Vol. 44 No. 1
SCIENCE IN CHINA (Series B)
February 2001
Synthesis and crystal structure of nickel(II) and zinc(II)
complexes with 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl1,3,5-triazine
YANG Chi (w ^)1,2, WONG Wing-Tak2, CUI Yingde (Áç)1
& YANG Yansheng (wi])3
1. Department of Chemical Engineering, Guangdong University of Technology, Guangzhou 510090, China;
2. Department of Chemistry, University of Hong Kong, Hong Kong, China;
3. Department of Chemistry, Zhongshan University, Guangzhou 510275, China
Correspondence should be addressed to Yang Chi (email: [email protected])
Received September 6, 2000
Abstract 2,4-Bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine(bpt) has been synthesized
by using a new, simple and general method with high yields. Reactions of bpt with Ni(ClO4)2 6H2O
and Zn(ClO4)2 6H2O in methanol gave mononuclear complex [Ni(bpt)2] (ClO4)2 H2O and
ternary complex [Zn(mpt)2(dmp)](ClO4)2 respectively, where mpt (2,4-dimethoxy-6-(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) and dmp(3,5-dimethylpyrazole) are the alcoholysis products of bpt in
the presence of Zn2+ ion. A possible mechanism for this catalytic reaction was proposed. X-ray
crystal structure for ligand bpt, Ni and Zn complexes are reported. The protonated form of the
ligand bpt crystallizes as its perchlorate salt including one molecule of water, [Hbpt H2O ClO4].
The proton is located on one pyrazole N-atom. [Hbpt H2O ClO4], in which [Hbpt]+ is in cis-cis
conformation, are packed in slipped stacks of approximately parallel layers. The π-π overlap
interactions between the non-protonized pyrazoles of the adjacent layers give a zigzag
arrangement of the planar aromatic [Hbpt]+ molecules. In [Ni(bpt)2](ClO4)2 H2O, bpt are
meridionally three-coordinated with Ni2+. The coordination sphere around Ni2+ is a slightly distorted
square bipyramid, where four pyrazole nitrogen atoms occupy the basal positions and two triazine
nitrogen atoms the apical one. In [Zn(mpt)2(dmp)](ClO4)2, the Zn atom is coordinated with a pair of
bidentate mpt ligands and one monodentate dmp ligand, forming a distorted trigonal bipyramid,
where the two triazine nitrogen atoms of mpt and one nitrogen atom of dmp occupy the basal
positions, and the two pyrazole nitrogen atoms of mpt the apical one.
Keywords: dipyrazoltriazine, zinc(II), nickel(II), catalytic methanolysis, crystal structure.
There has been increasing interest in terpyridine-like ligands of 2,4-bis(pyrazol-1-yl)-1,3,5triazine derivatives showing more rich coordination and redox properties[1
5]
. 1,3,5-Triazine
derivatives substituted with pyrazole at 2-, 4-, or 6-positions with c1, c2 or c3 symmetry are readily
available by stepwise substitution reaction of 2,4,6-trichloro-1,3,5-triazine[2,4]. As bi-, tri-, or
poly-dentate chelator, 2, 4, or 6-substituted-1,3,5-triazine can bind to one or more metal ions,
giving mononuclear or polynuclear complexes. We found that 2,4-bis(pyrazol-1-yl)-6-R-1,3,5triazine derivatives incorporating NR1R2 groups are good chiral ligands showing charge-transfer
properties[5]. 2,4-Bis(pyrazol-1-yl)-6-R-1,3,5-triazine might be promising candidate for biomimics
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
81
based on their stability at physiological environment and decomposition at higher temperature or
at basic condition. As a part of our study for biomimics, we have explored a series of 2,4,6substituted-1,3,5-triazine derivatives. We previously reported the crystal structure and
luminescence properties of lanthanide complexes with 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-R1,3,5-triazine[1,3]. Crystal structure and bio-functional properties of their transition metal
complexes are thus investigated systematically. Herein we report synthesis and crystal structure of
nickel (II) and zinc(II) complexes with 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5triazine (bpt).
1 Experimental
1.1
Instruments and reagents
The elemental analyses (C, H, N) were performed with a Perkin-Elmer 240C elemental
analyzer. Infrared spectra were measured on a Nicolet 170SX FT-IR spectrophotometer as KBr
pellets. UV-Vis spectra were carried out on a Shimadzu MPS-2000 UV-Vis spectrophotometer.
The 1H and 13C NMR spectra were recorded on a Bruker DPX-300 apparatus. Mass spectra (EI:
70 eV; FAB: nba) were performed with a ZAB VG ANALY mass spectrometer.
Solvents and starting materials were commercially available and purified with standard
method. All reactions were carried out under dry nitrogen atmosphere unless otherwise stated.
2-Methoxyl-4,6-dichloro-1,3,5-triazine was prepared by reaction of 2,4,6-trichloro-1,3,5-triazine
and methanol in the presence of N,N-dimethylaniline in anhydrous benzene[6].
1.2 Preparation
1.2.1 Synthesis of ligand. 2,4-Dihydrazol-6-methoxyl-1,3,5-triazine: 2,4-dichloro-6-methoxyl1,3,5-triazine and excess hydrazine hydrate was stirred at room temperature for 30 h. The resulting
reaction mixture was diluted with water, and the white precipitate was collected on a filter, washed
with water and dried in vacuum. Yield: 93%[3].
2,4-Dis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine (bpt): to a cold solution of 2,4dihydrazol-6-methoxyl-1,3,5-triazine (1.7 g, 0.01 mol) in dilute HClO4 was added acetylacetone
(2.0 g, 0.02 mol) dropwise, and the resulting mixture was stirred at room temperature overnight.
The mixture was neutralized with dilute Na2CO3, and the white precipitate was filtered, washed
with water and crystallized from aqueous methanol to give bpt as colorless needles. Yield: 95 %
(2.9 g). Characterization data obtained were in agreement with ref. [1].
1.2.2 Preparation of [Ni(bpt)2](ClO4)2
H2O. To a solution of bpt (0.6 g, 2 mmol) in methanol
was added methanolic solution of Ni(ClO4)2 6H2O (10 mL
resulting mixture was warmed to 60
70
0.1 mol
L−1) dropwise. The
and kept at this temperature for ~5 min. After
filtration, the filtrate was allowed to evaporate slowly at room temperature for several days. The
blue crystals formed was collected and dried in vacuum. Yield: 73% (0.63 g). Anal. calc. for
82
SCIENCE IN CHINA (Series B)
Vol. 44
C28H36N14O11Cl2Ni(%): C 38.43 H 4.12 N 22.42; found(%): C 38.25, H 4.09, N 22.40. FAB-MS
(nba): m/z 659; IR(KBr): 1630, 1590, 1553, 1447, 1405, 1370, 1321, 1089, 976, 807, 758 and 625
cm−1.
1.2.3
Preparation of [Zn(mpt)2(dmp)](ClO4)2.
To a solution of bpt (0.6 g, 2 mmol) in methanol
was added methanolic solution of Zn(ClO4)2 6H2O (10 mL 0.1 mol
resulting mixture was warmed to 60
70
L−1) dropwise. The
and kept at this temperature for ~5 min. After
filtration, the filtrate was allowed to evaporate at room temperature for several days. Colorless
crystals were obtained with the yield of 72% (0.6 g), from which X-ray quality crystals were
selected and used for X-ray crystal structure analysis. Anal. calc. for C25H34O12N12Cl2Zn(%): Zn
7.87, C 36.11, H 4.09, N 20.22; found(%): Zn 7.90, C 35.96, H 4.10, N 20.19. FAB-MS: 632
([Zn(mpt)2(dmp)]2+). IR(KBr): ν (C==N) + ν (C== C)/pz ring = 1610 and 1580 cm−1, ν (C== N)/Tz
ring = 1 553 cm−1, δ (C
H)/Pz ring = 751 cm−1. 1H-NMR(CD3OD, TMS, 25 ): δ = 6.49 (s, 2H,
ring-H/mpt), 5.86 (s, 1H, ring-H/dmp), 4.04 (s, 12H, OCH3), 3.35 (s, 1H, N-H/dmp), 2.85 (s, 6H,
CH3), 2.30 (s, 6H, CH3), 2.21 (s, 6H, CH3).
1.3 X-ray crystallography
Intensity data for [Hbpt
H2 O
ClO4], [Ni(bpt)2](ClO4)2
H2O and [Zn(mpt)2(dmp)](ClO4)2
were measured at room temperature on a Rigaku AFC 7R diffractometer fitted with graphite
monochromatized MoKα radiation, λ = 0.071069 nm. The ωY2θ scan technique was employed
to measure data in each case up to a maximum Bragg angle of 45 . No decomposition of the
crystals occurred during the data collections. Lorentz and polarization corrections were applied as
an empirical absorption correction.
The structures were solved by direct methods (SHELXS 86) and expanded by means of
Fourier techniques (DIRDIF 92). All calculations were performed with the teXsan crystal
structure analysis package developed by Molecular Structure Corp. (1992). Scattering factors for
all atoms were those incorporated in the teXsan program. Non-H atoms were refined with
anisotropic thermal parameters and H atoms were included in the models in their calculated
positions. The refinement was continued until convergence employing sigma weights that
yielded the final R = 0.050, Rw = 0.070 for [Hbpt H2O
[Ni(bpt)2] (ClO4)2
ClO4]; R = 0.056, Rw = 0.068 for
H2O; and R = 0.052, Rw = 0.052 for [Zn(mpt)2(dmp)](ClO4)2. The relevant
crystallographic data are given in table 1.
2
2.1
Results and discussion
Synthesis of ligand
Ligands of 2,4-bis(pyrazol-1-yl)-1,3,5-triazine were generally prepared by two substitution
reactions from 2,4,6-trichloro-1,3,5-triazine and the potassium salt of the corresponding pyrazole
(scheme 1)[4]. First, 2,4-dichloro-6-R-1,3,5-triazine was synthesized by condensation of
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
Table 1 Crystallographic data for [Hbpt H2O
[Hbpt H2O
Empirical formula
H2O and [Zn(mpt)2(dmp)](ClO4)2
[Ni(bpt)2](ClO4)2
H2O
C14H21N7O6Cl
C28H36N14O11Cl2Ni
418.82
874.29
Formula weight
Crystal dimension/mm3
ClO4]
ClO4], [Ni(bpt)2](ClO4)2
0.20
0.20
0.30
0.20
0.20
83
[Zn(mpt)2(dmp)](ClO4)2
C25H34O12N12Cl2Zn
830.90
0.30
0.20
0.20
0.30
Crystal colour
colorless
blue
Temperature/K
293
293
293
Crystal system
monoclinic
orthorhombic
orthorhombic
Space group
P21/c(#14)
Aba2(#41)
Pbca(#61)
a/nm
1.1123(3)
1.6196(3)
2.0154(2)
b/nm
c/nm
1.0308(2)
1.6824(2)
1.3857(7)
1.7472(5)
2.0696(4)
1.7365(2)
α /( )
90
90
90
β /( )
97.90(1)
90
90
γ /( )
V/nm3
90
90
90
1.9108(7)
3.921(3)
7.243(1)
4
4
8
Z
−3
colorless
ρ calc. /mg m
1.456
1.481
1.524
F(000)
876.00
1808.00
3424.00
θ max/( )
Reflections measured
25
25
23
3058
1948
4162
Independent reflections
(I 3.00σ (I ))
R
2865
1088
1649
0.050
0.056
0.052
Rw
0.070
0.068
0.052
compounds having reactive hydrogen atoms (e.g. amine, alcohol, thioalchol or aromatic
hydrogencarbons with reactive hydrogen atoms) with equivalent 2,4,6-trichloro-1,3,5-triazine at
low temperature under anhydrous reaction media. Second, the intermediate 2,4-dichloro-6-R1,3,5-triazine was then reacted with potassium salt of 1H-pyrazole derivatives (prepared from
pyrazole derivatives and potassium or potassium hydride in anhydrous non-protic solvent ) in
anhydrous tetrahydrogen furan or dioxane, giving the desired product 2,4-bis(pyrazol-1-yl)-6R-1,3,5-triazine. Many 1H-pyrazole derivatives can be used in this procedure, affording 2,4-bis
(pyrazol-1-yl)-6-R-1,3,5-triazine with high yields. However, the procedure is not suitable for
2,4-dichloro-1,3,5-triazine with reactive RX group at 6-position or pyrazole derivatives with R1 or
Scheme 1
84
SCIENCE IN CHINA (Series B)
Vol. 44
R3 groups having strong electron-withdrawing or spatial crowding effects. The most vigorous
requirement for the method is that reactions must be carried out in anhydrous media.
Thus, we have explored a new procedure to synthesize 2,4-bis(pyrazol-1-yl)-1,3,5-triazine
under mild conditions (scheme 2). In this procedure, condensation of 2,4-dihydrazol-1,3,5-triazine,
key intermediate prepared from 2,4-dichloro-1,3,5-triazine and excess hydrazine hydrate in water,
with β-diketonates in dilute acidic water at room temperature affords 2,4-bis(pyrazol-1-yl)-1,3,5triazine. The simplicity, efficiency, safety, and mildness of the reaction render the present method
a satisfactory procedure for synthesis of new terpyridine analogues of 2,4-bis(pyrazol-1-yl)-1,3,5triazine. Using this method, 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine has been
prepared by methoxylation, hydrozolation and condensation with acetylacetone of 2,4,6-trichloro1,3,5-triazine.
R = OCH3, R1 = R3 = CH3, R2 = H
Scheme 2
2.2
2.2.1
Description of crystal structure
X-ray crystal structure of the protonated ligand [Hbpt
ClO4
H2O]. The protonated
form of the ligand bpt crystallizes as its perchlorate salt including one molecule of water at the
presence of rare earth perchlorates. The role of rare earth perchlorates as hydrogen donors is also
known from several reports[4,7]. The molecular structure of [Hbpt]+ is shown in fig. 1. Atomic
coordinates are listed in table 2, and table 3 gives the selected bond distances and angles. The
cation [Hbpt]+ adopts a cis-cis-conformation. The structure presents no marked distortions from
typical bond lengths. The proton is localized on N5, with no essential interaction with the
counteranion ClO −4 , very similar to (Hbmbip)(ClO4) (bmbip = 2,6-bis(1 -methylbenzimidazol-2 yl)pyridine), and contrary to (H2qpy)(PF6)2 (qpy = quinquepyridine), where strong H
F
[8]
interactions force the protons to lie symmetrically with respect to two adjacent N atoms . Each
pyrazole ring is canted 4.06
and 11.57
The very smaller dihedral angles of 4.06
from perfect horizontality to the central triazine ring.
correspond to the protonated pyrazole (N4-N5) ring
and the central triazine ring, resulting from the hydrogen-bond interaction between N5 H8 N3.
The angle of 11.57
is larger compared to those found in coordinated (e.g. 6
2+
complexes, vide infra ) or in diprotonated (H2qpy)
angle between two pyridine rings equaling 6.2
in Ni and Eu
which is almost planar, with a maximum
and much smaller than in (Hbmbip)(ClO4) (the
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
85
Fig. 1. Molecular structure of the [Hbpt]+ cation showing the atomic numbering scheme.
fold angles between two benzimidazole units and the central pyridine ring are about 30.5
[7]
45.3 ) .
Table 2 Atomic coordinates and equivalent isotropic displacement parameters Beq for [Hbpt ClO4
H2O]
Atom
x
y
z
Cl( )
0.31328(9)
0.1271(1)
0.79762(6)
4.60(3)
Beq
O(1)
0.4149(2)
0.2816(3)
0.5609(2)
5.01(7)
O(2)
0.4360(3)
0.1602(4)
0.8037(3)
8.5(1)
O(3)
0.2841(7)
0.1057(5)
0.8727(3)
16.3(2)
O(4)
0.2458(4)
0.2362(5)
0.7687(4)
11.9(2)
O(5)
0.2883(4)
0.0140(4)
0.7525(3)
10.0(1)
O(6)
0.0865(3)
0.0321(4)
0.6230(2)
4.21(8)
N(1)
0.2074(3)
0.2827(3)
0.5360(2)
3.28(7)
N(2)
0.3301(3)
0.1372(3)
0.4731(2)
3.72(7)
N(3)
0.1154(2)
0.1334(3)
0.4390(2)
2.96(6)
N(4)
−0.0019(3)
0.2657(3)
0.5072(2)
3.09(6)
N(5)
−0.1020(3)
0.2065(3)
0.4646(2)
3.45(7)
N(6)
0.2364(2)
−0.0012(3)
0.3748(2)
3.16(7)
N(7)
0.1344(3)
−0.0635(3)
0.3403(2)
3.31(7)
and
86
SCIENCE IN CHINA (Series B)
Vol. 44
Table 3 Selected bond distances (nm) and angles ( ) for [Hbpt ClO4
H2O]
O(1)
C(1)
0.1315(4)
C(1)
O(1)
C(14)
N(1)
C(1)
0.1322(5)
C(1)
N(2)
C(3)
112.2(3)
N(2)
C(1)
0.1337(4)
N(5)
N(4)
C(2)
118.3(3)
N(3)
C(2)
0.1323(4)
C(2)
N(4)
C(5)
130.6(3)
N(4)
N(5)
0.1381(4)
N(7)
N(6)
C(3)
120.0(3)
O(1)
C(14)
0.1459(6)
C(3)
N(6)
C(12)
131.3(3)
N(1)
C(2)
0.1326(4)
O(1)
C(1)
N(1)
120.4(3)
N(2)
C(3)
0.1309(4)
N(1)
C(1)
N(2)
126.3(3)
N(3)
C(3)
0.1327(4)
C(1)
N(1)
C(2)
113.6(3)
N(4)
C(2)
0.1392(4)
C(2)
N(3)
C(3)
111.8(3)
N(4)
C(5)
0.1393(4)
N(5)
N(4)
C(5)
111.0(3)
N(6)
N(7)
0.1362(4)
N(4)
N(5)
C(7)
105.3(3)
N(6)
C(12)
0.1376(4)
N(7)
N(6)
C(12)
108.6(3)
N(5)
C(7)
0.1324(5)
N(6)
N(7)
C(10)
109.0(3)
C(3)
0.1412(4)
O(1)
C(1)
N(2)
113.2(3)
N(1)
C(2)
N(3)
127.0(3)
N(6)
117.5(4)
In the crystal, the [Hbpt]+ molecules arrange themselves in layers thanks to weak
intermolecular interactions between the methyl group on the unprotonated pyrazole unit of one
molecule and the methoxyl group of the triazine ring of the next molecule (C C or C
N
contacts are in the range 0.35 0.37 nm). In this way, each molecule is linked to two others in
AABB sequence. The perchlorate anion and H2O molecules are located between the layers. These
layers are stacked along c-axis in an alternative mode giving a zigzag arrangement of the planar
aromatic bpt molecules. The layers are connected together in the c-axis direction by aromatic π-π
stacking interactions between two parallel protonized pyrazole rings (fold angle
1 ) situated
at a distance of 0.346 0.349 nm. It is a known fact that protonation of this type of ligand induces
0.6 nm) in the structure of
intermolecular distances being much shorter than those observed (
neutral ligands such as 4 -phnyl-2,2 Y6 ,2 -terpyridine .
[9]
2.2.2
X-ray crystal structure of [Ni(bpt)2](ClO4)2
H2O.
Atomic coordinates are given in table
4 and selected bond lengths and angles in table 5. Fig. 2 shows the atomic numbering scheme
showing the stereoscopic view of the complex [Ni(bpt)2]2 .
Being
in
[Ni(bpt)2](ClO4)2
agreement
with
IR
and
1
H-NMR
spectra, the
2+
H2O shows that it is composed of a [Ni(bpt)2]
crystal
structure
of
cation, two uncoordinated
perchlorate anions and one water molecule (fig. 2). The anions and solvent molecules are slightly
distorted but otherwise show no features of interest. As previously reported for [Ni(tpy)2]2+, the
two ligands in [Ni(bpt)2]2+ are meridionally three-coordinated to the metal ion and wrapped about
a pseudo-c2 axis defined by approximately linear N(5)-Ni-N(5*)(173.8(6) ). The coordination
sphere around Ni2+ may be best described as a slightly distorted square bipyramid, where four
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
87
pyrazole nitrogen atoms occupy the basal positions and two triazine nitrogen atoms the apical one.
Table 4 Atomic coordinates and equivalent isotropic displacement parameters Beq for [Ni(bpt)2](ClO4)2
Atom
Ni
Cl
O1
O2
O3
O4
O5
O6
N1
N2
N3
N4
N5
N6
N7
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
x
0.5000
0.7274(3)
0.8440(5)
0.808(2)
0.679(2)
0.706(1)
0.712(2)
0.5000
0.4990(7)
0.5716(6)
0.7128(6)
0.7551(6)
0.6145(5)
0.6488(5)
0.5644(6)
0.4514(9)
0.4881(10)
0.5646(9)
0.6367(8)
0.7687(7)
0.6757(7)
0.6898(9)
0.6303(9)
0.558(1)
0.358(1)
0.6376(9)
0.9074(10)
0.7802(8)
0.468(1)
y
0.0000
0.0812(3)
0.1430(7)
0.070(3)
0.044(2)
0.1766(10)
0.038(2)
0.0000
0.1210(6)
0.1703(7)
0.1648(7)
0.0258(8)
0.0481(6)
−0.0794(7)
−0.0914(8)
0.175(1)
0.258(1)
0.254(1)
0.1260(10)
0.1095(9)
0.001(1)
−0.147(1)
−0.205(1)
−0.168(1)
0.148(1)
0.325(1)
0.086(1)
−0.152(1)
−0.208(1)
z
0.4347
0.1707(3)
0.4441(8)
0.187(2)
0.226(1)
0.164(1)
0.101(1)
0.151(2)
0.5159(6)
0.5149(7)
0.4766(7)
0.4038(6)
0.4410(8)
0.3614(6)
0.3602(7)
0.5537(9)
0.5773(9)
0.5547(9)
0.4755(8)
0.442(1)
0.4014(7)
0.3196(8)
0.2895(9)
0.3144(10)
0.565(1)
0.5640(10)
0.410(1)
0.314(1)
0.297(1)
Table 5 Selected bond distances (nm) and angles ( ) for [Ni(bpt)2](ClO4)2
H2O
Beq
0.0371(5)
0.077(2)
0.074(3)
0.33(2)
0.24(1)
0.145(7)
0.22(1)
0.16(1)
0.041(3)
0.043(3)
0.049(3)
0.053(3)
0.038(2)
0.039(3)
0.048(3)
0.045(4)
0.059(5)
0.052(4)
0.044(4)
0.052(4)
0.043(3)
0.051(4)
0.055(5)
0.060(5)
0.074(6)
0.068(5)
0.105(8)
0.066(5)
0.079(6)
H2O
Ni N(1)
0.2196(9)
N(1)
Ni N(1)
99.5(5)
Ni N(1)
0.2196(9)
N(1)
Ni N(5)
73.3(4)
Ni N(5)
0.1974(8)
N(1)
Ni N(5)
102.4(4)
Ni N(5)
0.1974(8)
N(1)
Ni N(7)
150.1(4)
Ni N(7)
0.209(1)
N(1)
Ni N(7)
86.3(4)
Ni N(7)
0.209(1)
N(1)
Ni N(5)
102.4(4)
O(1)
C(5)
0.131(1)
N(1)
Ni N(5)
73.3(4)
O(1)
C(12)
0.143(2)
N(1)
Ni N(7)
86.3(4)
N(1)
N(2)
0.136(1)
N(1)
Ni N(7)
150.1(4)
N(1)
C(1)
0.126(2)
N(5)
Ni N(5)
173.6(8)
N(2)
C(3)
0.136(2)
N(5)
Ni N(7)
76.7(4)
N(2)
C(4)
0.140(2)
N(5)
Ni N(7)
107.4(4)
N(3)
C(4)
0.134(1)
N(5)
Ni N(7)
107.4(4)
N(3)
C(5)
0.133(2)
N(5)
Ni N(7)
76.7(4)
N(4)
C(5)
0.136(2)
N(7)
Ni N(7)
103.2(6)
N(4)
C(6)
0.133(1)
Ni N(1)
N(2)
111.7(7)
N(5)
C(4)
0.129(2)
Ni N(1)
C(1)
142.6(10)
N(5)
C(6)
0.137(1)
Ni N(7)
N(6)
114.3(8)
N(6)
N(7)
0.138(1)
Ni N(7)
C(9)
144(1)
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Fig. 2. Molecular structure of the [Ni(bpt)2]2+ cation showing the atomic numbering scheme.
The ligand bpt is almost planar, showing only small dihedral angles between the aromatic
triazine and pyrazole rings (6.6(1) , 6.3(1) ), and adopts a cis-cis-conformation leading to a
planar meridional coordination of the Ni-atom. The ligand bpt is asymmetrically bound to Ni2+ in
complex [Ni(bpt)2](ClO4)2
H2O, displaying one short Ni-N(5) (triazine) distance (0.1974(8) nm)
and two longer Ni-N(pyrazole) distances (0.209(1), 0.219(9) nm). These observations are in
agreement with the usual coordination of terpyridine-like ligands to transition metal ions where
the central aromatic ring is more tightly bound than the two aromatic side arms, but in contrast
with those of complex [EuL(NO3)3(H2O)][L] (L = bpt or tpt), in which the ligand L is roughly
symmetrically coordinated to EuIII with three Eu-N distances not significantly deviating from the
average value (0.26016 nm)[1,3].
2.2.3
X-ray crystal structure of [Zn(mpt)2(dmp)](ClO4)2.
The molecular structures of the
cations in [Zn(mpt)2(dmp)](ClO4)2 along with the atom-labeling schemes are shown in fig. 3. The
final atomic coordinates are given in table 6, and selected bond distances and angles pertaining to
the metal coordination sphere for structure [Zn(mpt)2(dmp)]2+ in table 7. Being in agreement with
MS(FAB), IR and 1H NMR results, the crystal structure of zinc complex shows that it consists of
one [Zn(mpt)2(dmp)]2+ cation and two uncoordinated perchlorate anions. The Zn atom is
coordinated by a pair of bidentate mpt ligands and one monodentate dmp ligand, forming a
distorted trigonal bipyramid , where the two triazine nitrogen atoms of mpt and one nitrogen atom
of dmp occupy the basal positions, and the two pyrazole nitrogen atoms of mpt the apical one. The
two pyrazole nitrogen atoms of mpt ligand are practically coordinated to Zn2+ in a linear fashion
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
89
(N(5)-Zn-N(10): 176.6(5) ). The Zn2+ ion lies at the basal plane defined by N(3), N(6) and N(11)
(110.4(4) (N(3)-Zn-N(6))+128.4(4) (N(3)-Zn-N(11))+121.1(5) (N(6)-Zn-N(11)) = 359.9(4) ).
Fig. 3. Molecular structure of the [Zn(mpt)2(dmp)]2+ cation showing the atomic numbering scheme.
Table 6 Atomic coordinates and equivalent isotropic displacement parameters Beq for [Zn(mpt)2(dmp)](ClO4)2
Atom
Zn
C1
C2
C3
C4
C5
N1
N2
N3
N4
N5
N6
N7
N8
N9
N10
N11
N12
x
0.24546(8)
0.161(1)
0.1606(9)
0.239(1)
0.3651(9)
0.3852(9)
0.2167(8)
0.1328(6)
0.2131(6)
0.2937(7)
0.3092(6)
0.1822(6)
0.1396(9)
0.0737(6)
0.1203(7)
0.1776(6)
0.3222(6)
0.3265(7)
y
0.19727(7)
0.4046(9)
0.3231(9)
0.3290(8)
0.2319(9)
0.289(1)
0.3846(7)
0.3792(7)
0.2946(5)
0.3037(8)
0.2400(7)
0.1380(5)
0.0902(6)
0.0925(6)
0.1360(5)
0.1582(5)
0.1595(6)
0.0952(6)
z
0.04302(8)
0.096(1)
0.0137(9)
0.1053(9)
0.1642(9)
0.1998(8)
0.1320(7)
0.0348(9)
0.0478(8)
0.1399(7)
0.1263(6)
0.1076(8)
0.2219(7)
0.1075(9)
−0.0016(7)
−0.0371(9)
−0.0176(6)
−0.0295(7)
Beq
0.0606(5)
0.086(8)
0.065(6)
0.063(6)
0.078(7)
0.090(7)
0.074(5)
0.071(5)
0.061(4)
0.065(5)
0.067(5)
0.055(4)
0.080(5)
0.071(5)
0.055(5)
0.074(5)
0.061(5)
0.074(5)
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Table 7 Selected bond distances (nm) and angles ( ) for [Zn(mpt)2(dmp)](ClO4)2
Zn—N(3)
Zn N(5)
Zn N(6)
Zn N(10)
Zn N(11)
O(1) C(1)
O(1) C(7)
O(2) C(2)
O(2) C(8)
O(4) C(18)
N(1) C(1)
N(1) C(3)
N(2) C(1)
N(2) C(2)
N(3) C(2)
N(3) C(3)
N(4) N(5)
N(4) C(3)
N(4) C(6)
0.212(1)
0.213(1)
0.209(1)
0.211(1)
0.203(1)
0.132(2)
0.133(2)
0.133(1)
0.144(1)
0.142(2)
0.135(2)
0.132(2)
0.131(2)
0.134(2)
0.135(2)
0.133(1)
0.137(1)
0.136(2)
0.137(2)
76.3(5)
110.4(4)
101.0(5)
128.4(4)
104.3(5)
176.6(5)
93.0(5)
74.6(5)
121.1(5)
90.3(5)
129(1)
114(1)
112(1)
143(1)
103(1)
129(1)
117(1)
111(1)
140(1)
N(3) Zn N(5)
N(3) Zn N(6)
N(3) Zn N(10)
N(3) Zn N(11)
N(5) Zn N(6)
N(5) Zn N(10)
N(5) Zn N(11)
N(6) Zn N(10)
N(6) Zn N(11)
N(10) Zn N(11)
Zn N(3) C(2)
Zn N(3) C(3)
Zn N(5) N(4)
Zn N(5) C(4)
N(4) N(5) C(4)
Zn N(6) C(11)
Zn N(6) C(13)
Zn N(10) N(9)
Zn N(10) C(16)
Owing to the coordination, mpt ligands are slightly bent with dihedral angles of 17.8(8) and
9.19 , respectively, and two mpt planes in one [Zn(mpt)2(dmp)]2+ unit are almost perpendicular to
each other(dihedral angles between the triazine rings: 92.20 , and 88.83
between the pyrazole
rings). The dmp ligand is almost perpendicular to one mpt ligand (82.04
deviates from another mpt plane with dihedral angles of 109.44
distances are in the range of 0.203
and 86.84 ), and
and 120.84 . The Zn-N
0.213 nm, with four Zn-N(mpt) bonds at 0.2091 0.2131 nm
and a shorter Zn-N(dmp) bond of 0.2031 nm.
2.3
Catalytic effect of Zn2+ ion
Catalytic effect of Zn2+ ion is well known, especially in living systems. Many of the active
sites in these enzymes present as tri- or tetra-coordinated Zn2+ ion. Five-coordinated zinc species,
which act as intermediates that control the stereochemistry and dynamics of reactions[10], have
been attracted increasing interest recently. Owing to the variability and flexibility in coordination
behavior of Zn2+, the biologically active zinc sites in hydrolytic enzymes are capable of executing
highly efficient and kinetically rapid catalytic hydrolysis of DNA. There has been much recent
interest in zinc complexes with biologically relevant ligands as synthetic analogues of zinc
enzymes. However, attempts to understand the detailed reaction mechanisms at these zinc-binding
centers, including the metal coordination environments, are only partially successful in several
spectroscopic and crystallographic investigations.
Contrary to the reaction of Ni(ClO4)2
Zn(ClO4)2
6H2O with bpt giving [M(bpt)2](ClO4)2, reaction of
6H2O with bpt in methanol affords a colorless crystal whose X-ray crystal structure
analysis reveals it to be a new ternary five-coordinated complex of [Zn(mpt)2(dmp)][ClO4]2,
No. 1
Zn & Ni COMPLEXES WITH BIPYRAZOLTRIAZINE
91
where mpt and dmp correspond to methanolysis products of bpt under Zn2+ ion. Being stable in
methanol even at high temperature, the formation of ternary complex of [Zn(mpt)2(dmp)][ClO4]2
indicates a new catalytic effect of Zn2+ in methanolysis reaction. The electronspray ionization
mass spectra of freshly prepared solution of Zn(ClO4)2
6H2O and bpt in methanol show m/z
peaks at 663.1, 599.5 and 631.5, corresponding to the species of [Zn(bpt)2]2+(664.05),
[Zn(bpt)(mpt)]2+(599.96) and [Zn(mpt)2(dmp)]2+(632.00), respectively. Based on these facts, we
proposed a possible mechanism for the methanolysis reaction of bpt at presence of Zn2+ ion as
shown in scheme 3.
Scheme 3
2+
In methanolic solution of Zn and bpt, species of [Zn(bpt)2]2+ are formed at the initial stage.
Coordination mode of bpt in [Zn(bpt)2]2+ is assumed to be similar to that in [Ni(bpt)2]2+, i.e. bpt is
asymmetrically bound to Zn2+ with the central triazine ring being bound to the metal ion more
tightly and one pyrazole ring relatively weak. One pyrazole ring of bpt with activated C-N bond is
substituted by solvent molecule (methanol), giving mpt and dmp products. Penta-coordinated
cation [Zn(bpt)(mpt)]2+ might be the transition state of [Zn(bpt)2]2+ to [Zn(mpt)2(dmp)]2+
processes.
3
Conclusions
2,4-Bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine (bpt) has been prepared by
hydrazolation of 2,4-dichloro-6-methoxyl-1,3,5-triazine and then condensed with acetylacetone in
high yields under mild conditions. Crystal structure analysis of [Hbpt H2O
[Ni(bpt)2](ClO4)2
ClO4],
H2O and [Zn(mpt)2(dmp)](ClO4)2 indicates that protonation or coordination of
bpt induces aromatic planarity of bpt molecule, or enhances the π-π overlap interactions between
pyrazole and triazine rings of adjacent bpt molecules. In transition metal complexes, bpt is
asymmetrically bound to metal ion with the central triazine ring being more tightly bound than the
two pyrazole side arms. In methanol, one pyrazole ring is easily substituted by solvent molecules
in the presence of Zn2+ ion. Reaction of bpt and Zn(ClO4)2
6H2O in methanol thus affords
penta-coordinated ternary complex of [Zn(mpt)2(dmp)](ClO4)2. A possible mechanism for this
92
SCIENCE IN CHINA (Series B)
Vol. 44
catalytic reaction has been proposed.
Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No.
29671034) and Natural Science Foundation of Guangdong Province (Grant Nos. 990128, 974174).
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