Haeri Lee

Construction of kagome-type networks via tridentate ligand: structural properties as alcohol reservoir

Self-assembly of CuX2 (X− = Cl− and Br−) with a new tridentate ligand, N,N′,N′′-tris(2-pyridinylethyl)-1,3,5-benzenetricarboxamide (L), yields a uniquely very thin kagome-type network consisting of both nano-sized hexagonal (Cu6L6) and triangular (Cu3L3) motifs with the former as an effective reservoir for small alcohol molecules.

A ball-joint-type host-guest system that consists of conglomerate helical metallacyclophanes.

If suitable molecular units could be advantageously arranged, what would the resultant properties of their molecular aggregates be? This sort has inspired molecular engineers for the past decade. The assembly and the related properties of novel supramolecular aggregates are a hot topic and, not entirely coincidentally, a great challenge in the field of molecular chemistry. A full understanding of the driving forces behind those aggregations is a prerequisite for the design and construction of molecular arrays. Cyclophanes are attractive models for understanding weak transannular interactions as well as distinct p···p systems. They can also serve as basic examples for explaining molecular recognition, chemosensing, molecular electronics, and electrical, magnetic, and capsule effects that are introduced by significant donor–acceptor and electron-transfer processes, or by through-space effects. Metallacyclophanes have been synthesized by the coordination-directed self-assembly of metals and multidentate ligands. These structures are of particular interest owing to the many and various advantages inherent to organic cyclophanes: easily accessible modularity for dimensions and topology, and straightforward incorporation of functions, such as catalytic effects, luminescence, redox-activity, electron transfer, and helicity. The elucidation of the thermodynamics and kinetics of such metallacyclophane systems would certainly provide important insights into the evolution and emergence of delicate supramolecular systems. To that end, three important synthetic approaches have been introduced: angular directional bonding, symmetry interaction, and weak interaction. Helical motifs are ubiquitous in nature and have provided an important impetus for the generation of helical molecules. Indeed, discrete or polymeric helicates the synthesis of which is driven by coordination is intriguing, because it enables various applications, including asymmetric catalysis, chiral chemistry, nonlinear optical materials, template precursors, memory devices, biomimetics, DNA, structural biology, specific ion sensors, and molecular reaction vessels. Helicity can be induced on purpose by means of conformational restrictions that are due to the coordination with metal ions. In this context, we employed a self-assembly approach that incorporates the three methods described above to construct racemic helical metallacyclophanes, (P,M)[Pd3X6(L )2], by the reaction of K2[PdX4] (X=Cl, Br) with the C3-symmetric tridentate ligand L 1 as a programmed discrete helical component. A subsequent partial substitution reaction of (P,M)-[Pd3X6(L )2] with another C3-symmetric tridentate ligand L, or direct self-assembly of K2[PdX4] with both L and L, produced unprecedented conglomerate crystals forming a ball-joint-type host–guest system, (P)[Pd3X6(L )2]@(M)-[Pd3X6(L )(L)] and (M)-[Pd3X6(L )2]@ (P)-[Pd3X6(L )(L)] (X=Cl, Br; L=N,N’,N’’-tris(2-pyridinylethyl)-1,3,5-benzenetricarboxamide; L=N,N’,N’’-tris(3-pyridinylpropyl)-1,3,5-benzenetricarboxylate; P= righthanded helix; M= left-handed helix). The synthesis of this host–guest system is an effective method for obtaining useful aggregates. Herein, we present a very effective strategy for the synthesis of such a system. Its crystal structures, the driving aggregative force behind it, and the reversible equilibrium between the aggregate and its dissociated species in solution are also discussed. The self-assembly of K2[PdX4] with L 1 at room temperature produced racemic crystalline products of helical trimetallacyclophanes, (P,M)-[Pd3X6(L )2] (X=Cl: (P,M)-1-Cl; X=Br: (P,M)-1-Br). Subsequent reaction of (P,M)-1-X with L at 70 8C yielded unprecedented conglomerate crystals of chiral (P)-[Pd3X6(L )2]@(M)-[Pd3X6(L )(L)] (X=Cl: (P)-1Cl@(M)-2-Cl; X=Br: (P)-1-Br@(M)-2-Br) and its enantiomeric (M)-[Pd3X6(L )2]@(P)-[Pd3X6(L )(L)] (X=Cl: (M)-1Cl@(P)-2-Cl; X=Br: (M)-1-Br@(P)-2-Br; Scheme 1). At this temperature, a partial substitution reaction was achieved in N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). A change in the molar ratio of the reactants did not have a significant effect on product formation in any case. Direct reaction of K2[PdX4] with both L 1 and L in appropriate molar ratios produced the same conglomerate crystals, even at room temperature. However, at room temperature, the second step of the two-step reaction does not occur, which indicates that the partial substitution reaction of (P,M)-1-X with L requires slightly more vigorous conditions than the direct reaction. The crystalline solids are soluble in DMSO and DMF, but are almost insoluble in common organic solvents such as acetone, chloroform, and tetrahydrofuran. Recrystallizations of all of the products from DMF or DMSO yielded the same results irrespective of the co-solvent (acetone, EtOH, and MeOH), which indicates that all of the products were thermodynamically stable. The carbonyl stretching frequencies of (P,M)-1-Cl (1656 cm ) and (P,M)[*] H. Lee, T. H. Noh, Prof. Dr. O.-S. Jung Department of Chemistry and Chemistry Institute for Functional Materials Pusan National University, Pusan 609-735 (Korea) E-mail: oksjung@pusan.ac.kr

In situ crystalline transformation of bis(halo)mercury(II) coordination polymers to ionic chloro-bridged-bis(halo)mercury(II) species via UV irradiation in chloroform media

Self-assembly of HgX2 (X− = Br− and I−) with new 1,1,2,2-tetramethyl-1,2-di(pyridin-3-yl)disilane (L) ligand affords single crystals consisting of sinusoidal-strand coordination polymers, [HgX2L]. Specifically, 350 nm UV irradiation of crystalline products [HgBr2L] and [HgI2L] in chloroform media forms in situ single crystals of extraordinary chloro-bridged mercury species, [H2L]2+[Hg2Br4(μ-Br)(μ-Cl)]2− and [H2L]2+[HgI2(μ-Cl)]22−, respectively, in high yields that cannot be synthesized by general synthetic procedures. For all of the compounds, the coordination geometries around the Hg(II) ions along with the mechanistic aspects of the formation of chloro-bridged species are discussed herein.

Coordination-cyclodimeric array containing both channels and cages: photoluminescence recognition of diiodomethane

Self-assembly of a series of ZnX2 (X− = Cl−, Br−, and I−) with 2,3-bis(4′-nicotinamidephenoxy)naphthalene (L) as a new hemi-circular bidentate ligand yields systematic 46-membered metallacyclodimeric species of [ZnX2L]2. These metallacyclodimers constitute, via inter-digitated π⋯π interactions, a characteristically staggered molecular array containing both channels and cages. The slightly different features between the channel and cage have been investigated by 1H NMR and TGA. The crystals with such vacant volumes effectively stabilize the unstable CH2I2 molecule and are monitored by UV spectroscopy. Furthermore, the photoluminescence intensity via the chromophore naphthyl moiety of [ZnCl2L]2 gradually decreases with the addition of CH2I2.

Recyclable scavengers for photo-cyclopropanation via an in situ crystallization process

The palladium(ii) cyclophane systems, constructed by previously reported proof-of-concept self-assembly, represent a crucial landmark in the field of effective and recyclable scavenging of triiodide (I3-) in the photo-cyclopropanation of alkenes with CH2I2. The scavengers driving force behind photo-cyclopropanation is the efficient in situ crystallization of triiodide-exchanged species. The exact quantitative photoreaction yields according to the mole ratios of the cyclophane system are impressive. The recycling behavior can be ascribed to the rigidity and stability of the four-layered tripalladium(ii)cyclophane.

Haloalkane adsorption into 1D ensembles’ channels: Zn(II) coordination polymers

Abstract Self-assembly of ZnX2 (X– = Cl–, Br–, and I–) with 2,7-bis(isonicotinoyloxy)naphthalene (L) in a mixture of ethanol and dichloromethane yields 1-D zigzag chains of [ZnX2L·2CH2Cl2]n composition. The 1-D chains form an ensemble constituting hydrophobic suprachannels of 4.0–4.4 × 4.4–5.0 Å2 with repeat units of ZnL for [ZnCl2L] and [ZnBr2L], and those of 5.2 × 12.0 Å2 with repeat units of Zn2L2 for [ZnI2L] in the appropriate arrays via C–H···π and π···π interactions. The most interesting feature is that alcohol molecules are not incorporated into the haloalkane-philic channels. That is, the channels discriminate haloalkanes from alcohols. Furthermore, the exchange of solvate molecules in a crystalline state indicates that the unique channels show different absorptions of haloalkanes such as CH2Cl2, CH2Br2, CH2I2, CHCl3, 1,2-dichloroethane, and 1,2-dibromoethane. Graphical Abstract

Interfacial effects of crystal surface through free quinolinyl groups on crystal organization and catalysis

Reaction of MX2 (M = Cu(II), Hg(II); X− = Cl−, Br−) with C3-symmetric tris(6-quinolyl)trimesic ester (L) produces crystals consisting of C2-symmetric metallacyclodimeric species with two free quinolinyl N-donors, [MX2L]2. The crystals self-aggregate in aqueous media. Furthermore, the reaction with cotton-threads and glass-fibers forms unique crystal organization on and with cotton-threads and glass-fibers, respectively. Such crystal aggregation and organization are ascribed to the hydrogen-bonding interactions between the free quinolinyl N-donors on the crystal surface and the hydroxyl (–OH) groups of water, cotton-threads, or glass-fibers. The composite organization of crystals on or with glass-fiber, [CuX2L]2@glass, is an effective recyclable heterogeneous catalytic system in catechol oxidation, which indicates the significant role played by the free quinolinyl N-donors. The treatment of [CuX2L]2 crystals with K2PdCl4 produces, via Pd(II)–N interactions, conceptually advanced PdCl2@[CuX2L]2 composite materials that are useful for Suzuki–Miyaura C–C coupling reactions.

CCDC 855883: Experimental Crystal Structure Determination

Related Article: Eun Ji Kim, Jungmin Ahn, Haeri Lee, Tae Hwan Noh, Ok-Sang Jung|2012|Tetrahedron Lett.|53|1240|doi:10.1016/j.tetlet.2011.12.112

CCDC 855880: Experimental Crystal Structure Determination

Related Article: Eun Ji Kim, Jungmin Ahn, Haeri Lee, Tae Hwan Noh, Ok-Sang Jung|2012|Tetrahedron Lett.|53|1240|doi:10.1016/j.tetlet.2011.12.112