Lanthanoid “Bottlebrush” Clusters: Remarkably Elongated Metal–Oxo Core Structures with Controllable Lengths

Large
metal–oxo clusters consistently assume spherical or
regular polyhedral morphologies rather than high-aspect-ratio structures.
Access to elongated core structures has now been achieved by the reaction
of lanthanoid salts with a tetrazole-functionalized calix­arene
in the presence of a simple carboxylate co-ligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused
Ln5O6 trigonal bipyramids and are formed consistently
under a range of reaction conditions and reagent ratios. Altering
the carboxylate co-ligand structure reliably controls the cluster
length, giving access to a new class of rod-like clusters of variable
length.