Synthesis of a new tetra-cyanomethylated macrocyclic ligand with a nanotubular structure. X-Ray crystal structures of mono-, di-nuclear and polymeric metal complexes

Abstract

A new pendant-armed macrocyclic ligand, L¹, bearing four cyanomethyl pendant groups has been synthesized by N-alkylation of the tetraazamacrocyclic precursor L with bromoacetonitrile. The X-ray structural analysis of the ligand L¹ shows the formation of tubular arrays, and reveals intra- and inter-molecular π-stacking interactions between the pyridyl groups of the macrocyclic backbone. Metal complexes of L¹ have been synthesized and characterized by microanalysis, MS-FAB, conductivity measurements, IR, UV-Vis, ¹H and ¹³C NMR spectroscopy and magnetic studies. Crystal structures of the ligand L¹ as well as of the complexes [ZnL¹](NO₃)₂·2H₂O, [Ag₂L¹(NO₃)₂] and [Ag₂L¹](ClO₄)₂·4CH₃CN have been determined by single crystal X-ray crystallography. Different macrocyclic disposition has been found in relation to the metal ion employed and even when different salts of the same metal are used. The X-ray studies show the presence of two metal atoms within the macrocyclic ligand in [Ag₂L¹(NO₃)₂] and [Ag₂L¹](ClO₄)₂·4CH₃CN showing a monomeric and a polymeric nature respectively. The crystal structure of [ZnL¹(NO₃)₂]·2H₂O shows a mononuclear endomacrocyclic complex with the metal ion coordinated to the six nitrogen atoms in a distorted octahedral environment.