Zinc(II) and cadmium(II) complexes based on 2-(3,5-dimethyl-1H-pyrazol-1- yl)-6-(4-methoxyphenyl)pyrimidine-4-carboxylic acid: Synthesis, structure and luminescence

Article abstract of DOI:10.1016/j.inoche.2011.02.027

Zinc(II) and cadmium(II) complexes, ZnL₂·0.5H ₂O, ZnL₂·2MeOH and CdL₂·1.5H ₂O, based on a new hybrid compound, 2-(3,5-dimethyl-1 H-pyrazol-1-yl)-6-(4-methoxyphenyl)pyrimidine-4-carboxylic acid (HL), have been synthesized. They are the first examples of metal complexes with pyrazolylpyrimidinecarboxylates. The complex ZnL₂·2MeOH was structurally characterized. It has mononuclear structure; zinc atom is in the distorted octahedral coordination polyhedron 4N + 2O formed by donor atoms of two coordinated L^- ions. The compounds HL, ZnL₂·0. 5H₂O and CdL₂·1.5H₂O manifest bright blue photoluminescence.

Full text of DOI:10.1016/j.inoche.2011.02.027

Inorganic Chemistry Communications 14 (2011) 749–752
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Zinc(II) and cadmium(II) complexes based on
2-(3,5-dimethyl-1H-pyrazol-1-yl)-6-(4-methoxyphenyl)pyrimidine-4-carboxylic
acid: Synthesis, structure and luminescence
c
c
a
Mark B. Bushuev a,b, , Viktor P. Krivopalov , Elena B. Nikolaenkova , Natalia V. Pervukhina ,
⁎
Dmitrii Yu. Naumov a, Marianna I. Rakhmanova a
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, 3, Akad. Lavrentiev Ave., Novosibirsk, 630090, Russia
Novosibirsk State University, 2, Pirogova str., Novosibirsk, 630090, Russia
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences, 9, Akad. Lavrentiev Ave., Novosibirsk, 630090, Russia
a
b
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a r t i c l e i n f o
a b s t r a c t
Article history:
Zinc(II) and cadmium(II) complexes, ZnL2 ⋅0.5H2O, ZnL2 ⋅2MeOH and CdL2 ⋅1.5H2O, based on a new hybrid
compound, 2-(3,5-dimethyl-1 H-pyrazol-1-yl)-6-(4-methoxyphenyl)pyrimidine-4-carboxylic acid (HL), have
been synthesized. They are the first examples of metal complexes with pyrazolylpyrimidinecarboxylates. The
complex ZnL2 ⋅2MeOH was structurally characterized. It has mononuclear structure; zinc atom is in the
distorted octahedral coordination polyhedron 4N+2O formed by donor atoms of two coordinated L− ions. The
compounds HL, ZnL2 ⋅0.5H2O and CdL2 ⋅1.5H2O manifest bright blue photoluminescence.
© 2011 Elsevier B.V. All rights reserved.
Received 15 December 2010
Accepted 26 February 2011
Available online 5 March 2011
Keywords:
Pyrazole
Pyrimidine
Carboxylate
Zinc(II)
Cadmium(II)
Luminescence
Among various pyrazolylpyrimidines, 2-(pyrazolyl)pyrimidines
have attracted most attention as the ligands for the synthesis of
transition metal complexes [1–19]. These complexes are of fundamental
and practical importance since they manifest various kinds of biological
and catalytic activity [8,14,19]. Other pyrimidine-based compounds,
pyrimidine-4(6)-carboxylic acids and corresponding carboxylates also
were reported as the ligands [20–23]. In this context, studying
pyrazolylpyrimidines and their complexes with metals, we decided to
combine the pyrazolyl and the carboxylic groups within a single
molecule on the base of the pyrimidine core and to study coordination
behavior of a new hybrid compound, 2-(3,5-dimethyl-1H-pyrazol-1-yl)-
6-(4-methoxyphenyl)pyrimidine-4-carboxylic acid (HL, Scheme 1),
with respect to zinc(II)andcadmium(II). It ought to note, that previously
some of us synthesized a series of 2-hydrazinylpyrimidine-4(6)-
carboxylic acids and used them for the preparation of reagent indicator
paper for the detection of iron(II) and iron(III) [24]. In the present work
we modified one of these compounds to obtain HL. To the best of our
knowledge, the complexes reported here are the first examples of
compounds based on pyrazolylpyrimidinecarboxylic acids. Taking into
account that the complexes of zinc(II) and cadmium(II) with hetero-
aromatic ligands are one of the main groups of luminescent compounds
[25–28], we were also endeavored to obtain compounds demonstrating
luminescence. In this communication we report the synthesis and study
of four new compounds, i.e., HL, ZnL2⋅0.5H2O (1), ZnL2⋅2MeOH (2) and
CdL2⋅1.5H2O (3).
A new hybrid heteroaromatic compound, HL (Scheme 1), can be
obtained by condensation of 2-hydrazinyl-6-(4-methoxyphenyl)
pyrimidine-4-carboxylic acid (4) with acetylacetone [29]. The
compound 4 and its phenyl analog previously were used for
preparation of reagent paper by treating a modified chromatographic
paper based on aldehyde cellulose [24]. The complexes 1 and 3 can be
prepared as powder products by the reaction of corresponding acetate
salt with HL in MeOH solutions at M:HL=1:2 molar ratio (Scheme 1)
[30,31]. IR-spectra of these compounds are similar [30,31]. The
positions of the stretching-deformation vibrations of heteroaromatic
rings, (ν+δ)ring, in IR-spectra of these complexes are changed in
comparison with the spectrum of HL. The bands of carboxylic group in
the spectra of 1 and 3 also shifted. The far-IR spectra of the complexes
exhibit the bands of ν(M–L) vibrations. These observations are
consistent with the coordination of the heteroaromatic rings and
carboxylic group of L− ions. Water molecules seem to be non-
coordinated. Attempts to crystallize 1 from MeOH solution afforded
single crystals of 2 [32].
According to X-ray diffraction data [33], the structure of 2 is molecular
mononuclear (Fig. 1). Two L− ions (carboxylic group is deprotonated) are
coordinated to zinc atom through N(1), N(3) and O(1) atoms adopting
⁎
Corresponding author.
E-mail address: bushuev@niic.nsc.ru (M.B. Bushuev).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.02.027

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M.B. Bushuev et al. / Inorganic Chemistry Communications 14 (2011) 749–752
thus tridentate chelating coordination mode. The coordination geometry
around zinc atom is distorted octahedral (4 N+2O). As a result of the
ligand coordination, practically planar ZnCN3 and ZnC2NO chelate cycles
are closed. The (hetero)aromatic system of L− ligand is nearly planar. The
pyrazolyl and methoxyphenyl groups are rotated by 5.4° and 10.0° in
respect to the pyrimidine plane. The structure is stabilized through
formation of hydrogen bonds (O(1)…H(53)′ 2.431 Å, O(2)…H(56)′
2.516 Å, O(1 S)…H(55)′ 2.518 Å) (Fig. 2). MeOH molecules form hydrogen
bonds with non-coordinated O atoms of carboxylic group (O(1)…H(1 S)
1.891 Å).
Single crystals of 2 become non-transparent within ca. several
days probably due to loss of MeOH molecules. IR-spectra of 1 and
decomposition product of single crystals of 2 are almost identical
which induces to think that structures for 1 and probably for 3 are
similar.
The compounds HL, 1 and 3 manifest bright photoluminescence in
the solid state, the excitation and emission spectra are displayed in
Figs. 3–5. The spectra of the compounds display a broad emission
band with two maxima (for HL and 3) or an unsymmetrical band with
a shoulder (for 1). The origin of luminescence of HL, having an
extended conjugated π-system, seems to be due to π*→π transitions.
Since the profile and location of the emission bands in the spectra of
the complexes are similar to those in the spectrum of HL, it seems to
be reasonable that the luminescence mechanism for the complexes
can be attributed to intra-ligand transitions as usual for zinc(II) and
Scheme 1. The synthesis of HL and complexes 1–3.
Fig. 1. The molecule [ZnL2] in the structure of 2. Selected bond lengths (Å) and bond angles (°): Zn(1)–N(1), 2.185(1); Zn(1)–N(3), 2.040(1); Zn(1)–O(1), 2.162(1); N(3)–Zn(1)–N(3)#1, 163.88
(7); N(3)–Zn(1)–O(1), 75.66(4); N(3)#1–Zn(1)–O(1), 92.87(4); N(3)–Zn(1)–O(1)#1, 92.87(4); N(3)#1–Zn(1)–O(1)#1, 75.66(4); O(1)–Zn(1)–O(1)#1, 90.36(6); N(3)–Zn(1)–N(1), 74.36(5);
N(3)#1–Zn(1)–N(1), 116.90(5); O(1)–Zn(1)–N(1), 149.95(4); O(1)#1–Zn(1)–N(1), 93.04(5); N(3)–Zn(1)–N(1)#1, 116.90(5); N(3)#1–Zn(1)–N(1)#1, 74.36(5); O(1)–Zn(1)–N(1)#1, 93.04
(5); O(1)#1–Zn(1)–N(1)#1, 149.95(4); N(1)–Zn(1)–N(1)#1, 98.68(7). Symmetry transformations used to generate equivalent atoms: #1 −x+1, y, −z+1/2.
Fig. 2. Packing of the molecules in the structure of 2.

M.B. Bushuev et al. / Inorganic Chemistry Communications 14 (2011) 749–752
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cadmium(II) complexes with heteroaromatic ligands [27]. Within the
series of compounds the band of emission in the spectra of complexes
somewhat shifted toward higher wavelengths relatively to its position
in the spectrum of HL. The slight red shift can be due to deprotonation
of HL ligand leading to the decreasing of π*→π gap [27].
In summary, a series of zinc(II) and cadmium(II) complexes,
ZnL2 ⋅0.5H2O, ZnL2 ⋅2MeOH and CdL2 ⋅1.5H2O (HL=2-(3,5-dimethyl-
1H-pyrazol-1-yl)-6-(4-metoxyphenyl)pyrimidine-4-carboxylic acid)
have been synthesized. The compounds HL, ZnL2 ⋅0.5H2O and
CdL2 ⋅1.5H2O manifest bright blue photoluminescence.
100
50
0
Acknowledgements
The authors are grateful to Prof. Stanislav V. Larionov for the useful
discussion and to Dr. Lilia A. Sheludyakova for recording of IR-spectra.
The work was supported by Russian Foundation for Basic Research
(Grant 11-03-00221-a).
300
350
400
450
500
550
600
Wavelength, nm
Fig. 3. Excitation (solid line, λem=420 nm) and emission (dashed line) spectra of HL,
exc=350 nm. Spectra were recorded on Cary Eclipse spectrophotometer, ex. slit 5 nm, em.
slit 5 nm, PMT voltage 500 V.
λ
Appendix A. Supplementary Material
CCDC 804373 contains the supplementary crystallographic data for
this article. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.
uc/data_request/cif. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.inoche.2011.02.027.
200
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Wavelength, nm
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[31] Synthesis of 3. A suspension of HL (0.150 mmol, 48.7 mg) in 2 ml of warm MeOH
(ca. 40 °C) was added to a solution of Cd(OAc)2 ⋅2H2O (0.075 mmol, 20.0 mg) in
1 ml of warm MeOH (ca. 40 °C). Light beige precipitate was formed immediately.
Reaction mixture was refluxed for 2 h and then allowed to stay at room
temperature for 3 days. The precipitate was filtered off, washed with MeOH and
dried in ambient air. Yield: 48.0 mg (81%). Anal. calcd. for C34H33CdN8O7.5: C, 52.0;
H, 4.2; N, 14.3. Found: C, 51.9; H, 4.1; N, 14.1%. Selected IR data: 3391 (H2O), 1650
(CO), 1590 ((ν+δ)ring), 1537 ((ν+δ)ring), 1417, 1265, 1188, 1006, 981, 888, 846,
[29] Synthesis of HL. A mixture of 2-hydrazinyl-6-(4-methoxyphenyl)pyrimidine-4-
carboxylic acid (3.85 mmol, 1.0 g) and acetylacetone (4.85 mmol, 0.5 ml) in 30 ml of
EtOH was refluxed for 5 h. After cooling, the foam precipitate obtained was filtered
off and washed with EtOH. The precipitate was recrystallized from EtOH and dried in
vacuo. Yield: 1 g (80%). Anal. calcd. for C17H16N4O3: C, 63.0; H, 5.0; N, 17.3. Found: C,
62.5; H, 4.9; N, 17.0%. M.p. 197–199 °C. 1H NMR (CDCl3, δ, ppm): 2.30 (s, 3H, Me),
2.81 (s, 3H, Me), 3.88 (s, 3H, MeO), 6.08 (s, 1H, 4−Hpyrazole), 7.02 (d, J=8.8 Hz, 2H,
Ph), 8.12 (d, J=8.8 Hz, 2H, Ph), 8.25 (s, 1H, 5−Hpyrimidine). Selected IR data: 3150,
1736, 1702, 1592 ((ν+δ)ring), 1541 ((ν+δ)ring), 1423, 1258, 1174, 1027, 990, 881,
839, 772, 745, 586, 528, 511, 495 cm−1. A high-resolution mass spectrum (direct
776, 742, 593, 524, 507, 434 (Cd–O), 223 (Cd–N), 180, 168 cm−1
.
[32] A small tip of a spatula of ZnL2 ⋅0.5H2O was dissolved in MeOH (2 ml). Beige
single crystals were obtained in a month. They were used in X-ray diffraction
analysis and their composition was determined as ZnL2 ⋅2MeOH.
introduction of
a sample to the ionic source): Anal. calcd. for C17H16N4O3:
M=324.1217. Found: m/z 324.1219 [M+].
[33] Single crystal data for
2 were collected at 150 K with MoKα radiation
[30] Synthesis of 1. A suspension of HL (0.150 mmol, 48.7 mg) in 2 ml of warm MeOH
(ca. 40 °C) was added to a solution of Zn(OAc)2 ⋅2H2O (0.075 mmol, 16.5 mg) in
1 ml of warm MeOH (ca. 40 °C). Beige precipitate was formed immediately.
Reaction mixture was refluxed for 1 h and then allowed to stay at room
temperature overnight. The powder product was separated from the mother
liquor by filtration and washed according to the following technique. MeOH
(2 ml) was added to precipitate; the mixture was heated for 3 h and allowed to
stay for 2 days at room temperature. After that, the precipitate was filtered off and
dried in ambient air. Yield: 40.0 mg (74%). Anal. calcd. for C34H31N8O6.5Zn: C, 56.6;
H, 4.3; N, 15.6. Found: C, 56.5; H, 4.3; N, 15.5%. Selected IR data: 3414 (H2O), 1656
(CO), 1596 ((ν+δ)ring), 1541 ((ν+δ)ring), 1421, 1257, 1178, 1013, 978, 887, 846,
(λ=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. The structures were solved by direct
methods and refined by full-matrix least-squares calculations using SHELXTL
software. All the non-H atoms were refined in the anisotropic approximation.
Crystallographic data for 2: C36H36N8O8Zn, M=774.10, 0.15×0.12×0.08 mm3,
monoclinic, C2/c, a=23.0795(6), b=10.1204(2), c=21.6279(5) Å, β=134.578
(2)°, V=3598.3(1) Å3, Z=4, Dc=1.429 g/cm3, Goodness-of-fit on F2=1.062,
R1=0.0275, wR2=0.0792 [IN2 σ(I)], R1 =0.0310, wR2=0.0812.
778, 744, 597, 537, 509, 442 (Zn–O), 244 (Zn–N), 178, 164 cm−1
.