Two morphologies of stable, highly ordered assemblies of a long-chain-substituted [2 x 2]-grid-type FeII complex adsorbed on HOPG

The programmed self-assembly of a multimetallic grid-type supramolecular architecture and its hierarchical organization on graphite are described. The doubly functionalized 4,6-bis(2,2'-bipyridyl-6-yl)-2-phenylpyrimidine derivative 1, equipped with CH2OC16H33 moieties at the terminal pyridine rings, was designed as a new bis(tridentate) ligand and synthesized using Stille-type coupling reactions. Treatment of ligand 1 with Fe(BF4)(2)center dot 6H(2)O in CHCl3/CH3CN led to the spontaneous formation of a [2x2]-grid-type FeII complex 2 in quantitative yield. The self-assembled tetranuclear complex 2 was adsorbed onto highly oriented pyrolytic graphite (HOPG) and studied by scanning tunneling microscopy (STM), which showed two morphologies of highly ordered two-dimensional arrays of the metallo-supramolecular architectures. The resulting monolayers of the grid-type complex 2 are much more stable than that obtained from the corresponding unsubstituted grid-type complex owing to the additional attractive forces between the hexadecyl moieties in 2 and the HCPG surface. Moreover, the reproducibility of the STM images of the hexadecyl-substituted grid 2 was strongly improved compared to the unsubstituted one. These results suggest that the introduction of long alkyl chains into metallo-supramolecular architectures would have general advantages for their organization and STM investigation on HOPG. Details of the preparation and the STM investigation of ligand 1 are also presented. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).