Moonhyun Oh

Chemically tailorable colloidal particles from infinite coordination polymers

Micrometre- and nanometre-sized particles play important roles in many applications, including catalysis, optics, biosensing and data storage. Organic particles are usually prepared through polymerization of suitable monomers or precipitation methods. In the case of inorganic materials, particle fabrication tends to involve the reduction of a metal salt, or the controlled mixing of salt solutions supplying a metal cation and an elemental anion (for example, S-, Se-, O-), respectively; in some instances, these methods even afford direct control over the shape of the particles produced. Another class of materials are metal-organic coordination polymers, which are based on metal ions coordinated by polydentate organic ligands and explored for potential use in catalysis, gas storage, nonlinear optics and molecular recognition and separations. In a subset of these materials, the use of organometallic complexes as ligands (so-called metalloligands) provides an additional level of tailorability, but these materials have so far not yet been fashioned into nano- or microparticles. Here we show that simple addition of an initiation solvent to a precursor solution of metal ions and metalloligands results in the spontaneous and fully reversible formation of a new class of metal–metalloligand particles. We observe initial formation of particles with diameters of a few hundred nanometres, which then coalesce and anneal into uniform and smooth microparticles. The ease with which these particles can be fabricated, and the ability to tailor their chemical and physical properties through the choice of metal and organic ligand used, should facilitate investigations of their scope for practical applications.

Self-Template-Directed Formation of Coordination-Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings†

This template will self-destruct: A unique particle-growth mechanism involves growth of new coordination polymers on the surface of initially formed hexagonal blocks and concomitant dissolution of the blocks to form hexagonal tubes (see scheme and scanning electron, optical, and fluorescence microscopy images). Calcination of the tubes yields ZnO particles of the same shape.

Growth-Controlled Formation of Porous Coordination Polymer Particles

Diversely shaped porous coordination polymer particles (CPPs) were synthesized by a simple solvothermal reaction of 1,4-benzenedicarboxylic acid (H2BDC) and In(NO3)3 x xH2O in DMF. The growth of crystalline CPPs was controlled through a particle growth blocking event involving blocking agent interaction with particular facets of CPPs and simultaneous particle growth interruption in a specific direction. Systematic reactions in the presence of various amounts of pyridine as a blocking agent were conducted to see the controlled CPP formation. Long rod, short rod, lump, and disk-shaped CPPs with hexagonal faces resulted in the presence of none, 1 equiv, 2 equiv, and 25 equiv of pyridine, respectively. The ultimate particle shape produced depends upon the amount of blocking agents used.

Monitoring Shape Transformation from Nanowires to Nanocubes and Size‐Controlled Formation of Coordination Polymer Particles

Infinite coordination polymers in which metal ions or metal clusters are connected bymolecular building blocks consisting of organic molecules or organometallic complexes have received a great deal of attention due to their useful applications in gas storage, catalysis, optics, recognition, and separation. Rationalization of their chemical and physical properties from structural studies is of fundamental interest in the field of coordination polymer materials. Similarly, microand nanostructured materials are essential in many different areas, such as catalysis, optics, biosensing, medical diagnostics, and data storage, and their size, shape, and composition are the key parameters that dictate chemical and physical properties. Recently, a synthetic strategy for the preparation of microand nanoparticles made from infinite coordination polymers has been demonstrated by several groups. This new class of materials promises to advance nanoparticle science into the realm of infinite coordination polymers, and thereby circumvent the nominal composition limitations generally ascribed to nanoparticles. Control of the composition of nanoparticles generated from functionally defined precursors is a promising research area due to the fundamental interest in materials that have practical applications in chemistry, biology, physics, and related interdisciplinary fields. Coordination polymer particles (CPPs) made from functional metalloligand building blocks have been shown to have a high degree of tailorability. The development and application of CPP materials requires an understanding of how the particles are formed, and the ability to control their size and shape. Herein we describe a solvothermal approach for the synthesis of CPPs made from transition-metal ions and metallosalen (salen= N,N’-bis(salicylidene)ethylenediamine) building blocks. We also describe an interesting nanoparticle wire-to-cube morphological transformation, and the utilization of this transformation process to control CPP formation. In a typical synthesis, fluorescent cubic nanoparticles were prepared by the following simple procedure (Scheme 1): carboxy-functionalized salen ligand N,N’-phenylenebis(salicylideneimine)dicarboxylic acid (1, 3 mg) was dissolved in DMSO (1 mL), and the solution was added to DMF (2 mL) containing two equivalents Zn(OAc)2. One equivalent of Zn coordinates to the salen pocket to give Zn-metalated salen (Zn-MS) complex. The other Zn ion acts as a node that connects to the Zn-MS metalloligands through the carboxylate groups to form coordination polymer (Zn-MSZn); when one equivalent Zn is used, the coordination polymer does not form. The resulting solution was heated at 120 8C for 60 min. During this time, formation of particles was observed. The reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation and washed several times with DMSO and methanol. The resulting particles were found to be stable in organic solvents (methanol, acetone, DMF, DMSO, and nonpolar solvents), water, and in the dried state. The morphology was characterized by field-emission scanning electron microscopy (SEM; Figure 1). The images show cubic particles with an average size of (308 36) nm. Dynamic light scattering (DLS) measurements on a colloidal Scheme 1. Preparation of Zn-MS-Zn coordination polymers as nanowires and their subsequent transformation into nanocubes.

Coordination polymer nanorods of Fe-MIL-88B and their utilization for selective preparation of hematite and magnetite nanorods

Coordination polymer nanorods are synthesized from the hexagonal 3D structure of Fe-MIL-88B. Subsequently, hematite (α-Fe(2)O(3)) and magnetite (Fe(3)O(4)) nanorods are selectively prepared by controlling the calcination conditions of coordination polymer nanorods.

Multi Ball‐In‐Ball Hybrid Metal Oxides

Scheme 1 . Preparation of multi ball-in-ball hybrid metal oxides. Many examples of microand nanoscale particles made from atomic or molecular building blocks are known, with these systems having been extensively explored due to their useful properties. [ 1–6 ] Currently, efforts are ongoing to manipulate the composition, as well as its size and morphology, of particles as part of systematic attempts to alter their chemical and physical properties. Within this context, chemical transformation has emerged a useful method for tuning the composition. [ 7 , 8 ]

One-pot synthesis of magnetic particle-embedded porous carbon composites from metal-organic frameworks and their sorption properties.

Nano- and micro-composites comprised of porous carbon and magnetic particles are prepared by one-step pyrolysis of metal-organic frameworks (MOFs). The porosity and composition of resulting magnetic porous carbons are facilely regulated by altering the pyrolysis temperature and changing the organic building blocks incorporated within the initial MOFs.

Dual Changes in Conformation and Optical Properties of Fluorophores within a Metal–Organic Framework during Framework Construction and Associated Sensing Event

Microsized chemosensor particle (CPP-16, CPP means coordination polymer particle), which is made from a metal-organic framework (MOF), is synthesized using pyrene-functionalized organic building block. This building block contains three important parts, a framework construction part, a Cu(2+) detection part, and a fluorophore part. PXRD studies have revealed that CPP-16 has a 3D cubic structure of MOF-5. During both MOF formation and sensing event, fluorophores within CPP-16 undergo dual changes in conformation and optical properties. After MOF construction, pyrene moieties experience an unusual complete conversion from monomer to excimer form. This conversion takes place due to a confinement effect induced by space limitations within the MOF structure. The selective sensing ability of CPP-16 on Cu(2+) over many other metal ions is verified by emission spectra and is also visually identified by fluorescence microscopy images. Specific interaction of Cu(2+) with binding sites within CPP-16 causes a second conformational change of the fluorophores, where they change from stacked excimer (CPP-16) to quenched excimer states (CPP-16·Cu(2+)).

Cellulose pretreatment with 1-n-butyl-3-methylimidazolium chloride for solid acid-catalyzed hydrolysis

This study has been focused on developing a cellulose pretreatment process using 1-n-butyl-3-methylimidazolium chloride ([bmim]Cl) for subsequent hydrolysis over Nafion(R) NR50. Thus, several pretreatment variables such as the pretreatment period and temperature, and the [bmim]Cl amount were varied. Additionally, the [bmim]Cl-treated cellulose samples were characterized by X-ray diffraction analysis, and their crystallinity index values including CI(XD), CI(XD-CI) and CI(XD-CII) were then calculated. When correlated with these values, the concentrations of total reducing sugars (TRS) obtained by the pretreatment of native cellulose (NC) and glucose produced by the hydrolysis reaction were found to show a distinct relationship with the [CI(NC)-CI(XD)] and CI(XD-CII) values, respectively. Consequently, the cellulose pretreatment step with [bmim]Cl is to loosen a crystalline cellulose through partial transformation of cellulose I to cellulose II and, furthermore, the TRS release, while the subsequent hydrolysis of [bmim]Cl-treated cellulose over Nafion(R) NR50 is effective to convert cellulose II to glucose.

Facile Synthetic Route for Thickness and Composition Tunable Hollow Metal Oxide Spheres from Silica‐Templated Coordination Polymers

chemical sensors, [ 2 ] photonic devices, [ 3 ] energy storage, [ 4 ] chemical reactors, [ 5 ] and drug delivery. [ 6 ] Several methods, including template-free methods [ 7 ] and templating methods using either hard or soft templates, [ 8 ] have been developed to fabricate hollow structures. Templating methods often yield products with narrow size distributions and clear-cut structural features. In addition, the size of hollow products prepared using templating methods can be controlled easily by varying the size of the templates used in the reactions. However, there are inherent drawbacks involved in immobilizing desired materials on template surfaces due to potential incompatibilities between materials. On the other hand, coordination polymer materials, including macroscaled crystalline products [ 9 ] and nanoor microsized coordination polymer particles (CPPs), [ 10 ] have attracted much attention because of their unique applications in gas storage, catalysis, separation, and optics. The merger of coordination poly mers with other solid materials is expected to expand the scope of their utilization. [ 11 , 12 ] Recently, we developed a coordination-induced approach to immobilize coordination polymers consisting of In 3 + and isophthalic acid (H 2 IPA) building blocks onto carboxylatefunctionalized silica beads to derive the formation of silica@ coordination polymer core/shell structures, in which the thickness of the resulting coordination polymer shells was easily controlled by altering the quantities of shell components. [ 12 ] Herein, we report a novel general method for the preparation of hollow metal oxides using various metals. We demonstrate that considerably monodisperse hollow metal oxides can be produced from silica@coordination polymer core/shell precursors through a calcination process that transforms coordination polymers into metal oxides, followed by an etching process to remove silica templates ( Scheme 1 ). In addition, we show that the layer thicknesses of the hollow structures can be controlled by adjusting the shell thicknesses of the coordination polymers within the silica@ coordination polymer core/shell precursors. First, silica@coordination polymer core/shell microspheres were prepared using a solvothermal method. A N,N -dimethylformamide (DMF) solution of coordination