No abstract

The chemistry of d-block metal–metal multiple bonds has been extensively investigated in the past 5 decades. However, the synthesis and characterization of species with f-block metal–metal multiple bonds are significantly more challenging and such species remain extremely rare. Here, we report the identification of a uranium–rhodium triple bond in a heterometallic cluster, which was synthesized under routine conditions. The uranium–rhodium triple-bond length of 2.31 Å in this cluster is only 3% longer than the sum of the covalent triple-bond radii of uranium and rhodium (2.24 Å). Computational studies reveal that the nature of this uranium–rhodium triple bond is 1 covalent bond with 2 rhodium-to-uranium dative bonds. This heterometallic cluster represents a species with f-block metal–metal triple bond structurally authenticated by X-ray diffraction. These studies not only demonstrate the authenticity of the uranium–metal triple bond, but also provide a possibility for the synthesis of other f-block metal–metal multiple bonds. We expect that this work may further our understanding of the bonding between uranium and transition metals, which may help to design new d-f heterometallic catalysts with uranium–metal bonds for small-molecule activation and to promote the utilization of abundant depleted uranium resources.

Compared with the prevalent metal–metal bond in transition metals, examples of the actinide–metal bond in heterometallic clusters are rare.

Although a series of complexes with rare earth (RE) metal−metal bonds have been reported, complexes which have multiple RE−Rh bonds are unknown. Here we present the identification of the first example of a molecule containing multiple RE−Rh bonds. The complex with multiple Ce−Rh bonds was synthesized by the reduction of a d−f heterometallic molecular cluster Ce{N[(CH 2 CH 2 NP i Pr 2 )RhCl(COD)] 3 } with excess potassium-graphite. The oxidation state of Ce in 3a appears to be a mixture of Ce(III) and Ce(IV), which was confirmed by X-ray photoelectron spectroscopy, magnetism, and theoretical investigations (DFT and CASSCF). For comparison, the analogous species with multiple La(III)−Rh and Nd(III)−Rh bonds were also constructed. This study provides a possible route for the construction of complexes with multiple RE metal−metal bonds and an investigation of their potential properties and applications.

An alumanyl anion possessing N, N′-bis(2,6-diisopropylphenyl)-1,3-propanediamine ligand was synthesized and characterized. Transmetalation of this Al anion with diaminoscandium chloride precursors afforded the corresponding Al−Sc complexes possessing an unprecedented Al−Sc bond. The Al−Sc[N(SiMe 3 ) 2 ] complex underwent intramolecular C−H cleavage to form a bridged dinuclear complex with μ-hydrido and μ-methylene ligands. The Al− Sc(N i Pr 2 ) 2 complex reacted with benzene in the presence of alkyl bromide to furnish a 1,4-dialuminated cyclohexadiene product with a concomitant formation of the alkyl−alkyl coupled product. Although the latter product seems to form through the radical mechanism, DFT calculations revealed an ionic mechanism involving bimetallic reaction pathways to react with alkyl bromide and benzene, which provides new insight into the chemistry of metal−metal bonded compounds.

The incorporation of various functionalities into porous metal-organic frameworks (MOFs) represents an efficacious strategy to improving their gas adsorption properties. In this work, a carbonylated tetracarboxylic acid ligand (5,5'-carbonyldiisophthalic acid) was synthesized, and a ketone-functionalized MOF with exposed metal sites based on this ligand was formed successfully. Structural analysis reveals that the new MOF possesses channels decorated by the carbonyl groups and rhombicuboctahedral cages, with open Cu sites pointing toward the cage center. The framework exhibits exceptionally high CO (46.7 wt % at 273 K and 1 bar) and H (2.8 wt % at 77 K and 1 bar) uptake. Furthermore, it displays high selectivities of CO adsorption over N and CH at 298 K.

The cavity of a [2+3] organic molecular cage was partitioned and functionalized by inserting inner-directed P[double bond, length as m-dash]O bonds, which shows CO2 capture and CH4 exclusion due to the size-matching and polarity effects. Computational results demonstrate that the successful segmentation via polar P[double bond, length as m-dash]O bonds facilitates the CO2 molecules to reside selectively inside the cavity.

Two 46-membered [2 + 2] Schiff-base macrocyclic dinuclear Zn(II) complexes (1a and 1b) were investigated deeply by the postmodification strategy, and two types of supramolecular processes (ring-contraction and self-assembly) have been achieved after the addition of specific anions as stimulus for the equilibrium of Schiff-base macrocyclic complexes. Namely, in the presence of linear three-atom SCN(-), 1a was degraded into two 23-membered [1 + 1] Schiff-base macrocyclic complexes simultaneously (mononuclear Zn(II) complex 2 and dinuclear Zn(II) complex 3). In contrast, 1b was only transformed into the macrocyclic mononuclear complex 5. More interestingly, in the case of pseudolinear five-atom N(CN)2(-), supramolecular self-assembly took place instead of the above-mentioned ring-contraction. Finally, 1a was assembled into a unique molecular box 4 with two 46-membered [2 + 2] Schiff-base macrocyclic heteronuclear Zn4Na4 substrates and double μ2-N(CN)2(-) bridges, while no similar assembly process was observed for 1b. The geometry of anions and pH values slightly adjusted by the pendant arms on the macrocyclic skeletons are believed to be the critical factors for the different supramolecular processes originating from the dynamic covalent chemistry of Schiff-base imine bonds.