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Synthesis, crystal structures and characterization of two heterometallic compounds: Ba3[Fe(C2O4)3]2(H2O)12 and Ba4.5[Fe4O(OH)3(C2O4)8](H2O)19
Inorganica Chimica Acta 421 (2014) 399–404
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Synthesis, crystal structures and characterization of two heterometallic compounds: Ba3[Fe(C2O4)3]2(H2O)12 and Ba4.5[Fe4O(OH)3(C2O4)8](H2O)19 Bin Zhang a,⇑, Yan Zhang b, Guangcai Chang c, Zengqiang Gao c, Dongwei Wang d, Daoben Zhu a a
OSL, BNLMS, CMS & Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China Institute of Condensed Matter and Materials Physics Department, Department of Physics, Peking University, Beijing 100871, PR China BSRF, Institute of High-Energy Physics, Chinese Academy of Sciences, Beijing 100047, PR China d National Centre for Nanoscience and Technology, Beijing 100190, PR China b c
a r t i c l e
i n f o
Article history: Received 16 April 2014 Received in revised form 21 June 2014 Accepted 1 July 2014 Available online 10 July 2014 Keywords: Iron Oxalate Hydroxo Oxo Magnetism
a b s t r a c t Heterometallic yellow compound Ba3[Fe(C2O4)3]2(H2O)12 (1) with mononuclear anion [Fe(C2O4)33 ] can be transformed to heterometallic red compound Ba4.5[Fe4O(OH)3(C2O4)8](H2O)19 (2) with OH/O bridged tetranuclear anion [Fe4O(OH)3(C2O4)98 ] in the mother liquor. Ba2+ and Fe3+ form three-dimensional networks thorough oxalate anion and H2O molecules in 1 and 2. 1 is a paramagnet and a strong antiferromagnetic interaction as the ground state S = 0 exists in 2. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The oxalate anion (C2O24 ) is an excellent ligand for metal ions, and the relationships between the crystal structures and physical properties of oxalate-based coordinated compounds, including their photochemical, magnetic and conductive properties, have been studied extensively [1]. The magnetic interactions between transition metal atoms bridged by oxalate units can lead to the formation of molecular crystals from long-range magnetic ordering magnet with dimensionality resulting from the one-dimensional chains, two-dimensional (2D) layers and three-dimensional (3D) metal–oxalate-frameworks, to quantum magnet as single molecular magnet and single chain magnet [2–5]. Oxo and hydroxo anions play important roles in molecular magnets, such as the crystal-tocrystal transformation from a hydroxo-bridged Fe(III) compound: {(C2H5NH3)[Fe2(C2O4)2](i-OH)}2H2O}n to a oxo-bridged Fe(III) compound: {(H3O)(C2H5NH3)[Fe2(C2O4)2Cl2(i-O)]H2O}n, where the colour of crystal changed from yellow to red and the canted angle of the spin changed, but the antiferromagnetic ordering temperature remained the same [6]. The 2D homometallic and heterometallic metal–oxalate-frameworks of transition metal atoms ⇑ Corresponding author. Tel.: +86 10 62558982. E-mail address: [email protected] (B. Zhang). http://dx.doi.org/10.1016/j.ica.2014.07.001 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
exhibit interesting magnetic properties, including the ferromagnetic compound [(n-C4H9)4N][CrMn(C2O4)3] and [(n-C4H9)4N] [NiV(C2O4)3]0.20{[(n-C4H9)4N](BF4)}0.20MeCN, the ferrimagnetic compound [(n-C4H9)4N][FeIIFeIII(C2O4)3], [C4H9)4N][MIIMnIII (C2O4)3] (MII = Fe, Co, Ni, Zn), and antiferromagnetic compounds [C4H9)4N][FeIIRuIII(C2O4)3], (Ammonium)[M2(C2O4)3] (M = Fe, Co) and Fe(C2O4)(CH3OH) [3,7]. Antiferromagnetic interactions were also observed in the 3D homometallic frameworks Mn(C2O4) (H2O)0.25 and [(C2H5)3NH]2[Cu2(C2O4)3] [4]. Compared with the homometallic and heterometallic 2D and 3D metal–oxalateframeworks of transition metal atoms, research towards the heterometallic 2D and 3D metal–oxalate-frameworks of main metal and transition metal atoms has been scare. When Li+ was used in this context with a transition metal, a 3D (10,3) network was obtained in [LiCr(C2O4)23 ], whereas a 2D (6,3) network was observed in [LiFe(C2O4)23 ] [8]. In terms of conductivity, the heterometallic ternary oxalate-based compounds A–M(C2O4)2–H2O, where A is an alkaline earth metal such as Mg2+, Ca2+, Sr2+, Ba2+, and the square-coordinate Pt(C2O4)22 anions show high levels of conductivity, for example, the room-temperature conductivity of Mg0.82[Pt(C2O4)2]5.3H2O was 0.2 S/cm [1,9]. Furthermore, the molecular semiconductor (BEDT–TTF)4KFe(C2O4)3(C6H5CN) (BEDT–TTF = bis(ethylenedithio)tetrathiafulvalene) was obtained when the 2D honeycomb anion [KFe(C2O4)23 ]n was used as
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counteranion [10]. Studies concerning the crystals structure, conductivity and magnetic properties of alkaline earth metal and octahedral-coordinate oxalate-based anions, however, remains scarce in the literature. Herein, we report the synthesis and characterization of two oxalate-based heterometallic compounds composed of Ba2+, Fe3+ ions.
were corrected for the diamagnetism of the sample using Pascal constants ( 190.75 10 6 emu/mol for compound 1 and 160.25 10 6 emu/mol for compound 2 for one Fe3+ unit in both cases) and corrected for background effects via the experimental measurement of the sample holder [13].
3. Results and discussion 2. Experimental All reagents were obtained from commercial sources and were used as received without further purification. The yellow and red block crystals of 1 and 2, respectively, were obtained using the diffusion method. A solution of BaCl22H2O (345.5 mg, 1.23 mmol) in H2O (20 mL) was placed in one arm of a H-cell, where a solution of [(C2H5)4N]3Fe(C2O4)3 (452.4 mg, 0.64 mmol) in H2O (20 mL) was placed in the other. After one week, yellow crystal (100 mg) of compound 1 had formed on the bottom and arm of cell. After 2-months, red crystals of 2 (200 mg) has formed on the arm and the bottom of cell. When 1 was soaking in mother solution, the colour of crystal changed from yellow to red slowly, and 2 was obtained at last after months. Elemental analysis (%) of 1: Anal. Calc. for C12H24Ba3Fe2O36 (1268.3): C, 11.37; H, 1.91. Exp.: C, 11.20; H, 1.92. Selected IR data (single crystal): 794(s), 853(w), 898(m), 1040(w), 1281(s), 1352(m), 1404(vs), 1631(vs), 1883(w), 2565(vw), 2857(s), 2928(s), 3369(br) cm 1. Elemental Anal. (%) of 2: Calc. for C16H41Ba4.5Fe4O55 (1954.93): C 9.83; H 2.11. Exp.: C, 9.90; H, 2.20. Selected IR data (single data): 740(m), 796(s), 853(w), 901(m), 1060(brw), 1266(s), 1284(s), 1348(m), 1407(s), 1638(bvs), 1883(vw), 2594(w), 2854(m), 2921(m), 3370(brs) cm 1. The Ba and Fe contents of 2 were found 2.21:2 by ICP. X-ray diffraction experiment was carried out on 1W2B working station in Beijing Synchrotron Radiation facility to check the quality of single crystal at first. X-ray diffraction data were collected on a Nonius Kappa CCD diffractometer with graphite monochromated Mo Ka (k = 0.71073 Å) radiation of 1 at room temperature and on a Rigaku M007HF diffractometer with focused Mo Ka (k = 0.71073 Å) radiation of 2 at 173 K [11]. The structures were solved by direct methods and refined by full-matrix least-square on F2 using a SHELX program, with anisotropic thermal parameters for all non-hydrogen atoms [12]. The hydrogen atoms of H2O molecules in 1 and 2 were omitted during refinement. The hydrogen atoms of OH in 2 were found by difference Fourier map and refined isotropically. The occupations of Ba and H in 2 were refined. Crystallographic data of 1: C12H24Ba3Fe2O36, F.W. = 1268.3, monoclinic, space group P21/c, a = 10.8416(1) Å, b = 17.6498(3) Å, c = 18.5049(3) Å, a = 90°, b = 92.707(1)°, c = 90°, V = 3537.00(9) Å3, Z = 4, Dcalc = 2.381 g cm 3, l = 4.213 mm 1, 16,479 measured data, 8409 unique, Rint = 0.0273, 487 parameters, R1 = 0.0295 for 6296 observation of I P 2r(I0), wR2 = 0.0779 for all data, Goodness-of-fit = 1.019. 2: C16H41Ba4.5Fe4O55, F.W. = 1954.93, orthorhombic, space group P nma, a = 19.885(4) Å, b = 18.906(4) Å, c = 13.727(3) Å, a = 90°, b = 90°, c = 90°, V = 5160.8(18) Å3, Z = 4, Dcalc = 2.516 g cm 3, l = 4.603 mm 1, 42 356 measured data, 6063 unique, Rint = 0.0608, 398 parameters, R1 = 0.0493 for 5998 observation of I P 2r(I0), wR2 = 0.1300 for all data, Goodness-of-fit = 1.115. Powder X-ray diffraction patterns were obtained on a Rigaku RINT 2000 diffractometer with Cu Ka radiation at roomtemperature. The conductivity measurements were carried out by the twoprobe method. Two gold wires were attached to two sides of the single crystal with gold paste. The I–V curve was measured by a Keithely 4200 SCS at room-temperature. Magnetization measurements were performed on polycrystalline samples, which were tightly packed into capsules on a Quantum Design MPMS 7XL SQUID system. Susceptibility data
The compounds Ba3[Fe(C2O4)3]2(H2O)12 (1) and Ba4.5[Fe4(OH)3 O(C2O4)8](H2O)19 (2) were obtained from same cell by diffusion method, but their compositions were different. The compound 1 existed as a dynamic phase, whereas 2 existed as the thermodynamically stable product in the mother liquors together with Ba2+, Fe3+, Cl , C2O24 and ammonium ions [14]. Crystal of 1 was obtained after few days. When yellow crystal of 1 remained in mother liquors at ambient temperature for weeks, its colour changed from yellow to red slowly. Crystal of 2 was the main product after months and stable in solution. This suggested that a transformation from yellow crystal 1 to red crystal 2 (Fig. 1) and compound 2 can be obtained from compound 1 in the solution of Ba2+, Fe3+, C2O24 and H2O. Compound 1 crystallizes in the monoclinic space group P21/c. There are three Ba2+, two Fe3+, six oxalate anions, ten H2O molecules and four of half H2O molecules in an independent unit. Each Fe3+ ion is octahedrally coordinated by six O atoms from three bidentate oxalate anions with mean Fe–O bond lengths in the range of 1.982(3)–2.040(2) Å as well as cis O–Fe–O bond angles in the range of 79.24(9)–80.86(9)°, 80.60(8)–81.1(1)° and trans O–Fe–O bond angles in the range of 162.2(1)–173.36(9)°, which is similar to those previously reported in the literature [8,15]. Two enantiomers of Fe(C2O4)33 are found in the crystal of 1, including the K enantiomer (Fe1) and D enantiomer (Fe2), the crystal is a racemate (Fig. 2). The main plane of the propeller-like mononuclear Fe1 is lying on the ac plane, whereas the main-plane of the propeller-like mononuclear Fe2 is lying on the (2 1 0) plane. Ba2+ ions are surrounded by O atoms from oxalate anions and H2O molecules. Ba1 exists in a cave formed by eight O atoms from four oxalate anions (two Fe1, two Fe2) and two O atoms from two H2O molecules. Ba2 sites in the cavity formed from two O atoms from one oxalate anion (Fe1), three O atoms from three oxalate anions (one Fe1 and two Fe2), two O atoms from two terminal H2O molecules and two O atoms from two bridged H2O molecules. Ba3 occupies the vacant position formed among five O atoms from five oxalate anions (three Fe1, two Fe2), three O atoms from three terminal H2O molecules and two O atoms from two bridged H2O molecules. Fe1 atom connects to one Ba1 atom through two O atoms (O11, O12) from one oxalate anion, two Ba2 atoms through two O atoms (O8; O7, O8) of one oxalate anion, two Ba3 atoms through two O atoms (O3; O3, O4) of one oxalate anion. Fe2 atom is connected to four Ba1 atoms through six O atoms (O15; O15, O16; O19, O20; O23, O24) on three oxalate anions, two Ba2 atoms through
Fig. 1. Morphologies of 1 and 2.
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Fig. 2. Configuration of anions in 1.
two O atoms (O16, O20) on two oxalate anions and one Ba3 atom through O19 (Fig. 3). Two Ba2 [4.7226(3) Å] atoms and two Ba3 [4.8658(3) Å] atoms arrange alternately to form a zigzag chain along the b axis with a Ba2 Ba3 distance of 5.2963(3) Å. These zigzag chains are connected by Ba1 along the c axis with Ba1 Ba2 and Ba1 Ba3 distances of 4.4809(3) and 4.5537(3) Å, respectively. A Ba layer with the Ba Ba distance less than 5.3 Å is formed in the bc plane (Figs. 4 and 5). Fe(C2O4)33 anions and H2O molecules exist in the cavities of Ba layers as shown in Fig. 3. Two of the metal layers are connected by oxalate anions between the Ba and Fe atoms from neighbouring layers along the a axis as shown in Fig. 5. Compound 2 crystallizes in the orthorhombic Pnma space group. The asymmetric unit consists of four Ba2+ (i.e., Ba1, Ba2, Ba3 and Ba4), two Fe3+ (Fe1, Fe2), four oxalate anion, one hydroxide ions, two of half hydroxide ions, and one H2O molecule (Fig. 6). The occupations of Ba1, Ba2, Ba3 and Ba4 atoms are 0.50, 1.0, 0.50 and 0.25, respectively. The Fe3+ ion is octahedrally coordinated by two O atoms from the hydroxide anion, and four O atoms from two bidentate oxalate anions. All of Fe atoms in the Fe4O4 core are coplanar. O17 and O18 are displaced from the metal plane on one side, O19 is displaced from the other side. Because all of the atoms on a single anion are related by a mirror plane through O17 and O19 atoms and perpendicular to the main plane of
Fig. 4. Metallic network in 1 on the bc plane. Colour code: Ba Ba, light orange, Ba Fe grey. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fe4O4 core, half of atoms on one tetranuclear anion [Fe4O(OH)3 (C2O4)98 ] exist in an independent unit. The occupations of H17, H18 and H19 on bridged hydroxide are 0.5, 0.5 and 0.5. The configuration of Fe4O4 core is similar as [Fe4O(OH)3(O2CCH3)4(bpy)4] (ClO4)3 [16]. The Fe–O bond distances from the Fe ion to the O atoms of the oxalate anions are in the range of 2.022(4)– 2.125(4) Å (Fe1) and 2.033(4)–2.096(4) Å (Fe2), whereas the Fe–O bond distances from the Fe ion to the O atoms of the hydroxide anion are shorter. Fe1–O18 1.879(4) Å, Fe2–O18 1.879(4) Å is shorter than Fe1–O17 1.946(2) Å and Fe2–O19 1.984(2) Å because O18 is composed of half of OH and half of O2 . The Fe–O(H) bond
Fig. 3. Crystal structure of 1 viewed along the a axis. The H atoms have been omitted for clarity. Colour code: Ba–O, orange; Fe–O, C–O and C–C, white. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 5. Three-dimensional network formed by Ba2+ and Fe3+ in 1 connected by oxalate anion or H2O. Colour code: Ba Ba, light orange; Ba Fe, grey. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 6. Configuration of anion in 2. The occupation of H atom bonded to O18 is 0.5.
lengths are in the range of the reported value, for example, the Fe–O(H) distances are in the range of 1.942–1.952 Å in {[Fe(OEP)2]2(OH)}+, whereas the Fe–O(H) bond distances in [(tpp)Fe–O(H)–Fe(tpp)]+ and [Fe2(OH)(O2CCH3)2(HB(pz)3)2]+ are 1.92(3) Å, and 1.960(4) Å and 1.952(4) Å, respectively [17]. The Fe–O(H)–Fe bond angles are 135.1(3)° (O17), 140.5(2)° (O18) and 132.7(3)° (O19), whereas the O(H)–Fe–O(H) bond angles are 93.0(2)° (Fe1) and 93.6(2)° (Fe2). The sum of the angles of the Fe4O4 core is 1080°. The Ba2+ ions are surrounded by O atoms from oxalate anions and H2O molecules, with cation layer composed of Ba2+ ions and H2O forming in the bc plane. Ba1 is surrounded by three O atoms from two oxalate anions in one Fe4O4 unit, one O atom from H2O molecule forming a bridge to Ba2, and seven terminal H2O molecules. Ba2 is surrounded by nine O atoms from five oxalate anions, which belong to five Fe4O4 units, and one O atom from H2O molecule. Ba3 is surrounded by three O atoms from three oxalate anions, two O atoms from two bridging H2O molecules, and four O atoms from four terminal H2O molecules. Ba4 is surrounded by six O atoms from four oxalate anion, two bridging H2O molecules which connect to Ba3 and two terminal H2O molecules. The cation
and anion layers are stacked alternatively along the a axis, as shown in Fig. 7. A three-dimensional heterometallic network is formed with Ba Ba, Ba Fe and Ba Fe connected by oxalate anion and H2O molecules. The conductivity measurements revealed that the crystal 1 and 2 behaved as insulator at room-temperature. These results were different to those reported for ternary A–Pt(C2O4)2–H2O compounds which behaved as molecular conductor [9]. The magnetic properties of compounds 1 and 2 were studied. Compound 1 exhibits paramagnetic behaviour from room-temperature to 2 K. At 300 K, the vT value was 4.45 cm3 K mol 1 (v is the magnetic susceptibility per Fe3+ ions). It is in the same range of an isolated, spin-only ion with S = 5/2 and g = 2.00 [18]. The vT value remained stable when the temperature was decreased from 300 K to 50 K. Below, the vT value decreased and reached 3.6 cm3 K mol 1 at 2 K. The susceptibility data above 2 K fit the Curie–Weiss law with C = 4.375(1) cm3 K mol 1, h = 0.52(2) K and R = 1.23 10 4. At 2 K, the isothermal magnetization saturated at 5 Nb. The small Weiss constant means a weak antiferromagnetic interaction between Fe3+ atoms. This result can be explained in terms of the isolated Fe(C2O4)33 well. At 300 K, the vT value of compound 2 was 1.10 cm3 K mol 1 (v is the magnetic susceptibility per Fe3+ ions). It is lower than 4.375 cm3 K mol 1 of an isolated, spin only Fe3+ ion, and in the range of [Fe4O(OH)3(O2CCH3)4(bpy)4](ClO4)3 [16]. The vT value decreased in a linear manner when the temperature was decreased, and reached 0.05 cm3 K mol 1 at 20 K, then the vT value decreased at a slow rate to ultimately reached 0.03 cm3 K mol 1 at 2 K. The data above 20 K was fitted with Fisher mode, J = 19.2(3) cm 1, g = 1.74(2), R = 7.34 10 5 [19]. This result indicates the occurrence of a strong antiferromagnetic interaction between the Fe3+ ions in four-member ring of compound 2. It is similar to the oxobridged four-, six-, eight, ten- and twelve-member Fe3+ rings compounds with a ground state of S = 0 [20]. The v valued decreased slowly when the temperature was decreased from room-temperature to 20 K, further reduction in the temperature below 20 K led to an increase of the v value. At 2 K, the isothermal magnetization increased with increasing field and reached a saturation level of 0.03 Nb at 40 kOe (Fig. 8, inset). This result indicated the existence of a small amount of a paramagnetic impurity, with the impurity being responsible for the rapid rise of magnetization with increasing field in the low field region at 2 K and v value increased below 20 K while the temperature was decreased.
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Fig. 7. Three-dimensional network formed by Ba2+ and Fe3+ connected by oxalate anion or H2O molecules in 2. Colour code: Ba Ba, light orange; Ba Fe, grey; Fe Fe, green. The occupation of Ba1, Ba2, Ba3 and Ba4 are 0.50, 1.0, 0.50 and 0.25. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
with colour, composition and structure changed and three-dimensional heterometallic framework were formed by oxalate anion and H2O molecules. 1 shows paramagnet, a strong antiferromagnetic interaction was observed in 2 as the ground state of S = 0. Acknowledgments This work was supported by NSFC 21173240, 973 project 2011CB932302, 2013CB933402, and XDB12030100, PR China. The X-ray diffraction experiment in BSRF 1W2B work station was supported by project 11090. Appendix A. Supplementary material
Fig. 8. vT vs. T plots of 1 and 2. Red solid line is fit of Fisher model. Inset, M–H plots at 2 K.
The differences in the magnetic behaviours of 1 and 2 can be readily explained in terms of their crystal structures. In 1, mononuclear Fe(C2O4)33 was surrounded by H2O and Ba2+, and the magnetic interaction between the Fe3+ ions was consequently inefficient. In 2, the Fe3+ ions were bridged by hydroxide groups which led to the observed antiferromagnetic interaction between the Fe atoms. Compound 2 could therefore be used to construct new molecular antiferromagnetic conductors, providing the isolated tetranuclear anion could be used as a counteranion for a chargetransfer salt and studied towards constructing these materials are currently underway in our laboratory. 4. Conclusion The compound 2 containing hydroxo/oxo bridged four-member ring [Fe4(OH)3O(C2O4)98 ] can be obtained from mononuclear [Fe(C2O4)33 ] compound 1 in solution of Ba2+, Fe3+, C2O24 and H2O
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[10] M. Kurmoo, A. Graham, P. Day, S. Coles, M. Hursthouse, J. Caulfield, J. Singleton, F. Pratt, W. Hayes, L. Ducasse, P. Guionneau, J. Am. Chem. Soc. 117 (1995) 12209. [11] (a) O. Minor, HKL DENZO, SCALPACK, Enraf-Nonius, The Netherlands, 1997; (b) CRYSTALCLEAR, Rigaku, Japan, 2008 [12] G. Sheldrick, SHELXL-97, University of Göttingen, Göttingen, Germany, 1997. [13] O. Kahn, Molecular Magnetism, John Wiley & Sons Inc., New York, 1993, p. 3. [14] Z. Duan, Y. Zhang, B. Zhang, D.B. Zhu, CrystEngComm 13 (2011) 6801. [15] (a) E. Merrachi, B. Mentzen, F. Chassagneus, J. Bouix, Rev. Chim. Miner. 24 (1987) 56; (b) J. Declercq, J. Feneau-Dupont, J. Ladriere, Polyhedron 12 (1993) 1031. [16] T.C. Stamatatos, A.G. Christou, C.M. Jones, B.J. O’Callaghan, K.A. Abboud, T.A. O’Brien, G. Christou, J. Am. Chem. Soc. 129 (2007) 9840. [17] (a) W. Armstrong, S. Lippard, J. Am. Chem. Soc. 106 (1984) 4632; (b) W. Scheidt, B. Cheng, M. Safo, F. Cukiernik, J. Marchon, P. Debrunner, J. Am. Chem. Soc. 114 (1992) 4420; (c) D. Evans, R. Mathur, K. Heerwegh, C. Reed, Z. Xie, Angew. Chem. Int. Ed. Engl. 36 (1997) 1335. [18] O. Kahn, Molecular Magnetism, John Wiley & Sons Inc., New York, 1993, p. 10. [19] T. Smith, S.A. Friedberg, Phys. Rev. 176 (1968) 660. [20] (a) R. Saalfrank, I. Bernt, E. Uller, F. Hampel, Angew. Chem. Int. Ed. Engl. 36 (1997) 2482; (b) A. Caneschi, A. Cornia, S.J. Lippard, Angew. Chem. Int. Ed. Engl. 34 (1995) 467; (d) K. Taft, C. Delfs, G. Papaefthymiou, S. Foner, D. Gatteschi, S. Lippard, J. Am. Chem. Soc. 116 (1994) 823; (d) A. Caneschi, A. Cornia, A. Fabretti, D. Gatteschi, Angew. Chem. Int. Ed. 38 (1999) 1295; (e) T. Liu, Y. Zhang, Z. Wang, S. Gao, J. Am. Chem. Soc. 130 (2008) 10500.
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Synthesis, crystal structures and characterization of two heterometallic compounds: Ba3[Fe(C2O4)3]2(H2O)12 and Ba4.5[Fe4O(OH)3(C2O4)8](H2O)19 Bin Zhang a,⇑, Yan Zhang b, Guangcai Chang c, Zengqiang Gao c, Dongwei Wang d, Daoben Zhu a a
OSL, BNLMS, CMS & Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China Institute of Condensed Matter and Materials Physics Department, Department of Physics, Peking University, Beijing 100871, PR China BSRF, Institute of High-Energy Physics, Chinese Academy of Sciences, Beijing 100047, PR China d National Centre for Nanoscience and Technology, Beijing 100190, PR China b c
a r t i c l e
i n f o
Article history: Received 16 April 2014 Received in revised form 21 June 2014 Accepted 1 July 2014 Available online 10 July 2014 Keywords: Iron Oxalate Hydroxo Oxo Magnetism
a b s t r a c t Heterometallic yellow compound Ba3[Fe(C2O4)3]2(H2O)12 (1) with mononuclear anion [Fe(C2O4)33 ] can be transformed to heterometallic red compound Ba4.5[Fe4O(OH)3(C2O4)8](H2O)19 (2) with OH/O bridged tetranuclear anion [Fe4O(OH)3(C2O4)98 ] in the mother liquor. Ba2+ and Fe3+ form three-dimensional networks thorough oxalate anion and H2O molecules in 1 and 2. 1 is a paramagnet and a strong antiferromagnetic interaction as the ground state S = 0 exists in 2. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The oxalate anion (C2O24 ) is an excellent ligand for metal ions, and the relationships between the crystal structures and physical properties of oxalate-based coordinated compounds, including their photochemical, magnetic and conductive properties, have been studied extensively [1]. The magnetic interactions between transition metal atoms bridged by oxalate units can lead to the formation of molecular crystals from long-range magnetic ordering magnet with dimensionality resulting from the one-dimensional chains, two-dimensional (2D) layers and three-dimensional (3D) metal–oxalate-frameworks, to quantum magnet as single molecular magnet and single chain magnet [2–5]. Oxo and hydroxo anions play important roles in molecular magnets, such as the crystal-tocrystal transformation from a hydroxo-bridged Fe(III) compound: {(C2H5NH3)[Fe2(C2O4)2](i-OH)}2H2O}n to a oxo-bridged Fe(III) compound: {(H3O)(C2H5NH3)[Fe2(C2O4)2Cl2(i-O)]H2O}n, where the colour of crystal changed from yellow to red and the canted angle of the spin changed, but the antiferromagnetic ordering temperature remained the same [6]. The 2D homometallic and heterometallic metal–oxalate-frameworks of transition metal atoms ⇑ Corresponding author. Tel.: +86 10 62558982. E-mail address: [email protected] (B. Zhang). http://dx.doi.org/10.1016/j.ica.2014.07.001 0020-1693/Ó 2014 Elsevier B.V. All rights reserved.
exhibit interesting magnetic properties, including the ferromagnetic compound [(n-C4H9)4N][CrMn(C2O4)3] and [(n-C4H9)4N] [NiV(C2O4)3]0.20{[(n-C4H9)4N](BF4)}0.20MeCN, the ferrimagnetic compound [(n-C4H9)4N][FeIIFeIII(C2O4)3], [C4H9)4N][MIIMnIII (C2O4)3] (MII = Fe, Co, Ni, Zn), and antiferromagnetic compounds [C4H9)4N][FeIIRuIII(C2O4)3], (Ammonium)[M2(C2O4)3] (M = Fe, Co) and Fe(C2O4)(CH3OH) [3,7]. Antiferromagnetic interactions were also observed in the 3D homometallic frameworks Mn(C2O4) (H2O)0.25 and [(C2H5)3NH]2[Cu2(C2O4)3] [4]. Compared with the homometallic and heterometallic 2D and 3D metal–oxalateframeworks of transition metal atoms, research towards the heterometallic 2D and 3D metal–oxalate-frameworks of main metal and transition metal atoms has been scare. When Li+ was used in this context with a transition metal, a 3D (10,3) network was obtained in [LiCr(C2O4)23 ], whereas a 2D (6,3) network was observed in [LiFe(C2O4)23 ] [8]. In terms of conductivity, the heterometallic ternary oxalate-based compounds A–M(C2O4)2–H2O, where A is an alkaline earth metal such as Mg2+, Ca2+, Sr2+, Ba2+, and the square-coordinate Pt(C2O4)22 anions show high levels of conductivity, for example, the room-temperature conductivity of Mg0.82[Pt(C2O4)2]5.3H2O was 0.2 S/cm [1,9]. Furthermore, the molecular semiconductor (BEDT–TTF)4KFe(C2O4)3(C6H5CN) (BEDT–TTF = bis(ethylenedithio)tetrathiafulvalene) was obtained when the 2D honeycomb anion [KFe(C2O4)23 ]n was used as
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counteranion [10]. Studies concerning the crystals structure, conductivity and magnetic properties of alkaline earth metal and octahedral-coordinate oxalate-based anions, however, remains scarce in the literature. Herein, we report the synthesis and characterization of two oxalate-based heterometallic compounds composed of Ba2+, Fe3+ ions.
were corrected for the diamagnetism of the sample using Pascal constants ( 190.75 10 6 emu/mol for compound 1 and 160.25 10 6 emu/mol for compound 2 for one Fe3+ unit in both cases) and corrected for background effects via the experimental measurement of the sample holder [13].
3. Results and discussion 2. Experimental All reagents were obtained from commercial sources and were used as received without further purification. The yellow and red block crystals of 1 and 2, respectively, were obtained using the diffusion method. A solution of BaCl22H2O (345.5 mg, 1.23 mmol) in H2O (20 mL) was placed in one arm of a H-cell, where a solution of [(C2H5)4N]3Fe(C2O4)3 (452.4 mg, 0.64 mmol) in H2O (20 mL) was placed in the other. After one week, yellow crystal (100 mg) of compound 1 had formed on the bottom and arm of cell. After 2-months, red crystals of 2 (200 mg) has formed on the arm and the bottom of cell. When 1 was soaking in mother solution, the colour of crystal changed from yellow to red slowly, and 2 was obtained at last after months. Elemental analysis (%) of 1: Anal. Calc. for C12H24Ba3Fe2O36 (1268.3): C, 11.37; H, 1.91. Exp.: C, 11.20; H, 1.92. Selected IR data (single crystal): 794(s), 853(w), 898(m), 1040(w), 1281(s), 1352(m), 1404(vs), 1631(vs), 1883(w), 2565(vw), 2857(s), 2928(s), 3369(br) cm 1. Elemental Anal. (%) of 2: Calc. for C16H41Ba4.5Fe4O55 (1954.93): C 9.83; H 2.11. Exp.: C, 9.90; H, 2.20. Selected IR data (single data): 740(m), 796(s), 853(w), 901(m), 1060(brw), 1266(s), 1284(s), 1348(m), 1407(s), 1638(bvs), 1883(vw), 2594(w), 2854(m), 2921(m), 3370(brs) cm 1. The Ba and Fe contents of 2 were found 2.21:2 by ICP. X-ray diffraction experiment was carried out on 1W2B working station in Beijing Synchrotron Radiation facility to check the quality of single crystal at first. X-ray diffraction data were collected on a Nonius Kappa CCD diffractometer with graphite monochromated Mo Ka (k = 0.71073 Å) radiation of 1 at room temperature and on a Rigaku M007HF diffractometer with focused Mo Ka (k = 0.71073 Å) radiation of 2 at 173 K [11]. The structures were solved by direct methods and refined by full-matrix least-square on F2 using a SHELX program, with anisotropic thermal parameters for all non-hydrogen atoms [12]. The hydrogen atoms of H2O molecules in 1 and 2 were omitted during refinement. The hydrogen atoms of OH in 2 were found by difference Fourier map and refined isotropically. The occupations of Ba and H in 2 were refined. Crystallographic data of 1: C12H24Ba3Fe2O36, F.W. = 1268.3, monoclinic, space group P21/c, a = 10.8416(1) Å, b = 17.6498(3) Å, c = 18.5049(3) Å, a = 90°, b = 92.707(1)°, c = 90°, V = 3537.00(9) Å3, Z = 4, Dcalc = 2.381 g cm 3, l = 4.213 mm 1, 16,479 measured data, 8409 unique, Rint = 0.0273, 487 parameters, R1 = 0.0295 for 6296 observation of I P 2r(I0), wR2 = 0.0779 for all data, Goodness-of-fit = 1.019. 2: C16H41Ba4.5Fe4O55, F.W. = 1954.93, orthorhombic, space group P nma, a = 19.885(4) Å, b = 18.906(4) Å, c = 13.727(3) Å, a = 90°, b = 90°, c = 90°, V = 5160.8(18) Å3, Z = 4, Dcalc = 2.516 g cm 3, l = 4.603 mm 1, 42 356 measured data, 6063 unique, Rint = 0.0608, 398 parameters, R1 = 0.0493 for 5998 observation of I P 2r(I0), wR2 = 0.1300 for all data, Goodness-of-fit = 1.115. Powder X-ray diffraction patterns were obtained on a Rigaku RINT 2000 diffractometer with Cu Ka radiation at roomtemperature. The conductivity measurements were carried out by the twoprobe method. Two gold wires were attached to two sides of the single crystal with gold paste. The I–V curve was measured by a Keithely 4200 SCS at room-temperature. Magnetization measurements were performed on polycrystalline samples, which were tightly packed into capsules on a Quantum Design MPMS 7XL SQUID system. Susceptibility data
The compounds Ba3[Fe(C2O4)3]2(H2O)12 (1) and Ba4.5[Fe4(OH)3 O(C2O4)8](H2O)19 (2) were obtained from same cell by diffusion method, but their compositions were different. The compound 1 existed as a dynamic phase, whereas 2 existed as the thermodynamically stable product in the mother liquors together with Ba2+, Fe3+, Cl , C2O24 and ammonium ions [14]. Crystal of 1 was obtained after few days. When yellow crystal of 1 remained in mother liquors at ambient temperature for weeks, its colour changed from yellow to red slowly. Crystal of 2 was the main product after months and stable in solution. This suggested that a transformation from yellow crystal 1 to red crystal 2 (Fig. 1) and compound 2 can be obtained from compound 1 in the solution of Ba2+, Fe3+, C2O24 and H2O. Compound 1 crystallizes in the monoclinic space group P21/c. There are three Ba2+, two Fe3+, six oxalate anions, ten H2O molecules and four of half H2O molecules in an independent unit. Each Fe3+ ion is octahedrally coordinated by six O atoms from three bidentate oxalate anions with mean Fe–O bond lengths in the range of 1.982(3)–2.040(2) Å as well as cis O–Fe–O bond angles in the range of 79.24(9)–80.86(9)°, 80.60(8)–81.1(1)° and trans O–Fe–O bond angles in the range of 162.2(1)–173.36(9)°, which is similar to those previously reported in the literature [8,15]. Two enantiomers of Fe(C2O4)33 are found in the crystal of 1, including the K enantiomer (Fe1) and D enantiomer (Fe2), the crystal is a racemate (Fig. 2). The main plane of the propeller-like mononuclear Fe1 is lying on the ac plane, whereas the main-plane of the propeller-like mononuclear Fe2 is lying on the (2 1 0) plane. Ba2+ ions are surrounded by O atoms from oxalate anions and H2O molecules. Ba1 exists in a cave formed by eight O atoms from four oxalate anions (two Fe1, two Fe2) and two O atoms from two H2O molecules. Ba2 sites in the cavity formed from two O atoms from one oxalate anion (Fe1), three O atoms from three oxalate anions (one Fe1 and two Fe2), two O atoms from two terminal H2O molecules and two O atoms from two bridged H2O molecules. Ba3 occupies the vacant position formed among five O atoms from five oxalate anions (three Fe1, two Fe2), three O atoms from three terminal H2O molecules and two O atoms from two bridged H2O molecules. Fe1 atom connects to one Ba1 atom through two O atoms (O11, O12) from one oxalate anion, two Ba2 atoms through two O atoms (O8; O7, O8) of one oxalate anion, two Ba3 atoms through two O atoms (O3; O3, O4) of one oxalate anion. Fe2 atom is connected to four Ba1 atoms through six O atoms (O15; O15, O16; O19, O20; O23, O24) on three oxalate anions, two Ba2 atoms through
Fig. 1. Morphologies of 1 and 2.
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Fig. 2. Configuration of anions in 1.
two O atoms (O16, O20) on two oxalate anions and one Ba3 atom through O19 (Fig. 3). Two Ba2 [4.7226(3) Å] atoms and two Ba3 [4.8658(3) Å] atoms arrange alternately to form a zigzag chain along the b axis with a Ba2 Ba3 distance of 5.2963(3) Å. These zigzag chains are connected by Ba1 along the c axis with Ba1 Ba2 and Ba1 Ba3 distances of 4.4809(3) and 4.5537(3) Å, respectively. A Ba layer with the Ba Ba distance less than 5.3 Å is formed in the bc plane (Figs. 4 and 5). Fe(C2O4)33 anions and H2O molecules exist in the cavities of Ba layers as shown in Fig. 3. Two of the metal layers are connected by oxalate anions between the Ba and Fe atoms from neighbouring layers along the a axis as shown in Fig. 5. Compound 2 crystallizes in the orthorhombic Pnma space group. The asymmetric unit consists of four Ba2+ (i.e., Ba1, Ba2, Ba3 and Ba4), two Fe3+ (Fe1, Fe2), four oxalate anion, one hydroxide ions, two of half hydroxide ions, and one H2O molecule (Fig. 6). The occupations of Ba1, Ba2, Ba3 and Ba4 atoms are 0.50, 1.0, 0.50 and 0.25, respectively. The Fe3+ ion is octahedrally coordinated by two O atoms from the hydroxide anion, and four O atoms from two bidentate oxalate anions. All of Fe atoms in the Fe4O4 core are coplanar. O17 and O18 are displaced from the metal plane on one side, O19 is displaced from the other side. Because all of the atoms on a single anion are related by a mirror plane through O17 and O19 atoms and perpendicular to the main plane of
Fig. 4. Metallic network in 1 on the bc plane. Colour code: Ba Ba, light orange, Ba Fe grey. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fe4O4 core, half of atoms on one tetranuclear anion [Fe4O(OH)3 (C2O4)98 ] exist in an independent unit. The occupations of H17, H18 and H19 on bridged hydroxide are 0.5, 0.5 and 0.5. The configuration of Fe4O4 core is similar as [Fe4O(OH)3(O2CCH3)4(bpy)4] (ClO4)3 [16]. The Fe–O bond distances from the Fe ion to the O atoms of the oxalate anions are in the range of 2.022(4)– 2.125(4) Å (Fe1) and 2.033(4)–2.096(4) Å (Fe2), whereas the Fe–O bond distances from the Fe ion to the O atoms of the hydroxide anion are shorter. Fe1–O18 1.879(4) Å, Fe2–O18 1.879(4) Å is shorter than Fe1–O17 1.946(2) Å and Fe2–O19 1.984(2) Å because O18 is composed of half of OH and half of O2 . The Fe–O(H) bond
Fig. 3. Crystal structure of 1 viewed along the a axis. The H atoms have been omitted for clarity. Colour code: Ba–O, orange; Fe–O, C–O and C–C, white. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 5. Three-dimensional network formed by Ba2+ and Fe3+ in 1 connected by oxalate anion or H2O. Colour code: Ba Ba, light orange; Ba Fe, grey. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 6. Configuration of anion in 2. The occupation of H atom bonded to O18 is 0.5.
lengths are in the range of the reported value, for example, the Fe–O(H) distances are in the range of 1.942–1.952 Å in {[Fe(OEP)2]2(OH)}+, whereas the Fe–O(H) bond distances in [(tpp)Fe–O(H)–Fe(tpp)]+ and [Fe2(OH)(O2CCH3)2(HB(pz)3)2]+ are 1.92(3) Å, and 1.960(4) Å and 1.952(4) Å, respectively [17]. The Fe–O(H)–Fe bond angles are 135.1(3)° (O17), 140.5(2)° (O18) and 132.7(3)° (O19), whereas the O(H)–Fe–O(H) bond angles are 93.0(2)° (Fe1) and 93.6(2)° (Fe2). The sum of the angles of the Fe4O4 core is 1080°. The Ba2+ ions are surrounded by O atoms from oxalate anions and H2O molecules, with cation layer composed of Ba2+ ions and H2O forming in the bc plane. Ba1 is surrounded by three O atoms from two oxalate anions in one Fe4O4 unit, one O atom from H2O molecule forming a bridge to Ba2, and seven terminal H2O molecules. Ba2 is surrounded by nine O atoms from five oxalate anions, which belong to five Fe4O4 units, and one O atom from H2O molecule. Ba3 is surrounded by three O atoms from three oxalate anions, two O atoms from two bridging H2O molecules, and four O atoms from four terminal H2O molecules. Ba4 is surrounded by six O atoms from four oxalate anion, two bridging H2O molecules which connect to Ba3 and two terminal H2O molecules. The cation
and anion layers are stacked alternatively along the a axis, as shown in Fig. 7. A three-dimensional heterometallic network is formed with Ba Ba, Ba Fe and Ba Fe connected by oxalate anion and H2O molecules. The conductivity measurements revealed that the crystal 1 and 2 behaved as insulator at room-temperature. These results were different to those reported for ternary A–Pt(C2O4)2–H2O compounds which behaved as molecular conductor [9]. The magnetic properties of compounds 1 and 2 were studied. Compound 1 exhibits paramagnetic behaviour from room-temperature to 2 K. At 300 K, the vT value was 4.45 cm3 K mol 1 (v is the magnetic susceptibility per Fe3+ ions). It is in the same range of an isolated, spin-only ion with S = 5/2 and g = 2.00 [18]. The vT value remained stable when the temperature was decreased from 300 K to 50 K. Below, the vT value decreased and reached 3.6 cm3 K mol 1 at 2 K. The susceptibility data above 2 K fit the Curie–Weiss law with C = 4.375(1) cm3 K mol 1, h = 0.52(2) K and R = 1.23 10 4. At 2 K, the isothermal magnetization saturated at 5 Nb. The small Weiss constant means a weak antiferromagnetic interaction between Fe3+ atoms. This result can be explained in terms of the isolated Fe(C2O4)33 well. At 300 K, the vT value of compound 2 was 1.10 cm3 K mol 1 (v is the magnetic susceptibility per Fe3+ ions). It is lower than 4.375 cm3 K mol 1 of an isolated, spin only Fe3+ ion, and in the range of [Fe4O(OH)3(O2CCH3)4(bpy)4](ClO4)3 [16]. The vT value decreased in a linear manner when the temperature was decreased, and reached 0.05 cm3 K mol 1 at 20 K, then the vT value decreased at a slow rate to ultimately reached 0.03 cm3 K mol 1 at 2 K. The data above 20 K was fitted with Fisher mode, J = 19.2(3) cm 1, g = 1.74(2), R = 7.34 10 5 [19]. This result indicates the occurrence of a strong antiferromagnetic interaction between the Fe3+ ions in four-member ring of compound 2. It is similar to the oxobridged four-, six-, eight, ten- and twelve-member Fe3+ rings compounds with a ground state of S = 0 [20]. The v valued decreased slowly when the temperature was decreased from room-temperature to 20 K, further reduction in the temperature below 20 K led to an increase of the v value. At 2 K, the isothermal magnetization increased with increasing field and reached a saturation level of 0.03 Nb at 40 kOe (Fig. 8, inset). This result indicated the existence of a small amount of a paramagnetic impurity, with the impurity being responsible for the rapid rise of magnetization with increasing field in the low field region at 2 K and v value increased below 20 K while the temperature was decreased.
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Fig. 7. Three-dimensional network formed by Ba2+ and Fe3+ connected by oxalate anion or H2O molecules in 2. Colour code: Ba Ba, light orange; Ba Fe, grey; Fe Fe, green. The occupation of Ba1, Ba2, Ba3 and Ba4 are 0.50, 1.0, 0.50 and 0.25. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
with colour, composition and structure changed and three-dimensional heterometallic framework were formed by oxalate anion and H2O molecules. 1 shows paramagnet, a strong antiferromagnetic interaction was observed in 2 as the ground state of S = 0. Acknowledgments This work was supported by NSFC 21173240, 973 project 2011CB932302, 2013CB933402, and XDB12030100, PR China. The X-ray diffraction experiment in BSRF 1W2B work station was supported by project 11090. Appendix A. Supplementary material
Fig. 8. vT vs. T plots of 1 and 2. Red solid line is fit of Fisher model. Inset, M–H plots at 2 K.
The differences in the magnetic behaviours of 1 and 2 can be readily explained in terms of their crystal structures. In 1, mononuclear Fe(C2O4)33 was surrounded by H2O and Ba2+, and the magnetic interaction between the Fe3+ ions was consequently inefficient. In 2, the Fe3+ ions were bridged by hydroxide groups which led to the observed antiferromagnetic interaction between the Fe atoms. Compound 2 could therefore be used to construct new molecular antiferromagnetic conductors, providing the isolated tetranuclear anion could be used as a counteranion for a chargetransfer salt and studied towards constructing these materials are currently underway in our laboratory. 4. Conclusion The compound 2 containing hydroxo/oxo bridged four-member ring [Fe4(OH)3O(C2O4)98 ] can be obtained from mononuclear [Fe(C2O4)33 ] compound 1 in solution of Ba2+, Fe3+, C2O24 and H2O
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