Development of Self-Assembling Nanowires Consisted of One-Dimensional Metal Complexes

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The design and synthesis of electronically conjugated molecular wires are one of the important areas in chemistry due to their potential applications in nano-electronic devices. Quasi-one-dimensional, halogen-bridged mixed-valence complexes[Pt(en)_2][PtX_2(en)_2](ClO_4)_4(X=Cl,Br,I) are low-dimensional solids with the metal atoms in alternating valence(charge density wave,CDW) states. The linear complexes have been available only as structural motifs of bulk crystals, and they were not considered as candidates for the molecular wires.In this study, a novel class of chiral supramolecular assemblies is formed from chloro-bridged, mixed valence complex of platinum and newly developed chiral lipids. When ternary complexes of[Pt(en)_2][PtCl_2(en)_2](lipid)_4 are dispersed in dichloromethane, indigo-colored dispersions are obtained. The color is ascribed to the intervalence charge transfer(CT) absorption of the chloro-bridged complexes, indicating the maintenance of one-dimensional coordinat … More ion structures in solution. Circular dichroism(CD) spectra of these dispersions give intense Cotton effects at 490nm and at 600nm with opposite signs. They are assigned to the induced CD(ICD), since they are observed for the CT absorption bands of the achiral complexes and are in mirror symmetry with respect to the chirality of lipids. Nanocrystals with lamellar supramolecular structures are observed in transmission electron microscopy(TEM) and in high resolution TEM(HRTEM). Upon heating the indigo-colored dispersions to 30℃, fading of the indigo color occurred. Interestingly, the indigo-color is restored after cooling and formation of chiral nanocoils with widths of ca. 40nm and pitches of ca. 20nm are observed by atomic forcemicroscopy(AFM). The sense of these nanocoils is dependent on chirality of the amphiphiles, in good agreement with the observed ICD spectra. The supramolecular self-assembly of linear metal complexes and chiral molecular assemblies would be widely applied to the development of chiral organic/inorganic nanoarchitectures. Less