Lead(II) complexes with amide-appended tetraazamacrocyclic ligands – Synthesis, structure, characterization and calculation studies

Five new lead(II) complexes {[Pb(DOTAM)](OTf)2 (1a), [Pb(TETAM)](OTf)2·2H2O (2a), [Pb(TETAM)](ClO4)2·2.8H2O (2b), [Pb(TRITAM)]2(OTf)4 (3a), [Pb(TRITAM)](ClO4)2·nH2O (3b, n = 2.3 or 2.4)} with amide-appended tetraazamacrocyclic ligands were synthesized and characterized structurally, spectroscopically and thermogravimetrically. The crystal structures were solved based on the single-crystal X-ray diffraction and were compared with molecular geometries obtained from the DFT B3LYP/LANL2DZ,6-31G(d,p) calculations. The dimeric [Pb(TRITAM)]24+ (3a) and monomeric [Pb(TRITAM)]2+ (3b) complexes were obtained by reactions of lead(II) triflate and perchlorate with TRITAM. For the other ligands, the monomeric cationic complexes were only obtained. The total coordination number of the lead(II) ion is nine in 3a and eight in the remaining compounds. The coordination polyhedrons around the metal center adopt distorted mono-capped square antiprismatic and square antiprismatic geometries. The complexes were analyzed by FT-IR and UV–Vis techniques. UV–Vis and IR spectra of three simple cationic complexes were also simulated by DFT and TD-DFT calculations. TD-DFT simulations indicated that the lowest energy absorption band is mainly due to the 6s → 6p transition within the lead(II) ion. TGA studies demonstrated high thermal stability of the studied complexes which are stable even to about 300 °C.