Zhong-hua Cui

How can carbon favor planar multi-coordination in boron-based clusters? Global structures of CBxEy2− (E = Al, Ga, x + y = 4)

With the high preference in forming multi-center bonding, boron has been a miracle ligand in constructing diverse planar multi-coordinate (pM) (tetra/hyper) species. Unfortunately, the boron ligand usually dislikes encompassing a pM carbon (pMC) due to the high competition with pM boron (pMB), which makes the realization of boron-based pMC very difficult and quite challenging. Herein, we propose a strategy that by means of cooperative doping and charge-compensation, we can successfully improve and tune the stability of pMC relative to pMB for CB4(2-). In the free CBxEy(2-) (E = Al/Ga) species, ptC is thermodynamically less stable than the global ptB in mono- and di-substituted systems, in agreement with the results of Boldyrev and Wang. However, the thermodynamic preference of pMC increases along with the Al/Ga-doping. The pMC species can be further stabilized by the introduction of the alkaline-earth counterion (Mg(2+)). CB2E2Mg (E = Al, Ga) designed in the present study represents the first successful design of a boron-based planar penta-coordinate carbon (ppC) structures as the global minima. The strategy proposed in this study should be useful in the manipulation of competition between exotic pMC and pMB in B-based systems.

Structures and electron affinity of XO30,−, XOF40,− and XO2F20,− (X = P, As, Sb, Bi): a theoretical study of novel superhalogen formulae and exceptions of superhalogen formulae

Most superhalogen species are in the form of oxides or halides. To enrich the family of superhalogen species, herein, we investigated the structures and electron affinity (EA) values of higher group 15 elements (X = P, As, Sb, Bi) oxyfluoride species XO30,−, XOF40,− and XO2F20,−, at the CCSD(T)/aug-cc-pVTZ-pp & aug-cc-pVTZ //B3LYP/aug-cc-pVTZ-pp & aug-cc-pVTZ levels (aug-cc-pVTZ-pp for X = Sb and Bi). Some oxyfluoride species, i.e., PO2F20,−, AsO2F20,−, SbO2F20,−, POF40,−, AsOF40,−, SbOF40,− and BiOF40,−, were found to possess higher EA (VDE: 5.0–6.2 eV; ADE: 4.5–5.5 eV) than halogens (F: 3.4 eV; Cl: 3.6 eV). Thus, we recommended that the oxyfluorides in the form of XO2F20,− and XOF40,− should be considered as potential superhalogens, which have not been considered previously. Surprisingly, we showed that BiO3 and BiO2F2, in superhalogen formulae, possess a high vertical detachment energy (VDE) yet a low adiabatic detachment energy (ADE). This is in marked contrast to the previously reported superhalogens, which generally contain both the high VDE and high ADE values. It is the first report about exceptions of superhalogen formulae. These findings revealed that for the analogous main-group compounds with the same structural formula, the difference in the metallic property of the core element could lead to the significant difference in the ground structures of either the anionic or neutral structures, which would result in the much differed superhalogen features.

Bottom-up substitution assembly of AuF4−n0,−+nPO3 (n = 1–4): a theoretical study of novel oxyfluoride hyperhalogen molecules and anions AuF4−n(PO3)n0,−

Compounds with high electron affinity, i.e. superhalogens, have continued to attract chemists’ attention, due to their potential importance in fundamental chemistry and materials science. It has now proven very effective to build up novel superhalogens with multi-positively charged centres, which are usually called ‘hyperhalogens’. Herein, using AuF4− and PO3 as the model building blocks, we made the first attempt to design the Au,P-based hyperhalogen anions AuF4−n(PO3)n− (n = 1–4) at the B3LYP/6-311+G(d)&SDD and CCSD(T)/6-311+G(d)&SDD (single-point) levels (6-311+G(d) for O, F, P and SDD for Au). Notably, for all the considered Au,P systems, the ground state bears a dioxo-bonded structure with n ≤ 3, which is significantly more stable than the usually presumed mono-oxo-bonded one. Moreover, the clustering of the –PO3 moieties becomes energetically favoured for n ≥ 3. The ground states of AuP4O120,− are the first reported cage-like oxide hyperhalogens. Thus, the −PO3 moiety cannot be retained during the ‘bottom-up’ assembly. The vertical detachment energy (VDE) value of the most stable AuF4−n(PO3)n− (n = 1–4) ranges from 7.16 to 8.20 eV, higher than the VDE values of the corresponding building blocks AuF4− (7.08 eV) and PO3− (4.69 eV). The adiabatic detachment energy values of these four hyperhalogens exceed 6.00 eV. Possible generation routes for AuF4−n(PO3)n− (n = 1–4) were discussed. The presently designed oxyfluorides not only enriches the family of hyperhalogens, but also demonstrates the great importance of considering the structural transformation during the superhalogen → hyperhalogen design such as for the present Au–P based systems.

Can isocyanogen azide exist

Ever since the first attempt at its synthesis in 1912, cyanogen azide (NCN3) has continued to attract the attention of chemists in diverse fields such as photochemistry, organic chemistry, and energetic materials. However, to our great surprise, its isocyanide isomer, CNN3, has not been studied experimentally or theoretically. In this paper, for the first time, we report a theoretical spectroscopic and stability study of CNN3 employing the CCSD and CCSD(T) methods with the aug-cc-pVTZ basis set. In light of its potential multi-reference character, the isomers and transition state structures on the reaction pathway were re-optimized using the multi-configurational CASSCF method in conjunction with the cc-pVTZ basis set. It is shown that CNN3 should be intrinsically stable both with respect to isomerization and fragmentation. The structural and spectroscopic properties obtained in this study should provide useful information for the future laboratory identification of CNN3. For comparison, we also calculated the aug-cc-pVTZ-CCSD(T) and cc-pVTZ-CASSCF properties of NCN3.