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

Bis(pyrrol-2-ylmetyhleneamine) ligands linked by alkyl spacers between the imine nitrogens are shown to give di-nuclear dimers or mononuclear monomers, depending on the length of the alkyl linker, upon coordination with Cu-II. Ligands containing ethylene or hexylene linkers -(CH2)(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 Cu-II 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 Cu-II centers to form a rectangular macrocycle, while in 8b they are bonded to two Cu-II 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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).