Conglomeration of Uniform Submicrospheres via Sonication. Morphology on Ionic Platinum(II) Complexes of Dodecylmethylbis(m-pyridyl)silane

Abstract

Submicro-scale materials have been utilized in the fabrication of task-specific materials for catalysts, electronic devices, drug-delivery medicines, ceramics, pigments, molecular recognizers, decicants, and cosmetics. Thus, the ability to manipulate the submicro morphology via various factors such as chemical structures, surface properties, and formation condition is emerging as an important field of functional fine materials. Steric effects, surface tension, capillary effects, electric and magnetic forces, permanent dipoles, van der Waals interaction, hydrophilic interactions, surfactant/precursor ratio, covalent bond, and shape anisotropy have been applied as driving forces in the formation of artificial submicro/nano morphology. Among various morphologies, spherical metal oxides have been widely studied, but the submicrospheres of metal complexes are very rare. In order to explore the formation and conglomeration of submicrospheres on ionic platinum(II) complex containing dodecylmethylbis(m-pyridyl)silane (L) without addition of any additives, we carried out the reaction of (dppp)Pt(PF6)2 (dppp: 1,3-bis(diphenylphosphino)propane) with L. The ionic metal complex is interesting in the formation of submicrospheres since they have tractable amphiphilic properties. Furthermore, the platinum(II) chemistry can be attributed to catalysis and antitumor drugs. The ionic platinum(II) complex was prepared by the reaction of (dppp)Pt(PF6)2 with L in a mixture of acetone and water as shown in Scheme 1. In a typical preparation, L (0.1 mmol) in 5 mL of acetone was added slowly to (dppp)Pt(PF6)2 (0.1 mmol) in 5 mL of acetone solution, and then 10 mL of water was added into the reaction solution. The reaction mixture was refluxed for 12 h, and evaporation of acetone at ambient temperature gave a white spherical product of [(dppp)Pt(L)]2(PF6)4 in 81% yield. The spheres were collected by the filtration using a membrane (membrane filter, Advantec MFS Inc.) for further characterization. The submicrospheres were characterized by H NMR, IR (ν (PF6) = 847 cm−1), contact angle, and SEM along with satisfactory chemical analysis (Supporting Information). The spherical product is a stable solid under air and moisture. In order to measure the molecular weight of the product, the spheres were dissolved in acetone, and then the solution was mixed with 3-nitrobenzyl alcohol (Sigma, USA) on a FAB probe tip. The mass fragments indicate that the product is a cyclodimeric structure as depicted in Figure 1. SEM images show that the colloidal spheres have diameters in the range of 220-400 nm (average diameter ≈ 290 nm) as shown in Figure 2. The submicrosphere (SMS) is hardly soluble in water, but are soluble in a mixture of water and acetone, indicating that the SMS is typical amphiphilic materials. Such an amphiphilic solubility may be a driving force for the formation of spherical morphology. The part around platinum(II) cation and PF6 counteranions seems to be hydrophilic, and L moiety with a new long hydrophobic