Self-Assembly of an Imidazolate-Bridged Fe^III/Cu^II Heterometallic Cage

Abstract

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 ...

Synthesis and characterisation of two new tripodal metalloligands incorporating zinc(II)

“…S3) [24]. While the bands for pyrazine m C-H (very weak), imine m C=N (1591 cm -1 ) and perchlorate m Cl-O (*1055 and 621 cm -1 ) were also observed in the spectrum of 2 [24]. In addition, the spectrum of this compound showed bands at 3323 and 3275 m (amine, m N-H ), which are not present in the spectrum of 1 (Fig.…”

“…As an example, substitution of 4-formylimidazole for pyridinecarboxaldehyde in the Schiff base condensation with tren mentioned above yielded the corresponding tripodal ligand which then formed a 1:1 complex with iron(III), leaving the three imidazole NH groups available (following deprotonation) for coordination to additional metal centres [23]. Such an outcome was recently demonstrated for this system by our group [24]; by using the above iron(III) metalloligand we were successful in synthesising a discrete heterometallic iron(III)/copper(II) polyhedral nanocage of formula [Cu 6-Fe 8 L 8 ](ClO 4 ) 12 (where H 3 L = tris{[2-{(imidazole-4-yl)methylidene}amino]-ethyl}amine). In this product, each iron(III)-containing metalloligand complex links to three copper(II) centres to generate the overall cage structure.…”

“…S3) [24]. While the bands for pyrazine m C-H (very weak), imine m C=N (1591 cm -1 ) and perchlorate m Cl-O (*1055 and 621 cm -1 ) were also observed in the spectrum of 2 [24].…”

“…3a). Metallo-ligands with C 3 -symmetry such as this have the capability of acting as edge-directing corners in the formation of a metallosupramolecular cage [24]. Despite several attempts, crystals of complex 1 suitable for single-crystal X-ray diffraction could not be obtained.…”

Structural Invariance of a ZnII Coordination Polymer with 5-Aminoisophthalic Acid under Different Synthetic Conditions

“…8,9 The design of supramolecular materials can be governed by the careful choice of reaction conditions. 10 The final results of the reagent mixture can be driven by subtle kinetic and thermodynamic details of the chemical and crystal growth processes. 11 Temperature and concentration, e.g., are important variables that influence the thermodynamics and kinetics of a chemical reaction and crystal growth, and consequently the obtained solid phases.…”