Using density functional theory (DFT) with dispersion correction and ab initio post Hartree–Fock methods, we treat the bonding, the structure, the stability, and the spectroscopy of the complexes between Znq+ and imidazole (Im), Znq+Imn (where q = 0, 1 and 2; n = 1–4). These entities are subunits of zeolitic imidazolate frameworks (ZIFs) and Zn–enzymes, which possess relevant roles in industrial and biological domains, respectively. We also investigate the Imn (n = 2–4) clusters for comparison. For each species, we determine several new structures that were not found previously. Our calculations show a competition between atomic metal solvation, by either σ-type interactions or π-stacking type interaction, and proton transfer through hydrogen bonding (H-bonding) in charged species. This results in several geometrical environments around the metal. These are connected with structural properties and the functional role of Zn cation within ZIFs and Zn–enzymes. Moreover, we show that the Zn2+Imn subunits do not absorb in the visible domain, which may be related to the photostability of ZIFs. Our findings are important for the development of new applications of ZIFs and metalloenzymes.
The dications MgS2+ and SiN2+, experimentally observed by mass spectroscopy, are theoretically studied here. The potential energy curves of the electronic states of the two dications MgS2+ and SiN2+ are mapped and their spectroscopic parameters determined by analysis of the electronic, vibrational and rotational wave functions obtained by using complete active space self-consistent field (CASSCF) calculations, followed by the internally contracted multi-reference configuration interaction (MRCI)+Q associated with the AV5Z correlation consistent atomic orbitals basis sets. In the following, besides the characterization of the potential energy curves, excitation and dissociation energies, spectroscopic constants and a double-ionization spectra of MgS and SiN are determined using the transition moments values and Franck-Condon factors. The electronic ground states of the two dications appear to be of X3Σ− nature for MgS2+ and X4Σ− for SiN2+ and shows potential wells of about 1.20 eV and 1.40 eV, respectively. Several excited states of these doubly charged molecules also depicted here are slightly bound. The adiabatic double-ionization energies were deduced, at 21.4 eV and 18.4 eV, respectively, from the potential energy curves of the electronic ground states of the neutral and charged species. The neutral molecules, since involved, are also investigated here. From all these results, the experimental lines of the mass spectra of MgS and SiN could be partly assigned.
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