Shim Sung Lee

Distortional Supramolecular Isomers of Polyrotaxane Coordination Polymers: Photoreactivity and Sensing of Nitro Compounds†

Distortional isomers, or bond-stretch isomers, differ only in the length of one or more bonds, which is due to crystallographic disorder in most cases. The term distortional isomerism is introduced to describe the structures of polyrotaxane 2D coordination polymers (CPs) that differ only by the relative positions in the neighboring entangled axles. A large ring and a long spacer ligand in 2D CPs yielded four different supramolecular isomers, of which two have an entangled polyrotaxane structure. One pair of C=C bonds in the spacer ligand is well-aligned in one isomer and undergoes [2+2] cycloaddition reaction, whereas the other isomer is photoinert. They also have different sensing efficiency for several aromatic nitro compounds. However, both isomers show selective PL quenching for the Bradys reagent. Structurally similar supramolecular isomers with different photochemical reactivity and sensing abilities appear to be unprecedented.

Ligand- and Anion-Directed Assembly of Exo-Coordinated Mercury(II) Halide Complexes with O2S2-Donor Macrocycles

Assembly reactions of mercury(II) halides (Cl, Br, and I) with two O2S2 macrocycles (L(1) and L(2)) having different interdonor (S...S) distances were investigated, and four types of supramolecular complexes (1-4b) were obtained depending on the S...S distances as well as the size of the halide anions. Photoluminescence of these compounds was also studied.

Metal–Organic Organopolymeric Hybrid Framework by Reversible [2+2] Cycloaddition Reaction†

Organic polymers are usually amorphous or possess very low crystallinity. The metal complexes of organic polymeric ligands are also difficult to crystallize by traditional methods because of their poor solubilities and their 3D structures can not be determined by single-crystal X-ray crystallography owing to a lack of single crystals. Herein, we report the crystal structure of a 1D Zn(II) coordination polymer fused with an organic polymer ligand made in situ by a [2+2] cycloaddition reaction of a six-fold interpenetrated metal-organic framework. It is also shown that this organic polymer ligand can be depolymerized in a single-crystal-to-single-crystal (SCSC) fashion by heating. This strategy could potentially be extended to make a range of monocrystalline metal organopolymeric complexes and metal-organic organopolymeric hybrid materials. Such monocrystalline metal complexes of organic polymers have hitherto been inaccessible for materials researchers.

Supramolecular Networking of Macrocycles Based on Exo-Coordination: From Discrete to Continuous Frameworks

Macrocyclic ligands typically show high selectivity for specific metal ions and small molecules, and these features make such molecules attractive candidates for nanoscale chemical sensing applications. Crown ethers are macrocyclic structures with polyether linkages where the oxygen donors are often separated by an ethylene unit (-O-CH(2)-CH(2)-O-). Because the oxygen lone pairs in crown-type macrocycles are directed inward, the preorganized macrocyclic cavity tends to form complexes where metals coordinate inside the cavity (endo-coordination). However, sulfur-containing macrocycles often demonstrate metal coordination outside of the cavity (exo-coordination). This coordination behavior results from the different torsion arrangements adopted by the X-CH(2)-CH(2)-X atom sequence (X = O, gauche; X = S, anti) in these molecules. Exo-coordination is synthetically attractive because it would provide a means of connecting macrocyclic building blocks in diverse arrangements. In fact, exo-coordination could allow the construction of more elaborate network assemblies than are possible using conventional endocyclic coordination (which gives metal-in-cavity products). Exo-coordination can also serve as a tool for crystal engineering through the use of diverse controlling factors. Although challenges remain in the development of exo-coordination-based synthetic approaches and, in particular, for the architectural control of supramolecular coordination platforms, we have established several strategies for the rational synthesis of new metallosupramolecules. In this Account, we describe our recent studies of the assembly of metallosupramolecules and coordination polymers based on sulfur-containing macrocycles that employ simple and versatile exo-coordination procedures. Initially, we focus on the unusual topological products such as sandwich (1:2, metal-to-ligand), club sandwich (2:3), and cyclic oligomeric complexes as discrete network systems. The primary structures we achieve in these networked macrocycles are one to three dimensional coordination polymers based on homo- and heteronuclear metal systems. Using crystal engineering methods, we have also investigated variation in the donors, interdonor distances, ligand isomer structures, and the effect of counter anions on the chemical and physical properties of the products. Understanding the relationship between structure and function in these exo-coordination products is an important step in the design of these new supramolecules for practical applications. We investigated the photophysical properties of the exocyclic complexes and a chromogenic macrocycle, which exhibited cation-selective and anion-controlled color change depending on an exo- or endo- ligand binding mode. Overall, we suggest that the exocyclic coordination behavior provides a versatile strategy for the preparation of new molecular networks and materials.

Organic–inorganic hybrid nanomaterial as a new fluorescent chemosensor and adsorbent for copper ion

Functionalized silica nanotube (FSNT) possessing the phenanthroline moiety as a fluorescent receptor was fabricated by solgel reaction, and the binding ability of FSNT with metal ions was evaluated by fluorophotometry.

Silver(I)-selective membrane electrodes based on sulfur-containing podands

Some podands, acyclic polyethers, were utilized as membrane active components to prepare Ag(+)-selective polymeric membrane electrodes. The thiapodand-based electrodes exhibited considerable selectivity toward Ag(+) over other heavy metal ions including Cd(2+), Pb(2+), Cu(2+) and Hg(2+). Also, good selectivity over alkali and alkali earth metal ions were observed. Response slopes, pH effects, response time, and signal baseline return of the sensor systems were studied in static mode and/or in a flow-injection system. The Ag(+)-selectivity was explained by the soft-soft interaction of the Ag(+) ion with the sulfur donor atoms as well as the stacking interaction between aromatic end groups of the host molecule on complexation.

A Highly Sensitive and Selective Turn‐On Fluorogenic and Chromogenic Sensor Based on BODIPY‐Functionalized Magnetic Nanoparticles for Detecting Lead in Living Cells

A new fluoro-chromogenic chemosensor based on BODIPY-functionalized Fe(3)O(4)@SiO(2) core/shell nanoparticles 1 has been prepared. Chemosensor 1 exhibits a high affinity and selectivity for Pb(2+) over competing metal ions tested. Moreover, confocal microscopy, and flow cytometry experiments established that 1 can be used for detecting Pb(2+) levels within living cell.

Thiaoxaaza-macrocyclic chromoionophores as mercury(II) sensors: synthesis and color modulation.

Azo-coupled macrocyclic chromoionophores incorporating benzene (L(1)) and pyridine (L(2)) subunits were synthesized, respectively. In a cation-induced color change experiment, both receptors showed Hg(2+) selectivity. However, L(1) gave a larger cation-induced hypsochromic shift than L(2), suggesting that the presence of the pyridine unit in L(2) may inhibit the Hg...N-azo interaction. The observed Hg(2+)-selective color changes for L(1) and L(2) were found to be controlled by anion-coordination ability. NMR titration of the proposed receptor ligand with Hg(II) salt was accomplished.

Anion-controlled endo- and exocyclic disilver(I) complexes of an S2O3 macrocycle.

Anion-controlled endo- and exocyclic complexes were afforded in the reactions of an S(2)O(3) macrocycle with AgPF(6) and AgClO(4), respectively. The two coordination modes that provide the Ag ion position inside (by PF(6)(-)) or outside (by ClO(4)(-)) the macrocyclic cavity are explained by the anion-coordination ability toward the metal cation. Furthermore, each Ag center bridges two ligands via a regular coordinative bond or by pi coordination, forming a cyclic dimeric-type product. NMR titrations of the complex system in solution were also carried out.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo-Polymerization Reaction†

Getting suitable crystals for single-crystal X-ray crystallographic analysis still remains an art. Obtaining single crystals of metal-organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single-crystal-to-single-crystal manner. The spacer ligands with trans,trans,trans-conformation in the pillared-layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans-conformation prior to [2+2] photo-cycloaddition reaction and yield single crystals of MOF containing two-dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.