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The synthesis and characterization of fused aromatic networks composed of zinc tetrapyrazinoporphyrazines are reported. The steric repulsion of bulky substituents induced the formation of three-dimensional structures. Thus-obtained insoluble polymers adsorbed CO2 and had near-infrared absorption indicating their porosity and extended π-conjugation. [ABSTRACT FROM AUTHOR]

Author(s): Wenjing Meng [sup.1] [sup.8] , Shun Kondo [sup.2] , Takuji Ito [sup.3] , Kazuki Komatsu [sup.4] , Jenny Pirillo [sup.5] , Yuh Hijikata [sup.5] , Yuichi Ikuhara [sup.2] , [...], What particular mechanical properties can be expected for materials composed of interlocked backbones has been a long-standing issue in materials science since the first reports on polycatenane and polyrotaxane in the 1970s.sup.1-3. Here we report a three-dimensional porous metal-organic crystal, which is exceptional in that its warps and wefts are connected only by catenation. This porous crystal is composed of a tetragonal lattice and dynamically changes its geometry upon guest molecule release, uptake and exchange, and also upon temperature variation even in a low temperature range. We indented.sup.4 the crystal along its a/b axes and obtained the Young's moduli of 1.77 [plus or minus] 0.16 GPa in N,N-dimethylformamide and 1.63 [plus or minus] 0.13 GPa in tetrahydrofuran, which are the lowest among those reported so far for porous metal-organic crystals.sup.5. To our surprise, hydrostatic compression showed that this elastic porous crystal was the most deformable along its c axis, where 5% contraction occurred without structural deterioration upon compression up to 0.88 GPa. The crystal structure obtained at 0.46 GPa showed that the catenated macrocycles move translationally upon contraction. We anticipate our mechanically interlocked molecule-based design to be a starting point for the development of porous materials with exotic mechanical properties. For example, squeezable porous crystals that may address an essential difficulty in realizing both high abilities of guest uptake and release are on the horizon. A rubber-like, metal-organic crystal is reported with a mechanically interlocked catenane backbone, which could allow for easy guest molecule uptake and release.

Nanoporous solids, including metal-organic frameworks (MOFs), have long been known to capture small molecules by adsorption on their pore surfaces. Liquids are also known to accommodate small molecules by dissolution. These two processes have been recognized as fundamentally distinct phenomena because of the different nature of the medium—solids and liquids. Here, we report a dissolution-like gas accommodation so-called "adsorptive-dissolution" behavior in a MOF (PFAC-2) with pores densely filled with perfluoroalkyl chains. PFAC-2 does not have solvent-accessible voids; nevertheless, it captures oxygen molecules without changing the framework structure, analogous to molecular dissolution into liquids. Moreover, we demonstrate the selective capture of O2 by PFAC-2 in a mixture of O2 and Ar, which are difficult to separate due to their similarities such as boiling point and molecular size. Our results show the integration of molecular adsorption into nanospaces and dissolution into fluorous solvents, which can guide the design of crystalline adsorbents for selective molecular trapping and gas separation. A densely fluorinated nanospace demonstrates the integration of adsorption and dissolution, so-called "adsorptive-dissolution", which enables selective adsorption of O2 over Ar. [ABSTRACT FROM AUTHOR]

The photoirradiation to the Zn complex crystal having N‐(4‐pyridylmethylene)aniline (4‐pma) ligand with a central –C=N‐ bond led to no photodimerization reaction but only partial trans‐cis isomerization of 4‐pma. The reason why no photodimerization reaction occurred may be due to the stable twisted structure of 4‐pma causing the prevention from proper approaching of neighboring 4‐pma ligands. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) spectroscopy is one of the indispensable techniques in chemistry because it enables us to obtain accurate information on the chemical, electronic, and dynamic properties of molecules. Computational simulation of the NMR spectra requires time-consuming density functional theory (DFT) calculations for an ensemble of molecular conformations. For large flexible molecules, it is considered too high-cost since it requires time-averaging of the instantaneous chemical shifts of each nuclear spin across the conformational space of molecules for NMR timescales. Here, we present a Gaussian process/deep kernel learning-based machine learning (ML) method for enabling us to predict, average in time, and analyze the instantaneous chemical shifts of conformations in the molecular dynamics trajectory. We demonstrate the use of the method by computing the averaged 1H and 13C chemical shifts of each nuclear spin of a trefoil knot molecule consisting of 24 para-connected benzene rings (240 atoms). By training ML model with the chemical shift data obtained from DFT calculations, we predicted chemical shifts for each conformation during dynamics. We were able to observe the merging of the time-averaged chemical shifts of each nuclear spin in a singlet 1H NMR peak and two 13C NMR peaks for the knot molecule, in agreement with experimental measurements. The unique feature of the presented method is the use of the learned low-dimensional deep kernel representation of local spin environments for comparing and analyzing the local chemical environment histories of spins during dynamics. It allowed us to identify two groups of protons in the knot molecule, which implies that the observed singlet 1H NMR peak could be composed of the contributions from protons with two distinct local chemical environments. [ABSTRACT FROM AUTHOR]

Fluorocarbon gases are regarded as one of the largest contributors to serious environmental problems such as ozone‐depletion and global warming, and thus, the development of reclamation technologies is in great demand for reducing emission of such harmful compounds. So far, porous materials such as zeolites, activated carbons, and metal‐organic frameworks (MOFs) have been examined as solid‐state absorbents for fluorocarbon gases. However, such porous materials often suffer from a lack of size‐selectivity in fluorocarbon gas uptakes due to the large‐sized cavities (>1 nm). Herein, it is reported that macrocyclic pillar[n]quinones (P[n]Q, n = 5 or 6) in crystalline state show size‐selective uptake for fluorocarbon gases owing to their molecular‐scale cavities (<1 nm). The P[n]Q also show uptake behaviors for volatile halogenated organic compounds (VHOCs), which are highly toxic. Interestingly, the volatilities of VHOCs within the 1D channels of P[5]Q are drastically reduced compared with those of the bulk VHOC solvents. Experimental results and computational analyses revealed that the excellent storage abilities of the crystalline P[n]Q are a synergic result of their electron‐deficient macrocyclic scaffolds and the basic carbonyl oxygen atoms on their rims. [ABSTRACT FROM AUTHOR]

The exogenous administration of nitric oxide (NO) is considered a potential therapeutic treatment against a great variety of diseases due to its significant role in multiple physiological functions. Due to the gaseous nature, short lifetime and dose- and tissue-dependent activity of this molecule, the development of new administration procedures is required to control the NO delivery in terms of dosage, timing, and location. In this work, we propose a new molecular material based on robust metal–organic polyhedra (MOPs) for controlled NO release. We select dirhodium paddlewheel complex-based cuboctahedral MOPs (RhMOP), in which NO can chemically coordinate to the open-metal sites at the axial sites of dirhodium paddlewheel moieties. We further prepare amorphous coordination polymer particles (CPPs) by connecting RhMOP with bis(imidazole) linkers at the external axial sites. Both molecular MOPs and polymeric CPPs show relevant NO payloads and the release of NO can be triggered by two different stimuli: light and humidity. We show that imidazole ligands coordinating to the external axial sites of the paddlewheel moieties tune the light-triggered NO release property. We further demonstrate that the size and the extrinsic pores of CPPs are important for enhanced NO release. [ABSTRACT FROM AUTHOR]

We synthesized a (1‐propylpyridinium)2[ReN(CN)4]‐type organic–inorganic hybrid exhibiting water‐vapor‐induced drastic structural changes of the [ReN(CN)4]2− assemblies. Specifically, upon exposure to water vapor, dehydrated nitrido‐bridged chains were converted to hydrated cyanido‐bridged tetranuclear clusters via rearrangements of large molecular building units in the crystals. These switchable assembly forms display substantially different photo‐physical properties, although in both cases the emission is caused by a metal‐centered d–d transition. The nitrido‐bridged chain exhibited a near‐infrared (749 nm) emission, which blue‐shifted as the temperature increased, while a visible (561 nm) emission and its red shift was demonstrated by the cyanido‐bridged cluster. [ABSTRACT FROM AUTHOR]

The accurate determination of the spectral data for strained molecules is challenging, as their geometries in solid state and in solution may differ because the molecules undergo continuous dynamical changes between different conformations. Calix[3]pyrrole, the recently synthesized smallest calixpyrrole, has the Cs point group of symmetry in its crystal structure, despite showing a single chemical shift value for the N–H protons in solution, which suggests that the geometry of calix[3]pyrrole could take a time-averaged, bowl-shaped geometry having a C3v or C3 point group of symmetry in solution. Density functional theory calculations and molecular dynamics simulations showed the most stable geometry of calix[3]pyrrole in the Cs point group of symmetry, and continuous transformation among the equivalent geometries of calix[3]pyrrole. The rapid dynamical change among the conformations of calix[3]pyrrole in the Cs point group of symmetry is the reason behind the observed experimental chemical shift value. The presence of halide (X− = F−, Cl−, Br−, I−) anions can form stable, bowl-shaped calix[3]pyrrole·X− complexes, and the study on calix[3]pyrrole·F− showed that three NH···F hydrogen bonds are responsible for their stability. The chemical shift value for the N–H protons in calix[3]pyrrole·F− is highly deshielded, as the F− anion lowers electron density in the vicinity of these H-atoms. The consideration of dynamics is helpful in understanding the structure of strained molecules and associated spectral data. [ABSTRACT FROM AUTHOR]