КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 5, с. 290-297
SYNTHESIS, STRUCTURES, AND ANTIBACTERIAL ACTIVITIES OF TWO IRON(III) COMPLEXES WITH SCHIFF BASES
© 2014 F. Y. Wei* and P. H. Wen
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji, 721013 P.R. China
*E-mail: firstname.lastname@example.org Received July 25, 2013
Two Schiff base iron(III) complexes, [FeL1(AHA)] ■ H2O (I) and [Fe(L2)2] ■ ClO4 (II), where AHA is the deprotonated form of acetohydroxamic acid, and L1 and L2 are the anionic form of N,N'-bis(3-ethoxysali-cylidene)propane-1,2-diamine and 2-[1-(2-aminopropylimino)ethyl]phenol, respectively, have been synthesized and characterized by physical chemical methods and single crystal X-ray diffraction. Crystallo-graphic data for I: orthorhombic, space group Iba2, a = 20.781(3), b = 23.527(3), c = 10.071(2) Â, V = = 4923.7(12) Â3, Z = 8, R1 = 0.0374, wR2 = 0.0900. Crystallographic data for II: triclinic, space group P\, a = 12.748(1), b = 13.401(1), c = 19.007(1) Â, a = 106.623(2)°, в = 97.462(2)°, у = 112.543(2)°, V = = 2784.9(4) Â3, Z = 4, R1 = 0.0892, wR2 = 0.2434. X-ray crystal structural study indicated that the coordination environment around each Fe atom in the complexes is a six-coordinated distorted octahedron. The antibacterial activities of the complexes were assayed.
Iron is an important element for biological processes of human beings [1—3]. Iron is also an essential cofactor in metalloenzymes . Its importance in DNA synthesis, control of gene expression, and induction of cell apoptosis is becoming better understood . Schiff bases derived from benzaldehydes with various organic amines are important ligands in the coordination of transition metal atoms. Iron complexes with Schiff bases have been received particular interest for their biological effects, especially antibacterial and antitumor activities [6—10]. However, when compared to other transition metal ions, the number of complexes bearing iron centers is much less. In the present work, two new iron(III) complexes, [FeL1(AHA)] • H2O (I) and [Fe(L2)2] • ClO4 (II), where AHA is the deproto-nated form of acetohydroxamic acid, and L1 and L2 are the anionic form of N,N'-fe(3-ethoxysali-cylidene)propane-1,2-diamine (H2L1) and 2-[1-(2-aminopropylimino)ethyl]phenol (HL2), respectively, have been synthesized, characterized, and investigated for their antibacterial activities.
All chemical reagents and solvents were of analytical grade and were obtained from Sigma-Aldrich. Methanol was dried over molecular sieves (4 N) prior to use. Elemental analyses were performed on a PerkinElmer 2400 II elemental analyzer. Infrared
spectra were recorded on a PerkinElmer RX I FT-IR spectrophotometer with KBr discs. TG—DTA analysis was carried out under nitrogen with a heating rate of 10°C min-1 using a Perkin Elmer Pyris Diamond TG/DTA analyzer.
Iron perchlorate is potentially explosive, only small quantity should be used and handled with great care.
Synthesis of the Schiff bases. The Schiff bases H2L1 and HL2 were synthesized by refluxing hot ethanolic solution (30 mL) of propane-1,2-diamine (0.01 mol) with 3-ethoxysalicylaldehyde (0.02 mol) and 2-ace-tylphenol (0.02 mol), respectively for about 1 h. The precipitates formed during reflux were filtered, washed with cold EtOH, and recrystallized from hot EtOH. The yields were 83 and 77% for H2L1and HL2, respectively.
For C21H26N2O4 (H2L1)
anal. calcd., %: C, 68.1; H, 7.1; N, 7.6.
Found, %: C, 67.9; H, 7.2; N, 7.5.
For CuH16N2O (HL2)
anal. calcd., %: C, 68.7; H, 8.4; N, 14.6. Found, %: C, 68.6; H, 8.3; N, 14.4.
Synthesis of complex I. A methanolic solution (10 mL) of H2L1 (0.1 mmol, 37.0 mg) was mixed with a methanolic solution (10 mL) of Fe(ClO4)3 (0.1 mmol, 37.2 mg) and acetohydroxamic acid
(0.1 mmol, 7.5 mg), and refluxed in a water bath for 1 h. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of the solution in air for a few days. The yield was 43%.
anal. calcd., %: Found, %:
C, 53.5; C, 53.7;
H, 5.9; H, 6.0;
N, 8.1. N, 8.1.
Synthesis of complex II. A methanolic solution (10 mL) of HL2 (0.1 mmol, 19.2 mg) was mixed with a methanolic solution (10 mL) of Fe(ClO4)3 (0.1 mmol, 37.2 mg), and refluxed in a water bath for 1 h. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of the solution in air for a few days. The yield was 65%.
anal. calcd., %: C, 49.1; H, 5.6; N, 10.4. Found, %: C, 49.0; H, 5.7; N, 10.2.
Single crystal X-ray diffraction. X-ray data for the complexes were collected on a Bruker SMART APEXII diffractometer equipped with graphite -monochromated MoKa radiation (X = 0.71073 A). A preliminary orientation matrix and cell parameters were determined from three sets of ® scans at different starting angles. Data frames were obtained at scan intervals of 0.5° with an exposure time of 10 s frame-1. The reflection data were corrected for Lorentz and polarization factors. Absorption corrections were carried out using SADABS. The structures were solved by direct methods and refined by full-matrix least-squares analysis using anisotropic thermal parameters for non-H atoms with the SHELXTL program . All H atoms were calculated at idealized positions and refined with the riding models. Crystallographic data for the complexes are summarized in Table 1.
Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 950909 (I) and 950910 (II); deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.ac.uk).
Antibacterial activity test. The in vitro activity test was carried out using the growth inhibitory zone (well method) . The potency of components was determined against the Gram-positive bacteria: S. agalactiae and S. aureus and the Gram-negative bacteria: K. pneumoniae and P. aeruginosa. Microorganisms were cultured on Muller-Hinton agar medium. The inhibitory activity was compared with that of standard antibiotics, such as gentamicine (10 ^g). After drilling wells on medium using a 6 mm cork borer, 100 ^L of solution from different compounds were poured into each well. The plates were incubated at 37°C overnight. The diameter of the inhibition zone was measured to the nearest. Each test was carried out in triplicate and the average was calculated for inhibition
zone diameters. A blank containing only methanol showed no inhibition in a preliminary test. The macro-dilution broth susceptibility assay was used for the evaluation of minimal inhibitory concentration (MIC). By including 1 mL Muller-Hinton broth in each test, and then adding 1 mL extract with concentration 100 mg/mL in the first tube, we made serial dilution of this extract from first tube to last tube. Bacterial suspension prepared to match the turbidity of 0.5 Mcfarland turbidity standards. Matching this turbidity provides a bacterial inoculum concentration of 1.5 x 108 cfu/mL. Then 1 mL of bacterial suspension was added to each test tube. After incubation at 37°C for 24 h, the last tube was determined as the minimal inhibitory concentration (MIC) without turbidity.
RESULTS AND DISCUSSION
Two new mononuclear iron(III) complexes were synthesized by reaction of Schiff bases, acetohydrox-amic acid, with iron perchlorate in methanol. For complex I, acetohydroxamic acid was coordinated to the Fe atom, while for complex II, even though we had added the material, it has not participated in coordination.
The asymmetric unit of compound I contains a mononuclear iron complex molecule and a water molecule of crystallization (Fig. 1a). The Fe atom in the complex shows distorted octahedral coordination geometry, with O(1), N(2) atoms of the Schiff base ligand, and O(5) and O(6) atoms of the AHA ligand defining the equatorial coordination sites, and N(1) and O(2) atoms of the Schiff base ligand occupying the axial positions. The Fe atom deviates from the best coordination plane defined by the equatorial atoms by 0.145(1) A in direction of O(2) atom. The coordinate bond lengths and angles (Table 2) are in line with the corresponding values found in related six-coordinated iron(III) complexes with Schiff bases [13, 14]. The distortion of the octahedral coordination may be caused by the strain created by the five-membered chelate rings Fe(1)-N(1)-C(8)-C(9)-N(2) and Fe(1)-O(5)-C(22)-N(3)-O(6). The three trans angles are much deviated from the ideal value of 180°, ranging from 155.9(1)° to 161.7(1)°. The remaining bond angles are also deviated from the ideal value of 90°, ranging from 74.4(1)° to 112.4(1)°. The dihedral angle between the two benzene rings of the Schiff base ligand is 33.5(3)°.
In the crystal structure of complex I, the iron complex molecules and the water molecules are linked together by O—H-O and N—H-O hydrogen bonds (Table 3), to form 2D layers parallel to the yz plane (Fig. 2a).
The asymmetric unit of compound II contains two mononuclear iron complex cations and two perchlor-ate anions (Fig. 1b). The Fe atom in the complex shows distorted octahedral coordination geometry, with the three donor atoms of one Schiff base ligand
Table 1. Crystallographic data and experimental details for structures I and II
Formula weight 516.35 537.80
Crystal size, mm 0.30 x 0.27 x 0.27 0.30 x 0.27 x 0.27
Temperature, K 298(2) 298(2)
Crystal system Orthorhombic Triclinic
Space group Iba2 PI
a, A 20.781(3) 12.748(1)
b, A 23.527(3) 13.491(1)
c, A 10.071(2) 19.007(1)
a, deg 90 106.623(2)
P, deg 90 97.462(2)
Y, deg 90 112.543(2)
V, A3 4923.7(12) 2784.9(4)
Z 8 4
P calcd mg cm-3 1.393 1.283
^(MoKa), mm-1 0.660 0.677
/(000) 2168 1124
Number of measured reflections 24588 26141
Number of observations (I > 2ct(I)) 5071 10319
Unique reflections 4132 5591
Parameters 320 616
Number of restraints 5 48
R1, wR2 (I> 2ct(I))*
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