Formation of Two Diverse Classes of Poly(amino-alkoxide) Chelates and Their Mononuclear and Polynuclear Lanthanide(III) Complexes

Factors that influence aggregation of lanthanide(III) (Ln^III) ions to form polynuclear complexes were studied utilizing 1-aziridineethanol as a versatile source of macrocyclic and acyclic chelates. The facile ring-opening cyclo-oligomerization of 1-aziridineethanol leads to the formation of a series of polyaza cyclic oligomers (series A). In the presence of ethylenediamine, a competing N-alkylation reaction occurs to produce a new class of acyclic ligands (series B). The cyclo-oligomerization of four 1-aziridineethanol units is the most favorable process, leading to the formation of the 12-membered cyclen-type macrocycle, H₄L¹ (1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraaza-cyclododecane). Ring-opening cyclo-oligomerization of 1-aziridineethanol in the presence of Ln^III ions produces self-assembled mononuclear, tetranuclear, and pentanuclear compounds of H₄L¹. In the presence of ethylenediamine, oligomerization of 1-aziridineethanol results in a dinuclear complex of an acyclic poly(amino-alkoxide) H₂L². The coordinative unsaturation of (i) the alkoxy sites of [H_xL¹]^x-4 (where x < 4) and (ii) Ln^III ions in coordination numbers less than nine are critical factors in the formation of the polynuclear Ln^III complexes. The identities of mononuclear, dinuclear, tetranuclear, and pentanuclear complexes herein discussed were established by X-ray crystallography.