Postchemistry of inorganic-organic hybrid particles in aqueous solution: metal-cation exchange.

The inorganic–organic hybrid micro/nanoparticles have emerged as an exciting new research area owing to their highly tailorable properties, as well as their potential applications in drug delivery, catalysis, biosensing, biomedical imaging, gas storage, spin-crossover, and optics. Unlike inorganic particles, the inorganic–organic hybrid micro/nanostructures can be easily tuned by switching the different metal centers and linkers. So far, work in this area has predominatly focused on size/shape control, property-tailoring, and nano-technological applications. The inherent chemistry of inorganic–organic hybrid particles remains largely unexplored. The conversion of inorganic-organic hybrid particles into novel micro/nanostructures through the exchange of metal cations or organic ligands, could be technologically useful for creating novel inorganic– organic hybrid materials and achieving new physical phenomena. Recently, our group has already demonstrated the possibility of chemical reactions among organic particles. As part of our ongoing efforts to explore the chemical reactivity of organic and organic–inorganic hybrid micro/nanomaterials, we are increasingly interested in developing inorganic– organic hybrid micro/nanostructures with more-tunable properties through a judicious choice of coordination force and environment. Such procedures would allow for an additional level of control over their morphology as well as the optical, magnetic, and electrical properties. Herein, we report that the discovery of the sub-microspherical particles of polymerized ZnACHTUNGTRENNUNG(SPh)2 networks, formed by a reprecipitation method, can perform a metal– cation exchange in aqueous solution to produce crystalline nanoparticles and nanowires. In a typical experiment, the starting inorganic–organic hybrid material {Zn ACHTUNGTRENNUNG(SPh)2}n (1) was synthesized according to a previously reported procedure. The spherical particles of 1 formed spontaneously on slow addition of a solution of 1 in N,N-dimethylformamide into water in the presence of P123 (poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)) nonionic surfactant. The Zn cations in these spherical particles can be exchanged in aqueous solution by Pb , Cd , or Hg ions to form different shapes, such as wires or pebble-like particles. The successful exchange of metal cations in the framework is due to the different bond energy of the M S bonds and the solubility of the products, that is, the Ksp value. To the best of our knowledge, the metal–cation exchange in the metal–chalcogenide framework together with the change of shape is unprecedented, although the exchange of free-metal cations (not in a framework) in crystalline metal– chalcogenide materials has been demonstrated to enlarge the pore volume or remove hazardous metals from aqueous solution. In most cases, this kind of exchange does not affect the spatial arrange of frameworks. Scanning electron microscopy (SEM) and optical microscopy images of the as-prepared hybrid particles are shown in Figure 1. The SEM image (Figure 1a) of Zn ACHTUNGTRENNUNG(SPh)2 compositions shows spherical particles with an average diameter of 300 ( 200) nm, which is consistent with that measured by dynamic light scattering (DLS). After exchanging Zn ions with Pb , Cd , or Hg ions in aqueous solution, the spherical particles became wire-shaped structures for PbACHTUNGTRENNUNG(SPh)2 and Hg ACHTUNGTRENNUNG(SPh)2, and pebble-like particles for CdACHTUNGTRENNUNG(SPh)2. SEM images revealed that the diameter and length of Pb ACHTUNGTRENNUNG(SPh)2 nanowires were in the range of 500 nm–1 mm and above 5 mm, respectively (Figure 1b), whilst HgACHTUNGTRENNUNG(SPh)2 has a relatively narrow size distribution (200–500 nm) with [a] Dr. Y. Liu, Prof. F. Boey, Dr. L. L. Lao, Prof. H. Zhang, Prof. Q. Zhang School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 (Singapore) Fax: (+65)67909081 E-mail : [email protected] [b] Prof. X. Liu Department of Chemistry National University of Singapore 21 Lower Kent Ridge Road, Singapore 119077 (Singapore) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000865.