Nano-film structures constructed by self-assembly of Co(III) biuretato complexes and long alkyl imidazolium cations.

A Co(III) biuretato complex, [Co(III){ph(biu)2}]- (ph(biu)2 = o-phenylenebis(biuretato)) can form layer structures by its self-assembling with a multiply hydrogen bonding network. PPh4[Co(III)(ph(biu)2}]. 3CHCl3 (PPh4+ = Tetraphenylphosphonium cation) crystallizes in the triclinic, space group P1, with a = 9.740(5) A, b = 13.980(8) A, c = 16.792(9) A, alpha = 103.976(7) degrees, beta = 95.592(8) degrees, gamma = 103.165(8) degrees, V = 2132 A3, and Z=2. In the crystal, counter cations, PPh4+, are inserted between the layer structures of [Co(III){ph(biu)2}]- aggregates, resulting in formation of a multi-layered structure. A treatment of K[Co(III){ph(biu)2}] with C18MelmCl (C18Melm+ = 1-octadecyl-3-methyl-imidazolium cation) in an aqueous solution with a trace amount of PPh4Cl, gave the glaring silver solution containing self-organized nano-film structures. Optical microscopic and AFM studies clearly showed that rectangle-shaped nano-film structures were formed by self-assembly of [Co(III){ph(biu)2}]- and C18Melm+ in the solution, and their sizes were approximately ranged to 6-13 microm in length, 3-7 microm in width and 25.2 +/- 6.2 nm in thickness. Using spectroscopic and XRD data, we concluded that these nano-films have a alternatively accumulated multilayer-structure of [Co(III){ph(biu)2}]- layer and C18Melm+ bilayer structures, the repeating distance being d001 = 2.22 nm.