Photoelectron Spectroscopy and Ab Initio Study of the Structure and Bonding of Al7N- and Al7N

Breaking the Hoff/Le Bel rule by an electron-compensation strategy: the global energy minimum of NGa4S4. Phys Chem Chem Phys 2024;26:3907-3911. [PMID: 38230710 DOI: 10.1039/d3cp05290g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In tetracoordinate chemistry, there is an attractive scientific problem of how to make the planar configuration more stable than the tetrahedral configuration. For tetracoordinate nitrogen, the abundant studies indicate that the planar tetracoordinate nitrogen (ptN) is far less stable than the tetrahedral tetracoordinate nitrogen (ttN). Herein, we introduced four S atoms to the unstable ptN-NGa4+ and stable ttN-NGa4+ by following an electron-compensation strategy. Surprisingly, ptN-NGa4S4+ is more stable than ttN-NGa4S4+. Thermodynamically, ptN-NGa4S4+ is the global energy minimum, which is 46.7 kcal mol-1 lower in energy than ttN-NGa4S4+. Dynamically, the BOMD simulations indicated that ptN-NGa4S4+ has excellent dynamic stability at 4, 298, 500 and 1000 K, but the ttN-NGa4S4+ is isomerized at 1000 K. Electronically, the HOMO-LUMO gap of ptN-NGa4S4+ (6.91 eV) is much wider than that of ttN-NGa4S4+ (5.25 eV). Moreover, AdNDP analyses showed that the eight 2c-2e Ga-S σ-bonds eliminated the 4s2 lone pair/4s2 lone pair repulsion between the four Ga atoms and provided a strong spatial protection for ptN-NGa4S4+; and that the four 3c-2e Ga-S-Ga π back-bonds could compensate electrons for Ga, weakening the electron-deficiency of Ga. Simultaneously, the double 6σ/2π aromaticity further enhanced the stability of ptN-NGa4S4+. Thus, as the dynamically stable global energy minimum displaying double aromaticity, ptN-NGa4S4+ will be more promising than ttN-NGa4S4+ in gas phase generation.

A theoretical study of vibronic coupling in the photoelectron spectra of Al6N. Phys Chem Chem Phys 2023;25:12990-13003. [PMID: 37165932 DOI: 10.1039/d3cp00836c]

This work emphasizes the appearance of non-adiabatic effects in the photoelectron spectra of Al₆N^-. It includes ab initio electronic structure calculations obtained on the first seven low-lying electronic states of Al₆N^- and a nuclear dynamics study utilizing time-dependent and time-independent quantum chemistry approaches. A model vibronic Hamiltonian is constructed in a diabatic electronic representation to estimate the coupling parameters corresponding to the fifteen vibrational modes of Al₆N^-. Theoretical spectral bands are achieved by employing the vibronic coupling theory followed by reduced dimensional calculations to understand the role of individual vibrational modes in the overall photoelectron spectra. Finally, the theoretically obtained photodetachment spectra show good agreement with the experimental spectra revealing vibronic coupling among the closely spaced spectral bands.

Plasma-Assisted Dinitrogen Activation on Small Cobalt Clusters: Co4 N9 + with Enhanced Stability

We have performed a study on the accommodation of nitrogen doping toward superatomic states of transition metal clusters. By reacting cobalt clusters with N₂ in the presence of plasma radiation, a large number of odd-nitrogen clusters were observed, typically Co₃ N_2m-1 ⁺ (m=1-5) and Co₄ N_2m-1 ⁺ (m=1-6) series, showing N≡N bond cleavage in the mild plasma atmosphere. Interestingly, the Co₃ N₇ ⁺ , Co₄ N₉ ⁺ , and Co₅ N₉ ⁺ clusters exhibit prominent mass abundances. First-principles calculation results elucidate the stability of the diverse cobalt nitride clusters and find unique stability of Co₄ N₉ ⁺ with a swallow-kite structure of which four coordinated N₂ molecules causes a significantly enlarged HOMO-LUMO gap, while the single N atom doping gives rise to superatomic states of 1S² 1P³ ||1D⁰ . We reveal an efficient dinitrogen activation strategy by reacting multiple N₂ molecules with cobalt clusters under a plasma atmosphere.

Nitrogen versus carbon in planar pentacoordinate environments supported by Be5Hn rings

Nitrogen is a better fit for Be₅H_n rings, both geometrically and electronically, than carbon, leading to the viable planar pentacoordinate nitrogen species.

ReB6-: A Metallaboron Analog of Metallabenzenes

Metallabenzenes are a class of molecules in which a CH unit in benzene is replaced by a functionalized transition-metal atom. While all-boron analogues of aromatic and antiaromatic hydrocarbons are well-known, there have not been any metallaboron analogs. We have produced and investigated two metal-doped boron clusters, ReB₆^- and AlB₆^-, using high-resolution photoelectron imaging and quantum chemical calculations. Vibrationally resolved photoelectron spectra have been obtained and compared with the theoretical results. The ReB₆^- cluster is found to be perfectly planar with a B-centered hexagonal structure (C_2v, ¹A₁), while AlB₆^- is known to have a similar structure, but with a slightly out-of-plane distortion (C_s, ¹A'). Chemical bonding analyses show that the closed-shell ReB₆^- is doubly σ- and π-aromatic, while AlB₆^- is known to be σ-aromatic and π-antiaromatic. The out-of-plane distortion in AlB₆^- is due to antiaromaticity, akin to the out-of-plane distortion of the prototypical antiaromatic cyclooctatetraene. The π-bonding in ReB₆^- is compared with that in both benzene and rhenabenzene [(CO)₄ReC₅H₅], and remarkable similarities are found. Hence, ReB₆^- can be viewed as the first metallaboron analog of metallabenzenes and it may be viable for syntheses with suitable ligands.

Exploring the low-lying structures of Aun(CO)+ (n = 1–10): adsorption and stretching frequencies of CO on various coordination sites

Adsorption of CO on cationic gold clusters is insensitive to the structural details of the adsorption site.