Ryo Sekiya

Anion-Directed Formation and Degradation of an Interlocked Metallohelicate

Although there are many examples of catenanes, those of more complex mechanically interlocked molecular architectures are rare. Additionally, little attention has been paid to the degradation of such interlocked systems into their starting complexes, although formation and degradation are complementary phenomena and are equally important. Interlocked metallohelicate, [(Pd(2)L(4))(2)](8+) (2(8+)), is a quadruply interlocked molecular architecture consisting of two mechanically interlocked monomers, [Pd(2)L(4)](4+) (1(4+)). 2(8+) has three internal cavities, each of which encapsulates one NO(3)(-) ion (1:3 host-guest complex, 2⊃(NO(3)|NO(3)|NO(3))(5+)) and is characterized by unusual thermodynamic stability. However, both the driving force for the dimerization and the origin of the thermodynamic stability remain unclear. To clarify these issues, BF(4)(-), PF(6)(-), and OTf(-) have been used to demonstrate that the dimerization is driven by the anion template effect. Interestingly, the stability of 2(8+) strongly depends on the encapsulated anions (2⊃(NO(3)|NO(3)|NO(3))(5+) ≫ 2⊃(BF(4)|BF(4)|BF(4))(5+)). The origins of this differing thermodynamic stability have been shown through detailed investigations to be due to the differences in the stabilization of the interlocked structure by the host-guest interaction and the size of the anion. We have found that 2-naphthalenesulfonate (ONs(-)) induces the monomerization of 2⊃(NO(3)|NO(3)|NO(3))(5+) via intermediate 2⊃(ONs|NO(3)|ONs)(5+), which is formed by anion exchange. On the basis of this finding, and using p-toluenesulfonate (OTs(-)), the physical separation of 2⊃(NO(3)|NO(3)|NO(3))(5+) and 1(4+) as OTs(-) salt was accomplished.

Design and Structural Extension of a Supramolecular Inclusion‐Compound Host Made by the Formation of Dimers of Isonicotinic Acid and Thiocyanato Coordinating Bridges

A new host design for an inclusion compound with a preference for large planar aromatic guest molecules has been proposed. Our host design includes a rectangular cavity made using a long and a short building block based on the concept of supramolecular chemistry. The long building block facilitates the inclusion of large guests, and the short building block prevents the formation of an interpenetrated structure, which is often observed in frameworks with large void spaces. The long building block is made when dimers of 4-pyridinecarboxylic acid (isoH) form through hydrogen bonding between the two carboxylic acid moieties. This isoH dimer can link two transition metal centers using the N atoms at both ends to act as a long building block. For the short building block, the thiocyanato ion was used. This makes a bent bridge between two metal centers to form a 1D double-chain [M(SCN)2]infinity complex. From the self-assembly of isoH, SCN- and Ni2+, a 2D network of [Ni(SCN)2(isoH)2]infinity, in which the 1D [Ni(SCN)2]infinity complexes are linked by the isoH dimers, is built up. The rectangular cavity is formed as a mesh within the 2D network. The crystal of our inclusion compound has a layered structure of 2D networks, and a 1D channel-like cavity penetrating the layered 2D networks is formed where guests may be included. Moreover, our host design has the advantage of easy extension of the host structure. Replacement of isoH with another component and use of three components is possible for making the long building block. In the latter case, a linear spacer having two carboxy groups is inserted into the isoH dimer to form a long building block with a trimer structure. Based on our host design, a series of new inclusion compounds were synthesized. The crystal structures of three compounds were determined by single crystal X-ray diffraction. These were a biphenyl inclusion compound [Ni(SCN)2(isoH)2].1/2C12H10 (the basic case), a 9,10-dichloroanthracene inclusion compound [Ni(SCN)2(acrylH)2].1/2C14H8Cl2, where isoH is replaced with 3-(4-pyridinyl)-2-propenoic acid (acrylH), and a perylene inclusion compound [Ni(SCN)2(isoH)2(fumaricH2)].1/2C20H12, whose long building block is a trimer inserted with fumaric acid (fumaricH2) as a linear spacer.

Pd2+⋯O3SR− interaction encourages anion encapsulation of a quadruply-stranded Pd complex to achieve chirality or high solubility

Pd(2+)···O(3)SR(-) and CH···O(3)SR(-) interactions were found to play a crucial role in the encapsulation of organic sulfonates in a quadruply-stranded complex of Pd(2)L(4)-type. We have successfully employed this feature to achieve chirality induction by complexation with chiral guests as well as solubility increase by dendronization.

Synthesis, characterization, X-ray crystal structure, DFT calculations, and catalytic properties of a dioxidovanadium(V) complex derived from oxamohydrazide and pyridoxal: a model complex of vanadate-dependent bromoperoxidase.

A vanadium(V) complex with the formula [Et3NH][V(V)O2(sox-pydx)] with a new tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]methylene]hydrazinyl]-2-oxoacetamide (soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal (one of the forms of vitamin B6), has been synthesized. The compound was characterized by various analytical and spectroscopic methods, and its structure was determined by single-crystal X-ray diffraction technique. Density functional theory (DFT) and time-dependent DFT calculations were used to understand the electronic structure of the complex and nature of the electronic transitions observed in UV-vis spectra. In the complex, vanadium(V) is found to be pentacoordinated with two oxido ligands and a bianionic tridentate ONO-donor ligand. The vanadium center has square-pyramidal geometry with an axial oxido ligand, and the equatorial positions are occupied by another oxido ligand and a phenolato oxygen, an imine nitrogen, and a deprotonated amide oxygen of the hydrazone ligand. A DFT-optimized structure of the complex shows very similar metrical parameters as determined by X-ray crystallography. The O4N coordination environment of vanadium and the hydrogen-bonding abilities of the pendant amide moiety have a strong resemblance with the vanadium center in bromoperoxidase enzyme. Bromination experiments using H2O2 as the oxidizing agent, with model substrate phenol red, and the vanadium complex as a catalyst show a remarkably high value of kcat equal to 26,340 h(-1). The vanadium compound also efficiently catalyzes bromination of phenol and salicylaldehyde as well as oxidation of benzene to phenol by H2O2.

Adsorption and separation of poly-aromatic hydrocarbons by a hydrogen-bonded coordination polymer.

A residual-host prepared by thermal removal of naphthalene (NA) from the inclusion compound [Ni(SCN)(2)(isonicotinic acid)(2)]·(NA)(0.5) was found to function as an adsorbent for aromatic molecules and exhibit method-dependent selectivity.

Combination between metal–ligand coordination and hydrogen bond interaction: a facile route for the construction of 3D coordination networks with the ability to include relatively large aromatic molecules

A combination between metal–ligand coordination and hydrogen bond interaction allows the construction of new 3D coordination networks which exhibit the ability to include relatively large organic molecules.

Synthesis, X-ray crystal structures and inclusion properties of a hydrogen-bonded coordination polymer [Ni(SCN)2(pppeH)2]·(guest)x

This study reports three inclusion compounds [Ni(SCN)2(pppeH)2]·(guest)x (1–3) and a guest-free crystal [Ni(SCN)2(pppeH)2] (4), where pppeH = trans-3-[4-(4-pyridyl)phenyl]propenoic acid and guest = dibenz[a,h]anthracene (x = 1/2) (1), p-bromobenzoic acid (x = 1) (2) and 4,4′-dibromobiphenyl (x = 1) (3). The crystal structures of 1–4 are best described as consisting of layers. The layer, [Ni(SCN)2(pppeH)2]∞, is formed by R22(8) O–H⋯O hydrogen bonding between the pppeH ligands coordinating to Ni2+ ions of adjacent 1D coordination polymers. The layers of 1–3 have cavities surrounded by two pppeH dimers and four μ-1,3-SCN ligands with the dimensions of ca. 25.5 × 6.2–7.6 A2. On the other hand, the layer of 4 does not. This indicates that the guests act as templates for the formation of the cavity. Interlayer connection of the cavities gives channels penetrating through the crystals where the guests are arranged one-dimensionally. Detailed investigation on the crystal structures of 1–3 and [Ni(SCN)2(pppeH)2]·(benz[a]anthracene)2/3 (5) reported previously has revealed that the stacking manner of the layers, the interlayer separation and the structure of the layer are adjusted in response to the guests, and simultaneously the guests adjust their positions and orientations to form a close-packed structure.

Cu3(CN)4(NH3)2Hg(CN)2: a novel inter­penetrating framework formed from CuI, CuII, HgII and cyanide bridges

The title compound, poly[diamminehexa-mu-cyano-dicopper(I)copper(II)mercury(II)], [Cu3Hg(CN)6(NH3)2]n, has a novel threefold-interpenetrating structure of three-dimensional frameworks. This three-dimensional framework consists of two-dimensional network Cu3(CN)4(NH3)2 complexes and rod-like Hg(CN)2 complexes. The two-dimensional network complex contains trigonal-planar Cu(I) (site symmetry m) and octahedral Cu(II) (site symmetry 2/m) in a 2:1 ratio. Two types of cyanide group form bridges between three coordination sites of Cu(I) and two equatorial sites of Cu(II) to form a two-dimensional structure with large hexagonal windows. One type of CN- group is disordered across a center of inversion, while the other resides on the mirror plane. Two NH3 molecules (site symmetry 2) are located in the hexagonal windows and coordinate to the remaining equatorial sites of Cu(II). Both N atoms of the rod-like Hg(CN)2 group (Hg site symmetry 2/m and CN- site symmetry m) coordinate to the axial sites of Cu(II). This linkage completes the three-dimensional framework and penetrates two hexagonal windows of two two-dimensional network complexes to form the threefold-interpenetrating structure.

A preparative strategy for supramolecular inclusion compounds by combination of dimer formation of isonicotinic acid and coordination bonding

A new inclusion compound host [Ni(SCN)2(isoH)2], whose cavity is suitable to include large aromatic guests, has been synthesized by a method of combining the dimer formation of isonicotinic acid by double hydrogen bonds with a 1D Ni thiocyanato complex.

Chirality realized only in the crystalline state: inorganic and organic compounds

intercalated Na1-xCoO2-x, spin-state transitions of the Co ion in LaCoO3, a metal-insulator (MI) accompanied by structural transition in LnBaCo2O5.5 (where Ln is a rare earth). We present our recent results on crystal growth of cobaltites: La1-xSrxCoO3 and LnBaCo2O5+x using Optical Travelling Solvent Floating Zone method. The crystals were studied by different techniques and some of results will be discussed. A very small Sr doping level (0.2%) drastically changes magnetic properties of La1-xSrxCoO3 as found using inelastic neutron scattering and magnetisation measurements. This can be explained assuming that the slight hole doping in LaCoO3 matrix creates magnetic polarons, which leads to a spin-state transition of Co. On the background of the spin-state and orbitalordering transitions of the Co ion in LnBaCo2O5+x, the system shows a metal-insulator transition accompanied by structural one at temperatures above room temperature, three different magnetic phases below room temperature and a structural transition at temperature above MI transition. All these properties can be tuned by a kind of the rare earth ion and oxygen stoichiometry. Structural, magnetic and transport studies of layered cobaltites LnBaCo2O5.5 (Ln=Tb, Nd) especially near metal-insulator transition will be presented.