DFT Quantum-chemical consideration of M(V) (M= V, Cr, Mn, Fe) macrocyclic complexes consisting of porphyrazine and axial nitrido ligands

Using the DFT OPBE/TZVP and DFT B3PW91/TZVP model chemistries, the standard thermodynamic parameters of formation (enthalpy [Formula: see text], entropy [Formula: see text], and Gibbs energy [Formula: see text] and the energies of the M – nitrido ligand bond for heteroligand complexes of the general formula [M L(N)] ([Formula: see text] is a doubly deprotonated form of porphyrazine, M – 3[Formula: see text]-element) were calculated. Based on these data, it was concluded that the most stable of them are complexes V, and upon passing from M = V to M = Cr, their stability decreases, from M = Cr to M = Mn, it increases, and from M = Mn to M = Fe, it decreases again. At the same time, it was noted that compounds with [M L(N)] composition, where M = Sc, Ti, Co, Ni, Cu, Zn, cannot exist. The key parameters of molecular structures of [V L(N)], [Cr L(N)], [Mn L(N)], and [Fe L(N)], namely bond lengths and bond angles, were calculated from these coordination compounds. It was noted that in each of them, the MN ₄ chelate node has a square-pyramidal structure with the nitrogen atoms in a planar orientation. Moreover, the 5-membered and 6-membered non-chelate rings have a strictly planar structure, while the 6-membered chelate rings are non-coplanar, with the sum of the internal bond angles deviating from the sum of the internal angles in a planar hexagon by no more than [Formula: see text]. NBO analysis of these compounds was performed, and based on its data, a high degree of delocalization of the electron density in them was concluded. Good agreement was also observed among the structural parameters obtained using the above-mentioned alternative DFT model chemistries.