Pillared honeycomb nanoarchitectures formed on solid surfaces by the self-assembly of lipid-packaged one-dimensional Pt complexes

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Abstract
A highly lipophilic polyion complex [Pt(en)2][PtCl2(en)2](1)4 (en, 1,2-diaminoethane) is prepared from one-dimensional mixed valence PtII/PtIV complex and newly designed chiral amphiphile 1. The powdery sample showed purple color, which is a result of the mixed valence absorption of the linear chlorobridged complex (PtII-Cl-PtIV-Cl-)n. When the lipid complex is dispersed in dichloromethane, purple-colored dispersion is obtained at 0°C, whereas the color disappears after heating the solution to 21°C. The observed thermochromism is reversible with respect to the temperature changes and is ascribed to the reversible dissociation and reassembly of the self-assembling inorganic wires. Casting of the 0°C-purple dispersion on solid substrates affords honeycomb nanostructures in addition to the nanowires with the width of about 20 nm. The honeycomb patterns seem to be templated by the condensed water droplets that are formed and aligned on the rapidly evaporating dichloromethane solution. On the other hand, more regular honeycomb structures are exclusively obtained by casting the 21°C-colorless solution. These observations indicate that the ordered honeycomb structures are obtainable on solid surfaces by the self-assembly of molecularly dispersed components [Pt(en)2](1)2 and trans-[PtCl2(en)2](1)2. Very interestingly, formation of double-layered honeycomb nanostructure is observed by scanning electron microscopy. The unit hexagons and pillars of the honeycombs are made of nanowires that are hierarchically assembled from the lipid-packaged PtII/PtIV complexes. The surface self-organization of lipophilic inorganic complexes has a potential to fabricate novel nanoarchitectures with conjugated electronic structures.