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.