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

Abstract

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.

Versatility of Terpyridine‐Functionalised Aryl Tetrazoles: Photophysical Properties, Ratiometric Sensing of Zinc Cations and Sensitisation of Lanthanide Luminescence

“…For this reason, tetrazoles are considered to be more metabolically stable bioisosteres of carboxylic acids . The presence of four sp 2 ‐hybridised lone pairs on the nitrogen atoms allows the construction of complex molecular architectures by bridging multiple metal ions, and many of these examples have been reported for species containing both transition metals and lanthanide elements …”

Lanthanoid Complexation by a Tris‐Tetrazole‐Functionalised Calix[4]arene

“…No crystalline materials were isolated from these reactions. Attention was then turned to using carboxylate buffer systems, which previously resulted in the isolation of metal clusters with bis(tetrazole) 1 . The reaction of [Pr(NO 3 ) 3 (DMSO) 4 ] and 3 in the presence of 10 equiv.…”

“…The bis(tetrazole)–calix[4]arene ( 1 ) (Figure ) was found to form a typical 1:1 lanthanoid complex in the presence of triethylamine, with the metal atom bound to the four phenol O‐atoms and two N‐atoms . However, in the presence of an ammonium carboxylate buffer unprecedented elongated Ln 19 or Ln 12 clusters were isolated, where the calixarene interacted with the metal cations only through the tetrazole N‐atoms . The tetrakis(tetrazole) derivative 2 , in contrast, was found to be a surprisingly poor ligand for lanthanoids, where only a mixed triethylammonium/sodium salt was isolated, even in the presence of excess lanthanoid cations .…”

Influence of the Para-Substituent in Lanthanoid Complexes of Bistetrazole Substituted Calix[4]arenes

“…[3] Calixarene 2 has been reported previously, [9] synthesised by a different method as a control for para-phenylazo bis-tetrazole calixarenes that were exploited as colorimetric sensors for calcium ions. [2,3] and the structures of the target calixarene ligands 2, and 3. Derivative 3 was more problematic as the intermediate nitrile was not able to be purified in our hands.…”

“…[2] A similar approach was taken here, with the intent that DLS would provide a simple and readily accessible technique to observe potential cluster formation in the reaction mixtures. A distinct increase in the average particle size was observed upon addition of the aqueous ammonium carboxylate solution to a mixture of 1 and a lanthanoid salt dissolved in 1:1 ethanol/ethyl acetate.…”