Magnetism in metal–organic capsules

Abstract

Nickel and cobalt seamed metal-organic capsules have been isolated and studied using structural, 5 magnetic and computational approaches. Antiferromagnetic exchange in the Ni capsule results from coordination environments enforced by the capsule framework. The synthesis and characterisation of polymetallic cages of paramagnetic transition metal ions is an area of intense current research since such molecules may exhibit fascinating physical properties,1 potentially acting as, for example, single-molecule magnets (SMMs),2 molecular coolants3 and spin 10 phonon traps.4 Indeed the initial (serendipitous) discovery of all these phenomena has subsequently inspired much beautiful chemistry and physics that promises exciting potential application.5 Introducing new preparative routes towards the synthesis of transition metal cages is thus of interest for the discovery of completely new structural types and as a means of building up families of related compounds so that structure-property relations can be developed.6 Organic ligands thus play a crucial 15 role in successful cage construction, but their nature and variety is surprisingly restricted.7 A family of ligands almost completely ignored in this respect, with a few notable exceptions are calixarenes.8 C-Alkylpyrogallol[4]arenes (general formula PgCn) are cyclic molecules that are typically bowl-shaped and that have been shown to assemble through non-covalent interactions into a) nanotubular arrays,9 b) dimeric capsules,10 and c) hexameric nano-capsules.11 The dimeric and hexameric 20 capsules possess typical internal volumes of ~150 and ~1250 Å3 respectively, and this feature provides them with great potential for study as new host-guest systems. Nanometer scale metal-organic polyhedra are often assembled from many molecular components,12 and we have recently shown that various PgCns can be assembled with different metals into either open or closed shell hexameric metal-organic nano-capsules from Cu, Ga, Ga+Cu or Ga+Zn.13 In addition to this, closed shell 25 dimeric octa-metallated capsules have also been synthesized by reaction of PgCns with a pre-formed zinc(II) nitrate pyridine complex in either pyridine or methanol.14 Given that we had formed a Zn8 wheel as part of a molecular metal-organic capsule, we reasoned that the incorporation of paramagnetic metal centres (e.g. Co or Ni in place of Zn) in the capsule seam may be possible, though a search of the CCDC database reveals that there are no known isostructural Co8, Ni8 and Zn8 cages. 30This would therefore afford species with potential interest in molecular nanomagnetism, whilst also representing a paradigm shift in the chemistry of molecular capsules and their uses. We also reasoned that the inner phase of the capsule arrangement may have an important effect on the overall magnetic properties of these species by the incorporation of different guest molecules. Herein we report an expedient route to a new family of octa-metallated dimeric capsules comprising Ni8 and Co8 wheels, 35and their initial magnetic pro...

Exploring the Magnetic Behavior of Nickel-Coordinated Pyrogallol[4]arene Nanocapsules

“…16 The change in X m T value with respect to temperature indicates weak antiferromagnetic exchange between the nickel atoms. The computations on the Ni(catechol) 2 (pyridine) model complexes suggest that each individual nickel center has a triplet state but the X m T product versus T data demonstrate that the dimer is diamagnetic overall.…”

“…20,21 Given the structural differences between the metal-seamed hexamers and dimers, we compared these MONCs magnetically not only to help identify appropriate guests, ligands, and linker R groups for building molecular devices, but also to yield important prototypes for exploring their magnetic behavior. 16 Herein, we report the results of the first magnetic study on nickel-seamed C-propylpyrogallol [4]arene (PgC 3 Ni) hexamers in powder form and compare the magnetic properties of the PgC 3 Ni hexamers and dimers. This study affords magnetic differentiation between the penta-coordinated square pyramidal geometry of the nickel in the dimer with that of the octahedral geometry of the nickel in the hexamer.…”

“…20,21 Given the structural differences between the metal-seamed hexamers and dimers, we compared these MONCs magnetically not only to help identify appropriate guests, ligands, and linker R groups for building molecular devices, but also to yield important prototypes for exploring their magnetic behavior. 16 Herein, we report the results of the first magnetic study on nickel-seamed ABSTRACT The magnetic behavior of nickel-seamed C-propylpyrogallol[4]arene dimeric and hexameric nanocapsular assemblies has been investigated in the solid state using a SQUID magnetometer. These dimeric and hexameric capsular entities show magnetic differentiation both in terms of moment per nanocapsule and potential antiferromagnetic interactions within individual nanocapsules.…”

Mixed metal-organic nanocapsules

“…One pyridine guest molecule is bound in the dimeric nanocapsule, and 1 H NMR analysis indicates its chemical shifts change with the variation of the ligands bound to the zinc ions exterior to the nanocapsule [58]. Recent studies with this system have afforded Ni and Co analogs, the former of which displays unexpected and interesting magnetic properties due to the coordination environments imposed by the capsule seam [59].…”

Ferrocene as a Hydrophobic Templating Agent with Pyrogallol[4]arenes

“…Nanoscale materials based on the bowl‐shaped members of the calixarene extended family continue to capture the imagination of the scientific community with potential applications in pharmaceuticals,1–3 catalysis,4, 5 and as molecular magnets 6. 7 One particularly robust, yet less investigated member of this family is the C‐ alkylpyrogallol[4]arene (PgC) 8.…”