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Seed-mediated growth has been widely used to synthesize noble metal nanoparticles with controlled size and shape. Although it is becoming possible to directly observe the nucleation process of metal atoms at the single atom level by using transmission electron microscopy (TEM), it is challenging to control the formation and growth of seeds with only a few metal atoms in homogeneous solution systems. This work reports site-selective formation and growth of atomic scale seeds of the Au nanoparticle in a nanospace of an organic cage molecule. We synthesized a cage molecule with amines and phenols, which were found to both capture and reduce Au(III) ions to spontaneously form the atomic scale seeds containing Au(0) in the nanospace. The growth reaction of the atomic scale seeds afforded Au nanoparticles with an average diameter of 2.0±0.2 nm, which is in good agreement with the inner diameter of the cage molecule., (© 2023 Wiley-VCH GmbH.)

Combining metal complexes with amphiphilic molecules leads to a wide variety of functional self-assembled nanostructures. Metal complexes exhibiting spin transitions can be good candidates as the trigger to cause structural conversion of such assembly because they respond to various external stimuli. In this work, we studied a structural conversion of a supramolecular assembly containing a [Co 2 Fe 2 ] complex through a thermally induced electron transfer-coupled spin transition (ETCST). With an amphiphilic anion, the [Co 2 Fe 2 ] complex formed reverse vesicles in solution and showed thermal ETCST. In contrast, thermal ETCST in the presence of a bridging hydrogen-bond donor caused structural conversion from the reverse vesicle structure to entangled one-dimensional chains through hydrogen bond formation., (© 2023 Wiley-VCH Verlag GmbH.)

Invited for the cover of this issue is the group of Masayuki Nihei at the University of Tsukuba. The image depicts the electron transfer-triggered structural conversion of the supramolecular assembly of a [Co 2 Fe 2 ] complex between reverse vesicles and entangled one-dimensional chains. Read the full text of the article at 10.1002/chem.202300954., (© 2023 Wiley-VCH GmbH.)

Invited for the cover of this issue are Kentaro Tanaka at Nagoya University and co-workers. The image depicts the importance of the flexibility of bridging alkyl chains in a molecular conjugate to pack the components closely to generate efficient molecular communication. Read the full text of the article at 10.1002/chem.202200819., (© 2022 Wiley-VCH GmbH.)

Spatial distance is an important factor in controlling the functional interactions between molecular units in a conjugate; therefore, the bridging unit has been closely examined. Here, we examined the effect of the flexibility of bridging alkyl chains on the proximity of stacked porphyrin and phthalocyanine conjugated with a fourfold rotaxane linkage. We found that closely stacking two π systems requires bridging alkyl chains above a certain length, and the shorter bridges hinder stacking because of their lower flexibility. The stacking distance between porphyrin and phthalocyanine in the conjugate with decyl (C 10 ) chains was estimated to be 4.03 Å and showed a unique physical character arising from short-distance interactions. The longer alkyl chains minimized steric restriction inside the fourfold rotaxane and allowed efficient communication between the porphyrin and phthalocyanine units. This is due to the flexibility of the side chains., (© 2022 Wiley-VCH GmbH.)

Controlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 5+ , which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 5+ catalyzed ethane oxidation in the presence of H 2 O 2 at a relatively low temperature. The site-selective complexation of 3 5+ with an additional anionic porphyrin (TPPS 4- ) through π-π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 5+ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS 4- to 3 5+ enhanced the catalytic activity., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A μ-oxo-dinuclear iron complex of a supramolecular porphyrin-phthalocyanine conjugate was synthesized and its catalytic electrochemical oxygen reduction properties were investigated. In the conjugate, porphyrin and phthalocyanine units were connected to form a cofacial dimeric structure through a flexible fourfold rotaxane linkage, which was advantageous for accommodating small substrates between the iron centers. The conjugate showed efficient catalytic properties, at more positive potentials than those of other reported dinuclear porphyrinoid iron complexes, to selectively afford water through a four-electron reduction process., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)