Norikazu Ueyama

Self-Assembly of Frameworks with Specific Topologies: Construction and Anion Exchange Properties of M3L2 Architectures by Tripodal Ligands and Silver(I) Salts

Three five-component architectures, compounds 3, 4, and 5 were obtained by self-assembly of tripodal 1,3,5-tris(imidazol-1-ylmethyl )-2,4,6-trimethylbenzene (6) and 1,3,5-tris(benzimidazol-2-ylmethyl)benzene (7) ligands with silver(I) salts. The structures of these novel complexes have been determined by X-ray crystallography. The results of structural analysis indicate that these frameworks have same M3L2 components, but different structures. Compounds 3 and 4 are both M3L2 type cage-like complexes, while the 5 is an open trinuclear complex. The complex 3 is a cylindrical cage with simultaneous inclusion of a perchlorate anion inside of the cage as a guest molecule. Such guests can be exchanged for other anions through the open edge of the cage as evidenced by crystal structure of 4. The results demonstrate that the molecular M3L2 type cage can act as a host for anions and provide a nice example of supramolecular architectures with interesting properties and possible applications.

Synthesis and crystal structure of a luminescent infinite 2D brick-wall network with two- and three-coordinate silver(I) atoms and ligand-unsupported silver–silver interactions

Assembly of a novel flexible tetradentate ligand 1,7-bis(4′-pyridyl)-2,6-diazaheptane (py-hep) with silver perchlorate hydrate provides an interesting two-dimensional (2D) brick-wall network: [Ag3(py-hep)2](ClO4)3·0.5CH3CN. The X-ray crystal structural analysis indicates that the framework consists of trigonal and linearly coordinated silver(I) atoms and ligand-unsupported metal–metal interactions. The complex shows photoluminescence in both the solid state and in acetonitrile solution.

Highly oriented aragonite nanocrystal–biopolymer composites in an aragonite brick of the nacreous layer of Pinctada fucata

13C CP/MAS NMR and FE/TEM measurements of the aragonite brick of the nacreous layer of Pinctada fucata indicate that it assembles with highly oriented aragonite nanocrystals, which are regulated by biopolymers.

Cadmium(II) coordination polymers with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene: anion effect and reversible anion exchange property

Six new three-dimensional (3D) Cd(II) coordination polymers, {[Cd2(L)3](NO3)4·6H2O}n (1), {[Cd2(L)3](ClO4)4·2H2O}n (2), {[Cd2(L)3](BF4)4·2H2O}n (3), {[Cd(L)Cl2]·2H2O}n (4), {[Cd2(L)2(SO4)2(H2O)]·2H2O}n (5) and {[Cd2(L)(SO4)2(H2O)3]·4H2O}n (6), have been solvothermally synthesized by reactions of the corresponding Cd(II) salts with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L), respectively. The X-ray diffraction analysis revealed that the isostructural 1, 2 and 3 have 3D framework structures with (46·66·83)2(42·63·8)3 topology. Complex 4 has a different 3D framework structure with (65·8) topology, while 5 and 6 possess pillared-layer and plywood-like 3D framework structures, respectively. The distinct structures of 1 (2, 3), 4 and 5 indicate that the counter anions with different coordination abilities play an important role in the formation of coordination polymers. Complexes 5 and 6, synthesized by the same reactants in the same solvent, have different structures due to the different metal/ligand ratio. In addition, the results also demonstrated that the flexible tetradentate ligand L can adopt varied conformations and coordination modes to form complexes with different structures. L adopts up,up,down,down-conformation in 1–3, while in 4, it has a up,down-conformation. It is interesting that two different conformations of up,down,down,up- and H-type of L coexist in 5. In the case of 6, L has H-type conformation. Furthermore, the reversible anion exchange property of 1 was studied.

Novel Pb(ii) coordination frameworks: synthesis, crystal structures and unusual third-order nonlinear optical propertiesElectronic supplementary information (ESI) available: crystal packing diagram of complex 2. See http://www.rsc.org/suppdata/jm/b3/b315682f/

Three novel Pb(II) coordination complexes, [Pb(dimb)(DMF)(NO3)2]n1, [Pb(dimb)(SCN)2]n2 [dimb = 1,3-bis(imidazol-1-ylmethyl)-benzene], {[Pb(bimb)1.5(NO3)2](DMF)}n3 [bimb = 4,4′-bis(imidazol-1-methyl)-biphenyl], were synthesized and characterized by X-ray crystallography. Complex 1 exhibits a one-dimensional (1D) zigzag chain structure, which has two crystallographically independent Pb(II) atom centers. Complex 2 possesses a two-dimensional (2D) corrugated network, which contains 24-membered M2L2 metallocyclic rings. Complex 3 has a 1D infinite non-interpenetrated molecular ladder, which has very large cavities with dimensions of 17.89 × 20.34 A, and DMF molecules fill the channel formed by adjacent two ladders. The third-order nonlinear optical (NLO) properties of the three complexes were measured by a Z-scan technique in DMF solution. All three complexes possess weak absorption and strong refraction. Their third-order NLO refractive coefficients, n2, are −5.96 × 10−19 m2 W−1 for 1, −8.34 × 10−19 m2 W−1 for 2, and −7.15 × 10−19 m2 W−1 for 3. It is notable that two Pb(II) complexes 1 and 3 with 1D structure show strong self-defocusing behavior, which are different from the reported 1D coordination complexes containing d10 metal ions; also, complex 2 is the first 2D coordination compound that possesses strong self-defocusing behavior. The χ(3) values of complexes 1, 2 and 3 were calculated to be 4.46 × 10−13, 6.25 × 10−13 and 5.42 × 10−13 esu, respectively.

Syntheses and crystal structures of 1D tubular chains and 2D polycatenanes built from the asymmetric 1-(1-imidazolyl)-4-(imidazol-1-ylmethyl)benzene ligand with metal salts

Reactions of a new asymmetric ligand, 1-(1-imidazolyl)-4-(imidazol-1-ylmethyl)benzene (IIMB), with various metal [Cd(II), Mn(II), Zn(II)] salts led to the formation of molecular, one- (1D) and two-dimensional (2D) architectures [Cd(IIMB)2(H2O)(SO4)]·7.5H2O 1, [Cd(IIMB)2Cl2]·H2O 2, [Cd(IIMB)4(H2O)2](NO3)2·5H2O 3, [Cd(IIMB)(OAc)2]·H2O 4, [Mn(IIMB)2(SO4)(H2O)]·8.2H2O 5, [Mn(IIMB)4(H2O)2]Cl2·5H2O 6 and [Zn(IIMB)2]4(NO3)8·13.5H2O 7. All the structures were established by single-crystal X-ray diffraction analysis. Both compounds 1 and 5 with sulfate anion are 2D polycatenanes formed by the interlocking of 1D double-stranded chains, while 2 and 4 with chloride and acetate anions are 1D chains. The results provide nice examples of topologies of metal-organic frameworks controlled by the counter anions. Interestingly, 3 and 6 are discrete molecular complexes with monometallic cores and form 2D networks through strong intermolecular hydrogen bonds. Complex 7, obtained under the same conditions as 3, is a 1D tubular chain. The structural difference between 3 and 7 suggests the metal ions also have a significant effect on the construction of supramolecular architectures. Furthermore, the photoluminescence properties of these compounds were investigated in the solid state at room temperature.

Three-dimensional photoluminescent pillared metal-organic framework with 4.82 topological channels obtained from the assembly of cadmium(II) acetate and trimellitic salt

Reaction of the piperidinium salt of trimellitic acid (BTC3−) with cadmium(II) acetate dihydrate yields an unprecedented 3D pillared metal-organic framework, [Cd3(BTC)2(H2O)6]·3H2O, showing strong blue luminescence. The framework contains 4.82 topological channels, in which the ‘floors’ are directly connected by the pillars of the BTC3− benzene rings.

Structure-based functional identification of a novel heme-binding protein from Thermus thermophilus HB8.

The TT1485 gene from Thermus thermophilus HB8 encodes a hypothetical protein of unknown function with about 20 sequence homologs of bacterial or archaeal origin. Together they form a family of uncharacterized proteins, the cluster of orthologous group COG3253. Using a combination of amino acid sequence analysis, three-dimensional structural studies and biochemical assays, we identified TT1485 as a novel heme-binding protein. The crystal structure reveals that this protein is a pentamer and each monomer exhibits a β-barrel fold. TT1485 is structurally similar to muconolactone isomerase, but this provided no functional clues. Amino acid sequence analysis revealed remote homology to a heme enzyme, chlorite dismutase. Strikingly, amino acid residues that are highly conserved in the homologous hypothetical proteins and chlorite dismutase cluster around a deep cavity on the surface of each monomer. Molecular modeling shows that the cavity can accommodate a heme group with a strictly conserved His as a heme ligand. TT1485 reconstituted with iron protoporphyrin IX chloride gave a low chlorite dismutase activity, indicating that TT1485 catalyzes a reaction other than chlorite degradation. The presence of a possible Fe–His–Asp triad in the heme proximal site suggests that TT1485 functions as a novel heme peroxidase to detoxify hydrogen peroxide within the cell.

Antiferromagnetic spin couplings between iron ions in iron—sulfur clusters. A localized picture by the spin vector model

Abstract Antiferromagnetic spin correlation effects for iron—sulfur clusters in ferredoxins were investigated on the basis of ab initio UHF and Heisenberg models. The electronic structures with two (helical) and three (general) dimensional spin modulations are found to be the ground states for these species because of the near degeneracies between several MOs in the frontier region. The spin vector model is found to be useful for a localized representation of complex antiferromagnetic spin couplings between the high-spin iron atoms (ions) in the clusters.

First example of a dumbbell-like architecture containing M3L2 cages and terephthalate anions

A novel complex [Ag3(titmb)2]2[1,4-C6H4(COO)2]3·23 H2O [titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene] contains two M3L2 cages and three terephthalate anions, one of which is embedded in the two cages to form a dumbbell-like architecture and shows photoluminescence in the solid state when the titmb reacts with [Ag(NH3)2]NO3, an individual M3L2 cage [Ag3(titmb)2][NO3]3·5 H2O without luminescent properties was obtained.