научная статья по теме SYNTHESIS AND CRYSTAL STRUCTURES OF MANGANESE(IV) COMPLEXES WITH TRIDENTATE SCHIFF BASES Химия

Текст научной статьи на тему «SYNTHESIS AND CRYSTAL STRUCTURES OF MANGANESE(IV) COMPLEXES WITH TRIDENTATE SCHIFF BASES»

КООРДИНАЦИОННАЯ ХИМИЯ, 2013, том 39, № 8, с. 507-512

УДК 541.49

SYNTHESIS AND CRYSTAL STRUCTURES OF MANGANESE(IV) COMPLEXES WITH TRIDENTATE SCHIFF BASES

© 2013 D. L. Peng

Key Laboratory of Surface & Interface Science of Henan, School of Material & Chemical Engineering, Zhengzhou University of Light Industry, Zhengzhou, 450002 P.R. China E-mail: pengdonglai@yahoo.cn

Received December 12, 2011

The complexes with the formulae [Mn(L1)2] • 0.5Н20 (I) and [Mn(L2)2] (II), where L1 and L2 are the dianionic form of 2,4-dichloro-6-[(2-hydroxyethylimino)methyl]phenol and 2-{[1-(3-ethoxy-2-hydroxyphenyl)meth-ylidene]amino}-2-methylpropane-1,3-diol, respectively, were obtained and characterized by elemental analysis and IR spectroscopy. The crystal structures of complexes I and II were determined using X-ray diffraction. The crystal of I is orthorhombic space group Fdd2: a = 24.170(2), b = 32.021(3), c = 11.352(2) Â, V = 8785.9(19) Â3, Z = 8. The crystal of II is monoclinic space group C2/c: a = 13.931(4), b = 18.381(5), c = 12.444(5) Â, P = = 121.980(3)°, V = 2702.9(15) Â3, Z = 4. The Mn atom in each of the complexes is in an octahedral coordination.

DOI: 10.7868/S0132344X13070086

INTRODUCTION

Schiff bases have been widely studied in coordination chemistry mainly due to their facile syntheses, easily tunable steric, electronic properties and good solubility in general solvents [1—3]. Transition metal complexes derived from N and O-containing multi-dentate Schiff bases are of particular interest because of their versatile structures and wide applications [4—6]. In addition, the hydroxy-containing Schiff bases and their complexes have been proved to have interesting biological activities, such as antibacterial, antiviral, antifungal, and anticancer [7—9]. Manganese is an essential component ofvarious biological redox processes, as in catalases [10—12], and in photosynthesis by oxidizing water to dioxygen [13]. In the processes, the intermediate generated has manganese in its +4 oxidation state and hence the studies associated with Mn(IV) are important in the coordination and biomimetic chemistry. The manganese Schiff base complexes have also received considerable attention for their application in catalytic and bioinorganic chemistry [14—16]. In this paper, we describe the synthesis and structures of two new manganese(IV) complexes, [Mn(L1)2] ■ 0.5H2O (I) and [Mn(L2)2] (II), where L1 and L2 are the dianionic form of the tridentate Schiff bases 2,4-dichloro-6-[(2-hydroxyethylimino)me-thyl]phenol (H2L1) and 2-{[1-(3-ethoxy-2-hydroxyphe-

nyl)methylidene]amino}-2-methylpropane-1,3-diol (H2L2).

Л

N ' OH

Y^OH

C1

(H2L1)

EXPERIMENTAL

Materials and methods. The infrared spectra of the compounds were recorded on a PerkinElmer RX 1 FT-IR spectrophotometer with KBr discs. Elemental analyses were carried out using a PerkinElmer 2400 II elemental analyser. All the chemicals and solvents used for the syntheses were of reagent grade. 3,5-Dichlorosalicylaldehyde and 3-ethoxysalicylaldehyde (Fluka) were used as received. Mn(ClO4)2 • 6H2O was prepared by the reaction of manganese carbonate with perchloric acid in distilled water. The Schiff base H2L1 was prepared according to the literature method [17].

Caution! Although no problems were encountered in this work, perchlorate salts are potentially explosive.

They should be prepared in small quantities and handled with great care.

Synthesis of H2L2. 3-Ethoxysalicylaldehyde (1.66 g, 10 mmol) and 2-amino-2-methylpropane-1,3-diol (1.05 g, 1 mmol) were stirred in 80 mL methanol, resulting in a yellow solution containing H2L2 and this was used for the preparation of the complex II without further purification.

Synthesis of I. A 10 mL methanolic solution of Mn(ClO4)2 • 6H2O (0.362 g, 1 mmol) was added to a stirred 16 mL methanolic solution of H2L1 (0.466 g, 2 mmol). The mixture was stirred for 1 h at ambient condition to give a brown solution. Brown block-shaped single crystals of I suitable for single crystal X-ray diffraction were obtained after a few days during evaporation. The yield was 0.312 g (59.2%).

IR spectrum (KBr; v, cm-1): 3454 w, 1625 s, 1520 m, 1438 s, 1413 w, 1383 w, 1310 s, 1210 m, 1178 m, 1161 m, 1058 w, 1038 w, 1016 w, 886 w, 867 m, 758 m, 593 m, 537 m, 493 w, 419 w.

but no corrections for extinction were made. Both structures of the complexes were solved by direct methods using the SHELXL 97 program [18]. The non-hydrogen atoms were located in successive difference Fourier syntheses. The final refinement was performed by full matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F2. All hydrogen atoms were unambiguously located by difference maps and refined isotropically. The occupancy of the water molecule for I was estimated at 50% based on obtaining an equivalent isotropic displacement parameter of 0.0732 which is not unreasonable for a solvent molecule in a structure determined at room temperature. Crystallographic data and experimental details for structure analyses are summarized in Table 1. Selected bond lengths and angles of the complexes are listed in Table 2.

Supplementary materials for two compounds have been deposited with Cambridge Crystallographic Data Centre (nos. 859156 (I) and 859157 (II); deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.ac.uk).

For C36H29N4O9Cl8Mn2

anal. calcd., %: C, 40.98; H, 2.77; N, 5.31. Found, %: C, 40.72; H, 2.83; N, 5.39.

Synthesis of II. A 10 mL methanolic solution of Mn(ClO4)2 • 6H2O (0.362 g, 1 mmol) was added to a stirred 16 mL methanolic solution of H2L2 (0.506 g, 2 mmol). The mixture was stirred for 1 h at ambient condition to give an amount of precipation. The mixture was transferred to a Teflon-lined vessel, which was sealed and held at 150°C for 12 h. The vessel was allowed to slowly cool to room temperature. Brown block-shaped single crystals of II suitable for single crystal X-ray diffraction were obtained. The yield was 0.273 g (49.0%).

IR spectrum (KBr; v, cm-1): 3331 w, 1624 s, 1526 m, 1456 s, 1390 w, 1318 m, 1198 w, 1180 m, 1129 w, 1078 w, 991 w, 951 w, 907 w, 863 w, 823 m, 776 m, 707 m, 667 w, 594 w, 550 w, 460 w.

For C26H34N2O8Mn

anal. calcd., %: Found, %:

C, 56.01; C, 55.89;

H, 6.12; H, 6.26;

N, 5.02. N, 4.90.

X-ray crystallography. Suitable single crystals of complexes I and II were selected and mounted in air onto thin glass fibers. Accurate unit cell parameters were determined by a least-squares fit of 29 values, and intensity data sets were measured on a Bruker Smart 1000 CCD diffractometer with Mo^ radiation (X = = 0.71073 A) at room temperature. The intensities were corrected for Lorentz and polarization effects,

RESULTS AND DISCUSSION

The Schiff bases H2L1 and H2L2 were readily prepared by the reaction of equimolar quantities of 3,5-dichlorosalicylaldehyde with 2-aminoethanol and 3-ethoxysalicylaldehyde with 3-ethoxysalicylalde-hyde, respectively, in methanol. The complex I was prepared by the reaction of H2L1 with manganese per-chlorate in methanol at room temperature, while the complex II was prepared by the reaction of H2L2 with manganese perchlorate in methanol under solvother-mal condition. During the search of literature, we found that most of the similar manganese(IV) complexes were prepared by the reaction of the Schiffbases with KMnO4 [19, 20]. It is interesting that in the present paper, the Mn2+ in the metal salt was oxidized to Mn(IV) by air in the complexes.

Molecular structure of I contains a manganese(IV) complex molecule and half of one water molecule of crystallization, which is shown in Fig. 1. The molecular structure of II possesses a crystallogaphic inversion center symmetry, with the Mn(1) atom located at the inversion center, as shown in Fig. 2. In each of the complexes, two Schiff base ligands are bonded to the Mn atom in a tridentate fashion through the phenolate oxygen, imine nitrogen, and one hydroxy O atoms, resulting in an octahedral geometry. The largest deviations from octahedral geometry arise from the geometric constraints of this chelating ligand. The trans coordinate angles are in the range 159.6(3)°-173.8(3)° for I and 171.0(3)°-173.3(2)° for II, and the remaining coordinate bond angles are in the range 76.8(3)°-

SYNTHESIS AND CRYSTAL STRUCTURES OF MANGANESE(IV) COMPLEXES 509

Table 1. Crystallographic data and structure refinement parameters for I and II

Parameter Value

I II

M 1055.1 557.5

Shape and color Block and brown Block and brown

Temperature, K 298(2) 298(2)

Crystal system Orthorhombic Monoclinic

Space group Fdd2 C2/c

a, A 24.170(2) 13.931(4)

b, A 32.021(3) 18.381(5)

c, A 11.352(2) 12.444(5)

ß, deg 90 121.980(3)

V, A3 8785.9(19) 2702.9(15)

Z 8 4

Pcalcd g cm-3 1.594 1.370

Absorption coefficient, mm-1 1.117 0.539

/(000) 4240 1172

Crystal size, mm 0.18, 0.17, 0.16 0.33, 0.33, 0.29

9 Range for data collection, deg 2.54-26.99 2.22-27.00

Index ranges -26 < h < 30, -40 < k < 34, -14 < l< 14 -17 < h < 16, -22 < k < 23, -12 < l< 15

Reflections collected/unique (Rint) 10815/4656 (0.1026) 7156/2944 (0.0605)

Observed reflections 2711 1570

Data/restraints/parameters 4656/7/271 2944/0/171

Goodness-of-fit 0.976 1.025

Final R indices (I> 2a(T)) 0.0818, 0.1855 0.0763, 0.2116

R indices (all data) 0.1339, 0.2214 0.1507, 0.2580

Largest diff. peak and hole, e A-3 0.876 and -0.762 1.214 and -0.448

Table 2. Coordinate bond lengths (A) and angles (deg) for complexes I and II*

Bond d, A Bond d, A

Mn(1)—O(1) Mn(1)—O(3) Mn(1)—N(1) Mn(1)—O(1) Mn(1)—N(1) ] 1.896(6) 2.052(6) 2.012(6) I 1.874(4) 1.963(5) [ Mn(1)—O(2) Mn(1)—O(4) Mn(1)—N(2) I Mn(1)—O(4) 1.861(6) 2.343(6) 2.100(7) 1.846(4)

Angle ю, deg Angle ю, deg

O(2)Mn(1)O(1) O(1)Mn(1)N(1) O(1)Mn(1)O(3) O(2)Mn(1)N(2) N(1)Mn(1)N(2) O(2)Mn(1)O(4) N(1)Mn(1)O(4) N(2)Mn(1)O(4) O(4)Mn(1)O(4A) O(4)Mn(1)O(1A) O(4)Mn(1)N(1) O(1)Mn(1)N(1) N(1)Mn(1)N(1A) I 173.8(3) 90.2(3) 88.7(2) 89.0(3) 159.6(3) 92.9(2)

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