The calculations were carried out using the Gaussian09 program package. We also used two other versions of the DFT method, the functionals of which are most adequate for describing the parameters of the molecular and electronic structures of d-elements, namely, DFT M06/TZVP and DFT M062X/Def2TZVP, the details of which are described in. In addition to them, we also calculated the molecular and electronic structures of these compounds using the DFT OPBE/TZVP method, which combines the above TZVP basis and the non-hybrid OPBE functional, which, according to the data of works, in the case of compounds of 3 d-elements, gives a fairly accurate ratio of the energy stability of the high-spin state with respect to the low-spin state and, at the same time, reliably characterizes the key geometric parameters of the molecular structures of the metal compounds under consideration. The use of the given version of the DFT method, in this case, is because, according to, it allows one to obtain, as a rule, the most accurate (i.e., close to experimental) values of the geometric parameters of molecular structures, as well as much more accurate values of thermodynamic and other physical–chemical parameters in comparison with other variants of the DFT method. For comparison, the other version of the DFT method, namely DFT with B3PW91 functional, is described in detail in Refs. In this work, we used the density functional theory (DFT), which combines the standard extended split-valence basis set TZVP and the most modern hybrid functional M06, described in detail in. A discussion of the possibility of the existence of type II compounds for various M of 3 d elements, as well as the dependence of the parameters of their molecular and electronic structure on the nature of M, is the subject of this article. It should be noted that almost every one of these works mentioned the possible use of such compounds as potential high-energy materials. Be that as it may, there is no information about the compounds of formula II in the literature, although a number of publications have considered two-element chemicals containing atoms of s-, p- or d-elements and nitrogen atoms (see, in particular, ).
Although there are six such elements (Mn, Fe, Co, Ni, Cu, and Zn), one can actually expect their formation only for two of them, namely Mn and Fe, for which compounds are known where these elements form seven covalent bonds with other atoms (namely, KMnO 4 and KFeO 4).
Taking into account the number of valence electrons in the 4 s and 3 d orbitals and the valence capabilities of the M atoms of the 3 d elements, it can be expected that compounds with the structural formula II can form a few of these M, namely, only those that have seven or more in the above orbitals more electrons. In this regard, it seems interesting to find out whether, in principle, the existence of chemical compounds of general formula (II) ( Figure 2) is possible, which, like the compounds described in, contain a 12-membered cycle of nitrogen atoms and a nitride anion in an axial position relative to the group of the four nitrogen atoms bonded to the M atom in a total of seven covalent bonds, as follows: Due to the formation of such a structure with the participation of the central atom of the 3d element, stabilization of the structural fragment of twelve nitrogen atoms takes place, which, according to the data presented in, if capable of existing as a separate molecule, is very unstable. In our previous article, a quantum-chemical calculation of the molecular and electronic structures of 3d-element (M) compounds with nitrogen, having a structural formula (I) (see Figure 1) with a ratio between the number of atoms M and nitrogen equal to 1:12, where M = Ti, V, Cr, Mn, Fe, Co, Ni, or Cu, was carried out, and the fundamental possibility of their existence was shown using quantum-chemical methods DFT B3PW91/TZVP, M06/TZVP, OPBE/TZVP, and MP2/TZVP for each of the above d-elements. Among the possible ways to solve this problem is the stabilization of these structures through their “metallization”, the meaning of which is the formation of chemical bonds by nitrogen atoms with atoms of various metals, primarily with atoms of d-elements. One of the very interesting problems of modern inorganic chemistry is the problem of stabilization of polynuclear structures consisting only of nitrogen atoms, and in particular, of various polynitrogens.
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