New macrocyclic dioxotetraamines bearing 2-pyridylmethyl as functional donor pendant(s): synthesis, properties and crystal structure of their copper(II) complexes†

Abstract

Two new macrocyclic dioxotetraamines 4-(pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione (H₂L¹) and 4,7-bis(pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione (H₂L²) have been synthesized and characterized. The solution behaviors of their copper(II) complexes have been studied with ESR, UV/VIS and cyclic voltammetric techniques. Reaction of H₂L² with Cu(O₂CMe)₂ in methanol solution yielded a doubly deprotonated dioxotetraamine copper(II) complex, [CuL²]·6H₂O, the structure of which has been determined by X-ray diffraction analysis. The Cu atom is five-co-ordinated by four basal nitrogens and one pendant pyridine nitrogen, forming a distorted square pyramid in which N(21) of the pendant pyridine nitrogen is at the apical site. The Cu–N(21) bond distance [2.203(7) Å] is longer than the basal average Cu–N bond length [1.985(4) Å] due to the Jahn–Teller effect.