Challenges in the Structure Determination of Self-Assembled Metallacages: What Do Cage Cavities Contain, Internal Vapor Bubbles or Solvent and/or Counterions?

Abstract

Proving the structures of charged metallacages obtained by metal ion coordination-driven solution self-assembly is challenging, and the common use of routine NMR spectroscopy and mass spectrometry is unreliable. Carefully determined diffusion coefficients from diffusion-ordered proton magnetic resonance (DOSY NMR) for six cages of widely differing sizes lead us to propose a structural reassignment of two molecular cages from a previously favored trimer to a pentamer or hexamer, and another from a trimer to a much higher oligomer, possibly an intriguing tetradecamer. In the former case, strong support for the reassignment to a larger cage is provided by an observation of a slow reversible transformation of the initially formed cage into a smaller but spectrally very similar one upon dilution. In the latter case, freeze-fracture transmission electron micrographs demonstrate that at least some of the solutions are colloidal, and high-resolution electron transmission and atomic force microscopy images are compatible with a tetradecamer but not a trimer. Comparison of solute partial molar volumes deduced from measurement of solution density with volumes anticipated from molecular models argues strongly against the presence of large voids (solvent vapor bubbles) in cages dissolved in nitromethane. The presence of bubbles was previously proposed in an attempt to account for the bilinear nature of the Eyring plot of the rate constant for pyridine ligand edge exchange reaction in one of the cages and for the unusual activation parameters in the high-temperature regime. An alternative interpretation is proposed now.

Correction to “Pyridine Ligand Rotation in Self-Assembled Trigonal Prisms. Evidence for Intracage Solvent Vapor Bubbles”

“…(ii) In certain instances the pair listing algorithm omitted some interactions and doubled others. The erroneous result suggested a possible explanation of experimental observations, but more recent results showed that the cage is filled with solvent, in agreement with correctly performed UFF molecular simulations.…”

Coordination-Driven Self-Assembly of Heterotrimetallic Barrel and Bimetallic Cages Using a Cobalt Sandwich-Based Tetratopic Donor

“…Cobalt sandwich-based symmetric tetratopic donors have been well investigated and are appreciated because of their potential to provide unique face-based conformational isomerism. − Previously, two such symmetrical tetratopic donors with different dimensions have been employed in combination with Pt­(II)- and Pd­(II)-based acceptors to produce trigonal and tetragonal barrels. − …”

On degree based topological indices of self‐assembled tetraphenylethylene and terpyridine rosettes

“…Inside this boundary of research, the combination of metallo supramolecules with chromophores resulted as materials with light emitting property has gathered accountable observation due to their broad applications in photoelectric devices, sensors, diodes with light emitting property, bioimaging extra [21–24]. Presently, the following frame works and abbreviated terms such as covalent organic frameworks (COFs) [25–27], metal organic frameworks (MOFs) [28–31], metallomacrocycles [32–35], an effect caused by the restriction of intramolecular rotation (RIR) [36, 37], to construct luminescent materials based on aggregation induced emission (AIE) [38] using metallo cages [39–43], has incorporated tetraphenylethylene (TPE) as an archetypal fluorophore.…”