КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 2, с. 100-106
A BINUCLEAR IRON(III) SCHIFF BASE COMPLEX DOUBLY BRIDGED BY HYDROXYL GROUPS: SYNTHESIS, STRUCTURE, AND CHARACTERIZATION
© 2015 X. Feng1, *, J. L. Chen2, G. Y. Luo1, L. Y. Wang1, 2, *, and J. Z. Guo1
1College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, 471022 P.R. China 2School of Life Science and Technology, Nanyang Normal University, Nanyang, 473061 P.R. China *E-mail: firstname.lastname@example.org Received July 7, 2014
A novel binuclear iron(III) Schiff base complex [Fe2(NO2-Salpn)2(^-OH)2] • H2O (I) (NO2-Salpn = 5-nit-rosalicylaldehyde-1,3-propanediamine) has been obtained through one-pot refluxing and condensation. Complex I was established by single-crystal X-ray diffraction analysis (CIF file CCDC no. 1005239) and further characterized by elemental analysis, IR spectroscopy, electrochemical and magnetochemical measurements. Complex I consists of two pseudooctahedral high-spin iron(III) units doubly bridged by two hydroxyl groups. The inter hydrogen bonding interactions connect the adjacent binuclear units into one dimensional (1D) infinite chain, and these 1D chains are further propagated into the two dimensional (2D) supramolec-ular network by weak intermolecular interactions. Variable temperature magnetic measurements indicate the presence of strong antiferromagnetic interactions between the two adjacent iron(III) ions.
Recent years have witnessed that the ligand of sali-cylaldehyde Schiff base has elicited considerable attention due to the interests in the biology and chemistry fields, and many ligands of salicylaldehyde Schiff base have been documented [1—3]. Meanwhile, iron is an essential trace element, and is the main component of hemoglobin in human blood. Because the iron(III) ion has the most self-spin single electrons, the design, synthesis, and characterization of iron complexes with Schiff-base ligands play the vital role in coordination chemistry due to the importance as synthetic models for the functional materials [4—7]. In addition, as we all know, the pseudohalide ions, N3 , diamine , and oxygen atom  have been well exploited for their ability to bridge paramagnetic moieties into dimers, clusters, and even polymers. However, the iron Schiff base complex incorporating electron-withdrawing groups, such as nitro group and neural water bridge, are seldom reported, to the best of our knowledge [11, 12]. Hydroxyl group is one of the component substances of water, which is an important resource for the survival of all life on the plane, and the most important part of the organism. In this contribution, an unique binuclear iron complex based on substituted salicylaldehyde Schiffbase ligand, [Fe2(NO2-Salpn)2(|-OH)2] ■ H2O (I), has been synthesized and characterized systematically, in which the two Fe-Schiff base moieties were doubly bridged by two hydroxyl moieties.
Materials and physical measurements. All reagents used in the syntheses were of analytical grade. Elemental analysis (C, H, and N) was performed on a PerkinElmer 2400 element analyzer. The infrared spectra (4000—650 cm-1) were recorded by using KBr pellet on a VECTOR-22 spectrometer. The variable temperature solid-state magnetic susceptibilities of title complex have been performed using a MPMS-7 SQUID magnetometer in the range 2—300 K at a magnetic field of 2000 Oe. Diamagnetic corrections were made with Pascal's constants for all constituent atoms. Electrochemical measurements were executed on RST3000 series electronic work station (Suzhou Risetech Instrument Co. Ltd. China). The electrochemical cell used in cyclic-voltammetry was a closed standard three-electrode cell connected to a solution reservoir through a Teflon tube under nitrogen atmosphere. A platinum disk (1.5 mm diameter) was used as the working electrode, and a Hg/Hg2Cl2 as the reference electrode equipped with a wire counter electrode. The ferrocene/ferrocinium (Fc/Fc+) redox couple served as the internal standard.
Synthesis of complex I. The mixture of Fe(NO3)3 • • 9H2O (80.799 mg, 0.2 mmol) and KSCN (38.872 mg, 0.2 mmol) was refluxed in anhydrous methanol (10 mL) at 60°C for 3 h in air, decanted off, and filtered. To the resulting red solution was added 10 mL DMF solution of freshly distilled 5-nitrosalicylalde-
hyde and 1,3-propanediamine at a molar ratio of 2 : 1 simultaneously. Then the solution was vigorously stirred for a further 2.5 h. After that, the mixture was cooled down to the room temperature naturally and filtered. One week later, dark red crystals were obtained and filtered. The yield was 0.038 g (41% based on Fe element).
anal. calcd., %: C, 44.23; H, 3.80; N, 12.14; Fe, 12.10. Found, %: C, 44.19; H, 3.74; N, 12.11; Fe, 12.04.
IR (KBr; v, cm-1): 3564 br, 1638 s, 1600 s, 1439 s, 1366 m, 1480 m, 874 m, 56 m.
X-ray structure determination. A single crystal of complex I (0.32 x 0.21 x 0.19 mm) was mounted on a Bruker SMART APEX II CCD diffractometer equipped with a graphite-monochromatized MoZ„ radiation (k = 0.71073 A) by using a 9/® scan mode at room temperature in the range of 2.44° < 9 < 25.50°. Corrections for Lp factors were applied and all non-hydrogen atoms were refined with anisotropic thermal parameters. The structure was solved by direct methods with SHELXS-97 . The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by use of geometrical restrains. A full-matrix least-squares refinement on F2 was carried out using SHELXL-97 . The final R1 = 0.0381, wR2 = 0.0759 (w = 1/[a2(Fo2) +
+ (0.0220P2) + 2.2693P], where P = (Fo2 + 2Fc2 )/3), ^ = 1.013, (Ap)max = 0.298 and (Ap)mix = -0.317 e/A3. Crystallographic and experimental details are summarized in Table 1. The selected bond lengths and bond angles are listed in Table 2.
Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (no. 1005239; email@example.com or http://www.ccdc.cam. ac.uk).
RESULTS AND DISCUSSION
In IR spectrum of complex I, the presence of strong bands ranging from 1439 to 1600 cm-1 indicates the existence ofbenzene ring. The broad band at ~3564 cm-1 is attributed to the free water molecule. Besides, the strong vibration peaks appear around 1638 cm-1, corresponding to the stretching vibrations of the C=N group. In addition, the absorption of 1366 to 1480 cm-1 confirms the existence of nitro groups in complex I.
The X-ray diffraction analysis reveals that the title compound crystal structure consists of a Schiff base Fe complex and an uncoordinated water molecule. The perspective view of complex I with atom labeling scheme is illustrated in Fig. 1. In the Schiff base complex, there exist two [Fe(NO2-Salpn)] moieties and two coordinated water molecules, exhibiting the cen-
Table 1. Crystallographic data and experimental details for complex I
Crystal shape/color Block/red
Formula weight 460.70
Temperature, K 296(2)
Crystal system Monoclinic
Space group P2x/c
Unit cell dimensions:
a, A 11.633(3)
b, A 9.668(2)
c, A 16.799(4)
P, deg 98.118(3)
V, A3 1870.4(7)
Pcalcd g cm-3 1.640
Absorption coefficient, mm-1 0.863
9 Range for data collection, deg 2.44-25.50
Limiting indices ranges -14 < h < 14
-11 < k < 11
-20 < l < 20
Reflections measured/independent 10716/3460
Reflections with I > 2a(I) 2423
Max and min transmissions 0.8532 and 0.7698
R indices (I > 2ct(I)) Rx = 0.0381, wR2 = 0.0759
R indices (all data) Rj = 0.0659, wR2 = 0.0895
Largest diff. peak and hole, e/A3 0.298 and -0.317
trosymmetric configuration. The coordination environment around the Fe3+ ion can be described as a distorted octahedronEach Fe3+ ion is six-coordinated by two N atoms of 1,3-propanediamine, two O atoms of 5-nitrosalicylaldehyde and two lattice water O atoms, which results in one fourmembered ring and three six-membered rings around the Fe3+ ion. The bond lengths of Fe(1)-O(2), Fe(1)-O(3), Fe(1)-O(4), Fe(1)—N(2) in equatorial plane are found to be 1.984, 1.946, 1.963, 2.133 Â, respectively; axial Fe(1)-N(1), Fe(1)—O(2)#1 is 2.135, 1.993 Â, respectively. A slightly
Table 2. Selected bond lengths and angles for compound I
Bond d, Â Bond d, Â Bond d, Â
Fe(1)-O(3) 1.946(2) Fe(1)-O(2) 1.9843(19) Fe(1)-N(2) 2.133(3)
Fe(1)-O(4) 1.963(2) Fe(1)-O(2)#1 1.993(2) Fe(1)-N(1) 2.135(2)
Angle ю, deg Angle ю, deg Angle ю, deg
O(3)Fe(1)O(4) 91.63(9) O(4)Fe(1)N(2) 167.34(9) N(2)Fe(1)N(1) 83.32(10)
O(3)Fe(1)O(2) 92.13(9) O(2)Fe(1)N(2) 95.40(9) Fe(1)O(2)Fe(1)#1 105.03(9)
O(4)Fe(1)O(2) 96.78(9) O(2)#1Fe(1)N(2) 91.84(9) Fe(1)O(2)H(3w) 124.9
O(3)Fe(1)O(2)#1 166.22(8) O(3)Fe(1)N(1) 101.92(10) C(17)N(1)Fe(1) 118.3(2)
O(4)Fe(1)O(2)#1 94.62(9) O(4)Fe(1)N(1) 85.71(9) C(14)N(2)Fe(1) 122.9(2)
O(2)Fe(1)O(2)#1 74.97(9) O(2)Fe(1)N(1) 165.68(9) C(15)N(2)Fe(1) 118.5(2)
O(3)Fe(1)N(2) 84.48(10) O(2)#1Fe(1)N(1) 90.79(9) N(2)Fe(1)N(1) 83.32(10)
distorted octahedral geometry is also confirmed by the bond angles of O(2)Fe(1)O(2)#1, O(2)Fe(1)O(3), which are found to be 75.27(9)°, 91.99°. Interestingly, Fe(NO2-Salen) moieties are bridged via two hydroxyl groups, and the Fe2O2 core are completely coplanar. To the best of our knowledge, this is the first example that two adjacent iron(III) centers are bridged by hy-droxyl group simultaneously based on substituted sali-cylaldehyde Schiff base ligand. However, in this case, the Fe-Fe separation in the Fe2O2 core is mere 3.157 A, which is seldom reported.
In our previous work, another dinuclear iron(III) analogous complex containing N,N-ethylene-^is(sal-icylideneiminato) monobridged via 4,4-bipyridine
had been synthesized, in which the distance between the two Fe atoms is 11.570 Â .
Close inspection reveals that there present obvious hydrogen bonding between the O(2) atom from co
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