Methylene-bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]arenes and transition metal ions or 3d-4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.

The energy barrier to magnetisation relaxation in single-molecule magnets (SMMs) proffers potential technological applications in high-density information storage and quantum computation. Leading candidates amongst complexes of 3d metals ions are the hexametallic family of complexes of formula [Mn₆O₂(R-sao)₆(X)₂(solvent)_y] (saoH₂=salicylaldoxime; X=mono-anion; y=4–6; R=H, Me, Et, and Ph). The recent synthesis of cationic [Mn₆][ClO₄]₂ family members, in which the coordinating X ions were replaced with non-coordinating anions, opened the gateway to constructing families of novel [Mn₆] salts in which the identity and nature of the charge balancing anions could be employed to alter the physical properties of the complex. Herein we demonstrate initial experiments to show that this is indeed possible. By replacing the diamagnetic ClO₄⁻ anions with the highly anisotropic Re^IV ion in the form of [Re^IVCl₆]²⁻, the energy barrier to magnetisation relaxation is increased by up to 30 %.

Phenolic oxime and diethanolamine moieties have been combined into one organic framework, resulting in the formation of a novel ligand type that can be employed to construct a rare and unusual dodecametallic Mn wheel, within which nearest neighbours are coupled ferromagnetically.

A bis-phenolate that has structural similarities to both calix[4]arene and the oxacalix[n]arenes provides access to a “butterfly”-like Mn₄ cluster in which all metals are in the oxidation state+3. Specific properties of this ligand, in comparison to others in the literature, offer a route to influencing the orientation of the Jahn–Teller axes within this cluster motif, which possesses a rare oxidation state arrangement.

p-tert-Butylcalix[4]arene is a bowl-shaped molecule capable of forming a range of polynuclear metal clusters under different experimental conditions. p-tert-Butylcalix[8]arene (TBC[8]) is a significantly more flexible analogue that has previously been shown to form mono- and binuclear lanthanide (Ln) metal complexes. The latter (cluster) motif is commonly observed and involves the calixarene adopting a near double-cone conformation, features of which suggested that it may be exploited as a type of assembly node in the formation of larger polynuclear lanthanide clusters. Variation in the experimental conditions employed for this system provides access to Ln₁, Ln₂, Ln₄, Ln₅, Ln₆, Ln₇ and Ln₈ complexes, with all polymetallic clusters containing the common binuclear lanthanide fragment. Closer inspection of the structures of the polymetallic clusters reveals that all but one (Ln₈) are in fact based on metal octahedra or the building blocks of octahedra, with the identity and size of the final product dependent upon the basicity of the solution and the deprotonation level of the TBC[8] ligand. This demonstrates both the versatility of the ligand towards incorporation of additional metal centres, and the associated implications for tailoring the magnetic properties of the resulting assemblies in which lanthanide centres may be interchanged.

In the cone conformation calix[4]arenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition-metal centres. Reaction of these molecules with manganese salts in the presence of an appropriate base (and in some cases co-ligand) results in the formation of a family of calixarene-supported [Mn^III₂Mn^II₂] clusters that behave as single-molecule magnets (SMMs). Variation in the alkyl groups present at the upper-rim of the cone allows for the expression of a degree of control over the self-assembly of these SMM building blocks, whilst retaining the general magnetic properties. The presence of various different ligands around the periphery of the magnetic core has some effect over the extended self-assembly of these SMMs.

A family of planar disc-like hexa-, octa- and decametallic Ni^II complexes exhibit dominant ferromagnetic exchange. The deca- and octametallic clusters [Ni^II₁₀(tmp)₂(N₃)₈(acac)₆(MeOH)₆] (1, H₃tmp=1,1,1-tris(hydroxymethyl)propane; acac=acetylacetonate) and [Ni^II₈(thme)₂(O₂CPh)₄(Cl)₆(MeCN)₆(H₂O)₂] (2, H₃thme=1,1,1-tris(hydroxymethyl)ethane) represent rare examples of Ni^II-based single-molecule magnets, and [Ni^II₁₀] (1) possesses the largest barrier to magnetisation reversal of any Ni^II single-molecule magnet to date.