Synthesis and Characterization of Copper Complexes Containing the Tripodal N7 Ligand Tris{2‐[(pyridin‐2‐ylmethyl)amino]ethyl}amine (=N′‐(Pyridin‐2‐ylmethyl)‐N,N‐bis{2‐[(pyridin‐2‐ylmethyl)amino]ethyl}ethane‐1,2‐diamine): Equilibrium, Spectroscopic Data, and Crystal Structures of Mono‐ and Trinuclear Copper(II) Complexes

Abstract

AbstractThe stability constants of the CuII chelates with the tripodal heptadentate ligand tris{2‐[(2‐pyridylmethyl)amino]ethyl}amine (=N′‐(pyridin‐2‐ylmethyl)‐N,N‐bis{2‐[(pyridin‐2‐ylmethyl)amino]ethyl}ethane‐1,2‐diamine; tpaa), determined by potentiometry and UV spectrometry, show the formation of [Cu(tpaaH)]3+ and [Cu(tpaa)]2+ species. In the solid state, two mononuclear CuII compounds, [Cu(tpaa)](PF6)2 (1) and [Cu(tpaaH)](ClO4)3⋅H2O (2), and one trinuclear [Cu3(tpaa)2(ClO4)2](ClO4)4⋅2 H2O (3) complex were isolated and characterized by IR, UV/VIS, and EPR spectroscopy. An X‐ray structure of the mononuclear protonated complex 2 shows that the Cu2+ ion has a distorted square‐pyramidal geometry (τ=0.21). and the proton is bound to the secondary‐amine function of one uncoordinated arm of the tripod ligand (Fig. 4). The crystal lattice for 2 is stabilized by the H‐bonds between the N‐atom of the free pyridinyl group with the proton of the free secondary‐amine function of the neighboring molecule. The linear trinuclear complex 3 consists of two entities of the pyramidal mononuclear complex 1 bound to the third central Cu2+ ion by the free unprotonated arms of the ligands in equatorial position (Fig. 5). The octahedral geometry of the third CuII atom is achieved by two perchlorate anions in the axial positions. The redox properties of 1–3 compounds was examined by cyclic voltammetry.