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A family of Pd 2 L 4 cages prepared from ligands based on an axially chiral diamino-[1,1'-biazulene] motif (serving as a unique azulene-based surrogate of the ubiquitous BINOL moiety) is reported. We show that preparing a cage starting from the racemate of a shorter bis-monodentate ligand derivative, equipped with pyridine donor groups, leads to integrative ("social") chiral self-sorting, exclusively yielding the meso-trans product, but only in a selection of solvents. This phenomenon is driven by individual solvent molecules acting as hydrogen bonding tethers between the amino groups of neighboring ligands, thereby locking the final coordination cage in a single isomeric form. The experimental (solvent-dependent NMR, single-crystal X-ray diffraction) observations of this cooperative interaction could be explained by computational analyses only when explicit solvation was considered. Furthermore, we prepared a larger chiral ligand with isoquinoline donors, which, unlike the first one, does not undergo social self-sorting from its racemic mixture, further highlighting the importance of solvents bridging short distances between the amino groups. Homochiral cages formed from this larger ligand, however, furnish a cavity that can bind anionic and neutral metal complexes such as [Pt(CN) 6 ] 2- and Cr(CO) 6 and discriminate between the two enantiomers of chiral guest camphor sulfonate.

Metal ions are irreplaceable in many areas of chemistry, including (bio)catalysis, self-assembly and charge transfer processes. Yet, modelling their structural and dynamic properties in diverse chemical environments remains challenging for both force fields and ab initio methods. Here, we introduce a strategy to train machine learning potentials (MLPs) using MACE, an equivariant message-passing neural network, for metal-ligand complexes in explicit solvents. We explore the structure and ligand exchange dynamics of Mg 2+ in water and Pd 2+ in acetonitrile as two illustrative model systems. The trained potentials accurately reproduce equilibrium structures of the complexes in solution, including different coordination numbers and geometries. Furthermore, the MLPs can model structural changes between metal ions and ligands in the first coordination shell, and reproduce the free energy barriers for the corresponding ligand exchange. The strategy presented here provides a computationally efficient approach to model metal ions in solution, paving the way for modelling larger and more diverse metal complexes relevant to biomolecules and supramolecular assemblies.

Chirality analysis of small molecules for the determination of their enantiopurity is nowadays ruled by streamlined chromatographic methods which utilize chiral stationary phases. Chiroptical probes which rely on host-guest interactions are so far overshadowed by the latter but have the benefit of depending only on common spectroscopic techniques such as CD spectroscopy to distinguish enantiomers and to quantify their ratio. Interest into this receptor-based approach is constantly rising because non-invasive high-throughput screenings with a minimal waste production can be performed. In this study we investigate the possibility to utilize metal-based containers in form of charge-neutral helicates able to recognize anions for this purpose. Key building block of the helicates are triazole units which show rotational freedom and give rise to either a meso-structure or a racemic mixture of the right- and left-handed complex. A chiroptical response of the probe is observed upon recognition of chiral mono- or dicarboxylates and chirality analysis of tartrate is conducted by CD spectroscopy., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Two chiral derivatives of 18-crown-6, namely the host molecules 2,3-diphenyl- and 2-phenyl-18c6, serve as model systems to investigate whether VCD spectroscopy can be used to monitor conformational changes occurring upon complexation of guests. Host-guest complexes of both crown ethers were prepared by addition of KNO 3 . The more bulky 2,3-diphenyl-18c6 is found to undergo major conformational changes upon encapsulation of K + , which are revealed as characteristic changes of the VCD spectral signatures. In contrast, while 2-phenyl-18c6 also incorporates K + into the macrocycle, strong conformational changes are not occurring and thus spectral changes are negligible. With an octyl ammonium cation as guest molecule, 2,3-diphenyl-18c6 shows the same conformational and spectral changes that were observed for K + -complexes. In addition, the asymmetric NH 3 -deformation modes are found to gain VCD intensity through an induced VCD process. An analysis of the vibrational spectra enables a differentiation of VCD active and inactive guest modes: There appears to be a correlation between the symmetry of the vibrational mode and the induced VCD intensity. While this finding makes the host-guest complexes interesting systems for future theoretical studies on the origin of induced VCD signatures, the observations described in this study demonstrate that VCD spectroscopy is indeed a suitable technique for the characterization of supramolecular host-guest complexes.