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Molecular iron clusters, wheels and cages: Syntheses, structural aesthetics and magnetic properties
Inorganic Chemistry Communications 14 (2011) 337–342
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Mini-Review
Molecular iron clusters, wheels and cages: Syntheses, structural aesthetics and magnetic properties Anup Kumar Dutta, Rajarshi Ghosh ⁎ Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
a r t i c l e
i n f o
Article history: Received 12 August 2010 Accepted 3 November 2010 Available online 21 November 2010
a b s t r a c t Structural features and synthetic strategies of iron clusters, wheels and cages of nuclearities from 6 to 64 are discussed. Synthetic methodologies are categorized in a few groups. Magnetic behaviours of the polynuclear iron species are also highlighted. © 2010 Elsevier B.V. All rights reserved.
Keywords: Iron clusters Wheels and cages Syntheses Structures Magnetic properties
Contents Introduction . . . . . . . . . . . . . . . . . . . . . Syntheses and structures . . . . . . . . . . . . . . . Template synthesis of purely inorganic iron clusters Hydrolysis to iron clusters . . . . . . . . . . . . Metathesis reaction . . . . . . . . . . . . . . . Methanolysis and phenolysis route to iron clusters . Hierarchical assembly of iron clusters . . . . . . . Magnetic behaviour . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . .
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Introduction In recent years polyoxometallates have become the focus of intensive research activity since this class of inorganic compounds exhibits an enormous variety of structures as well as magnetic properties [1,8–38]. Actually these systems often are excellent practical realizations of nanomagnets, with properties changing gradually from those of simple paramagnets to those of bulk magnets. A particular aesthetic class covers the iron cluster compounds denoted as iron wheels and cages (Figs. 1 and 2). Single strand
⁎ Corresponding author. Tel.: +91 342 2533913x424; fax: +91 342 2530452. E-mail address: [email protected] (R. Ghosh). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.11.007
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molecular wheels [2] of paramagnetic 3d metals are of growing interest for reasons such as their high symmetry, which makes them good model systems of the study of one dimensional magnetism [3], magnetic anisotropy and quantum effects such as coherent tunneling of the Neel vectors [4] as a result a growing number of Mx (x ≥ 8) molecular wheels are being studied. There are, however, relatively few other 3d Mx loop-like closed topologies [5] when compared to those containing diamagnetic 4d and 5d metals such as Pd, Pt, Au, etc., or metal–metal-bonded M2 repeating units [5]. These span a variety of metals and ligands and have resulted in a wide range of loop and multi-loop structures, from squares, rectangles, boxes, etc., to complicated three-dimensional polyhedra [6]. In addition their inherent properties, such species are also potential building blocks for molecular nanodevices [7].
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model complexes for protein active sites [10]. Iron-oxo centres are found in several non-heme metalloproteins as for example hemerythrin, ribonucleotide reductase and methane monooxygenase. In most living organisms iron is stored in the protein ferritin which can contain upto 4500 FeIII ions in a polymeric oxohydroxo lattice [11]. High nuclearity transition metal clusters with appropriate topologies can sometimes cause large ground-state spin (S) values and can even occasionally function as Single Molecule Magnets (SMMs) [12]. In addition to these, there is a possible functional analogy in terms of host–guest interaction(s) between the iron(III) rings and crown ethers [13]. The alkali metal ions as guests on hexanuclear iron(III) rings can vary the extent of magnetic coupling between the metal ions, thus providing an important tool for the modulation of the properties of molecular magnets [13]. To date, a series of polynuclear ferric aggregates with different nuclearities [8–37] and a very recent Fe64 aggregates have been reported [14] (Fig. 2). Numerous naturally occurring iron oxide minerals with extended structures are also known [15]. Here in this short review we shall discuss synthetic strategies, structural beauties as well as similarities with organic crown ethers, unusual magnetic properties and host–guest chemistry of iron aggregates. Fig. 1. The iron atoms are in red, oxygen in yellow, carbon in grey and chlorine in green (taken from Ref. [1]).
Syntheses and structures Analogous access to a greater range of loop-like closed topologies or paramagnetic 3d metals would often benefits to a variety of spectroscopic, electrochemical, magnetic and host–guest binding studies. The decanuclear wheel [Fe10{(OMe)2(O2CCH2Cl)}10] reported by Lippard et al. [8] may be regarded as the prototype of this class [9]. Ferric systems represent an important subfamily of polynuclear aggregates and attract much attention owing to their relevance as
Fig. 2. The structure of Fe64 cubic cage (a and b). Top and side view of the Fe8 corner. Atomic scheme: Fe, large green (peripheral) and yellow (central) spheres; O, small red and purple (the three μ4-O2-) spheres; N, blue spheres; C, grey spheres (taken from Ref. [14]).
Template synthesis of purely inorganic iron clusters Almost all wheel compounds were originally prepared serendipitously, but methods of deliberately altering the wheel size after the initial synthesis are very few and all based on a template approach. Saalfrank et al. [16] elegantly showed that the size of certain Fex wheels could be controlled by the central Group 1 metal ion template around which the wheel forms, thus giving {Fe6M} for M = Li+ or Na+, but {Fe8M} for M = Cs+. Similarly, Winpenny, Timco and co-workers found that the organic amine template controls the nuclearity of the Mx (x = 8–10) homo- or heterometallic wheels [17]. Rao et al. has reported diethylenetriamine [H2N(CH2)2NH(CH2)2NH2] templated [FeII9F18(SO4)6]12− ferric wheel [18] (Fig. 3). Because almost all single-strand wheels are of nuclearity 12 or less and because a template approach is much less feasible for larger wheels (since it requires a correspondingly larger template). Alternative means of modifying the wheel size is sought for by Christou et al. [19]. They report a non-template route for reversibly interconverting the Fe wheels between M10 and M18.
Fig. 3. ORTEP plot of [C16N12H64][FeII9F18(SO4)6]0.9H2O (from Ref. No. [18]).
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Hydrolysis to iron clusters Hydrolysis of iron salts in the presence of carboxylate groups, with or without other chelating ligands, has proven to be a very useful method for obtaining both oxide- and hydroxide containing clusters. This approach has resulted in a number of compounds with diverse nuclearities and Fex topological arrangements. Ligand heidi [(H3heidi =N(CH2COOH)2(CH2CH2OH)] in different controlled hydrolysis reactions of iron(III) two different compounds with nuclearities 2 and 36 are reported by Powell et al. [20]. A number of polynuclear wheels are synthesized using the process of hydrolysis by Weighardt et al. [21] (Fig. 4) and Raptopoulou et al. [22]. Metathesis reaction A very common approach for obtaining alkoxide-containing compounds has been the metathesis reaction between iron salts and metal alkoxides. Some examples include the use of lithium methoxide for the synthesis of the iron alkoxide cube [Fe4(OMe)5(MeOH)3 (O2CPh)4] [23], [LiFe6(OCH3)12(dbm)6] [Hdbm = 1,3-diphenyl-1,3propanedione(dibenzoylmethane)] [13a] (Fig. 5), potassium or cesium methoxide for the preparation of [Fe(OMe)2(dbm)]12 [24], and sodium ethoxide for the preparation of [Fe9O3(OEt)21] [25]. Very recently, a similar reaction was reported that employed aluminum alkoxides in a reaction with a preformed cluster rather than a simple iron salt. In this way, [Fe4O2(O2CPh)8(py)2] was converted with Al (OR)3 (R = Pri, Bu) to the hexanuclear product [Fe6O2(OR)8(O2CPh)6] [26]. Methanolysis and phenolysis route to iron clusters Chirstou et al. reported this novel route to iron clusters (one representative figure is given in Fig. 6) in the year 2003 [27]. The work described there continues using preformed Fe4 and Fe6 compounds as starting materials. We have also explored for the first time the use of the aromatic alcohol PhOH in such reactions and compared the products obtained from a given alcoholysis reaction when the alcohol is either MeOH or PhOH. PhOH was chosen primarily because of its
Fig. 4. Molecular structure of a trinuclear wheel (from Ref. [21]).
Fig. 5. ORTEP plot of a hexanuclear ferric wheel (from Ref. [13a]).
relative bulkiness and acidity (pKa = 9.98 vs 15.5 for MeOH). The latter property makes PhOH an attractive reagent, because an early step in the alcoholysis reaction of Fex clusters likely involves proton transfer from the alcohol to a bound ligand. Although phenol is a widely used substance, there are very few examples of phenoxide as a ligand in iron chemistry. For example, the only crystallographically characterized compounds containing Fe bound phenoxide groups are a small number of iron–sulfur clusters [28] and two porphyrin-based mononuclear compounds [29].
Hierarchical assembly of iron clusters Hierarchical materials can be regarded as systems in which small units are incorporated into larger superstructures. In a recent report to synthesize Fe13 oxygen bridged clusters by Powell et al. [30] (Fig. 7)
Fig. 6. One decanuclear ferric wheel (from Ref. [27]).
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(FeA–O + FeB–O)/2. When multiple atom bridges like carboxylates are present, only the Fe–O(bridge) distances are taken into account to calculate the average length of the interaction pathway. The correlation established from 36 sets of experimental data is: −1 10 = −1:753 × 10 exp −12:663 P ) J cm The coupling constant is largely insensitive to the Fe–O–Fe angle for α N 120° [33]. For smaller angles an effect is clearly observed, J becoming smaller as the angle α is reduced. A systematic study has been performed in a series of binuclear complexes with two alkoxobridges [33] and similar Fe–O distances. The values of α range from 102 to 106°, while J varies between ca. 15 and 21 cm− 1. The simplest correlation was found to be of the type given by the following equation: −1 = 1:48αðdegÞ−135 J cm
Fig. 7. Molecular structure of Fe13 cluster (from Ref. [30]).
the conceptual hierarchy begins at the atomic level with FeIII ions in water in the form of the hexaaqua ion [Fe(H2O)6]3+. It is observed that supply of tripodal chelating ligands of the general form N(RCOOH)2R′ (in which R′ can be any organic residue) to such solutions can halt this process through the stabilization of captured intermediate phases composed of close-packed cores, which are portions of the brucite structure (exemplified by Mg(OH)2) encased in a shell of the ligand units. In the hydrolysis process, we can imagine the starting point (first generation) to be a hexaaqua metal ion which will link to six further metal ions (second generation) on production of the hexahydroxo metal ion, and the process will continue through production of the hydroxide ions and coordination to a further six metal centres (third generation), then twelve (fourth generation), and so on. Similar type of syntheses to generate iron(III) structures from a small precursor is tabulated below: Small unit (precursor)
Large resulting molecule
Reference
[Fe3O(O2CPh)6(H2O)3]Cl
[Fe12(μ2-O)4(μ3O)4(O2CPh)14 (C10H17PO3H)6] [C10H17PO3H = camphyl phosphor-nic acid] [Fe9(O)2(OH)(O2CPh)10 (C10H17PO3H)6(H2O)2](CH3CN)7 [Fe3(μ3-O)(μ-OAc)6(H2O)3] [Fe3(μ3-O)(μ-OAc)7.5(H2O)2].7H2O [Fe(OMe)2(O2CCH2Cl)]10
[12a]
[Fe3O(O2CPh)6(H2O)3]Cl [Fe3O(OAc)6(H2O)3]Cl.6H2O [Fe3O(O2CCH2Cl)6 (H2O)3](NO3).4H2O
Extended Huckel calculation indicate that [1] for small angles (~ 90°) the coupling should become antiferromagnetic due to importance of direct overlap between the iron(III) magnetic orbitals. The discovery that individual molecules can function as magnets provided a new ‘bottom-up’ approach to nanoscale magnetic materials and such molecules have since been called Single Molecule Magnets (SMMs). Each molecule is a single-domain magnetic particle that below its blocking temperature exhibits the classical macroscale property of a magnet, viz. magnetization hysteresis. In addition, SMMs straddle the classical/quantum interface in also displaying quantum tunneling of magnetization (QTM), quantum phase interference, etc., the properties of microscale. At the beginning of the 1990s it was discovered [34] that a molecule, comprising 12 Mn ions, and characterized by a ground-state S = 10 [Mn12O12(CH3COO)16(H2O)4] (Mn12ac) shows slow relaxation of magnetization at low temperature (of the order of months at 2 K). Under these conditions a single molecule becomes like a tiny magnet, in the sense that if magnetized by an external field it retains magnetization for days. In fact it gives rise to magnetic hysteresis, which is one condition for storing
[37] [12b] [31]
Magnetic behaviour The exchange interactions in oxobridged iron(III) pairs have been much investigated both theoretically and experimentally, also due to the relevance of these systems to non-heme metalloproteins containing binuclear iron units in their active sites [32]. An interesting correlation concerns [3] the dinuclear Fe(III) centres bridged by a ligand oxygen atom like oxo, hydroxo, alkoxo and at least one other bridging ligand, in general carboxylate, but also sulphate or phosphate. In all these cases, the interaction is antiferromagnetic. The J interaction parameter has been found to correlate with a P parameter defined as half of the shortest interaction pathway i.e.,
Fig. 8. Schematic structure of Fe8 (taken from Ref. [35]).
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information in a particle. Under this respect, therefore, Mn12ac behaves like a classical magnet. These molecules are often called SMMs and Mn12ac was the first SMM isolated synthetically. The second molecule that has been intensively investigated for its SMM behaviour is commonly indicated as Fe8 [35]. The formula is [Fe8O2 (OH)12(tacn)6]Br8 (tacn = 1,4,7-triazacyclononane) (Fig. 8) and comprises an octanuclear cation [36]. From magnetic point of view, this structure gives rise to spin frustration effects which make the prediction of ground-state spin arrangement difficult. The temperature dependence of χT clearly indicates a ferromagnetic behaviour with an S = 10 ground-state [21], confirmed by high-field magnetization measurements. At the simplest possible approach, the groundstate can be justified by putting six S = 5/2 spin up and two down (Fig. 8). Antiferromagnetic rings of different size, but so far only even membered, have been reported. This is a pity because in odd membered rings spin frustration effects might be observed, giving rise to a rich spin dynamics. Interesting quantum effects have been observed in antiferromagnetic rings, of the type [Fe10(OMe)2(CH2ClCOO)10](Fe10), the so called ferric wheel [37]. Below 1 K, Fe10 is in the ground S = 0 state, so that the low-field magnetization is zero. However, on increasing the field the excited states with S N 0 rapidly decrease their energies, and a crossover between the ground states S = 0 and S = 1 is observed as a step in the magnetization curve. At higher fields analogous crossovers occur, for example between S = 2 and S = 1 and, in strong pulsed fields, it was possible to observe the crossover to an S = 9 ground state. The position of the steps provides information on the energy separation of the excited states in zero field, assuming that the g values are known, a reasonable assumption for iron(III) compounds. The stepped magnetization indicates the appearance of the quantum size effects in molecular clusters on a macroscopic scale. However, if the same measurements are performed on [Mo 7 2 Fe 3 0 O 2 5 2 {Mo 2 O 7 (H 2 O)} 2 {Mo 2 O 8 H 2 (H 2 O)} (CH3COO)12(H2O)91].150H2O (Fe30), completely different results are observed [38]. The molybdenum ions are diamagnetic, therefore the magnetic properties are associated with the 30 iron(III) ions which are located on the vertices of an icosidodecahedron. Because of the geometry of the spin sites and the antiferromagnetic exchange, spin frustration and competing ordered states are expected to occur. The temperature dependence of the magnetic susceptibility gave (using classical spins) J ~ 1.6 K, and the field dependence of the magnetization did not show any quantum size effect down to 0.46 K. The linear increase in magnetization for Fe30 is characteristic of an antiferromagnet. This situation suggests that for Fe30 the spin levels define a quasicontinuum and quantum effects are only expected to show up below 100 mK. In this sense Fe30 can be considered as a tiny antiferromagnet, exactly as Mn12ac can be considered as a tiny ferrimagnet. Several features of these antiferromagnetic rings are as yet not completely understood.
Conclusion Now in short, we can conclude that synthesis and characterization of iron clusters are of utmost importance because of their SMM behaviour, relevance as model complexes for protein active site(s), etc. To prepare SMMs with high blocking temperatures, the number of coupled spins and interactions among them in a molecule should be increased. In this target ferrimagnetic approach, i.e., assembling either different antiferromagnetically coupled spins or different number of antiferromagnetically coupled spins is the easiest way as strong ferromagnetic coupling is rather difficult to develop. Possible applications of magnetic clusters range from magnetic storage media, magnetic drug delivery, contrast agents for magnetic resonance imaging (MRI) to quantum computing. In all these aspects iron aggregates may be a potential candidate.
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Acknowledgements We sincerely thank all the Hon'ble Reviewers of this manuscript for their valuable suggestions to develop the quality of this review.
References [1] D. Gatteschi, R. Sessoli, A. Cornia, Chem. Commun. (2000) 725. [2] (a) R.E.P. Winpenny, in: J.A. McCleverty, T.J. Thomas (Eds.), Comprehensive Coordination Chemistry II, vol. 7, Elsevier, Oxford, 2004, pp. 125–1768, (b); (d) 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. [3] O. Kahn, Molecular Magnetism, VCH Publishers, New York, 1993. [4] F. Meier, D. Loss, Phys. Rev. Lett. 86 (2001) 5373. [5] (a) J.-M. Lehn, Supramolecular Chemistry, VCH Publishers, New York, 1995; (b) M. Fujita, Chem. Soc. Rev. 27 (1998) 417; (c) S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 100 (2000) 853; (d) F.A. Cotton, C. Lin, C.A. Murillo, Acc. Chem. Res. 34 (2001) 759. [6] Q.-H. Yuan, L.-J. Wan, H. Jude, P.J. Stang, J. Am. Chem. Soc. 127 (2005) 16279. [7] S.I. Stupp, Guest Editor. Thematic Issue: Functional Nanostructures. Chem. Rev. 105 (2005) 1023. [8] K.L. Taft, S.J. Lippard, J. Am. Chem. Soc. 112 (1990) 9629. [9] O. Waldmann, R. Koch, S. Schromm, J. Schu1lein, P. Mu1ller, I. Bernt, R.W. Saalfrank, F. Hampel, E. Balthes, Inorg. Chem. 40 (2001) 2986. [10] Z.-M. Zhang, Y.-G. Li, S. Yao, E.-B. Wang, Y.-H. Wang, R. Clerac, Angew. Chem. Int. Ed. 48 (2009) 1581. [11] (a) E.Y. Tshuva, S.J. Lippard, Chem. Rev. 104 (2004) 987; (b) M. Costas, M.P. Mehn, M.P. Jensen, L. Que Jr., Chem. Rev. 104 (2004) 93; (c) K.N. Ferreira, T.M. Iverson, K. Maghlaoui, J. Barber, S. Iwata, Science 303 (2004) 1831; (d) A. Mishra, W. Wernsdorfer, K.A. Abboud, G. Christou, Chem. Commun. (2005) 54. [12] (a) S. Konar, A. Clearfield, Inorg. Chem. 47 (2008) 5573; (b) Y.Z. Zheng, M.L. Tong, W. Xue, W.X. Zhang, X.M. Chen, F. Grandjean, G.J. Long, Angew. Chem. Int. Ed. 46 (2007) 6076; (c) M. Moragues-Canovas, E. Riviere, L. Ricard, C. Paulsen, W. Wernsdorfer, G. Rajaraman, E.K. Brechin, T. Mallah, Adv. Mater. 16 (2004) 1101; (d) C.F. Wang, J.L. Zuo, B.M. Bartlett, Y. Song, J.R. Long, X.Z. You, J. Am. Chem. Soc. 128 (2006) 7162; (e) G.W. Powell, H.N. Lancashire, E.K. Brechin, D. Collison, S.L. Heath, T. Mallah, W. Wernsdorfer, Angew. Chem. Int. Ed. 43 (2004) 5772. [13] (a) G.L. Abbati, A. Cornia, A.C. Fabretti, W. Malavasi, L. Schenetti, A. Caneschi, D. Gatteschi, Inorg. Chem. 36 (1997) 6443; (b) A. Caneschi, A. Cornia, S.J. Lippard, Angew. Chem. Int. Ed Engl. 34 (1995) 467. [14] T. Liu, Y.-J. Zhang, Z.-M. Wang, S. Gao, J. Am. Chem. Soc. 130 (2008) 10500. [15] C.M. Flynn Jr., Chem. Rev. 84 (1984) 31. [16] R.W. Saalfrank, I. Bernt, E. Uller, F. Hampel, Angew. Chem. Int. Ed Engl. 36 (1997) 2482. [17] (a) G.A. Timco, A.S. Batsanov, F.K. Larsen, C.A. Muryn, J. Overgaard, S.J. Teate, R.E.P. Winpenny, Chem. Commun. (2005) 3649; (b) R.H. Laye, F.K. Larsen, J. Overgaard, C.A. Muryn, E.J.L. McInnes, E. Rentschler, V. Sanchez, H.U. Gudel, O. Waldmann, G.A. Timco, R.E.P. Winpenny, Chem. Commun. (2005) 1125. [18] J.N. Behera, C.N.R. Rao, Inorg. Chem. 45 (2006) 9475. [19] P. King, T.C. Stamatatos, K.A. Abboud, G. Christou, Angew. Chem. Int. Ed. 45 (2006) 7379. [20] A.K. Powell, S.L. Heath, D. Gatteschi, L. Pardi, R. Sessoli, G. Spina, F. Del Giallo, F. Pierallill, J. Am. Chem. Soc. 117 (1995) 2491. [21] C. Delfs, D. Gatteschi, L. Pardi, R. Sessoli, K. Wieghardt, D. Hade, Inorg. Chem. 32 (1993) 3099. [22] C.P. Raptopoulou, V. Tangoulis, E. Devlin, Angew. Chem. Int. Ed. 41 (2002) 2386. [23] K.L. Taft, A. Caneschi, L.E. Pence, C.D. Delfs, G.C. Papaefthymiou, S.J. Lippard, J. Am. Chem. Soc. 115 (1993) 11753. [24] G.L. Abbati, A. Caneschi, A. Cornia, A.C. Fabretti, D. Gatteschi, Inorg. Chim. Acta 297 (2000) 291. [25] M. Veith, F. Gratz, V. Huch, Eur. J. Inorg. Chem. 2 (2001) 367. [26] P.S. Ammala, S.R. Batten, J.D. Cashion, C.M. Kepert, B. Moubaraki, K.S. Murray, L. Spiccia, B.O. West, Inorg. Chim. Acta 331 (2002) 90. [27] C. Canada-Vilalta, T.A. O'Brien, M. Pink, E.R. Davidson, G. Christou, Inorg. Chem. 42 (2003) 7819. [28] (a) B.K. Teo, M.R. Antonio, R.H. Tieckelmann, H.C. Silvis, B.A. Averill, J. Am. Chem. Soc. 104 (1982) 6126; (b) W.E. Cleland, D.A. Holtman, M. Sabat, J.A. Ibers, G.C. DeFotis, B.A. Averill, J. Am. Chem. Soc. 105 (1983) 6021; (c) M.G. Kanatzidis, N.C. Baenziger, D. Coucouvanis, A. Simopoulos, A. Kostikas, J. Am. Chem. Soc. 106 (1984) 4500. [29] (a) H. Nasri, J. Fischer, R. Weiss, E. Bill, A. Trautwein, J. Am. Chem. Soc. 109 (1987) 2549; (b) M.P. Byrn, C.J. Curtis, Y. Hsiou, S.I. Khan, P.A. Sawin, S.K. Tendick, A. Terzis, C.E. Strouse, J. Am. Chem. Soc. 115 (1993) 9480. [30] M. Murugesu, R. Clerac, W. Wernsdorfer, C.E. Anson, A.K. Powell, Angew. Chem. Int. Ed. 44 (2005) 6678.
342
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[31] K.L. Taft, C.D. Delfs, G.C. Papaefthymiou, S. Foner, D. Gatteschi, S.J. Lippard, J. Am. Chem. Soc. 116 (1994) 823. [32] (a) D.M. Kurtz, Chem. Rev. 90 (1990) 585; (b) S.M. Gorun, S.J. Lippard, Inorg. Chem. 30 (1991) 1625. [33] F.L. Gall, F.F. de Biani, A. Caneschi, P. Cinelli, A. Cornia, A.C. Fabretti, D. Gatteschi, Inorg. Chim. Acta 262 (1997) 123. [34] (a) A. Caneschi, D. Gatteschi, R. Sessoli, A.-L. Barra, L.C. Brunet, M. Guillot, J. Am. Chem. Soc. 113 (1991) 5873; (b) R. Sessoli, D. Gatteschi, A. Caneschi, M.A. Novak, Nature 365 (1993) 141. [35] D. Gatteschi, R. Sessoli, Angew. Chem. Int. Ed. 42 (2003) 268. [36] K. Wieghardt, K. Pohl, I. Jibril, G. Huttner, Angew. Chem. Int. Ed. 23 (1984) 77. [37] K.L. Taft, C.D. Delfs, G.C. Papaefthymiou, S. Foner, D. Gatteschi, S.J. Lippard, J. Am. Chem. Soc. 116 (1994) 823. [38] A. Muller, M. Luban, C. Schroder, R. Modler, P. Kogerler, M. Axenovich, J. Schnack, P. Canfield, S. Bud'ko, N. Harrison, ChemPhysChem 2 (2001) 517.
Dr. Rajarshi Ghosh was born in the year 1979 in Barrackpore, the famous historical town in India. After completion of his graduation and post graduation studies in Chemistry from the University of Kalyani, he completed his doctoral research in the department of Chemistry, the University of Burdwan under the supervision of Prof. B. K. Ghosh in the year 2007. From 2007-2008 he worked as post-doctoral fellow under Prof. Ghosh in Burdwan. In 2008 he joined as a Lecturer in the same department from where he obtained his doctoral degree. Right now he is completely involved in post graduation teaching and research. His research interest covers synthetic coordination chemistry, supramolecular chemistry, molecular magnetism, etc.
Anup Kumar Dutta was born in 1986 in Purulia in India. He completed his graduation and post graduation from the University of Burdwan. During his post graduation studies he worked with Dr. Rajarshi Ghosh in the field of polynuclear iron chemistry.
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Inorganic Chemistry Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i n o c h e
Mini-Review
Molecular iron clusters, wheels and cages: Syntheses, structural aesthetics and magnetic properties Anup Kumar Dutta, Rajarshi Ghosh ⁎ Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
a r t i c l e
i n f o
Article history: Received 12 August 2010 Accepted 3 November 2010 Available online 21 November 2010
a b s t r a c t Structural features and synthetic strategies of iron clusters, wheels and cages of nuclearities from 6 to 64 are discussed. Synthetic methodologies are categorized in a few groups. Magnetic behaviours of the polynuclear iron species are also highlighted. © 2010 Elsevier B.V. All rights reserved.
Keywords: Iron clusters Wheels and cages Syntheses Structures Magnetic properties
Contents Introduction . . . . . . . . . . . . . . . . . . . . . Syntheses and structures . . . . . . . . . . . . . . . Template synthesis of purely inorganic iron clusters Hydrolysis to iron clusters . . . . . . . . . . . . Metathesis reaction . . . . . . . . . . . . . . . Methanolysis and phenolysis route to iron clusters . Hierarchical assembly of iron clusters . . . . . . . Magnetic behaviour . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . .
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Introduction In recent years polyoxometallates have become the focus of intensive research activity since this class of inorganic compounds exhibits an enormous variety of structures as well as magnetic properties [1,8–38]. Actually these systems often are excellent practical realizations of nanomagnets, with properties changing gradually from those of simple paramagnets to those of bulk magnets. A particular aesthetic class covers the iron cluster compounds denoted as iron wheels and cages (Figs. 1 and 2). Single strand
⁎ Corresponding author. Tel.: +91 342 2533913x424; fax: +91 342 2530452. E-mail address: [email protected] (R. Ghosh). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.11.007
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molecular wheels [2] of paramagnetic 3d metals are of growing interest for reasons such as their high symmetry, which makes them good model systems of the study of one dimensional magnetism [3], magnetic anisotropy and quantum effects such as coherent tunneling of the Neel vectors [4] as a result a growing number of Mx (x ≥ 8) molecular wheels are being studied. There are, however, relatively few other 3d Mx loop-like closed topologies [5] when compared to those containing diamagnetic 4d and 5d metals such as Pd, Pt, Au, etc., or metal–metal-bonded M2 repeating units [5]. These span a variety of metals and ligands and have resulted in a wide range of loop and multi-loop structures, from squares, rectangles, boxes, etc., to complicated three-dimensional polyhedra [6]. In addition their inherent properties, such species are also potential building blocks for molecular nanodevices [7].
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model complexes for protein active sites [10]. Iron-oxo centres are found in several non-heme metalloproteins as for example hemerythrin, ribonucleotide reductase and methane monooxygenase. In most living organisms iron is stored in the protein ferritin which can contain upto 4500 FeIII ions in a polymeric oxohydroxo lattice [11]. High nuclearity transition metal clusters with appropriate topologies can sometimes cause large ground-state spin (S) values and can even occasionally function as Single Molecule Magnets (SMMs) [12]. In addition to these, there is a possible functional analogy in terms of host–guest interaction(s) between the iron(III) rings and crown ethers [13]. The alkali metal ions as guests on hexanuclear iron(III) rings can vary the extent of magnetic coupling between the metal ions, thus providing an important tool for the modulation of the properties of molecular magnets [13]. To date, a series of polynuclear ferric aggregates with different nuclearities [8–37] and a very recent Fe64 aggregates have been reported [14] (Fig. 2). Numerous naturally occurring iron oxide minerals with extended structures are also known [15]. Here in this short review we shall discuss synthetic strategies, structural beauties as well as similarities with organic crown ethers, unusual magnetic properties and host–guest chemistry of iron aggregates. Fig. 1. The iron atoms are in red, oxygen in yellow, carbon in grey and chlorine in green (taken from Ref. [1]).
Syntheses and structures Analogous access to a greater range of loop-like closed topologies or paramagnetic 3d metals would often benefits to a variety of spectroscopic, electrochemical, magnetic and host–guest binding studies. The decanuclear wheel [Fe10{(OMe)2(O2CCH2Cl)}10] reported by Lippard et al. [8] may be regarded as the prototype of this class [9]. Ferric systems represent an important subfamily of polynuclear aggregates and attract much attention owing to their relevance as
Fig. 2. The structure of Fe64 cubic cage (a and b). Top and side view of the Fe8 corner. Atomic scheme: Fe, large green (peripheral) and yellow (central) spheres; O, small red and purple (the three μ4-O2-) spheres; N, blue spheres; C, grey spheres (taken from Ref. [14]).
Template synthesis of purely inorganic iron clusters Almost all wheel compounds were originally prepared serendipitously, but methods of deliberately altering the wheel size after the initial synthesis are very few and all based on a template approach. Saalfrank et al. [16] elegantly showed that the size of certain Fex wheels could be controlled by the central Group 1 metal ion template around which the wheel forms, thus giving {Fe6M} for M = Li+ or Na+, but {Fe8M} for M = Cs+. Similarly, Winpenny, Timco and co-workers found that the organic amine template controls the nuclearity of the Mx (x = 8–10) homo- or heterometallic wheels [17]. Rao et al. has reported diethylenetriamine [H2N(CH2)2NH(CH2)2NH2] templated [FeII9F18(SO4)6]12− ferric wheel [18] (Fig. 3). Because almost all single-strand wheels are of nuclearity 12 or less and because a template approach is much less feasible for larger wheels (since it requires a correspondingly larger template). Alternative means of modifying the wheel size is sought for by Christou et al. [19]. They report a non-template route for reversibly interconverting the Fe wheels between M10 and M18.
Fig. 3. ORTEP plot of [C16N12H64][FeII9F18(SO4)6]0.9H2O (from Ref. No. [18]).
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Hydrolysis to iron clusters Hydrolysis of iron salts in the presence of carboxylate groups, with or without other chelating ligands, has proven to be a very useful method for obtaining both oxide- and hydroxide containing clusters. This approach has resulted in a number of compounds with diverse nuclearities and Fex topological arrangements. Ligand heidi [(H3heidi =N(CH2COOH)2(CH2CH2OH)] in different controlled hydrolysis reactions of iron(III) two different compounds with nuclearities 2 and 36 are reported by Powell et al. [20]. A number of polynuclear wheels are synthesized using the process of hydrolysis by Weighardt et al. [21] (Fig. 4) and Raptopoulou et al. [22]. Metathesis reaction A very common approach for obtaining alkoxide-containing compounds has been the metathesis reaction between iron salts and metal alkoxides. Some examples include the use of lithium methoxide for the synthesis of the iron alkoxide cube [Fe4(OMe)5(MeOH)3 (O2CPh)4] [23], [LiFe6(OCH3)12(dbm)6] [Hdbm = 1,3-diphenyl-1,3propanedione(dibenzoylmethane)] [13a] (Fig. 5), potassium or cesium methoxide for the preparation of [Fe(OMe)2(dbm)]12 [24], and sodium ethoxide for the preparation of [Fe9O3(OEt)21] [25]. Very recently, a similar reaction was reported that employed aluminum alkoxides in a reaction with a preformed cluster rather than a simple iron salt. In this way, [Fe4O2(O2CPh)8(py)2] was converted with Al (OR)3 (R = Pri, Bu) to the hexanuclear product [Fe6O2(OR)8(O2CPh)6] [26]. Methanolysis and phenolysis route to iron clusters Chirstou et al. reported this novel route to iron clusters (one representative figure is given in Fig. 6) in the year 2003 [27]. The work described there continues using preformed Fe4 and Fe6 compounds as starting materials. We have also explored for the first time the use of the aromatic alcohol PhOH in such reactions and compared the products obtained from a given alcoholysis reaction when the alcohol is either MeOH or PhOH. PhOH was chosen primarily because of its
Fig. 4. Molecular structure of a trinuclear wheel (from Ref. [21]).
Fig. 5. ORTEP plot of a hexanuclear ferric wheel (from Ref. [13a]).
relative bulkiness and acidity (pKa = 9.98 vs 15.5 for MeOH). The latter property makes PhOH an attractive reagent, because an early step in the alcoholysis reaction of Fex clusters likely involves proton transfer from the alcohol to a bound ligand. Although phenol is a widely used substance, there are very few examples of phenoxide as a ligand in iron chemistry. For example, the only crystallographically characterized compounds containing Fe bound phenoxide groups are a small number of iron–sulfur clusters [28] and two porphyrin-based mononuclear compounds [29].
Hierarchical assembly of iron clusters Hierarchical materials can be regarded as systems in which small units are incorporated into larger superstructures. In a recent report to synthesize Fe13 oxygen bridged clusters by Powell et al. [30] (Fig. 7)
Fig. 6. One decanuclear ferric wheel (from Ref. [27]).
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(FeA–O + FeB–O)/2. When multiple atom bridges like carboxylates are present, only the Fe–O(bridge) distances are taken into account to calculate the average length of the interaction pathway. The correlation established from 36 sets of experimental data is: −1 10 = −1:753 × 10 exp −12:663 P ) J cm The coupling constant is largely insensitive to the Fe–O–Fe angle for α N 120° [33]. For smaller angles an effect is clearly observed, J becoming smaller as the angle α is reduced. A systematic study has been performed in a series of binuclear complexes with two alkoxobridges [33] and similar Fe–O distances. The values of α range from 102 to 106°, while J varies between ca. 15 and 21 cm− 1. The simplest correlation was found to be of the type given by the following equation: −1 = 1:48αðdegÞ−135 J cm
Fig. 7. Molecular structure of Fe13 cluster (from Ref. [30]).
the conceptual hierarchy begins at the atomic level with FeIII ions in water in the form of the hexaaqua ion [Fe(H2O)6]3+. It is observed that supply of tripodal chelating ligands of the general form N(RCOOH)2R′ (in which R′ can be any organic residue) to such solutions can halt this process through the stabilization of captured intermediate phases composed of close-packed cores, which are portions of the brucite structure (exemplified by Mg(OH)2) encased in a shell of the ligand units. In the hydrolysis process, we can imagine the starting point (first generation) to be a hexaaqua metal ion which will link to six further metal ions (second generation) on production of the hexahydroxo metal ion, and the process will continue through production of the hydroxide ions and coordination to a further six metal centres (third generation), then twelve (fourth generation), and so on. Similar type of syntheses to generate iron(III) structures from a small precursor is tabulated below: Small unit (precursor)
Large resulting molecule
Reference
[Fe3O(O2CPh)6(H2O)3]Cl
[Fe12(μ2-O)4(μ3O)4(O2CPh)14 (C10H17PO3H)6] [C10H17PO3H = camphyl phosphor-nic acid] [Fe9(O)2(OH)(O2CPh)10 (C10H17PO3H)6(H2O)2](CH3CN)7 [Fe3(μ3-O)(μ-OAc)6(H2O)3] [Fe3(μ3-O)(μ-OAc)7.5(H2O)2].7H2O [Fe(OMe)2(O2CCH2Cl)]10
[12a]
[Fe3O(O2CPh)6(H2O)3]Cl [Fe3O(OAc)6(H2O)3]Cl.6H2O [Fe3O(O2CCH2Cl)6 (H2O)3](NO3).4H2O
Extended Huckel calculation indicate that [1] for small angles (~ 90°) the coupling should become antiferromagnetic due to importance of direct overlap between the iron(III) magnetic orbitals. The discovery that individual molecules can function as magnets provided a new ‘bottom-up’ approach to nanoscale magnetic materials and such molecules have since been called Single Molecule Magnets (SMMs). Each molecule is a single-domain magnetic particle that below its blocking temperature exhibits the classical macroscale property of a magnet, viz. magnetization hysteresis. In addition, SMMs straddle the classical/quantum interface in also displaying quantum tunneling of magnetization (QTM), quantum phase interference, etc., the properties of microscale. At the beginning of the 1990s it was discovered [34] that a molecule, comprising 12 Mn ions, and characterized by a ground-state S = 10 [Mn12O12(CH3COO)16(H2O)4] (Mn12ac) shows slow relaxation of magnetization at low temperature (of the order of months at 2 K). Under these conditions a single molecule becomes like a tiny magnet, in the sense that if magnetized by an external field it retains magnetization for days. In fact it gives rise to magnetic hysteresis, which is one condition for storing
[37] [12b] [31]
Magnetic behaviour The exchange interactions in oxobridged iron(III) pairs have been much investigated both theoretically and experimentally, also due to the relevance of these systems to non-heme metalloproteins containing binuclear iron units in their active sites [32]. An interesting correlation concerns [3] the dinuclear Fe(III) centres bridged by a ligand oxygen atom like oxo, hydroxo, alkoxo and at least one other bridging ligand, in general carboxylate, but also sulphate or phosphate. In all these cases, the interaction is antiferromagnetic. The J interaction parameter has been found to correlate with a P parameter defined as half of the shortest interaction pathway i.e.,
Fig. 8. Schematic structure of Fe8 (taken from Ref. [35]).
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information in a particle. Under this respect, therefore, Mn12ac behaves like a classical magnet. These molecules are often called SMMs and Mn12ac was the first SMM isolated synthetically. The second molecule that has been intensively investigated for its SMM behaviour is commonly indicated as Fe8 [35]. The formula is [Fe8O2 (OH)12(tacn)6]Br8 (tacn = 1,4,7-triazacyclononane) (Fig. 8) and comprises an octanuclear cation [36]. From magnetic point of view, this structure gives rise to spin frustration effects which make the prediction of ground-state spin arrangement difficult. The temperature dependence of χT clearly indicates a ferromagnetic behaviour with an S = 10 ground-state [21], confirmed by high-field magnetization measurements. At the simplest possible approach, the groundstate can be justified by putting six S = 5/2 spin up and two down (Fig. 8). Antiferromagnetic rings of different size, but so far only even membered, have been reported. This is a pity because in odd membered rings spin frustration effects might be observed, giving rise to a rich spin dynamics. Interesting quantum effects have been observed in antiferromagnetic rings, of the type [Fe10(OMe)2(CH2ClCOO)10](Fe10), the so called ferric wheel [37]. Below 1 K, Fe10 is in the ground S = 0 state, so that the low-field magnetization is zero. However, on increasing the field the excited states with S N 0 rapidly decrease their energies, and a crossover between the ground states S = 0 and S = 1 is observed as a step in the magnetization curve. At higher fields analogous crossovers occur, for example between S = 2 and S = 1 and, in strong pulsed fields, it was possible to observe the crossover to an S = 9 ground state. The position of the steps provides information on the energy separation of the excited states in zero field, assuming that the g values are known, a reasonable assumption for iron(III) compounds. The stepped magnetization indicates the appearance of the quantum size effects in molecular clusters on a macroscopic scale. However, if the same measurements are performed on [Mo 7 2 Fe 3 0 O 2 5 2 {Mo 2 O 7 (H 2 O)} 2 {Mo 2 O 8 H 2 (H 2 O)} (CH3COO)12(H2O)91].150H2O (Fe30), completely different results are observed [38]. The molybdenum ions are diamagnetic, therefore the magnetic properties are associated with the 30 iron(III) ions which are located on the vertices of an icosidodecahedron. Because of the geometry of the spin sites and the antiferromagnetic exchange, spin frustration and competing ordered states are expected to occur. The temperature dependence of the magnetic susceptibility gave (using classical spins) J ~ 1.6 K, and the field dependence of the magnetization did not show any quantum size effect down to 0.46 K. The linear increase in magnetization for Fe30 is characteristic of an antiferromagnet. This situation suggests that for Fe30 the spin levels define a quasicontinuum and quantum effects are only expected to show up below 100 mK. In this sense Fe30 can be considered as a tiny antiferromagnet, exactly as Mn12ac can be considered as a tiny ferrimagnet. Several features of these antiferromagnetic rings are as yet not completely understood.
Conclusion Now in short, we can conclude that synthesis and characterization of iron clusters are of utmost importance because of their SMM behaviour, relevance as model complexes for protein active site(s), etc. To prepare SMMs with high blocking temperatures, the number of coupled spins and interactions among them in a molecule should be increased. In this target ferrimagnetic approach, i.e., assembling either different antiferromagnetically coupled spins or different number of antiferromagnetically coupled spins is the easiest way as strong ferromagnetic coupling is rather difficult to develop. Possible applications of magnetic clusters range from magnetic storage media, magnetic drug delivery, contrast agents for magnetic resonance imaging (MRI) to quantum computing. In all these aspects iron aggregates may be a potential candidate.
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Acknowledgements We sincerely thank all the Hon'ble Reviewers of this manuscript for their valuable suggestions to develop the quality of this review.
References [1] D. Gatteschi, R. Sessoli, A. Cornia, Chem. Commun. (2000) 725. [2] (a) R.E.P. Winpenny, in: J.A. McCleverty, T.J. Thomas (Eds.), Comprehensive Coordination Chemistry II, vol. 7, Elsevier, Oxford, 2004, pp. 125–1768, (b); (d) 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. [3] O. Kahn, Molecular Magnetism, VCH Publishers, New York, 1993. [4] F. Meier, D. Loss, Phys. Rev. Lett. 86 (2001) 5373. [5] (a) J.-M. Lehn, Supramolecular Chemistry, VCH Publishers, New York, 1995; (b) M. Fujita, Chem. Soc. Rev. 27 (1998) 417; (c) S. Leininger, B. Olenyuk, P.J. Stang, Chem. Rev. 100 (2000) 853; (d) F.A. Cotton, C. Lin, C.A. Murillo, Acc. Chem. Res. 34 (2001) 759. [6] Q.-H. Yuan, L.-J. Wan, H. Jude, P.J. Stang, J. Am. Chem. Soc. 127 (2005) 16279. [7] S.I. Stupp, Guest Editor. Thematic Issue: Functional Nanostructures. Chem. Rev. 105 (2005) 1023. [8] K.L. Taft, S.J. Lippard, J. Am. Chem. Soc. 112 (1990) 9629. [9] O. Waldmann, R. Koch, S. Schromm, J. Schu1lein, P. Mu1ller, I. Bernt, R.W. Saalfrank, F. Hampel, E. Balthes, Inorg. Chem. 40 (2001) 2986. [10] Z.-M. Zhang, Y.-G. Li, S. Yao, E.-B. Wang, Y.-H. Wang, R. Clerac, Angew. Chem. Int. Ed. 48 (2009) 1581. [11] (a) E.Y. Tshuva, S.J. Lippard, Chem. Rev. 104 (2004) 987; (b) M. Costas, M.P. Mehn, M.P. Jensen, L. Que Jr., Chem. Rev. 104 (2004) 93; (c) K.N. Ferreira, T.M. Iverson, K. Maghlaoui, J. Barber, S. Iwata, Science 303 (2004) 1831; (d) A. Mishra, W. Wernsdorfer, K.A. Abboud, G. Christou, Chem. Commun. (2005) 54. [12] (a) S. Konar, A. Clearfield, Inorg. Chem. 47 (2008) 5573; (b) Y.Z. Zheng, M.L. Tong, W. Xue, W.X. Zhang, X.M. Chen, F. Grandjean, G.J. Long, Angew. Chem. Int. Ed. 46 (2007) 6076; (c) M. Moragues-Canovas, E. Riviere, L. Ricard, C. Paulsen, W. Wernsdorfer, G. Rajaraman, E.K. Brechin, T. Mallah, Adv. Mater. 16 (2004) 1101; (d) C.F. Wang, J.L. Zuo, B.M. Bartlett, Y. Song, J.R. Long, X.Z. You, J. Am. Chem. Soc. 128 (2006) 7162; (e) G.W. Powell, H.N. Lancashire, E.K. Brechin, D. Collison, S.L. Heath, T. Mallah, W. Wernsdorfer, Angew. Chem. Int. Ed. 43 (2004) 5772. [13] (a) G.L. Abbati, A. Cornia, A.C. Fabretti, W. Malavasi, L. Schenetti, A. Caneschi, D. Gatteschi, Inorg. Chem. 36 (1997) 6443; (b) A. Caneschi, A. Cornia, S.J. Lippard, Angew. Chem. Int. Ed Engl. 34 (1995) 467. [14] T. Liu, Y.-J. Zhang, Z.-M. Wang, S. Gao, J. Am. Chem. Soc. 130 (2008) 10500. [15] C.M. Flynn Jr., Chem. Rev. 84 (1984) 31. [16] R.W. Saalfrank, I. Bernt, E. Uller, F. Hampel, Angew. Chem. Int. Ed Engl. 36 (1997) 2482. [17] (a) G.A. Timco, A.S. Batsanov, F.K. Larsen, C.A. Muryn, J. Overgaard, S.J. Teate, R.E.P. Winpenny, Chem. Commun. (2005) 3649; (b) R.H. Laye, F.K. Larsen, J. Overgaard, C.A. Muryn, E.J.L. McInnes, E. Rentschler, V. Sanchez, H.U. Gudel, O. Waldmann, G.A. Timco, R.E.P. Winpenny, Chem. Commun. (2005) 1125. [18] J.N. Behera, C.N.R. Rao, Inorg. Chem. 45 (2006) 9475. [19] P. King, T.C. Stamatatos, K.A. Abboud, G. Christou, Angew. Chem. Int. Ed. 45 (2006) 7379. [20] A.K. Powell, S.L. Heath, D. Gatteschi, L. Pardi, R. Sessoli, G. Spina, F. Del Giallo, F. Pierallill, J. Am. Chem. Soc. 117 (1995) 2491. [21] C. Delfs, D. Gatteschi, L. Pardi, R. Sessoli, K. Wieghardt, D. Hade, Inorg. Chem. 32 (1993) 3099. [22] C.P. Raptopoulou, V. Tangoulis, E. Devlin, Angew. Chem. Int. Ed. 41 (2002) 2386. [23] K.L. Taft, A. Caneschi, L.E. Pence, C.D. Delfs, G.C. Papaefthymiou, S.J. Lippard, J. Am. Chem. Soc. 115 (1993) 11753. [24] G.L. Abbati, A. Caneschi, A. Cornia, A.C. Fabretti, D. Gatteschi, Inorg. Chim. Acta 297 (2000) 291. [25] M. Veith, F. Gratz, V. Huch, Eur. J. Inorg. Chem. 2 (2001) 367. [26] P.S. Ammala, S.R. Batten, J.D. Cashion, C.M. Kepert, B. Moubaraki, K.S. Murray, L. Spiccia, B.O. West, Inorg. Chim. Acta 331 (2002) 90. [27] C. Canada-Vilalta, T.A. O'Brien, M. Pink, E.R. Davidson, G. Christou, Inorg. Chem. 42 (2003) 7819. [28] (a) B.K. Teo, M.R. Antonio, R.H. Tieckelmann, H.C. Silvis, B.A. Averill, J. Am. Chem. Soc. 104 (1982) 6126; (b) W.E. Cleland, D.A. Holtman, M. Sabat, J.A. Ibers, G.C. DeFotis, B.A. Averill, J. Am. Chem. Soc. 105 (1983) 6021; (c) M.G. Kanatzidis, N.C. Baenziger, D. Coucouvanis, A. Simopoulos, A. Kostikas, J. Am. Chem. Soc. 106 (1984) 4500. [29] (a) H. Nasri, J. Fischer, R. Weiss, E. Bill, A. Trautwein, J. Am. Chem. Soc. 109 (1987) 2549; (b) M.P. Byrn, C.J. Curtis, Y. Hsiou, S.I. Khan, P.A. Sawin, S.K. Tendick, A. Terzis, C.E. Strouse, J. Am. Chem. Soc. 115 (1993) 9480. [30] M. Murugesu, R. Clerac, W. Wernsdorfer, C.E. Anson, A.K. Powell, Angew. Chem. Int. Ed. 44 (2005) 6678.
342
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[31] K.L. Taft, C.D. Delfs, G.C. Papaefthymiou, S. Foner, D. Gatteschi, S.J. Lippard, J. Am. Chem. Soc. 116 (1994) 823. [32] (a) D.M. Kurtz, Chem. Rev. 90 (1990) 585; (b) S.M. Gorun, S.J. Lippard, Inorg. Chem. 30 (1991) 1625. [33] F.L. Gall, F.F. de Biani, A. Caneschi, P. Cinelli, A. Cornia, A.C. Fabretti, D. Gatteschi, Inorg. Chim. Acta 262 (1997) 123. [34] (a) A. Caneschi, D. Gatteschi, R. Sessoli, A.-L. Barra, L.C. Brunet, M. Guillot, J. Am. Chem. Soc. 113 (1991) 5873; (b) R. Sessoli, D. Gatteschi, A. Caneschi, M.A. Novak, Nature 365 (1993) 141. [35] D. Gatteschi, R. Sessoli, Angew. Chem. Int. Ed. 42 (2003) 268. [36] K. Wieghardt, K. Pohl, I. Jibril, G. Huttner, Angew. Chem. Int. Ed. 23 (1984) 77. [37] K.L. Taft, C.D. Delfs, G.C. Papaefthymiou, S. Foner, D. Gatteschi, S.J. Lippard, J. Am. Chem. Soc. 116 (1994) 823. [38] A. Muller, M. Luban, C. Schroder, R. Modler, P. Kogerler, M. Axenovich, J. Schnack, P. Canfield, S. Bud'ko, N. Harrison, ChemPhysChem 2 (2001) 517.
Dr. Rajarshi Ghosh was born in the year 1979 in Barrackpore, the famous historical town in India. After completion of his graduation and post graduation studies in Chemistry from the University of Kalyani, he completed his doctoral research in the department of Chemistry, the University of Burdwan under the supervision of Prof. B. K. Ghosh in the year 2007. From 2007-2008 he worked as post-doctoral fellow under Prof. Ghosh in Burdwan. In 2008 he joined as a Lecturer in the same department from where he obtained his doctoral degree. Right now he is completely involved in post graduation teaching and research. His research interest covers synthetic coordination chemistry, supramolecular chemistry, molecular magnetism, etc.
Anup Kumar Dutta was born in 1986 in Purulia in India. He completed his graduation and post graduation from the University of Burdwan. During his post graduation studies he worked with Dr. Rajarshi Ghosh in the field of polynuclear iron chemistry.