Star‐Burst Prisms with Cyclotriveratrylene‐Type Ligands: A [Pd₆L₈]¹²⁺ Stella Octangular Structure

Abstract

Cyclotriveratrylene (CTV) is a macrocyclic host molecule with a shallow molecular cavity and a distinctly spiked, pyramidal shape. CTV and/or its derivatives have application as molecular hosts, [1] as precursors to cryptophanes and extended-arm cavitands, [1,2] as components in hydrogenbonded or coordination networks, [3,4] and as ligands within 3D capsular or prismatic metallo-supramolecular assemblies. [4][5][6] In this last area the bowl shape of a CTV derivative provides a convergent binding mode and such ligands can form assemblies with greater internal volumes than could a corresponding planar analogue. Furthermore, the CTV-type ligands impart embedded molecular recognition sites within the assemblies, and it has been shown that simple host-guest interactions at these sites can have a directing influence on the overall self-assembly process.[4] The self-assembly of 3D metallo-supramolecular species from transition-metal ions and multifunctional ligands is well established, and a spectacular range of cagelike polyhedral/prismatic structures have been reported.[7] The use of cavitand or host molecules within these structures is still under-developed, and most reported examples utilize cavitands with fourfold symmetry. The majority of the examples involve dimeric capsule structures, [8] with only rare examples of higher structures known.[9] Metalbased structures incorporating threefold symmetric cyclotriveratrylene ligands are particularly unusual and only three types have been previously reported: capsule-like [M 3 L 2 ] complexes by Shinkai and co-workers, [10] capsules, [4,5] and [Ag 4 L 4 ] 4+ "star-burst" tetrahedra. [4][5][6] The star-burst aspect to these structures comes from the rigid pyramidal shape of the CTV-related ligands.Herein we report a new star-burst metallo-supramolecular assembly with a stella octangular structure that was characterized by single-crystal and solution studies. The stella octangular structure was obtained from the self-assembly of "naked" Pd II ions with the CTV-related ligand tris(isonicotinoyl)cyclotriguaiacylene. Like all symmetrical tris-substituted CTV derivatives, this is a chiral ligand, and the [Pd 6 (L1) 8 ] 12+ complexes produced are likewise chiral. Tris(isonicotinoyl)-cyclotriguaiacylene has previously been shown to form 1D coordination chains with Ag I ions.[3b] "Naked" Pd II ions form square-planar complexes with highly labile ligands such as NO 3À ions, and its use with multifunctional ligands has led to the formation of several large 3D metallo-supramolecular structures. [11] A solution containing a mixture of tris(isonicotinoyl)cyclotriguaiacylene and Pd(NO 3 ) 2 in a 3:4 metal/ligand ratio and an excess of o-carborane in dimethylsulfoxide (DMSO) gave two types of single crystals on diffusion of acetone vapor. CTV is known to form host-guest complexes with o-carborane, hence its inclusion as a potential bulky guest molecule.

Controllable Coordination Self‐Assembly Based on Flexible Tripodal Ligands: From Finite Metallocages to Infinite Polycatenanes Step by Step

“…[45] In addition to these M 6 L 8 metallocages based on organic tripodal linkers, two M 6 L 8 cages based on organic-metal linkers have been developed. In 2009, Wang and colleagues constructed M 6 L 8 metallocages based on organic-metal ligands L 12 and Pd(en)(NO 3 ) 2 ( Figure 12).…”

Tuning the coordination chemistry of cyclotriveratrylene ligand pairs through alkyl chain aggregation

“…Tripodal derivatives such as those shown in Scheme 1 are chiral. The self-assembly of derivatised CTVs with metal cations is well established, and coordination polymers, [35][36][37] discrete metallocages, [38][39][40][41][42] and mechanically interlocked architectures [43][44][45] are known. However, the chemistry of mixed ligand systems is generally limited to the solution-phase, and we have recently demonstrated how the formation and manipulation of homo-and heteroleptic [Pd 6 L 8 ] 12+ octahedral cages can be controlled with high fidelity.…”

Lanthanide coordination polymers with pyridyl-N-oxide or carboxylate functionalised host ligands

“…The self-assembly of derivatised CTVs with metal cations is well established, and coordination polymers, [35][36][37] discrete metallo-cages, [38][39][40][41][42] and mechanically interlocked architectures [43][44][45] are known. However, the chemistry of mixed ligand systems is generally limited to the solution-phase, and we have recently demonstrated how the formation and manipulation of homo-and heteroleptic [Pd 6 L 8 ] 12+ octahedral cages can be controlled with high fidelity.…”