КООРДИНАЦИОННАЯ ХИМИЯ, 2009, том 35, № 11, с. 840-844
SYNTHESIS AND CRYSTAL STRUCTURES OF TWO ZINC(II) COMPLEXES DERIVED FROM 4-BROMO-2-(CYCLOPENTYLIMINOMETHYL)PHENOL
WITH DIFFERENT SOLVENTS
© 2009 Z. Hong
College of Chemical Engineering & Material Science, Liaodong University, Dandong 118003, PR. China
E-mail: email@example.com Received February 16, 2009
Two new mononuclear zinc(II) complexes, [ZnL2] (I) and [ZnL2] ■ 2MeOH (II) (HL = 4-bromo-2-(cyclopentyl-iminomethyl)phenol), were synthesized by the reaction of the Schiff base HL with zinc acetate in ethanol and methanol solutions, respectively. Both complexes were characterized by elemental analyses and single-crystal X-ray diffraction. The crystal of I is orthorhombic: space group Pbca, a = 14.711(3), b = 13.223(3), c = 24.870(5) À, V = 4837.8(18J) À3, Z = 8. The crystal of II is monoclinic: space group C2/c, a = 20.581(5), b = 10.660(3), c = 15.428(4) À, в = 119.919(3)°, V = 2933.7(13) À3, Z = 4. The Zn atom in each complex is four-coordinated by two imine N and two phenolic O atoms, forming a tetrahedral geometry. Complex II possesses crystallographic two-fold rotation axis symmetry.
Schiff bases prepared by the condensation of salicyla-ldehydes with primary amines are an important class of versatile ligands. Transition metal complexes derived from Schiff bases have been wide investigated due to their versatile structures and wide applications [1-3]. The study of the variety of products in self-assembly processes between labile metal atoms and Schiff bases is an interesting topic in supramolecular and coordination chemistry. Factors that affect the coordination topologies include not only the highly influential factors of metal and ligand coordination preferences, but also solvent-based influences, which have extensively been investigated for silver(I) complexes [4, 5]. However, for zinc complexes with Schiff bases, solvent-based influences on the structures have seldom been reported . In the present paper, two new mononuclear zinc(II) complexes [ZnL2] (I) and [ZnL2] ■ MeOH (II) (HL = 4-bromo-2-(cyclopentylimi-nomethyl)phenol) have been synthesized from different solvents.
Materials and measurements. 5-Bromosalicylalde-hyde and cyclopentylamine of AR grade were purchased from Aldrich. CHN elemental analyses were performed with a PerkinElmer 240C elemental analyzer. IR spectra (KBr disks) were recorded on a PerkinElmer 257 spectro-photometer.
Synthesis of HL. The Schiff base HL was prepared by the condensation reaction of equimolar 5-bromosalicylal-
dehyde with cyclopentylamine in a methanol solution at room temperature. The yield was 97%.
anal. calcd, %: C, 53.8; H, 5.3; N, 5.2.
Found, %: C, 54.1; H, 5.4; N, 5.0.
Synthesis of [ ZnL2] (I). An ethanol solution (50 ml) of Zn(CH3COO)2 ■ 2H2O (110.0 mg, 0.5 mmol) was added to an ethanol solution (50 ml) of HL (268.2 mg, 1.0 mmol), and the mixture was stirred at room temperature for 30 min. Colorless, X-ray quality crystals of I were obtained after a week by allowing the solution to evaporate in air. The yield was 201.0 mg (67%).
For C24H26Br2N2O2Zn (M = 599.66)
anal. calcd, %: C, 48.1; H, 4.4; N, 4.7.
Found, %: C, 48.6; H, 4.7; N, 4.5.
Synthesis of [ZnL2] • 2MeOH (II). Complex II was synthesized by a similar procedure as that for I, with the solvent ethanol replaced by methanol, yielding colorless X-ray quality crystals of II after a week. The yield was 172.8 mg (52%).
For C26H34Br2N2O4Zn (M = 663.74)
anal. calcd, %: C, 47.0; H, 5.2; N, 4.2.
Found, %: C, 46.6; H, 5.4; N, 4.2.
X-ray structure determination. The single crystals of the two complexes were chosen and glued to thin glass fibers by epoxy glue in air for data collection. The diffraction data were collected on a Bruker Apex2 CCD with Mo^a radiation (X = 0.71073 A) at 298(2) K using the o>
scan method. The structures were solved by direct methods and difference Fourier synthesis. Crystal data collection, parameters, and refinement statistics for the two complexes are listed in Table 1. All of the non-H atoms were refined anisotropically. The H atoms of the two complexes were included in calculated positions and assigned to isotropic thermal parameters, which were set to ride on the parent atoms. All calculations were performed using the SHELXTL-97 package .
The atomic coordinates and other parameters of structures I and II have been deposited with the Cambridge Crystallographic Data Center (no. 718319 (I) and 718320 (II); firstname.lastname@example.org).
RESULTS AND DISCUSSION
The condensation reactions of aldehydes with primary amines readily produce Schiff bases with quantitative yields and high purity. The Schiff base HL is yellow crystallite, which can be dissolved by methanol and ethanol. Both complexes were synthesized according to the procedure as shown by eqs. (1) and (2):
Table 1. Crystallographic and experimental data for the complexes I and II
Crystal shape/color Block/colorless Block/colorless
Crystal size, mm 0.20 x 0.18 x 0.17 0.37 x 0.35 x 0.32
Crystal system Orthorhombic Monoclinic
Space group Pbca C2/c
a, A 14.711(3) 20.581(5)
b, A 13.223(3) 10.660(3)
c, A 24.870(5) 15.428(4)
P, deg 90 119.919(3)
V, A3 4837.8(18) 2933.7(13)
Z 8 4
Mmo, mm1 1.224 3.593
T -'min 0.477 0.350
T -'max 0.526 0.393
Reflections/parameters 5544/280 3316/161
Independent reflections 2165 2231
F(000) 2400 1344
Goodness of fit on F2 1.003 1.041
R1, wR2 (I > 2a(I))* 0.0792, 0.1198 0.0461, 0.1136
R1, wR2 (all data)* 0.2228, 0.1624 0.0787, 0.1306
The only difference is the solvent used in the synthesis and crystallization of the complexes: EtOH for I and MeOH for II.
The IR spectrum of HL shows the characteristic v(O-H) absorption band at 3437 cm1, which absents after
• Ri = E||F0| - |Fcii/Z|F0|, wR2 = [Zw (Fo - F^f /Zw(Fo) ]
complexation. The absorption attributed to the v(C=N) vibrations is at 1635 cm-1 for HL. However, the corresponding vibrations in the two complexes are shifted 16 cm-1 to lower wave numbers as that described in similar Schiff base complexes [8, 9]. The strong absorption band observed for HL at 1281 cm-1 can be attributed to the phenolic stretch. The bands are observed at higher wave numbers at 1302 cm-1 for both complexes, suggesting involvement of the oxygen atom of the C-O group in coordination. The close resemblance of the shape and the positions of the absorption bands in the IR spectra suggests similar structures of the complexes. The absorption band of the methanol O-H vibration is not observed in II, what might be caused by the escape of the methanol molecules during grind under the infrared lamp.
Selected bond lengths and angles are listed in Table 2. The molecular structure of I is shown in Fig. 1. Both complexes are mononuclear zinc compounds. The major difference between the complexes is in the components of the molecules: complex I synthesized and crystallized in ethanol solution has no ethanol molecules in the crystal
Table 2. Selected bond lengths (A) and bond angles (deg) for the complexes
Table 3. Hydrogen bond distances (A) and bond angles (deg) for the complexes I and II*
Bond d, À Bond d, À
Zn(1)-O(1) 1.905(5) Zn(1)-O(1) 1.925(2)
Zn(1)-N(1) 2.001(6) Zn(1)-N(1) 1.991(3)
Angle ю, deg Angle ю, deg
I O(1)Zn(1)O(2) 118.8(2) II O(1)Zn(1)O(1y 114.23(17)
O(2)Zn(1)N(1) 114.4(2) O(1)Zn(1)N(1y 113.42(11)
O(2)Zn(1)N(2) 95.8(2) O(1)Zn(1)N(1) 97.04(11)
O(1)Zn(1)N(1) 95.1(2) N(1)Zn(1)N(1)¿ 122.79(16)
Contact D-H-A Distance, À Angle D-H-A, deg
D-H H-A D-A
C(3)-H(3>"Br(1)i7 C(6)-H(6>"O(1yi7 O(2)-H(2)-O(1)iv 0.93 0.93 0.82 I 2.92 2.53 II 1.95 3.739(4) 3.456(4) 2.758(4) 148 177 171
* Symmetry codes: "1/2 - x, -1/2 + y, z; iii1/2 - x, 1/2 + y, z; iV1/2 - x,
Symmetry code: i1 - x, y, 1/2 - z.
structure, while complex II synthesized and crystallized in methanol solution has methanol molecules in the crystal structure.
In both complexes, the Zn atom is four-coordinated in a tetrahedral geometry by two phenolic O and two imine N atoms from two Schiff base ligands. The structure of the zinc complex molecule of II is similar to that of I but possesses crystallographic two-fold rotation axis symmetry.
-1/2 + y, 1/2 - z.
The ZnO2N2 tetrahedral coordination in each complex is slightly distorted with angles subtended at the Zn atom in the range 95.1(2)°-122.7(2)° for I and 97.0(2)°-122.8(2)° for II. The coordinate bond lengths in both complexes are comparable to each other and also comparable to those in the similar Schiff base zinc complexes [10-12]. The dihedral angle between the two benzene rings in I and II are 79.7(6)° and 87.2(3)°, respectively.
In the crystal structure of I, molecules are linked through intermolecular C-H—Br and C-H—O hydrogen bonds (Table 3), forming chains running along the y axis (Fig. 2). In the crystal structure of II, the methanol molecules are linked to the zinc complex molecules through intermolecular O-H-O hydrogen bonds (Table 3, Fig. 3).
Fig. 1. Molecular structure of I at 30% ellipsoid.
КООРДИНАЦИОННАЯ ХИМИЯ том 35 № 11 2009
The author acknowledges the Liaodong University for funding this study.
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