DFT STUDY ON THE RELATIVE STABILITY OF ISOMERIC MACROCYCLIC METAL CHELATES OF DIVALENT 4d-ELEMENT IONS WITH TETRADENTATE (NSSN)- AND (NNNN)- “TEMPLATE” LIGANDS
Using the density functional method (DFT) in the OPBE/TZVP//QZP approximation and the Gaussian09 program, geometric parameters and total energies of molecular structures of the Mo(II), Tc(II), Ru(II), Rh(II), Pd(II), Ag(II) and Cd(II) macrotricyclic complexes with (NSSN)- and (NNNN)-coordinations of the ligand donor centers to the complex, arising as a result of complexing between M(II) indicated above, dithiooxamide H2N–C(= S)–C(= S)–NH2 and glyoxal HC(=O)–CH (=O), were calculated. Based on the data of this calculation, it is shown that in the case of Mo(II), Tc(II), Ru(II), Rh(II) and Pd (II) complexes with (NSSN)-coordination of ligand are more stable, whereas in the case of Ag(II) and Cd(II), with (NNNN)-coordination; in addition, for the Mo(II) and Ru(II) complexes, a pseudo-tetrahedral environment of the central metal ion takes place by donor atoms, while for the complexes Tc(II), Rh(II), Pd(II), Ag(II), and Cd(II) are planar ones. The bond lengths and bond angles in the indicated coordination compounds are given and it is noted that the Ag(II) and Cd(II) complexes are almost flat, the Tc(II), Rh(II), and Pd(II) complexes are small, while the Ru(II), a fairly significant deviation from coplanarity. The five-membered metal chelate cycles formed as a result of complexing, in most of these complexes are either practically flat, or exhibit a slight (within 5°) deviation from coplanarity; the only exceptions are the Mo(II) and Ru(II) complexes.