6H2O, NaClO4 · H2O, NaOH and betaine (Aldrich) were used as supplied. Variable-temperature magnetic sus- ceptibility data were obtained on a Quantum ...
195
Transition Metal Chemistry 26: 195±197, 2001.
Ó 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Synthesis, crystal structure and magnetic properties of triaquahexakis(l2-betaine)(l3-oxo)triiron(III) perchlorate heptahydrate Ming-Liang Tong and Xiao-Ming Chen* School of Chemistry and chemical engineering, Zhongshan University, Guangzhou 510275, P.R. China Zi-Ming Sun and David N. Hendrickson Department of Chemistry, University of California at San Diego, California 92093-0358, USA Received 17 April 2000; accepted 26 May 2000
Abstract The synthesis and characterization of the oxo-centered carboxylato-bridged trinuclear iron(III) complex, triaquahexakis(l2-betaine)(l3-oxo)triiron(III) perchlorate heptahydrate are described. X-ray crystallography shows that the FeIII atom in the complex has a slightly distorted octahedral geometry, coordinated by four oxygen atoms from dierent betaine ligands [FeAO = 2.009(3) 2.034(3) AÊ], one aqua ligand [FeAO = 2.028(4) and 2.031(3) AÊ] and the central l3-oxo atom [FeAO = 1.917(2) and 1.917(3) AÊ]. The central oxygen is ideally coplanar with the plane of the three metal atoms. Magnetic susceptibility data (4±320 K) show the presence of an antiferromagnetic exchange interaction with a coupling constant of J = )20.2 cm)1.
Introduction Oxo-centered carboxylato-bridged trinuclear complexes of general formula [M3(l3-O(O2CR)6L3]n are known for several transition metal ions [1]. Since the triangular oxocentered structure was con®rmed in 1965 [2], attention has not only focused on various properties of these complexes in the solid state [3±5], but the stable [Fe3O]7+ core has also be used as a building block to prepare larger clusters with 11 and 16 iron(III) ions [6]. Recently we took advantage of the zwitterionic characteristics of betaines to prepare metal carboxylate complexes containing anionic ligands [7, 8]. In particular, we have synthesized several dimeric copper(II) complexes of betaines, and described the very important eect of the axial ligands on CuáááCu separation [9]. We describe herewith the synthesis, crystal structure and properties of a new oxo-centered trinuclear iron(III) complex of betaine (bet) which contains the highest valent cations among analogous complexes so far documented, namely [Fe3O(bet)6(H2O)3](ClO4)7 á 7H2O (1). Experimental All manipulations were carried out in air. Fe(NO3)3 á 6H2O, NaClO4 á H2O, NaOH and betaine (Aldrich) were used as supplied. Variable-temperature magnetic susceptibility data were obtained on a Quantum Design SQUID magnetometer. The experimental susceptibil* Author for correspondence
ities were corrected for the diamagnetism of the constituent atoms [10]. The eective molar magnetic moments were calculated using the equation le = 2.828(vM T)1/2. The C, H and N elemental analyses were performed on a Perkin-Elmer elemental analyser. I.r. spectra were recorded on a Nicolet 5DX FT-IR spectrophotometer with KBr discs in 4000 400 cm)1 region. Complex (1) was prepared as follows. A mixture of Fe(NO3)3 (1.0 mmol), bet (2.0 mmol) and NaClO4 (3 mmol) was dissolved in small amount of distilled H2O, the pH of which was adjusted by addition of aqueous NaOH. The mixture was stirred for 10 min to give a clear reddish solution. After slow evaporation of the resulting solution at room temperature during 2 weeks, deep red polyhedral crystals of the title complex were obtained (yield: 75%). (Found: C, 20.5; H, 4.7; N, 5.1. C30H86Cl7Fe3N6O50 calcd.: C, 20.6; H, 5.0; N, 4.8%). I.r. (cm)1): 3388(m), 3268(m), 3050(m), 2987(m), 2959(m), 1637(s), 1560(w), 1489(m), 1454(s), 1405(m), 1356(m), 1236(w), 1145(s), 1110(s), 1082(s), 997(m), 962(m), 927(m), 906(m), 723(w), 632(s), 603(w), 568(w), 442(w). (Caution: metal perchlorate salts containing organic ligands are potentially explosive and should be handled with great care.) Diraction intensities (crystal size 0.48 ´ 0.38 ´ 0.36 mm; hmax 25:01 , 6363 unique data of which 4242 were observed) for complex (1) were collected at 295 K on a Siemens R3 diractometer using the x-scan technique. Lorentz-polarization and absorption corrections were applied [11]. The structure solution and full-matrix least-squares re®nement based on F 2 were performed with the SHELXS-97 and SHELXL-97
196 program packages, respectively [12, 13]. All the nonhydrogen atoms were re®ned anisotropically. Hydrogen atoms of the organic ligands were generated geometrically (CAH = 0.96 AÊ) and those of the aqua ligands were located from a dierence map; all the hydrogen atoms were assigned the same isotropic temperature factors (U = 0.08 AÊ2) and were included in the structure-factor calculations. Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated [14]. Structure solution and re®nement based on 4242 re¯ections with I > 2r(I) and onP 535 parameters Pgave kFo j ÿ jFc k= jFo j, R1
wR2 0:0647
0:1808 fR1 P P wR2 w
Fo2 ÿ Fc2 2 = w
Fo2 2 1=2 g. Crystallographic data: C30H86Cl7Fe3N6O50, monoclinic, space group C2/c; a = 24.481(4), b = 12.661(2), c = 24.325(5) AÊ, b 106:68(2)°, V 7222(2) AÊ3, Z = 4, k(MoKa = 0.71073 AÊ. Drawings were produced with SHELXTL [15]. CIF ®le has been deposited with the Cambridge Crystallographic Data Centre, deposition number CCDC-142892. Results and discussion Crystal structure Selected bond lengths and angles of complex (1) are listed in Table 1. The crystal structure consists of [Fe3O(bet)6(H2O)3]7+ cations, perchlorate anions and Table 1. Selected bond lengths (AÊ) and angles (°) for (1) Bond lengths Fe(1)áááFe(1a) Fe(1)AO(1) Fe(1)AO(11) Fe(1)AO(21) Fe(1)AO(32a) Fe(1)AO(1w) Fe(1)AO(31) Fe(2)AO(1) Fe(2)AO(22)
3.3143(11) 1.9174(17) 2.009(3) 2.013(3) 2.027(3) 2.031(3) 2.030(3) 1.917(3) 2.011(3)
Bond angles O(1)AFe(1)AO(11) O(1)AFe(1)AO(21) O(11)AFe(1)AO(21) O(1)AFe(1)AO(32a) O(11)AFe(1)AO(32a) O(21)AFe(1)AO(32a) O(1)AFe(1)AO(31) O(11)AFe(1)AO(31) O(21)AFe(1)AO(31) O(32a)AFe(1)AO(31) O(1)AFe(1)AO(1w) O(11)AFe(1)AO(1w) O(21)AFe(1)AO(1w) O(32a)AFe(1)AO(1w) O(31)AFe(1)AO(1w) Fe(1)AO(1)AFe(1a) Fe(2)AO(1)AFe(1) O(32)AC(31)AO(31)
91.99(9) 97.19(10) 92.86(12) 94.77(9) 173.13(11) 87.54(11) 93.88(10) 88.10(11) 168.85(11) 90.20(11) 177.21(9) 86.61(11) 85.30(11) 86.59(11) 83.67(11) 119.60(16) 120.20(8) 126.9(4)
Fe(1)áááFe(2) Fe(2)AO(2w) Fe(2)AO(12) O(11)AC(11) O(12)AC(11) O(21)AC(21) O(22)AC(21) O(31)AC(31) O(32)AC(31)
3.3244(9) 2.028(4) 2.034(3) 1.253(5) 1.244(5) 1.239(5) 1.256(5) 1.255(5) 1.244(4)
O(1)AFe(2)AO(22) O(1)AFe(2)AO(22a) O(22)AFe(2)AO(22a) O(1)AFe(2)AO(2w) O(22)AFe(2)AO(2w) O(22a)AFe(2)AO(2w) O(1)AFe(2)AO(12) O(22)AFe(2)AO(12) O(22a)AFe(2)AO(12) O(2w)AFe(2)AO(12) O(1)AFe(2)AO(12a) O(22)AFe(2)AO(12a) O(22a)AFe(2)AO(12a) O(2w)AFe(2)AO(12a) O(12)AFe(2)AO(12a) O(12)AC(11)AO(11) O(21)AC(21)AO(22)
symmetry codes: a) )x, y, )z + 1/2.
96.56(8) 96.56(8) 166.88(17) 180.000(1) 83.44(8) 83.44(8) 91.75(8) 93.06(12) 86.54(12) 88.25(8) 91.75(8) 86.54(12) 93.06(12) 88.25(8) 176.50(15) 126.8(4) 126.4(4)
Fig. 1. ORTEP plot showing the structure of the cation in (1).
lattice water molecules. Figure 1 illustrates the structure of the cation in (1). The coordination environment about each iron(III) atom is approximately octahedral, each iron atom being displaced by ca. 0.158 AÊ towards the central bridging oxygen atom from the plane de®ned by the four oxygen atoms from dierent betaine ligands. The central oxygen atom is coplanar with the plane of the three metal atoms [Fe Fe = 3.314(1) and 3.324(1) AÊ], which is similar to that in a recently reported complex [Fe3O(O2CPh)6(py)3](NO3) [16], but dierent from those in most complexes containing the Fe3O unit [1]. The FeAO (central) distances are 1.917(2) and 1.917(3) AÊ and the FeAO(central)AFe angles are 119.6(2) and 120.20(8)°, indicating that the Fe3O units only deviate slightly from 3-fold symmetry. The FeAOH2 distances [2.028(4) and 2.031(3) AÊ] are all longer than those [1.989(4) AÊ] found in the analogous mononuclear complex [17]. This con®rms that MAOH2 bonds in the oxo-centered trimer complexes are relatively weak, as suggested previously on the basis of vibrational spectroscopy [18] and reaction kinetics [19]. Finally, the extensive hydrogen bonds between the aqua ligands, lattice water molecules and perchlorate counterions may play a role in consolidating the crystal [O O = 2.632(5)±2.894(7) AÊ]. I.r. spectra The i.r. spectra show features attributable to each component of (1). The bands at 1637vs and 1454vs cm)1 can be assigned to mas (CO2) and msym (CO2) modes, respectively. The separation (D) between mas(CO2) and msym(CO2) lies at 183 cm)1, indicating that the carboxylate groups are coordinated to the iron(III) atoms in a bridging fashion [20±22], in agreement with the observed crystal structure of (1). The band at 603 cm)1 can be assigned to the masym (Fe3O) mode, which is similar to those found in the related complexes containing
197 Chemistry Department of the Chinese University of Hong Kong for donation of the R3m diractometer. References
Fig. 2. Plots of vM (r) and le (d) versus temperature for (1). The solid lines represent theoretical values.
[Fe3O]7+ [23]. The bands at 1145(vs), 1110(vs), 1082(vs) and 625(s) cm)1 are assigned to the m(ClO4) mode [24]. Magnetic properties The magnetic susceptibility data for complex (1) were measured over the 4±320 K range. The eective magnetic moments per trimer (leff ) versus temperature and molar magnetic susceptibility (vM ) versus temperature are shown in Figure 2. The eective moment of 6.72 B.M. per trimer at 319.9 K is typical for three highspin iron(III) centers. On lowering the temperature, leff decreases from 6.72 B.M. at 319.9 K to 1.84 B.M. at 4.0 K per trimer complex. This behavior is typical of an antiferromagnetic interaction. Based on the almost idealized trigonal Fe3O geometry, we assume that there is an equivalent coupling between each pair of adjacent ions. Values of the exchange integral, J, were calculated by the modi®ed method of Earnshaw et al. [25]. The best-®t parameters are g 2:05, J = )20.2 cm)1 with a monomer paramagnetic impurity of 4% and TIP P = 330 10)6. The P agreement factor de®ned as R
vobs ÿ vcalcd: 2 =
vobs 2 is equal to 0.6%. The exchange integral for the title complex compares favorably with those (J = 16 to )20 cm)1) reported for known oxo-centered trimer iron(III) complexes [1]. Acknowledgements This work was supported by the National Nature Science Foundation of China (No. 29625102, 29971033) and Zhongshan University and also by the National Science Foundation of the USA. We thank the
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