liuxinye

A molecular diuranium(III) oxide was prepared. It undergoes cleavage of one U−O bonding and effects the reductive coupling of pyridine and the two‐electron reduction of bipyridine by delivering a “U^II” synthon. These reactions provide a synthetic route to dinuclear U^III/U^III complexes bridged by redox‐active N‐heterocyclic ligands.

Abstract

Oxide is an attractive linker for building polymetallic complexes that provide molecular models for metal oxide activity, but studies of these systems are limited to metals in high oxidation states. Herein, we synthesized and characterized the molecular and electronic structure of diuranium bridged U^III/U^IV and U^III/U^III complexes. Reactivity studies of these complexes revealed that the U−O bond is easily broken upon addition of N‐heterocycles resulting in the delivery of a formal equivalent of U^III and U^II, respectively, along with the uranium(IV) terminal‐oxo coproduct. In particular, the U^III/U^III oxide complex effects the reductive coupling of pyridine and two‐electron reduction of 4,4′‐bipyridine affording unique examples of diuranium(III) complexes bridged by N‐heterocyclic redox‐active ligands. These results provide insight into the chemistry of low oxidation state metal oxides and demonstrate the use of oxo‐bridged U^III/U^III complexes as a strategy to explore U^II reactivity.

A reaction with the overall appearance of (OCP)⁻ concerted cleavage is revealed to proceed through a [2+2+1]‐cycloaddition reaction intermediate, introducing an unprecedented example of (OCP)⁻ cycloaddition under reducing conditions to the established neutral and oxidative cycloaddition classes of (OCP)⁻ reactivity.

Abstract

The reduction chemistry of the newly emerging 2‐phosphaethynolate (OCP)⁻ is not well explored, and many unanswered questions remain about this ligand in this context. We report that reduction of [Th(Tren^TIPS)(OCP)] (2, Tren^TIPS=[N(CH₂CH₂NSiPrⁱ ₃)]³⁻), with RbC₈ via [2+2+1] cycloaddition, produces an unprecedented hexathorium complex [{Th(Tren^TIPS)}₆(μ‐OC₂P₃)₂(μ‐OC₂P₃H)₂Rb₄] (5) featuring four five‐membered [C₂P₃] phosphorus heterocycles, which can be converted to a rare oxo complex [{Th(Tren^TIPS)(μ‐ORb)}₂] (6) and the known cyclometallated complex [Th{N(CH₂CH₂NSiPrⁱ ₃)₂(CH₂CH₂SiPrⁱ ₂CHMeCH₂)}] (4) by thermolysis; thereby, providing an unprecedented example of reductive cycloaddition reactivity in the chemistry of 2‐phosphaethynolate. This has permitted us to isolate intermediates that might normally remain unseen. We have debunked an erroneous assumption of a concerted fragmentation process for (OCP)⁻, rather than cycloaddition products that then decompose with [Th(Tren^TIPS)O]⁻ essentially acting as a protecting then leaving group. In contrast, when KC₈ or CsC₈ were used the phosphinidiide C−H bond activation product [{Th(Tren^TIPS)}Th{N(CH₂CH₂NSiPrⁱ ₃)₂[CH₂CH₂SiPrⁱ ₂CH(Me)CH₂C(O)μ‐P]}] (3) and the oxo complex [{Th(Tren^TIPS)(μ‐OCs)}₂] (7) were isolated.

This Review discusses synthetic approaches to fullerene‐based hybrids with low‐dimensional (LD) materials and their properties. Recent advances in the design of fullerene‐based LD nanomaterials for (photo)electrocatalytic applications are emphasized. The relationship between the electronic structures and the catalytic functions of the heterostructures is addressed to provide an understanding of these emerging materials at the molecular level.

Abstract

An emerging class of heterostructures with unprecedented (photo)electrocatalytic behavior, involving the combination of fullerenes and low‐dimensional (LD) nanohybrids, is currently expanding the field of energy materials. The unique physical and chemical properties of fullerenes have offered new opportunities to tailor both the electronic structures and the catalytic activities of the nanohybrid structures. Here, we comprehensively review the synthetic approaches to prepare fullerene‐based hybrids with LD (0D, 1D, and 2D) materials in addition to their resulting structural and catalytic properties. Recent advances in the design of fullerene‐based LD nanomaterials for (photo)electrocatalytic applications are emphasized. The fundamental relationship between the electronic structures and the catalytic functions of the heterostructures, including the role of the fullerenes, is addressed to provide an in‐depth understanding of these emerging materials at the molecular level.

Soaking crystals of K₆[Rh₄Zn₄O(l‐cysteinate)₁₂] in a lanthanide acetate solution results in the complete exchange of K⁺ with Ln³⁺ in a single‐crystal‐to‐single‐crystal process. For late lanthanides (Ln=Gd–Lu), this process afforded a series of lanthanide cubane clusters with a [Lu₄(μ₃‐OH)₄]⁸⁺ core, which connect the Rh^III ₄Zn^II ₄ complex anions in a 3D MOF structure, showing magnetic cooling and heterogeneous catalytic abilities.

Abstract

Postsynthetic installation of lanthanide cubanes into a metallosupramolecular framework via a single‐crystal‐to‐single‐crystal (SCSC) transformation is presented. Soaking single crystals of K₆[Rh₄Zn₄O(l‐cys)₁₂] (K₆[1]; l‐H₂cys=l‐cysteine) in a water/ethanol solution containing Ln(OAc)₃ (Ln³⁺=lanthanide ion) results in the exchange of K⁺ by Ln³⁺ with retention of the single crystallinity, producing Ln₂[1] (2_Ln ) and Ln_0.33[Ln₄(OH)₄(OAc)₃(H₂O)₇][1] (3_Ln ) for early and late lanthanides, respectively. While the Ln³⁺ ions in 2_Ln exist as disordered aqua species, those in 3_Ln form ordered hydroxide‐bridged cubane clusters that connect [1]⁶⁻ anions in a 3D metal‐organic framework through coordination bonds with carboxylate groups. This study shows the utility of an anionic metallosupramolecular framework with carboxylate groups for the creation of a series of metal cubanes that have great potential for various applications, such as magnetic materials and heterogeneous catalysts.

Mechanochemistry is demonstrated to be an effective and sustainable synthetic tool in the preparation of curved π‐materials with high electron affinity and a highly reversible nature of the electron‐transfer process.

Abstract

It is shown that corannulene‐based strained π‐surfaces can be obtained through the use of mechanochemical Suzuki and Scholl reactions. Besides being solvent‐free, the mechanochemical synthesis is high‐yielding, fast, and scalable. Therefore, gram‐scale preparation can be carried out in a facile and sustainable manner. The synthesized nanographene structure carries positive (bowl‐like) and negative (saddle‐like) Gaussian curvatures and adopts an overall quasi‐monkey saddle‐type of geometry. In terms of properties, the non‐planar surface exhibits a high electron affinity that was measured by cyclic voltammetry, with electrolysis and in situ UV/vis spectroscopy experiments indicating that the one‐electron reduced state displays a long lifetime in solution. Overall, these results indicate the future potential of mechanochemistry in accessing synthetically challenging and functional curved π‐systems.

By incorporating azobenzene photochromic units in the double functionalization of [60]fullerene, the regiochemistry of the double cyclopropanation reaction could be controlled by using either the E or the Z isomeric forms of the photoswitch. Once covalently linked to the C₆₀ sphere, the azobenzene unit changes its light‐ and thermally‐induced isomerization properties.

Abstract

Multi‐functionalization and isomer‐purity of fullerenes are crucial tasks for the development of their chemistry in various fields. In both current main approaches—tether‐directed covalent functionalization and supramolecular masks—the control of regioselectivity requires multi‐step synthetic procedures to prepare the desired tether or mask. Herein, we describe light‐responsive tethers, containing an azobenzene photoswitch and two malonate groups, in the double cyclopropanation of [60]fullerene. The formation of the bis‐adducts and their spectroscopic and photochemical properties, as well as the effect of azobenzene photoswitching on the regiochemistry of the bis‐addition, have been studied. The behavior of the tethers depends on the geometry of the connection between the photoactive core and the malonate moieties. One tether lead to a strikingly different adduct distribution for the E and Z isomers, indicating that the covalent bis‐functionalization of C₆₀ can be controlled by light.

The synergy between different non‐covalent interactions is modulated to achieve supramolecular hybrids as electron donor‐acceptor photoactive systems consisting of a tetracationic zinc(II) phthalocyanine and anionic water‐soluble fullerenes. In the resulting monocrystalline assemblies, all the fundamental processes of natural photosynthesis are operative and give rise to highly efficient artificial photosynthetic systems.

Abstract

In the scientific race to build up photoactive electron donor‐acceptor systems with increasing efficiencies, little is known about the interplay of their building blocks when integrated into supramolecular nanoscale arrays, particularly in aqueous environments. Here, we describe an aqueous donor‐acceptor ensemble whose emergence as a nanoscale material renders it remarkably stable and efficient. We have focused on a tetracationic zinc phthalocyanine (ZnPc) featuring pyrenes, which shows an unprecedented mode of aggregation, driven by subtle cooperation between electrostatic and π–π interactions. Our studies demonstrate monocrystalline growth in solution and a symmetry‐breaking intermolecular charge transfer between adjacent ZnPcs upon photoexcitation. Immobilizing a negatively charged fullerene (C₆₀) as electron acceptor onto the monocrystalline ZnPc assemblies was found to enhance the overall stability, and to suppress the energy‐wasting charge recombination found in the absence of C₆₀. Overall, the resulting artificial photosynthetic model system exhibits a high degree of preorganization, which facilitates efficient charge separation and subsequent charge transport.

Nature Communications, Published online: 03 August 2020; doi:10.1038/s41467-020-17684-6

The synthesis of hydrocarbons with attractive electronic structures remains challenging. Here, the authors describe the synthesis and properties of the C70 fragment as-indaceno[3,2,1,8,7,6-ghijklm]terrylene, which exhibits near-infrared (NIR) absorption.

Nature Communications, Published online: 10 August 2020; doi:10.1038/s41467-020-17795-0

In anoxic environments, soluble hexavalent uranium is reduced and immobilized, however, the underlying molecular-scale reduction mechanism remains unknown. Here, the authors find that U reduction can occur on the surface of magnetite via transient U nanowire structures which collapse into ordered UO2 nanoclusters, which may have implications for understanding nuclear waste evolution and remediation of uranium contamination.

By incorporating azobenzene photochromic units in the double functionalization of [60]fullerene, the regiochemistry of the double cyclopropanation reaction could be controlled by using either the E or the Z isomeric forms of the photoswitch. Once covalently linked to the C₆₀ sphere, the azobenzene unit changes its light‐ and thermally‐induced isomerization properties.

Abstract

Multi‐functionalization and isomer‐purity of fullerenes are crucial tasks for the development of their chemistry in various fields. In both current main approaches—tether‐directed covalent functionalization and supramolecular masks—the control of regioselectivity requires multi‐step synthetic procedures to prepare the desired tether or mask. Herein, we describe light‐responsive tethers, containing an azobenzene photoswitch and two malonate groups, in the double cyclopropanation of [60]fullerene. The formation of the bis‐adducts and their spectroscopic and photochemical properties, as well as the effect of azobenzene photoswitching on the regiochemistry of the bis‐addition, have been studied. The behavior of the tethers depends on the geometry of the connection between the photoactive core and the malonate moieties. One tether lead to a strikingly different adduct distribution for the E and Z isomers, indicating that the covalent bis‐functionalization of C₆₀ can be controlled by light.

The experimental electron density obtained from 20 K synchrotron X‐ray diffraction data was used here to quantify the zero‐field splitting parameter in a Co^II‐based single‐molecule magnet. The methodology uses the d‐orbital populations to derive the ground‐state wavefunction composition, which is shown to be strongly correlated to the zero‐field splitting.

Abstract

Reported here is an entirely new application of experimental electron density (EED) in the study of magnetic anisotropy of single‐molecule magnets (SMMs). Among those SMMs based on one single transition metal, tetrahedral Co^II‐complexes are prominent, and their large zero‐field splitting arises exclusively from coupling between the d and d_xy orbitals. Using very low temperature single‐crystal synchrotron X‐ray diffraction data, an accurate electron density (ED) was obtained for a prototypical SMM, and the experimental d‐orbital populations were used to quantify the d_xy‐d coupling, which simultaneously provides the composition of the ground‐state Kramers doublet wave function. Based on this experimentally determined wave function, an energy barrier for magnetic relaxation in the range 193–268 cm⁻¹ was calculated, and is in full accordance with the previously published value of 230 cm⁻¹ obtained from near‐infrared spectroscopy. These results provide the first clear and direct link between ED and molecular magnetic properties.

Spin ice‐like magnetic relaxation was found in a two‐dimensional network of Mn^III salen‐type single‐molecule magnets with S _T=4. The spin ice‐like behavior was a consequence of the competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on the single‐molecule magnets.

Abstract

Spin ice is an exotic type of magnetism displayed by bulk rare‐earth pyrochlore oxides. We discovered a spin ice‐like magnetic relaxation of [{Mn(saltmen)}₄{Mn(CN)₆}](ClO₄)⋅13 H₂O (saltmen²⁻=N,N′‐(1,1,2,2‐tetramethylethylene)bis(salicylideneiminate)). This magnetic system can be considered as a two‐dimensional network of Mn^III salen‐type single‐molecule magnets (SMMs) in which each SMM unit (S_T=4) has two orthogonally oriented axial anisotropies and is connected ferromagnetically through the [Mn(CN)₆]³⁻ unit (S=1). This work illustrates that a two‐dimensional SMM network with competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on SMMs is a new type of magnetic system exhibiting slow relaxation of magnetization with a Davidson‐Cole‐type broad distribution of the relaxation time.

Boracycles π‐captured : The first actinide‐based molecules featuring π‐ligated neutral diborabenzene (dbb) as sandwich‐type ligand are reported. Experimental and theoretical studies suggest that the unique strength of the actinide–dbb bond is mainly electrostatic in nature with distinct covalent ligand‐to‐metal orbital contributions.

Abstract

The π coordination of arene and anionic heteroarene ligands is a ubiquitous bonding motif in the organometallic chemistry of d‐block and f‐block elements. By contrast, related π interactions of neutral heteroarenes including neutral bora‐π‐aromatics are less prevalent particularly for the f‐block, due to less effective metal‐to‐ligand backbonding. In fact, π complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong π donor capabilities of a neutral 1,4‐diborabenzene. A series of remarkably robust, π‐coordinated thorium(IV) and uranium(IV) half‐sandwich complexes were synthesized by simply combining the bora‐π‐aromatic with ThCl₄(dme)₂ or UCl₄, representing the first examples of actinide complexes with a neutral boracycle as sandwich‐type ligand. Experimental and computational studies showed that the strong actinide–heteroarene interactions are predominately electrostatic in nature with distinct ligand‐to‐metal π donation and without significant π/δ backbonding contributions.