) G. Accorsi, A. Listorti, K. Yoosaf, N. Armaroli, Chem. Soc. Rev. 38 (2009)
1690;
(c) K.K.-W. Lo, Struct. Bond. 123 (2007) 205;
(d) L. Fabbrizzi, M. Licchelli, G. Rabaioli, A. Taglietti, Coord. Chem. Rev. 205
(2000) 85.
[10] A. Vogler, H. Kunkely, Top. Curr. Chem. 213 (2001) 143.
[11] Bruker AXS, Inc., APEX2 (version 1.08), SAINT (version 7.03), and SADABS (version
2.11). Bruker Advanced X-ray Solutions, Madison, Wisconsin, USA, 2004.
[12] G.M. Sheldrick, SHELX97 Release 97-2, University of Gottingen, Germany, 1998.
[13] F.H. Allen, O. Kennard, D.G. Watson, J. Chem. Soc., Perkin Trans. (1987) S1.
[14] R.H. Prince, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.),
Comprehensive Coordination Chemistry, vol. 5, Pergamon Press, Oxford, New
York, Beijing, Frankfurt, São Paulo, Sydney, Tokio, Toronto, 1987, pp. 926–
1045.
[8] (a) S.-L. Zheng, X.-M. Chen, Aust. J. Chem. 57 (2004) 703;
(b) V.W.-W. Yam, K.K.-W. Lo, Chem. Soc. Rev. 28 (1999) 323;
(c) A.V. Metelitsa, A.S. Burlov, S.O. Bezuglyi, I.G. Borodkina, V.A. Bren’, A.D.
Garnovskii, V.I. Minkin, Russ. J. Coord. Chem. 32 (2006) 858;
(d) M. Albrecht, M. Fiege, O. Osetska, Coord. Chem. Rev. 252 (2008) 812;
(e) S.N. Wang, Coord. Chem. Rev. 215 (2001) 79;
(f) A. Barbieri, G. Accorsi, N. Armaroli, Chem. Commun. (2008) 2185.