научная статья по теме SYNTHESIS, CHARACTERIZATION, AND X-RAY CRYSTAL STRUCTURES OF ZINC(II) COMPLEXES WITH SCHIFF BASES 2-[(2-ISOPROPYLAMINOETHYLIMINO)METHYL]-5-METHOXYPHENOL AND N,N-DIMETHYL-N-(1-PYRIDIN-2-YL-ETHYLIDENE)ETHANE- 1,2-DIAMINE Химия

КООРДИНАЦИОННАЯ ХИМИЯ, 2011, том 37, № 9, с. 669-674

УДК 541.49

SYNTHESIS, CHARACTERIZATION, AND X-RAY CRYSTAL STRUCTURES

OF ZINC(II) COMPLEXES WITH SCHIFF BASES 2-[(2-ISOPROPYLAMINOETHYLIMINO)METHYL]-5-METHOXYPHENOL AND N,N-DIMETHYL-N'-(1-PYRIDIN-2-YL-ETHYLIDENE)ETHANE-

1,2-DIAMINE

© 2011 H. Y. Liu*, G. W. Li, Z. L. Li, J. Y. Wu, Y. C. Cai

School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University,

Zhongshan 528453, P.R. China *E-mail: liuhuanyu03@163.com Received November 8, 2010

Two new zinc(II) complexes, [ZnB^L1] (I) and [ZnBr2L2] (II), where L1 is 2-[(2-isopropylaminoethylimi-no)methyl]-5-methoxyphenol and L is N,N-dimethyl-N'-(1-pyridin-2-yl-ethylidene)ethane-1,2-diamine, were prepared and characterized using elemental analysis, FT-IR spectroscopy, and X-ray single-crystal diffraction. In complex I, the Zn(II) atom is coordinated by one phenolic O and one imino N atoms of L1 and two Br atoms, forming a tetrahedral coordination geometry. In complex II, the Zn(II) atom is in a trigonal bipyramidal coordination geometry with the equatorial plane formed by the imino N atom of L2 and two Br atoms and with the two axial positions occupied by one pyridine N and one amino N atoms of L2. In the crystal structure of I, the mononuclear zinc complex molecules are linked through intermolecular N—H—O and N—H—Br hydrogen bonds, forming chains running along the y axis. The chains are further linked via intermolecular C—H—Br hydrogen bonds. In the crystal structure of II, the mononuclear zinc complex molecules are linked through intermolecular C—H—Br hydrogen bonds, forming a 3D network.

INTRODUCTION

Schiffbases are a kind ofversatile ligands in coordination chemistry. The compounds containing strong donor sites, such as phenoxo oxygen and imine nitrogen atoms, have attracted much attention in catalysis and biological application for their special coordination ability with transition metal atoms [1—3]. In particular, zinc complexes with Schiffbase ligands have received considerable interest in the fields of synthetic and biological chemistry for their antibacterial and antifungal activities [4—6]. The Zn atoms can adopt various coordination numbers, such as four, five, or six [7—9]. What coordination will be formed largely depends on the properties of the ligands. In this paper, two new zinc complexes with different Schiff bases, [ZnBr2L1] (I) and [ZnBr2L2] (II), have been prepared and structurally characterized.

EXPERIMENTAL

Materials and physical measurements. 4-Methoxysal-icylaldehyde, 2-acetylpyridine, N-isopropylethane-1,2-diamine, and N,N-dimethylethane-1,2-diamine were purchased from Lancaster Chemical Company Inc. Zinc(II) bromide was purchased from Sinpeuo Fine Chemical Company Inc. and used as received. All other chemicals were of AR grade. Elemental analyses for C, H, and N were performed using a PerkinElmer 240C elemental analyzer. Infrared spectra were recorded on a

Nicolet 170SX FT-IR spectrophotometer with KBr pellets in the 4000—400 cm-1 region. Molar conductance measurements were performed in a DDS-11A conductivity meter.

Synthesis of the Schiff base ligands L1 and L2. The

Schiff bases were obtained by refluxing equimolar quantities (1 mmol each) of a methanolic solution (30 ml) of amine and aldehyde for 1 h. The resulting orange solution containing the Schiffbases were used without purification.

Synthesis of complex I. A methanolic solution (10 ml) of ZnBr2 (22.5 mg, 0.1 mmol) was added dropwise to a methanolic solution (10 ml) of L1 (23.6 mg, 0.1 mmol) with stirring. The mixture was stirred under ambient conditions for 30 min to give a colorless solution. The colorless single crystals ofl suitable for X-ray analysis were obtained several days later. The yield was 72%.

For Ci3H2oN2O2Br2Zn

anal. calcd., %: Found, %:

C, 33.83; C, 33.62;

H, 4.37; H, 4.45;

N, 6.07. N 6.18%.

IR spectrum (KBr; v, cm-1): 1627 s, 1606 s, 1536 s, 1487 w, 1439 m, 1397 m, 1355 w, 1298 m, 1219 s, 1123 m, 1023 w, 973 w, 840 m, 617 w, 556 w, 437 w.

Synthesis of complex II. The complex was prepared by following the same procedure as that described for I,

Table 1. Crystallographic data and details of refinements for complexes I and II

Parameter Value

I II

Formula weight 461.5 416.5

Crystal system Monoclinic Triclinic

Space group P21/n P T

Unit cell dimensions:

a, A 6.4075(16) 9.675(2)

b, A 12.094(3) 10.160(3)

c, A 22.106(5) 15.808(2)

a, deg 90 75.672(2)

P, deg 96.991(3) 82.530(2)

Y, deg 90 77.326(2)

V, A3 1700.4(7) 1464.2(6)

Z 4 4

Pcalcd g cm-3 1.803 1.889

F(000) 912 816

^Mo^a), mm-1 6.146 7.118

Collected reflections 9853 7390

Independent reflections 3672 6129

Observed reflections (I > 2ct(T)) 2289 3435

9 range, deg 2.5-24.9 2.2-25.0

R (I> 2CT(T)) 0.0436 0.0727

wR2 (I > 2ct(T)) 0.0778 0.1871

Goodness-of-fit on F2 1.011 0.985

with L1 replaced by L2 (19.1 mg, 0.1 mmol). The yield was 83%.

For C11H17N3Br2Zn

anal. calcd., %: C, 31.72; H, 4.11; N, 10.09. Found, %: C, 31.56; H, 4.20; N, 10.15.

IR spectrum (KBr; v, cm-1): 1645 s, 1591 s, 1570 m, 1455 m, 1438 m, 1346 m, 1317 m, 1273 m, 1118 m, 1065 w, 1012 m, 932 m, 887 w, 772 m, 632 w, 613 w, 580 w, 453 w.

X-ray structure determination. The crystal and instrumental parameters used in the unit cell determination and data collection are summarized in Table 1. Diffraction measurements were made at 298(2) K on a Bruker APEX II X-ray diffractometer using graphite-mono-chromated Mo^Ta radiation using the ® scan mode. Unitcell dimensions were determined and refined in the 2.51° < 0 < 27.00° range for I and in the 2.16° < 0 < 27.00° range for II. The program SMART [10] was used for data collection, indexing reflection, and determination of lattice parameters; SAINT [10] was used for integration of the reflection intensity and scaling; and SADABS [11] was used for absorption correction. The structures were solved by the direct methods using SHELXS-97 and refined by full-matrix least-squares techniques on F2 with SHELXL-97 [12, 13]. All non-hydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were included in their idealized positions and refined isotropically. Selected bond distances and angles for complexes I and II are listed in Table 2. Hydrogen bonding geometries are given in Table 3.

Supplementary material for complexes has been deposited with the Cambridge crystallographic data centre (nos. 797299 (I) and 797300 (II); depos-it@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

The Schiff bases L1 and L2 were prepared by the condensation of equimolar quantities of aldehydes with amines in methanol and were used without purification. The two zinc complexes were readily prepared by the reaction of the Schiff bases with zinc bromide in methanol at room temperature. The structures of the complexes were characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. The molar conductivity measurements of the complexes in DMSO at a concentration of 10-3 mol/l suggest that both complexes are nonelectrolytes with conductance values of 25.3 and 27.2 fi-1 cm2 mol-1 for I and II, respectively [14].

The molecular structure of complex I is shown in Fig. 1. The Zn atom is in a distorted tetrahedral coordination with one imine N and one phenolic O atoms ofL1 and with two Br atoms. The Zn-Br bond lengths are much longer than those of the Zn-O and Zn-N bonds. The coordinate bond angles are in the range 97.6(2)°-

KOOP^HH^HOHHAtf XHMH3 TOM 37 № 9 2011

SYNTHESIS, CHARACTERIZATION, AND X-RAY CRYSTAL STRUCTURES OF ZINC(II)

671

Table 2. Selected bond lengths and angles for complexes I Table 3. Geometric parameters of hydrogen bond for com-

and II

plexes I and II*

Bond d, Â Bond d, Â Distance, Â

I Contact D H-A Angle

Zn(1)-O(1) 1.941(3) Zn(1)-N(1) 1.993(4) D-H H-A D-A D-H - A, deg

Zn(1)-Br(1) 2.3883(9) Zn(1)-Br(2) 2.3628(8)

Zn(1)-N(1) 2.177(9) II Zn(1)-N(2) 2.103(9) I

Zn(1)-N(3) 2.202(10) Zn(1)-Br(1) 2.3808(17) N(2)-H(2^)-Br(2)i 0.90 2.71 3.477(4) 144

Zn(1)-Br(2) 2.3875(19) Zn(2)-N(4) 2.176(8)

Zn(2)-N(5) 2.117(9) Zn(2)-N(6) 2.233(10) N(2)-H(25)-O(1)i 0.90 1.96 2.815(5) 158

Zn(2)-Br(4) 2.3874(17) Zn(2)-Br(3) 2.4023(17) C(9)-H(95)-Br(2)ii 0.97 2.85 3.562(5) 131

Angle ro, deg Angle ro, deg

O(1)Zn(1)N(1) 97.58(15) I O(1)Zn(1)Br(2) 108.59(10) II

N(1)Zn(1)Br(2) 110.90(11) O(1)Zn(1)Br(1) 110.92(11) C(11)-H(115)-Br(1) 0.96 2.92 3.553(5) 124

N(1)Zn(1)Br(1) 111.34(11) Br(2)Zn(1)Br(1) 115.96(3)

II

N(2)Zn(1)N(1) 73.6(4) N(2)Zn(1)N(3) 78.3(4)

N(1)Zn(1)N(3) 150.1(4) N(2)Zn(1)Br(1) 110.0(3)

N(1)Zn(1)Br(1) 98.8(2) N(3)Zn(1)Br(1) 100.2(2)

N(2)Zn(1)Br(2) 135.8(3) N(1)Zn(1)Br(2) 95.4(2)

N(3)Zn(1)Br(2) 97.7(3) Br(1)Zn(1)Br(2) 114.00(7)

N(5)Zn(2)N(4) 74.7(3) N(5)Zn(2)N(6) 77.3(4)

N(4)Zn(2)N(6) 150.2(3) N(5)Zn(2)Br(4) 136.1(3)

N(4)Zn(2)Br(4) 95.8(2) N(6)Zn(2)Br(4) 97.2(2)

N(5)Zn(2)Br(3) 111.5(3) N(4)Zn(2)Br(3) 97.6(2)

N(6)Zn(2)Br(3) 102.1(2) Br(4)Zn(2)Br(3) 112.19(7)

♦Symmetry codes: '1/2 - x, -1/2 + y, 1/2 - z; u-1/2 - x, -1/2 + y, 1/2 - z.

116.0(1)°. The amine N atom is protonated and does not take part in coordination. The bond lengths are comparable with those observed in other Schiff base zinc complexes with tetrahedral coordination [15, 16]. In the crystal structure of the complex, the molecules are linked through intermolecular N—H—O and N—H—Br hydrogen bonds, forming chains running along the y axis. The chains are further linked via intermolecular C—H -Br hydrogen bonds, as shown in Fig. 2.

The molecular structures of complex II are shown in Fig. 3. The asymmetric unit of the complex contains two independent molecules. Each of the Zn atoms is in distorted trigonal bipyramidal coordination with one imine N of L2 and two Br atoms defining the equatorial plane and with the pyridine N and the amine N atoms ofL2 located at the axial positions. The Zn(1) and Zn(2 atoms deviate from the equatorial planes by 0

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