The coordination chemistry of 2,2′-bis-p-tBu-calix[4]arene

Abstract

A review of the coordination chemistry of 2,2′-bis-p-^tBu-calix[4]arene (H₈bisTBC[4]) reveals thirteen published structures, seven of which are homometallic complexes of manganese (×5) and copper (×2), and six which are heterometallic 3d–4f (4 × Mn–Gd, 1 × Fe–Gd and 1 × Cu–Tb). In the majority of cases the disposition of the inverted, fully deprotnated bisTBC[4] ligand favours the formation of [M₄] butterflies, with two metals housed in the polyphenolic TBC[4] pockets and two encapsulated in the space between the pockets. The dominant structure directing ability of the ligand is reflected in the similarity of compounds made, despite the differences in the metal ions employed. Indeed, in some 3d–4f cases transition metals (TM) and lanthanide metals (LnM) can be swapped out whilst retaining isostructural topologies. The metal ion binding rules established for TBC[4] are carried forward for bisTBC[4] such that chelating to TM^III is favoured over TM^II which is favoured over LnM^III. The addition of co-ligands is found to be both complementary and counter-complementary to cluster growth. Magnetic susceptibility and magnetisation data reveal the presence of both ferro- and antiferromagnetic exchange interactions in the mixed valent Mn species and the 3d–4f clusters. Strong antiferromagnetic exchange dominates the magnetism of the Cu^II compounds. Magneto-structural correlations aligned to theory are discussed for some of the Mn-based compounds.