Design of the Sandwich-like Compounds Based on the All-Metal Aromatic Unit Al3−

Chemical Bonding in Transition Metal Nitride Os3N3 + Cluster: 6π Inorganic Benzene and δ2δ*1δ*1 Aromaticity

Inorganic benzene-like clusters with a planar hexagonal ring are of interest in chemistry, as are new types of aromaticity, multifold aromaticity, and in particular δ aromaticity beyond carbon-based organic systems. Here we report on a computational study of chemical bonding in a binary Os₃N₃ ⁺ D _3h (⁷A₂″) cluster. This transition metal nitride cluster assumes a perfectly planar, heteroatomic, hexagonal geometry. An array of quantum chemistry tools is exploited to elucidate the electronic, structural, and bonding properties of D _3h Os₃N₃ ⁺ cluster, which include canonical molecular orbitals, adaptive natural density partitioning, natural bond orbital analysis, orbital composition calculations, and nucleus-independent chemical shifts. The computational data collectively support the bonding picture of 2-fold π/δ aromaticity: 6π electrons delocalized over all Os/N centers versus an Os-based 4δ framework in the unique δ²δ*¹δ*¹ configuration. The π sextet renders this heteroatomic cluster an inorganic analog of benzene. Transition metal-based inorganic benzenes are unknown in the literature, to our knowledge. The triplet 4δ electron-counting is a rare case of d-orbital aromaticity and δ-aromaticity, following the reversed 4n Hückel rule for aromaticity in a triplet system. This bonding picture is concrete, differing fundamentally from a recent study on the relevant system.

On the Nature of Bonding in Synthetic Charged Molecular Alloy [P7ZnP7]4- Cluster and Its Relevant [P7]3- Zintl Ion

Charged molecular alloys and Zintl ions are of interest in synthetic chemistry. However, their chemical bonding has seldom been elucidated using modern quantum chemistry tools. Herein, we report on in-depth chemical bonding analyses for a charged molecular alloy C ₂ [P₇ZnP₇]^4- cluster and its relevant Zintl ion C _3v [P₇]^3- ligand, making use of electronic structure calculations at PBE0/def2-TZVP level, natural bond orbital and orbital composition analyses, canonical molecular orbitals, and adaptive natural density partitioning (AdNDP). The computational data show that C _3v [P₇]^3- Zintl ion has three isolated, negatively charged, bridging P sites. Such charges are largely P 3p lone-pairs in nature, but they also participate in secondary P-P bonding along the bridging sites. C ₂ [P₇ZnP₇]^4- cluster is formulated as [P₇]^2-[Zn]⁰[P₇]^2-, in which [P₇]^2- ligands maintain the structural and bonding integrity of [P₇]^3- Zintl ion despite their difference in charge state. Two [P₇]^2- ligands collectively bind with Zn center via four bridging P sites, resulting in a quasi-tetrahedral ZnP₄ core with the eight-electron counting. This bonding picture can alternatively be rationalized using the superatom concept. The Zn-P bonds are weak with a bond order of around 0.5, because the P centers have partial nonbonding 3p character, akin to 3p² lone-pairs albeit with a lower occupation number.

Smallest deltahedra silicon dicarbide: C2Si32−

In this paper, we reported the smallest main-group dicarbide with all deltahedras, which is also the first main-group dicarbide with (n + 1) polyhedral skeletal electron pairs (PSEPs).

Investigation of the Typical Triangular Structure B3 in Boron Chemistry: Insight into Bare All-Boron Clusters Used as Ligands or Building Blocks

Even though boron clusters are quite significant, bare boron clusters as ligands in chemical compounds are still unknown. Triangular B(3) is a key constituent of all-boron clusters and widely applied in the boron compounds. As a basic step toward understanding the assembly and stabilization of bare all-boron clusters and the possibility of their fusion during the cluster-assembly process, we made the first attempt to assemble the smallest bare all-boron unit B(3)-. Both the "homo-decked sandwich" and "hetero-decked sandwich" schemes were applied to the assembly of B(3)- at the B3LYP/6-311++G(d, p) level. For all the considered alkali- and alkaline earth metals, B(3)- can only be assembled in "hetero-decked sandwich" scheme (e.g., CpMB(3)(q-)) so as to avoid cluster fusion, whereas it cannot be assembled in the traditional "homo-decked sandwich" scheme (B(3)MB(3)(q-)) because of thermodynamic and kinetic instability. Various assembled species in extended frameworks are designed. In particular, the dimerization of the hetero-decked sandwich-like CpMB(3)(q-) could lead to a new type of antiaromatic triple-decker sandwich-like complexes CpMB(6)Cp(2q-) that contain the all-boron antiaromatic unit B(6)(2-). Our work supports the experimental identification of the B(6)(2-) anion (with M+ counterions) in a photoelectron spectroscopy study. Additionally, the electronic and structural properties of B(3)- are well conserved during cluster-assembly, characteristic of a "superatom" feature. Our results are expected to be helpful for understanding the assembly and stabilization of bare all-boron cluster chemistry. Also, our work should give insight toward designing and understanding bare boron clusters as potential new ligands for coordination chemistry and as new building blocks for materials science. Interestingly, our results should provide hints to embellish, functionalize, isolate, and protect bare all-boron clusters.

Planar carbon radical’s assembly and stabilization, a way to design spin-based molecular materials

In this work, we report the first computational study on the assembly and stabilization of a novel kind of radical, i.e., the planar tetracoordinate carbon radical CAl(4)(-). Based on the 6-31+G(d)-UB3LYP, UMP2 and UCCSD(T) calculations on charged [D(CAl(4))M](q-), saturated [D(CAl(4))M(n)] and extended (CpM)(p)(CAl(4))(q) sandwich-like compounds (D = CAl(4)(-), Cp(-); M = Li, Na, K, Be, Mg, Ca), we find that for the six metals, the planar radical CAl(4)(-) can only be assembled in the "hetero-decked sandwich" scheme (e.g. [CpM(CAl(4))](q-)) rather than the traditional "homo-decked sandwich" scheme. Moreover, the low and high spin states of the designed sandwich-like species are perfectly degenerate during assembly. This can be ascribed to the good spin conservation of the CAl(4)(-) deck and the good spatial separation between two CAl(4)(-) decks. Our results show for the first time that the planar radical CAl(4)(-) can act as a new type of spin-embedded "superatom" for cluster assembly when it is assisted by a rigid partner like Cp(-). The good spin-conservation of CAl(4)(-) is very promising for the future design of novel paramagnetic and diamagnetic materials. The ionic, clustering and radical interactions between the two decks are analyzed in detail, which is quite crucial to improve the insight and understanding of the nature and origin of the interactions of the "deck-core-deck" in the metallocenes. Such information is also important in understanding the radical reactions and designing novel spin-based molecular materials. The present study should be expected to enrich the flat carbon chemistry, radical chemistry, metallocene chemistry and combinatorial chemistry.