Comparative stability of isomeric (565)macrotricyclic chelates of 3d-elements formed in the systems M(II)-thiosemicarbazide-formaldehyde according to DFT B3LYP data

Comparative stability of three types of (565)macrotricyclic chelates of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) with chelate nodes MN₂S₂ and MN₄ have been analyzed by means of hybrid density functional method B3LYP with the 6-31G(d) basis set using GAUSSIAN-09 software. These chelates may potentially be formed in template interaction between gelatin-immobilized hexacyanoferrate(II) of respective metal ions M(II), thiosemicarbazide H₂N-HN-C(=S)-NH₂, and formaldehyde H₂C=O. It has been demonstrated that for all M(II) considered, the complex with chelate nodes MN₂S₂ is more stable. Key structural parameters of the complexes (bond lengths, bond and torsion angles) are presented. It is noted that pseudotetrahedral coordination of ligand donor centers around M(II) is typical for Mn(II), Co(II), Cu(II), and Zn(II), whereas for Fe(II) and Ni(II) it is almost planar. Values of standard enthalpy ΔH _f,298 ⁰ and standard Gibbs energy ΔG _f,298 ⁰ are positive for nearly all the complexes studied.