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

A new pendant-armed macrocyclic ligand, L-1, 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 L-1 shows the formation of tubular arrays, and reveals intra- and inter-molecular pi-stacking interactions between the pyridyl groups of the macrocyclic backbone. Metal complexes of L-1 have been synthesized and characterized by microanalysis, MS-FAB, conductivity measurements, IR, UV-Vis, H-1 and C-13 NMR spectroscopy and magnetic studies. Crystal structures of the ligand L-1 as well as of the complexes [ZnL1](NO3)(2).2H(2)O, [Ag2L1(NO3)(2)] and [Ag2L1](ClO4)(2).4CH(3)CN 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).4CH(3)CN showing a monomeric and a polymeric nature respectively. The crystal structure of [ZnL1(NO3)(2)].2H(2)O shows a mononuclear endomacrocyclic complex with the metal ion coordinated to the six nitrogen atoms in a distorted octahedral environment.