Self-assembly of bis(pyrrol-2-ylmethyleneamine) ligands with Cu II controlled by bridging [-(CH2)n-] spacers and weak intermolecular C-H⋯Cu hydrogen bonding

Abstract

Bis(pyrrol-2-ylmetyhleneamine) ligands linked by alkyl spacers between the imine nitrogens are shown to give dinuclear dimers or mononuclear monomers, depending on the length of the alkyl linker, upon coordination with Cu II. Ligands containing ethylene or hexylene linkers -(CH 2)n- (n = 2, 6) give dinuclear dimers 5 and 8, while propylene and butylene chains (n = 3, 4) give mononuclear monomers 6 and 7. X-ray crystal structural analysis reveals that 5 exists as two very similar isomers 5a and 5b, in which the two ligands are bound to two CuII centers to form a distorted helical conformation. In the unit cells of 8, two entirely different isomers 8a and 8b are found. In 8a two ligands are side-by-side bound to two CuII centers to form a rectangular macrocycle, while in 8b they are bonded to two CuII centers to form a distorted double-stranded helix. Moreover, X-ray structural analysis reveals that complexes 5-8 are further assembled into one-dimensional polymers through weak, intermolecular C-H⋯Cu hydrogen bonding, which plays a crucial role in stabilizing the crystal lattice. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.