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We report the experimental observation and spectroscopic characterization, and structure and bonding analyses of copper–borozene complexes.

 

Borophenes are atom-thin boron layers that can be grown on coinage metal substrates and have become an important class of synthetic 2D nanomaterials. The interactions between boron and substrates are critical to understand the growth mechanisms of borophenes. Here, we report an investigation of copper-boron interactions in the Cu 2 B 8 − bimetallic cluster using photoelectron spectroscopy and quantum chemical calculations. Well-resolved photoelectron spectra are obtained at several photon energies and are combined with theoretical calculations to elucidate the structures and bonding of Cu 2 B 8 − . Global minimum searches reveal that Cu 2 B 8 − consists of a Cu 2 dimer atop a B 8 molecular wheel with a long Cu–Cu bond length close to that in Cu 2 + . Chemical bonding analyses indicate that there is clear charge transfer from Cu 2 to B 8 , and the Cu 2 B 8 − cluster can be viewed as a [Cu 2 + ]-borozene complex, [Cu 2 + ][B 8 2– ]. In the neutral cluster, no Cu–Cu bond exists and Cu 2 B 8 consists of two Cu + centers interacting with doubly aromatic B 8 2− borozene. The charge transfer interactions between Cu and boron in the Cu 2 B 8 − cluster are analogous to charge transfer from the copper substrate to the first borophene layer recently reported to be critical in the growth of bilayer borophenes on a Cu(111) substrate. 

A remarkable distinction between boron and carbon hydrides lies in their extremely different bonding patterns and chemical reactivity, resulting in diverse areas of application. Particularly, carbon, characterized by classical two‐center – two‐electron bonds, gives rise to organic chemistry. In contrast, boron forms numerous exotic and non‐intuitive compounds collectively called non‐classical structures. It is reasonable to anticipate that other elements of Group 13 exhibit their own unusual bonding patterns; however, our knowledge of the hydride chemistry for other elements in Group 13 is much more limited, especially for the heaviest stable element, thallium. In this work, we performed a conformational analysis of Tl₂H_xand Tl₃H_y(x=0–6, y=0–5) series via Coalescence Kick global minimum search algorithm, DFT, andab initioquantum chemistry methods; we investigated the bonding pattern using the AdNDP algorithm, thermodynamic stability, and stability toward electron detachment. All found global minimum structures are classified as non‐classical structures featuring at least one multi‐center bond.

 

Following an ongoing interest in the study of transition metal complexes with exotic bonding networks, we report herein the synthesis of a family of heterobimetallic triangular clusters involving Ru and Pd atoms. These are the first examples of trinuclear complexes combining these nuclei. Structural and bonding analyses revealed both analogies and unexpected differences for these [Pd 2 Ru] + complexes compared to their parent [Pd 3 ] + peers. Noticeably, participation of the Ru atom in the π-aromaticity of the coordinated benzene ring makes the synthesized compound the second reported example of ‘bottled’ double aromaticity. This can also be referred to as spiroaromaticity due to the participation of Ru in two aromatic systems at a time. Moreover, the [Pd 2 Ru] + kernel exhibits unprecedented orbital overlap of Ru d z2 AO and two Pd d xy or d x2−y2 AOs. The present findings reveal the possibility of synthesizing stable clusters with delocalized metal–metal bonding from the combination of non-adjacent elements of the periodic table which has not been reported previously. 

The unusual stability of cyclo[18]carbon arising from its aromaticity might be used to provide the kinetic trapping needed in the design of interlocked systems. The kinetic barrier separating the interlocked rings and the chemically bonded complex is about 30 kcal mol −1 . In addition, the rings can slide freely, which is a promising property for the design of molecular gears and motors.