Dalton Trans Research Articles

N,N,O and N,O,N Meridional cis Coordination of Two Guanines to Copper(II) by d(CGCGCG)2.

Many research groups study the generation of supramolecular n-dimensional arrays by combining metals with DNA building blocks. Most of the time, the natural nucleobases are modified to obtain higher-affinity metal binding sites. Using unmodified nucleobases avoids a potentially difficult synthesis; however, they have the possible disadvantage of a less defined and/or weaker coordination mode of the metal. Structural studies on the behavior of copper(II) as a linking metal and guanine as the natural ligand for metals in unmodified DNA are reported. Previously, the ability of mono- and dinuclear metal complexes to induce Z-DNA has been explored [Medina-Molner, A.; Spingler, B. Chem. Commun. 2012, 48, 1961; Medina-Molner, A.; Rohner, M.; Pandiarajan, D.; Spingler, B. Dalton Trans. 2015, 44, 3664]. Herein, X-ray crystallographic studies of the structures resulting from the combination of copper(II) ions with DNA hexamers of the general sequence d(CG)3 are presented. Three different packing motifs were observed in three crystal structures with resolutions ranging from 2.15 to 1.45 Å. The motifs are dependent upon other cations being present and/or the crystallization conditions. The first examples of intramolecular O6,N7-chelates of a neutral purine nucleobase to copper(II) were obtained as well as the first meridional N,N,O and N,O,N coordination modes of two guanines to copper(II). The fascinating coordination chemistry of copper(II) complexes generated by the Z-DNA oligonucleotides and the differences to simple nucleobases complexes with copper(II) are discussed in detail.

Directed Functionalization of Aromatic C-H Bonds in Electrocatalytic Phosphorylation and Fluoroalkylation Reactions with the Participant of Transition Metal Complexes

The formation of carbon-phosphorus and carbon-fluoroalkyl bonds catalyzed by transition metal complexes is considered as an important methodology for producing of various useful compounds. Many of these compounds exhibit a high biological activity and are widely used in organic synthesis, medical chemistry, materials or as versatile ligands in many catalytic reactions.1-2 However, it should be noted that in majority of papers as aromatic substrates are used organic halides, while examples of substituted C-H bonds, where the leaving group is hydrogen, are much smaller. Major reviews of the latest achievements in the field of formation of metal-catalyzed С-P bonds published in recent years almost do not consider examples of phosphorylation of aromatic C-H bonds.3 Known fluoroalkylation reactions also have the drawbacks: the high cost of the reagents, the frequent requirement for forcing reaction conditions, a modest substrate scope.4 That is why the purpose of our work is to develop a more economically and environmentally beneficial method of obtaining phosphorus, fluoroalkyl compounds by electrochemical activation of aromatic C-H bonds under electrocatalysis involving transition metal complexes. The interest in electrochemical fluoroalkylation and phosphorylation reactions is driven by a number of factors: mild conditions (moderate temperature, ambient pressure), the possibility of closed-loop implementation with a small amount of the catalyst reactant that is repeatedly recycled, and the high environmental safety of the synthesis, especially in comparison with the traditional organic chemistry techniques. Electrosynthesis is also useful in transition metal catalysis for generating the active form of the catalyst without the need to add external oxidizing or reducing agents.5-7 Thus in a series of experiments products of phosphorylation and fluoroalkylation of aromatic substrates (benzene, coumarin, caffeine, pyridine, ferrocene) were obtained under mild conditions (room temperature, normal pressure) from good to excellent yields (90%).8-9 Acknowledgements This work was supported by the Russian Science Foundation no. 14-23-00016. References Kirk, K.L. J. Fluorine Chem. 2006, 127, 1013.Demmer, C. S.; Krogsgaard-Larsen, N.; Bunch, L. Chem. Rev. 2011, 111, 7981.Evano, G.; Gaumont, A.-C.; Alayrac, C.; Wrona, I. E.; Giguere, J. R.; Delacroix, O.; Silvanus, A. C. Tetrahedron. 2014, 70, 1529. Loy, R. N.; Sanford, M. S. Org. Lett. 2011, 13, 2548.Khrizanforov, M.; Gryaznova, T.; Sinyashin, O.; Budnikova, Y. J. Organomet. Chem., 2012, 718, 101. Dudkina, Y. B.; Khrizanforov, M. N.; Gryaznova, T. V.; Budnikova, Y. H. J. Organomet. Chem., 2014, 751, 301.Budnikova, Y. H. Russ. Chem. Rev., 2002, 71, 111.Khrizanforov, M.; Strekalova, S.; Khrizanforova, V.; Grinenko, V.; Kholin, K.; Kadirov, M.; Burganov, T.; Gubaidullin, A.; Gryaznova, T.; Sinyashin, O.; Xu, L.; Vicic, D. A.; Budnikova, Y. Dalton Trans. 2015, 44, 19674. Khrizanforov, M. N.; Strekalova, S. O.; Gryaznova, T. V.; Khrizanforova, V. V.; Budnikova, Y. H. Russ. Chem. Bull. 2015, 8, 1926. Figure 1

(Invited) Effects of Sensitization Conditions on Photovoltaic and Photophysical Properties of Porphyrin-Sensitized Solar Cells

Elucidating the structural details of molecular assemblies formed on surfaces is essential to understand a variety of fundamental surface and interface phenomena as well as develop new types of functional surfaces and interfaces. Examples include molecular electronic devices and adsorption of biological molecules and materials. In the past the vast majority of such studies have been performed for thiol-based self-assembled monolayers (SAMs) which can be formed on gold surfaces by immersion. In contrast, the use of thiol-based SAMs on other metal and semiconducting surfaces has been limited technologically. Meanwhile, carboxylic and phosphonic acids have been frequently employed as an anchoring group for the immobilization of functional molecules on semiconducting surfaces. However, their studies have focused mainly on function rather than structure. As such, adsorption/desorption and exchange behaviour of functional molecules on semiconducting surfaces and their structure-function relationship have not been fully addressed. As a promising alternative to silicon-based solar cells, considerable efforts have been devoted to the development of dye-sensitized solar cells (DSSCs) where a SAM of dye is formed on a highly porous semiconducting electrode. In particular, porphyrin-sensitized solar cells (PSSCs) have drawn much attention in DSSCs because of potential advantage of porphyrins over ruthenium dyes in terms of cost, molecular design, and light-harvesting properties. On the basis of push-pull concept as well as asymmetrical pi-elongation, cell performances of PSSCs have been improved rapidly. In particular, push-pull porphyrins have been developed intensively in recent years with the aim of better matching between the absorption and solar spectra, reaching a power conversion efficiency more than 10%. To achieve further improvement of the cell performances, it is also important to elucidate close relationship between the dye structure, film structure, photophysics and photovoltaic properties, providing a guideline for the rational molecular design of high-performance dyes. During the course of our studies, we accidently encountered “memory effects” of the photovoltaic properties in the porphyrin SAMs on the TiO2 that could be regulated by choice of the sensitization solvents (MeOH vs. t-BuOH/MeCN) with and without the porphyrins. Although there are some examples of memory effects of SAMs induced by external stimuli, “memory effects” of photovoltaic properties by SAMs have not been reported in organic photovoltaics devices. Herein we report the first example of the memory effects in porphyrin SAMs on TiO2 electrodes that can be controlled by sensitization solvents, which have been evaluated by the photovoltaic properties of PSSCs, complemented by measurements of electron transfer kinetics and SAM composition and thickness. CN-labeled ZnP carboxylic acid (CNMP) and the reference porphyrin (MP) were used in this study.

(Invited) Dye Sensitized Solar Cell Based on Dicarboxylic Acid Substituted Benzoporphyrin and the Effect of Pi-Linkers Towards Their Photovoltaic Performances

In recent years, dye sensitized solar cells have attracted considerable attention due to their low cost and potential for getting higher light harvesting efficiency.1 Porphyrin derivatives have immerged as a promising candidate for DSSC due their photo stability, broad absorption within solar spectrum with high molar extinction coefficients and tunability of electrochemical properties toward synthetic modifications. Extensive studies have been done on meso-substituted porphyrins as sensitizers in DSSC.2 In 2014, highest efficiency of 13% has been archived by installing donor–Π-bridge–acceptor at the porphyrin meso-position.3Due to limited synthetic methods, there are very few β functionalized porphyrin used in DSSC. In this work, we report the synthesis, properties and photovoltaic performance of novel series of benzoporphyrins bearing two carboxyl anchoring groups through different П-linkers at their 23 and 24 positions. Palladium catalyzed double Heck reaction followed by electrocyclization/dehydrogenation strategy was used to obtain various 23, 24-functionalized benzoporphyrin from 2,3-dibromoporphyrin.4 The dyes bearing vinylene linkage and phenyl acetylene linkage at 23 and 24 position of benzoporphyrin displayed much broader and red shifted B and Q bands in UV-Vis absorption compared to its phenyl linker substituted derivative. Cyclic voltammetry results of all studied compounds confirms the thermodynamic feasiblity of electron injection from their excited states to the CB of TiO2 and regeneration of the resulting porphyrin radical cation by redox mediators. However, the photovoltaic performance of the cells sensitized with vinylene linker substituted benzoporphyrin showed highest power conversion efficiency with highest J sc and V oc values. On the other hand the photovoltaic performance of the cells sensitized with phenyl linker substituted benzoporphyrin showed lowest power conversion efficiency in this series. Our results reflect light harvesting efficiency (LHE), length and flexibility of the linker and dye loading mainly determined the difference in power conversion efficiency in this series. DFT calculation provided support that the electron density distribution in frontier molecular orbitals of vinylene linker substituted benzoporphyrin and phenyl acetylene substituted benzoporphyrin could facilitate the electron injection to semiconductor compared to phenyl linker substituted benzoporphyrin. (1) Clifford, J. N.; Martinez-Ferrero, E.; Viterisi, A.; Palomares, E. Chem. Soc. Rev. 2011, 40, 1635. (2) Higashino, T.; Imahori, H. Dalton Trans. 2015, 44, 448. (3) Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Nat. Chem. 2014, 6, 242. (4) Jinadasa, R. G. W.; Fang, Y.; Kumar, S.; Osinski, A. J.; Jiang, X.; Ziegler, C. J.; Kadish, K. M.; Wang, H. J. Org. Chem.[just accepted], DOI: 10.1021/acs.joc.5b01906 Nov., 18, 2015. Figure 1

B12-TiO2 Hybrid Catalyst for Light-Driven Hydrogen Production and Hydrogenation of Carbon-Carbon Multiple Bonds

Naturally-occurring B12(cobalamin)-dependent enzymes catalyze various molecular transformations that are of particular interest from the viewpoint of biological chemistry as well as synthetic organic chemistry and catalytic chemistry.1 For example, the B12-dependent enzyme catalyzes the rearrangement reactions and the methylation reaction as in the synthesis of methionine. All of these reactions are mediated by the cobalt alkylated complex which is generally formed by the reaction of the Co(I) state of the B12 with various electrophiles in vitro. Recently, we have reported the unique catalysis of the B12-titanium oxide (TiO2) hybrid catalyst in which the B12 complex, cyanoaquacobyrnic acid, is immobilized on the surface of TiO2 and the B12 complex is reductively activated to form the Co(I) species by electron transfer from TiO2 under UV-light irradiation.2 The hybrid catalyst mediated the dehalogenation of various organic halides and was applied to the radical-mediated organic reaction via an alkylated complex as a catalytic intermediate. The great advantage of the catalyst is the facile and efficent formation of Co(I) species by only UV light irradiation. This property prompted us to investigate further applications of the B12-TiO2 catalyst utilizing the high reactivity of the Co(I) species of the B12 complex. We now report the new catalysis of the B12-TiO2 for H2O reduction to form hydrogen. Cobalt complexes have been studied as excellent catalysts for hydrogen production, and the cobalt hydride complex is thought to be an intermediate for the reaction which could be formed by the reaction of Co(I) and a proton. As the metal hydride complexes are widely used for the reduction of unsaturated compounds, such as alkenes, an application of the B12-TiO2catalyst for the hydrogenation of C-C mutiple bonds was also investigated. [1] a) K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev. 2013, 42, 6605-6619; b) K. Gruber, B. Puffer, B. Kräutler, Chem. Soc. Rev. 2011, 40, 4346-4363; c) W. Buckel, B. T. Golding, Annun. Rev. Microbiol. 2006, 60, 27-49; d) K. L. Brown, Chem. Rev. 2005, 105, 2075-2149; e) T. Toraya, Chem. Rev. 2003, 103, 2095-2127, f) R. Banerjee, S. W. Ragsdale, Annu. Rev. Biochem. 2003, 72, 209-247. [2] a) H. Shimakoshi, Y. Hisaeda, Angew. Chem. Int. Ed. 2015, in press; b) H. Shimakoshi, Y. Hisaeda, ChemPlusChem 2014, 79, 1250-1253; c) H. Shimakoshi, M. Abiru, S. Izumi, Y. Hisaeda, Chem. Commun. 2011, 6427-6429; d) S. Izumi, H. Shimakoshi, M. Abe, Y. Hisaeda, Dalton Trans. 2010, 39, 3302-3307; e) H. Shimakoshi, M. Abiru, K. Kuroiwa, N. Kimizuka, M. Watanabe, Y. Hisaeda, Bull. Chem. Soc. Jpn. 2010, 83, 170-172; f) H. Shimakoshi, E. Sakumori, K. Kaneko, Y. Hisaeda, Chem. Lett. 2009, 38, 468-469. Figure 1

Optical limiting efficiency of an electroactive bis-iminopyridine ligand and its zinc complex

An electroactive based bis-iminopyridine ligand has been synthesized by a condensation reaction between (4-(6,7-dimethyldithio-tetrathiafulvalene)-aniline) with 2,6-diformylpyridine. The complexation of this ligand with ZnCl 2 afforded a tetrahedral neutral Zinc metal complex. optical measurements of these structures have given good results in picosecond regime. The nonlinear absorption of the ligand was significantly enhanced upon complexation with ZnCl 2 . This prompted us to conduct the experiment of optical limiting at wavelength 532nm. The nonlinear absorption properties of these structures were studied and compared to the reference material C 60 . Full Text: PDF References V. Rosso, J. Loicp, Y. Renotte, Y. Lion, Optical non-linearity in Disperse Red 1 dye-doped sol?gel, J. Non-Crystalline Solids 342 (1-3), 140 (2004). CrossRef L. Jiang, Q. Chang, Q.Y. Ouyang, H.B. Liu, Y.X. Wang, X.R. Zhang, et al., Fabrication and nonlinear optical properties of an ultrathin film with acceptor?donor periodically overlapping structure, Chemical Phys, 324(2-3), 556 (2006). CrossRef B. Sahraoui, X. Nguyen Phu, M. Salle, A. Gorgues, Electronic and nuclear contributions to the third-order nonlinear optical susceptibilities of new p-N, N?-dimethylaniline tetrathiafulvalene derivatives, Opt. Lett. 23(23), 1811 (1998). CrossRef A. Apostoluk, D. Chapron, C. Fiorini-Debuisschert, G. Gadret, J.-M. Nunzi, P. Raimond, B. Sahraoui, Quasi-phase-matched gratings printed by all-optical poling in polymer films, Opt. Lett. 27(22), 2028 (2002). CrossRef Ts. Kolev, I.V. Kityk, J. Ebothe, B. Sahraoui, Intrinsic hyperpolarizability of 3-dicyanomethylene-5,5-dimethyl-1-[2-(4-hydroxyphenyl)ethenyl]-cyclohexene nanocrystallites incorporated into the photopolymer matrices, Chem. Phys. Lett. 443(4-6), 309 (2007). CrossRef K. Iliopoulos, A. El-Ghayoury, B. Derkowska, A. Ranganathan, P. Batail, D. Gindre, B. Sahraoui, Effect of the counter cation on the third order nonlinearity in anionic Au dithiolene complexes, Appl.Phys. Lett. 101, 261105 (2012). CrossRef K. Iliopoulos, A. El-Ghayoury, H. El Ouazzani, M. Pranaitis, E. Belhadj, E. Ripaud, M. Mazari, M. Salle, D. Gindre, B. Sahraoui, Nonlinear absorption reversing between an electroactive ligand and its metal complexes, Opt. Expr. 20, 25311 (2012). CrossRef H. El Ouazzani, K. Iliopoulos, M. Pranaitis, O. Krupka, V. Smokal, A. Kolendo, B. Sahraoui, Second- and Third-Order Nonlinearities of Push?Pull Azobenzene Polymers, J. Phys. Chem. B 115, 1944 (2011). CrossRef F. Kajar, J. M. Nunzi, Functional Organic and Polymeric Materials (John Wiley and Sons Ltd., New York, 2000). K. Iliopoulos, I. Guezguez, A.P. Kerasidou, A. El-Ghayoury, D. Branzea, G. Nita, N. Avarvari, H. Belmabrouk, S. Couris, B. Sahraoui, Effect of metal cation complexation on the nonlinear optical response of an electroactive bisiminopyridine ligand, Dyes and Pigments 101, 229 (2014). CrossRef G. Nita, D. Branzea, F. Pop, A. El-Ghayoury, N. Avarvari, Electroactive Bisiminopyridine Ligands: Synthesis and Complexation Studies, Crystals 2, 338 (2012). CrossRef E. Coronado, J.R. Galan-Mascaros, C.J. Gomez-Garcia, V. Laukhin, Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound, Nature 408, 447 (2000). CrossRef M. Nihei, N. Takahashi, H. Nishikawa, H. Oshio, Spin-crossover behavior and electrical conduction property in iron(II) complexes with tetrathiafulvalene moieties, Dalton Trans 40, 2154 (2011). CrossRef G.J.P. Britovsek, V.C. Gibson, B.S. Kimberley, P.J. Maddox, S.J. McTavish, G.A. Solan, et al., Novel olefin polymerization catalysts based on iron and cobalt, Chem. Commun. 7, 849 (1998). CrossRef B.L. Small, M. Brookhart, A.M.A. Bennett, Highly Active Iron and Cobalt Catalysts for the Polymerization of Ethylene, J. Am. Chem. Soc. 120, 4049 (1998). CrossRef K. Iliopoulos, S. Couris, U. Hartnagel, A. Hirsch, Nonlinear optical response of water soluble C70 dendrimers, Chem. Phys. Lett. 448, 243 (2007). CrossRef N. Liaros, K. Iliopoulos, M.M. Stylianakis, E. Koudoumas, S. Couris, Optical limiting action of few layered graphene oxide dispersed in different solvents, Opt. Mat. 36, 112 (2014). CrossRef

Powder X-ray diffraction of Metastudtite, (UO2)O2(H2O)2

There has been some confusion in the published literature concerning the structure of Metastudtite (UO2)O2(H2O)2 where differing unit cells and space groups have been cited for this compound. Owing to the absence of a refined structure for Metastudtite, Weck et al. (2012) have documented a first-principles study of Metastudtite using density functional theory (DFT). Their model presents the structure of Metastudtite as an orthorhombic (space group Pnma) structure with lattice parameters of a = 8.45, b = 8.72, and c = 6.75 Å. A Powder Diffraction File (PDF) database entry has been allocated for this hypothetical Metastudtite phase based on the DFT modeling (see 01-081-9033) and aforementioned Dalton Trans. manuscript. We have obtained phase pure powder X-ray diffraction data for Metastudtite and have confirmed the model of Weck et al. via Rietveld refinement (see Figure 1). Structural refinement of this powder diffraction dataset has yielded updated refined parameters. The new cell has been determined as a = 8.411(1), b = 8.744(1), and c = 6.505(1) Å; cell volume = 478.39 Å3. There are only subtle differences between the refined structure and that of the first-principles model derived from DFT. Notably, the b-axis is significantly contracted in the final refinement as compared with DFT. There were also subtle changes to the U1, O1, and O3 atom positions. Tabulated powder diffraction data (d's and I's) for the Metastudtite have been derived from the refined model and these new values can serve to augment the PDF entry 01-081-9033 with a more updated entry based on observed X-ray powder diffraction data.

Constant-pH MD Simulations Portray the Protonation and Structural Behavior of Four Decapeptides Designed to Coordinate Cu(2+).

The cyclic decapeptide C-Asp, containing one Asp residue and three His residues, was designed by Fragoso et al. (Chem. Eur. J. 2013, 19, 2076) to bind Cu(2+) exclusively through the side chain groups and mimic copper coordination in metalloproteins. A variant of the cyclodecapeptide where Asp is substituted by Asn (C-Asn) has also been synthesized in addition to the linear ("open") counterparts of both forms (O-Asp and O-Asn), testing the importance of cyclization and the presence of Asp in Cu(2+) coordination (Chem. Eur. J. 2013, 19, 2076; Dalton Trans. 2013, 42, 6182). All peptides formed a major species at neutral pH that was able to coordinate Cu(2+) exclusively through the neutral imidazole groups and the Asp side chain, when present, with C-Asp being the most effective. A detailed description of the protonation behavior of each histidine could help understanding the coordination species being formed in the pH range and eventually further optimizing the peptide's design. However, the standard current methods (NMR titrations) are not very suited for proximal groups titrating in the same pH range. In this work, we used the stochastic titration constant-pH molecular dynamics method to calculate the protonation curves and pKa of each titrable residue in the four decapeptides, in the absence of Cu(2+) ions. The global protonation curves obtained in our simulations are in very good agreement with the existing potentiometric titration curves. The histidines are titrating very closely, and the Asp forms abundant salt bridges with the basic residues, displaying an unusually low pKa value. In addition, we could observe that the four peptides are very unstructured in the absence of copper, and not even the cyclic forms exhibit a significant β-sheet, unlike what could be expected from the presence of β-turn inducer units in this type of scaffold.

Efficient Separation of Europium Over Americium Using Cucurbit-[5]-uril Supramolecule: A Relativistic DFT Based Investigation.

Achieving an efficient separation of chemically similar Am(3+)/Eu(3+) pair in high level liquid waste treatment is crucial for managing the long-term nuclear waste disposal issues. The use of sophisticated supramolecules in a rigid framework could be the next step toward solving the long-standing problem. Here, we have investigated the possibility of separating Am(3+)/Eu(3+) pair with cucurbit-[5]-uril (CB[5]), a macrocycle from the cucurbit-[n]-uril family, using relativistic density functional theory (DFT) based calculations. We have explored the structures, binding, and energetics of metal-CB[5] complexation processes with and without the presence of counterions. Our study reveals an excellent selectivity of Eu(3+) over Am(3+) with CB[5] (ion exchange free energy, ΔΔGAm/Eu > 10 kcal mol(-1)). Both metals bind with the carbonyl portals via μ(5) coordination arrangement with the further involvement of three external water molecules. The presence of counterions, particularly nitrate, inside the hydrophobic cavity of CB[5], induces a cooperative cation-anion binding, resulting in enhancement of metal binding at the host. The overall binding process is found to be entropy driven resembling the recent experimental observations (Rawat et al. Dalton Trans. 2015, 44, 4246-4258). The optimized structural parameters for Eu(3+)-CB[5] complexes are found to be in excellent agreement with the available experimental information. To rationalize the computed selectivity trend, electronic structures are further scrutinized using energy decomposition analysis (EDA), quantum theory of atom in molecules (QTAIM), Mülliken population analysis (MPA), Nalewajski-Mrojek (NM) bond order, and molecular orbital analyses. Strong electrostatic ion-dipole interaction along with efficient charge transfer between CB[5] and Eu(3+) outweighs the better degree of covalency between CB[5] and Am(3+) leading to superior selectivity of Eu(3+) over Am(3+).

A two-dimensional coordination polymer constructed from binuclear copper(II) metalloligands and manganese(II) ions: Synthesis, crystal structure and magnetic properties

The self-assembly process between the binuclear [Cu2(HL)(L)]− complex and the manganese(II) ion affords a two-dimensional coordination polymer of formula [Mn{Cu2(HL)(L)}2(H2O)2]n (1) (H3L=3-hydroxyiminomethylsalicylic acid) where parallel ladder-like motifs of defective double cubanes of bis(phenoxo)dicopper(II) units as rods and anti-syn carboxylato bridges as rungs act as ligands towards tetraaqua-manganese(II) entities through the deprotonated oxime groups. The topology of 1 is compared with the one of another compound, [Mn{Cu2(HL)(L)}2(H2O)4]·4H2O·2DMF (1′) which was obtained in different conditions by Okawa et al. (J. Chem. Soc., Dalton Trans. (2001) 3119). Magnetic susceptibility measurements of 1 in the temperature range 2.0–300K are practically determined by the occurrence of a very large antiferromagnetic coupling between the two copper(II) ions through the double phenoxido bridge [J=−765(5)cm−1, the spin Hamiltonian being defined as H=−JSCu1·SCu2], a value which is as expected in the light of a recent magneto-structural correlation for bis(phenoxido)dicopper(II) complexes.

Microstructural evolution in NaNbO3-based antiferroelectrics

Our recent study found that CaZrO3 doping can effectively enhance the antiferroelectric P phase in NaNbO3 ceramics, leading to a double polarization hysteresis loop characteristic of a reversible antiferroelectric ↔ ferroelectric phase transition [Shimizu et al., Dalton Trans. 44, 10763 (2015)]. Here, a thorough transmission electron microscope study was performed to illustrate the CaZrO3 doping-assisted antiferroelectricity stabilization. In parallel to the bright-field imaging and selected area electron diffraction from multiple zone axes, detailed dark-field imaging was utilized to determine the superlattice structural origins, from either oxygen octahedral tilting or antiparallel cation displacements. By analogy with Pb(Zr1−xTix)O3 and rare-earth doped BiFeO3 systems, the chemical substitutions are such as to an induced polar-to-antipolar transition that is consistent with a tolerance factor reduction. The resultant chemical pressure has a similar effect to the compressive hydrostatic pressure where the antiferroelectric state is favored over the ferroelectric state.

Domain configuration changes under electric field-induced antiferroelectric-ferroelectric phase transitions in NaNbO3-based ceramics

We recently developed a feasible crystal chemistry strategy to stabilize the antiferroelectricity in NaNbO3 through a chemical substitution to decrease the tolerance factor and increase the average electronegativity of the system [Shimizu et al., Dalton Trans. 44, 10763 (2015) and Guo et al., J. Appl. Phys. 117, 214103 (2015)]. Two novel lead-free antiferroelectric (AFE) solid solutions, (1-x)NaNbO3-xCaZrO3 and (1-x)NaNbO3-xSrZrO3, have been found to exhibit the double polarization hysteresis typical of a reversible AFE ↔ ferroelectric (FE) phase transition. In this study, as demonstrated by (1-x)NaNbO3-xCaZrO3 system, the influence of chemical modification and electrical poling on the AFE/FE phase stability was investigated, primarily focusing on the microstructural and crystallographic evolutions. Together with the macroscopic polarization hysteresis measurements, a well-demonstrated structure-property relationship was presented. It was found that the CaZrO3 substitution into NaNbO3 can effectively destabilize the FE Q phase and correspondingly lead to a spontaneous reverting to AFE P phase. In contrast to the reversible AFE ↔ FE phase transition, the domain morphology evolution exhibits irreversible nature with a growing process of the orientational domains after applying electric field. Moreover, a multiple-zone axes electron diffraction map of P and Q phases has been summarized and is believed to be an efficient diagram to determine the AFE/FE nature of the NaNbO3-based systems.

Impact of Spark Plasma Sintering Conditions on Ionic Conductivity in La1.95Sr0.05Zr2O7-δ Electrolyte Material for Intermediate Temperature SOFCs

Solid Oxide Fuel Cells (SOFC) have attracted much attention as potential energy source. Their high operating temperatures (800°C-1000°C) can lead to thermal, mechanical and chemical problems such as densification of electrodes or formation of an insulating layer at the electrode/electrolyte interface by interdiffusion [1-2]. To overcome these drawbacks, the Proton Ceramic Fuel Cell (PCFC) technology was developed. This technology, where the electrolyte is an H+ ion conductor in the form of ceramic oxide material, exhibits the intrinsic benefits of proton conduction in Polymer Exchange Membrane Fuel Cells (PEMFC) and the advantages of the SOFC technologies. Since the discovery of high temperature protonic conductivity in cerates [3-4], many investigations about pyrochlore-type proton conductors are performed [5-6]. These systems are characterized by mixed valence oxides (often rare earth) and anion vacancies as primary lattice defects. Under wet atmosphere, the proton conduction occurs via the hydration of oxygen vacancies after the material is exposed to a vapour-containing atmosphere according to the following equation 1 (inserted as part of the image file). The conventional route for the preparation of lanthanum zirconate pyrochlore (LSZO) via solid-state reactions requires multiple milling and high temperature calcination steps. Also, this method leads generally to an heterogeneity of the final product, whereas wet chemical route, which consists of mixing precursors in a solution, could improve compositional homogeneity and stoichiometry. In this work, we have synthesized nano-sized La1,95Sr0,05Zr2O7- d using an oxalic co-precipitation method. As impedance spectroscopy measurements require high densification, only spark plasma sintering (SPS) gives dense materials. Other sintering processes such as hot isostatic pressing induce a segregation of strontium at the surface of the pellet[7],and thereby decrease proton conductivities. LSZO powders were densified using SPS apparatus under different sintering conditions: holding time, temperature and pressure. To maintain the same compacity for different grain sizes, starting powder materials were calcined at different temperatures in order to increase of the particle size. Thus several pellets with either different relative densities or grain sizes were obtained. The grain size increases with increasing of the sintering temperature. The proton conductivity behavior of those pellets was investigated by AC impedance spectroscopy under dry and wet atmospheres. The data were measured in the frequency range 0.1Hz – 6 MHz (Materials mates M2-7260 impedance analyzer) at intermediate temperatures 400-600°C. In order to verify the dependence of total resistance and capacitance, a DC-bias (UDC from 0 to 1V) was applied. The Nyquist diagrams were modeled by equivalent circuits based on resistors and constant phase elements (CPEs). The ionic conductivities are clearly dependent on grain sizes (see Figure 1). In order to elucidate this dependence, it will be necessary to assess a porosity correction equation. The activation energies, calculated using the Arrhenius equation, increase with increasing grain sizes. The proton conductivities are higher in wet atmosphere than dry atmosphere. For example, the ionic conductivities of 120 nm-LSZO are 2.45 × 10-5 S.cm-1 and 3.30 × 10-5 S.cm-1 under dry and wet atmosphere (5% H2O) at 600°C, respectively. Figure 1 - Nyquist plots of impedance spectra for LSZO with different particle sizes at 600°C References [1] S.C. Singhal, Solid State Ion. 135 (2000) 305. [2] C. Xia, W. Rauch, F. Chen, M. Liu, Solid State Ion. 149 (2002) 11. [3] F. Chen, O.T. Sørensen, G. Meng, D. Peng, J. Mater. Chem. 7 (1997) 481. [4] H. Iwahara, H. Uchida, K. Ono, K. Ogaki, J. Electrochem. Soc. 135 (1988) 529. [5] K.E.J. Eurenius, E. Ahlberg, C.S. Knee, Dalton Trans. 40 (2011) 3946. [6] T. Shimura, M. Komori, H. Iwahara, Solid State Ion. 86–88, Part 1 (1996) 685. [7] D. Huo, D. Gosset, G. Baldinozzi, D. Siméone, H. Khodja, B. Villeroy, S. Surblé, Solid State Ion. (submitted). Figure 1

Catalytic Activity of Double-Perovskite Type BalnMn2O5 for Oxygen Reduction Reaction Using in Rechargeable Zinc-Air Batteries

There have been increased demands for the development of high energy efficient and affordable energy storage devices as the alternatives to lithium-ion secondary batteries for electrical vehicles, portable electronic devices and so on. Recently, rechargeable zinc-air batteries have attracted much attention from the point of view of high-capacity and safety batteries. To realize the rechargeable zinc-air batteries, active cathode catalysts for oxygen reduction reaction and evolution reaction (ORR and OER) play important roles in the overall battery performance because of the majority of energy losses occurring at the cathode reactions. It is well known that the transition-metal oxide family with a perovskite-type ABO3 structure is one of the promising catalysts for ORR and OER. Especially, manganese oxides such as LaMnO3+δ and La1-xCaxMnO3 showed high ORR activities. Some researchers reported that the ORR activity for oxide catalysts primarily correlates to the electronic states and valence of Mn. However, a clear strategy has not been revealed to prepare active catalysts for ORR. On the other hand, more recently, in the case of high-temperature oxygen intake/release reactions of the double-perovskite type BaLnMn2O5+δ (Ln = Y, Gd, Nd and La; Fig. 1a), Motohashi et al. reported that the redox characteristics could be controlled by the radius of Ln ions, even though the valence of Mn remained unchanged [1]. Therefore, in this study, we focused on the ORR activity of the double-perovskite type BaLnMn2O5+δ (Ln: Y, Gd, Nd and La). BaLnMn2O5+δ (Ln: Y, Gd, Nd, and La) powder catalysts were synthesized via a citrate precursor route combined with the oxygen-pressure-controlled encapsulation technique. Ln 2O3 (fired at 1000°C overnight prior to use), Ba(NO3)2 and Mn(NO3)2·6H2O were used as starting materials. Appropriate amounts of these reagents were dissolved in diluted HNO3 (for Ln 2O3) or Milli-Q water [for Ba(NO3)2 and Mn(NO3)2·6H2O] to prepare Ln, Ba, and Mn nitrate solutions. These solutions were mixed in a crucible in which equimolar citric acid was subsequently added as a complexing agent. The citrate solution was stirred and heated at 60-70°C to promote polymerization. The gelatinous product was prefired at 450°C in air for 1 h and then at 1000°C in flowing N2 gas for 24 h. The resulting precursor powder was pressed into pellets and placed in an evacuated silica ampule together with an equal amount of FeO powder, which acts as a getter for excess oxygen. The silica ampule was heated at 1100°C for 24 h, followed by quenching into ice water. The crystallinity, morphology and particle size of the resultant samples were characterized with XRD and SEM. Electrochemical measurements were carried out using a rotating ring disk electrode (RRDE, Pt ring) with a conventional three electrode system. The catalyst ethanol ink (BaLnMn2O5: acetylene black: Nafion = 5: 1: 1) was dropped and dried on a glassy carbon electrode as a working electrode. A Pt plate and a Hg/HgO electrode were used as a counter electrode and a reference electrode, respectively. Argon- or oxygen-saturated 4 mol dm-3 potassium hydroxide aqueous solution was used as an electrolyte. The scan speed and rotating speed of the RRDE were 1 mV sec-1 and 1600 rpm, respectively. The XRD data indicate that all the as-synthesized BaLnMn2O5+δ products are essentially phase-pure of the fully reduced δ ≈ 0 form with a tetragonal unit cell. Both the a- and c-axis lengths are in agreement with those in the previous literature. As expected, these values systematically increase with the increasing ionic radius of Ln 3+ in the order of Y, Gd, Nd, and La. The oxygen content (5+δ) values determined by iodometry are close to 5.00 for all the Ln-products. The particle sizes of the samples were almost the same as 1~2 μm. Fig 1b shows onset potentials for ORR as a function of the radius of Ln ions of the samples. It can be seen that the onset potential is shifted toward positive side as the radius of the Ln ions increases, in spite of the fixed Mn valence for all the samples. The most active catalysts for ORR were BaNdMn2O5 and BaLaMn2O5, which contain larger Ln ions. The result implied that the size of A site ion played an important role in the catalytic activity for ORR.Fig. 1 (a) the crystal structure and (b) the onset potentials for ORR as a function of the radius of Ln ions of BaLnMn2O5+δ (Ln: Y, Gd, Nd, and La).[1] T. Motohashi, M. Kimura, T. Inayoshi, T. Ueda, Y. Masubuchi and S. Kikkawa, Dalton Trans. in press. Figure 1

Synthesis and Characterization of Tetra(pyridyl)cyclo­butadiene Iron Complexes [Cp*Fe(C4py4)]– (py = 3‐pyridyl and 4‐pyridyl, Cp* = C5Me5)

AbstractThe tetra(pyridyl)cyclobutadiene complexes [K([18{crown‐6){Cp*FeC4(3‐py)4}] (2) (3‐py = 3‐pyridyl) and [K([18{crown‐6){Cp*FeC4(4‐py)4}] (3) (4‐py = 4‐pyridyl) were synthesized by reacting two equivalents of bis(3‐pyridyl)acetylene and bis(4‐pyridyl)acetylene with the naphthalene complex [K([18{crown‐6){Cp*Fe(η4‐C10H8)}]. Compounds 2 and 3 were fully characterized by X‐ray crystallography, 1H and 13C{1H} NMR spectroscopy, UV/Vis spectroscopy, and elemental analysis. They display similar sandwich structures with an η5‐coordinated Cp* unit and an η4‐coordinated cyclobutadiene moiety. In the solid state, compounds 2 and 3 form distinct polymeric chain structures due to the interaction of the pyridyl nitrogen atoms with the potassium cations. Cyclic voltammetry measurements indicate that the [Cp*FeC4py4]– anions (py = 3‐py or 4‐py) undergo a reversible one electron oxidation to neutral [Cp*FeC4py4] complexes. A second quasi‐reversible redox event is attributed to the oxidation these products to unstable [Cp*FeC4py4]+ cations. The properties of 2 and 3 are compared with those of the previously reported 2‐pyridyl complex [K([18{crown‐6){Cp*FeC4(2‐py)4}] (1) [Dalton Trans. 2014, 43, 4247–4250].

Strategy for stabilization of the antiferroelectric phase (Pbma) over the metastable ferroelectric phase (P21ma) to establish double loop hysteresis in lead-free (1−x)NaNbO3-xSrZrO3 solid solution

A new lead-free antiferroelectric solid solution system, (1−x)NaNbO3-xSrZrO3, was rationalized through noting the crystal chemistry trend, of decreasing the tolerance factor and an increase in the average electronegativity of the system. The SrZrO3 doping was found to effectively stabilize the antiferroelectric (P) phase in NaNbO3 without changing its crystal symmetry. Preliminary electron diffraction and polarization measurements were presented which verified the enhanced antiferroelectricity. In view of our recent report of another lead-free antiferroelectric system (1−x)NaNbO3-xCaZrO3 [H. Shimizu et al. “Lead-free antiferroelectric: xCaZrO3 - (1−x)NaNbO3 system (0 ≤ x ≤ 0.10),” Dalton Trans. (published online)], the present results point to a general strategy of utilizing tolerance factor to develop a broad family of new lead-free antiferroelectrics with double polarization hysteresis loops. We also speculate on a broad family of possible solid solutions that could be identified and tested for this important type of dielectric.

Preparation and Structural Characterization of Mono‐Ru‐Substituted α2‐Dawson‐Type Phosphotungstate with a Carbonyl Ligand and Other Ru(CO)‐Substituted Heteropolytungstates

AbstractIn our previous article (Dalton Trans. 2008, 6692–6698) we reported that hydrothermal reaction of a mono‐lacunary Keggin‐type silicotungstate, [SiW11O39]8–, and Ru(acac)3 (acac: acetylacetonate) for 5–24 h produced a mono‐Ru‐substituted Keggin‐type silicotungstate with a terminal aqua ligand, [SiW11O39RuIII(H2O)]5–, which was further converted into a carbonyl (CO) derivative, [SiW11O39RuII(CO)]6–, by increasing the reaction time for several days. Here, reactions of Ru(acac)3 with other mono‐lacunary heteropolytungstates for the formation of other mono‐Ru(CO)‐substituted heteropolytungstates, including Keggin derivatives, [GeW11O39RuII(CO)]6– and [PW11O39RuII(CO)]5–, and Dawson‐type phosphotungstates, [α1‐P2W17O61RuII(CO)]8– and [α2‐P2W17O61RuII(CO)]8–, are presented. The desired α2‐isomer of Dawson‐type phosphotungstate, [α2‐P2W17O61RuII(CO)]8–, was produced in high purity and was fully characterized by CV, 31P NMR, 13C NMR, IR, UV/Vis, elemental analysis, mass spectroscopy, TG‐DTA, TPD‐MS, and single‐crystal structure analysis. On the other hand, Keggin‐type complexes, [GeW11O39RuII(CO)]6– and [PW11O39RuII(CO)]5–, were formed together with their aqua derivatives, [GeW11O39RuIII(H2O)]5– and [PW11O39RuIII(H2O)]4–, respectively, and the α1‐isomer of Dawson‐type phosphotungstate, [α1‐P2W17O61RuII(CO)]8–, was produced together with the α2‐derivative, as confirmed by CV, IR, mass spectroscopy, and 31P NMR spectroscopy.

Formation of Hydrogen-Bonded Supramolecular Assemblies Based on Functionalized Saddle-Distorted Porphyrins

Supramolecular assemblies consisting of porphyrins have been intensively investigated in the light of promising photo-functionality including photoinduced electron transfer, photo-conducting materials, dye-sensitized solar cells, and guest inclusion toward the emergence of novel functions on the basis of unique spatial host-guest arrangements and interactions. Along this line, we have developed a series of supramolecular assemblies using the diprotonated form of saddle-distorted dodecaphenylporphyrin (H2DPP) through intermolecular π-π interaction, such as Porphyrin Nanochannels, which include electron-donating guest molecules.1 In this presentation, we present formation and characterization of supramolecular assemblies based on H2DPP derivatives having hydrogen-bonding functional groups and their metal complexes. Introduction of carboxyl groups or hydroxyl groups to the meso-phenyl groups of H2DPP as hydrogen-bonding sites allows us to construct robust and well-organized supramolecular assemblies. A diprotonated tetracarboxyl-DPP derivative (1, Fig. 1a), for example, formed two-dimensional hydrogen-bonding networks (Fig. 1b) to form a porphyrin nanochannel structure, which were reminiscent of that formed by [H4DPP2+]Cl2 and was persistent up to 150°C, in contrast to that of [H4DPP2+]Cl2.2 To expand the size of the nanochannels, we also introduced 4-carboxylphenyl groups at the 4-positions of the meso-phenyl groups of H4DPP2+. A Zn(II) complex of H2DPP derivatives having hydroxyl groups at the 4-positions of the meso-phenyl groups (2) was prepared to form a dimer bridged by 4,4’-bypyridine.3 The dimer was revealed to form intermolecular hydrogen-bonding network among the hydroxyl groups in the crystal. In addition to the crystal structures, we will also mention adsorption of gaseous molecules such as N2 and CO2 with porous supramolecular assemblies of functionalized H2DPP derivatives in the solid state. References (a) R. Harada et al., Chem. Commun. 2005, 716. (b) T. Kojima et al., Chem.–Eur. J. 2007, 13, 8714. (c) T. Nakanishi et al., Chem. Mater. 2008, 21, 7492. (d) S. Fukuzumi et al., Coord. Chem. Rev. 2012, 256, 2488.T. Ishizuka et al. Chem. Commun. 2012, 48, 6481.T. Ishizuka et al. Dalton Trans. 2013, 42, 16073. Figure 1

Porphyrins and Other Chromophores with Antioxidant Substituents

Oxoporphyrinogens1,2 are a class of porphyrinoid generally containing a tetrapyrrole macrocycle with oxo or oxocyclohexadienylidene groups substituted at their periphery. They are unique in that their physical structures are coupled to their electronic structures depending on the electrochemical state of the molecule. Variations in electronic conjugation over the core tetrapyrrole and substituents affect electronic absorptive properties. Using these features we have developed oxoporphyrinogens as molecular switching elements and for sensing applications involving chemical species including water and chiral compounds.3,4 Tetrapyrroles with two or four conjugating substituents as well as corroles have been prepared and investigated for their properties depending on tautomerism,5 guest binding by hydrogen bonding and structural changes due to photoredox processes. The syntheses and mechanisms of action of the switching and sensing properties will be presented and discussed. Oxoporphyrinogens were developed from a porphyrin substituted with antioxidant 2,6-di-t-butylphenol groups. We have also investigated the synthesis and properties of other similarly substituted chromophores and will discuss some of the relevant properties.6,7 References (1) F. D’Souza, N. K. Subbaiyan, Y. Xie, J. P. Hill, K. Ariga, K. Ohkubo, S. Fukuzumi, J. Am. Chem. Soc. (2009) 131, 16138–16146. (2) J. P. Hill, I. J. Hewitt, C. E. Anson, A. K. Powell, A. L. McCarthy, P. Karr, M. Zandler, F. D’Souza, J. Org. Chem. (2004) 69, 5861–5869. (3) S. Ishihara, J. Labuta, T. Šikorský, J. V. Burda, N. Okamoto, H. Abe, K. Ariga, J. P. Hill, Chem. Commun. (2012) 48, 3933–3935 (4) A. Shundo, J. Labuta, J. P. Hill, S. Ishihara, K. Ariga, J. Am. Chem. Soc. (2009) 131, 9494–9495; J. Labuta, S. Ishihara, A. Shundo, S. Arai, S. Takeoka, K. Ariga, J. P. Hill, Chem. Eur. J. (2011) 17, 3558–3561. (5) Y. Xie, J. P. Hill, A. L. Schumacher, P. A. Karr, F. D’Souza, C. E. Anson, A. K. Powell, K. Ariga, Chem. Eur. J. 2007, 13, 9824–9833. (6) J. P. Hill, N. K. Subbaiyan, F. D’Souza, Y. Xie, S. Sahu, N. M. Sanchez-Ballester, K. Ariga, Chem. Commun. (2012) 48, 3951–3953. (7) A. Jana, H. Gobeze, M. Ishida, T. Mori, K. Ariga, J. P. Hill, F. D’Souza Dalton Trans. (2014) in press, DOI: 10.1039/C4DT03157A.

Synthesis of Phthalocyanines Using Triorganoindium Reagents

Phthalocyanines (Pcs) have attracted much attention due to their singular electronic properties, exceptional chemical and photochemical stabilities, and strong absorption of visible light [1]. Although there is a great variety of methods for the preparation of substituted phthalocyanines, introducing the substituents either on the phthalonitrile precursor or on the already formed phthalocyanine core, we have decided to explore the palladium-catalysed coupling reaction between haloaromatics and triorganoindium reagents [2]. The latter benefits from high reactivity, efficiency, versatility and chemoselectivity, together with the low toxicity associated with indium derivatives. We have indeed already experimented with this process, first exploring some basics about the scope [3] and new procedures for the synthesis of the triorganoindium reagents [4], and later using it in the preparation of hole transporting materials [5]. In this occasion we will discuss our more recent results in the preparation of substituted phthalocyanines using triorganoindium reagents. Taking advantage of the previously commented properties of Pcs, the synthesized compounds are excellent candidates for the preparation of photovoltaic devices, either Dye-Sensitized Solar Cells (DSSCs) or Bulk Heterojunction (BHJs) [6,7]. Acknowledgements. This work has been supported by the Spanish Ministerio de Economía y Competitividad, Generalitat Valenciana and the European FEDER funds (grants CTQ 2010-20349, CTQ2011-26455, CTQ2013-47922-R, PROMETEO 2012/010 and ISIC/2012/008). References Phthalocyanines: Properties and Applications, Leznoff, C. C.; Lever, A, B. P. Eds.; VCH Publishers, Weinheim, 1990-1996, Vols. 1-4.Pérez, I.; Pérez-Sestelo, J.; Sarandeses, L. A. Org. Lett. 1999, 1, 1267-1269.Font-Sanchis, E.; Céspedes-Guirao, F. J.; Sastre-Santos, A.; Fernández-Lázaro, F. J. Org. Chem. 2007, 72, 3589-3591.Font-Sanchis, E.; Sastre-Santos, A.; Fernández-Lázaro, F. Dalton Trans. 2009, 2470-2473. Lana-Villareal, T.; Font-Sanchis, E.; Sastre-Santos, A.; Fernández-Lázaro, F.; Gómez, R. ChemPhysChem 2011, 12, 1155-1164.Martín-Gomis, L.; Fernández-Lázaro, F.; Sastre-Santos, A. J. Mater. Chem. A 2014, 2, 15672-15682.Molina, D.; Guerrero, A.; García-Belmonte, G.; Fernández-Lázaro, F.; Sastre-Santos, A. Eur. J. Org. Chem. 2014, 4585-4591. Figure 1