ABSTRACT:A rare discrete mixed-valent heterometallic Fe(III)/Cu(II) cage, [Cu 6 Fe 8 L 8 ](ClO4)12·χsolvent (H 3 L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion directed selfassembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by Xray crystallography, ESI mass spectrometry, FT-IR and UV-vis-NIR spectroscopy.The self-assembly of coordination cages has continued to receive considerable attention over the past decade, 1 because of their many potential applications in gas adsorption, 2 drug delivery, 3 catalysis, 4 magnetic materials, 5 host-guest phenomena 6 and synthetic membranes for ion channels. 7 Although a number of coordination cage types have been developed, the design and successful construction of these systems, particularly those with heteronuclear coordination motifs, still represents a significant challenge. 5d,5e,8 Three synthetic procedures have been successfully exploited for the construction of discrete heteronuclear coordination architectures: 1) exploitation of the inherent coordination properties between ligands and different metal ions for the metal-directed assembly of discrete metallosupramolecular architectures; 9 2) formation of discrete metallo-assemblies preorganised for binding a second metal ion, or ions, to yield discrete heterometallic architectures; 10 3) employing preformed metalloligands functionalised for use as building blocks reacting with additional metal ions and sometimes extra ligands. 2b,5c,5e,8b,11 In a recent review, 12 we discussed the employment of planar di-, tri-and oligonuclear platforms, including both homo-and heteronuclear systems, as structural elements for the formation of both discrete and polymeric metallosupramolecular assemblies. As part of our continuing efforts to prepare heterometallic coordination architectures, we reported the synthesis of predesigned hexanuclear Cu II /Ni II metallocycles featuring unprecedented six-node metallocoronand structural motifs 10b and the preparation of a discrete heteronuclear metallomacrocycle (Ag I 3 /Fe II ) by metalion directed self-assembly via a Fe II template. 10aHerein we report an extension of the above studies leading to the construction of a new discrete coordination heterometallic nanocage 1 [Cu 6 Fe 8 L 8 ] (ClO4)12·χsolvent (H 3 L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine) enclosing a void space of 277Å 3 . 13 Thus, we have employed a suitable metalloligand together with an additional metal ion (Cu II ) that was anticipated to favour structure-specific selfassembly. A key feature of our design was to employ short organic components that would bridge the different metal ions in a way that would give the potential for magnetic exchange between metal centers. In addition, we have employed a cooperative effect to build a robust metalloligand which can react with additional metal ions to yield a heterometallic cage. To this end we demonstrated that a heterometallic polyhedral cage can be ...
Studies of the stability of the oxides schafarzikite, FeSb2O4, and tripuhyite, FeSbO4, have been undertaken to clarify the roles these secondary minerals may have in determining the dispersion of antimony in oxidizing environments. Solubilities were determined at 298.15 K in aqueous HNO3, and these data were used to calculate values of ΔGfϴ at the same temperature. The derived Δ Gfϴ (s, 298.15 K) values for FeSb2O4 and FeSbO4 are – 959.4±4.3 and – 836.8±2.2 kJ mol–1, respectively. These results have been compared with electrochemically derived data, extrapolated from 771–981 K. The present study shows conclusively that although the mobility of Sb above the water table is limited by simple Sb(III) and Sb(V) oxides and stibiconite-group minerals, depending upon the prevailing redox potential and pH, tripuhyite is an important ultimate sink for Sb in the supergene environment. It is highly insoluble even in strongly acidic conditions and its anomalous stability at ambient temperatures causes the common mineral goethite, FeOOH, to react to form tripuhyite at activities of Sb(OH)5(aq) as low as 10–11. The comparatively limited numbers of reported occurrences of tripuhyite in the supergene zone are almost certainly due to the fact that its physical properties, especially colour and habit, are remarkably similar to those of goethite. In contrast, the small number of reported occurrences of schafarzikite can be related to its decomposition to tripuhyite as redox potentials rise at the top of the supergene zone and the fact that it decomposes to sénarmontite, Sb2O3, in acidic conditions, releasing Fe2+ ions into solution. In general, the findings confirm the immobility of Sb in near-surface conditions. Geochemical settings favouring the formation of the above minerals have been assessed using the results of the present study and data from the literature.
A large discrete face-capped tetranuclear iron(II) cage, [Fe 4 L 4 ](BF 4 ) 8 Án(solvent), was synthesised via metal-ion directed self-assembly. The cage is formed from a rigid tritopic ligand that incorporates chelating imidazole-imine functional groups. The cage displays temperature induced spin-crossover and LIESST effects and is amongst the largest iron(II) tetrahedral cages with such properties reported. The synthesis, structure and magnetic properties of this new metallo-cage are presented.
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