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Abstract: Octahydridoborate, i.e. [B3H8]− containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3H8 from a monoclinic (α) to an orthorhombic (α′) structure at 15 °C via a second-order transition and eventually to a cubic (β) structure at 30 °C by a first-order transition. The β-polymorph of KB3H8 displays a high degree of disorder of the [B3H8]− anion, which facilitates increased cation mobility, reaching a K+ conductivity of ∼10−7 S cm−1 above 100 °C. β-KB3H8 starts to release hydrogen at ∼160 °C, simultaneously with the release of B5H9 and trace amounts of B2H6. KBH4 and K3(BH4)(B12H12) are identified as crystalline decomposition products above 200 °C, and the formation of a KBH4 deficient structure of K3−x(BH4)1−x(B12H12) is observed at elevated temperature. The hydrogen-uptake properties of a KB3H8–2KH composite have been examined under 380 bar H2, resulting in the formation of KBH4 at T ≥ 150 °C along with higher metal hydridoborates, i.e. K2B9H9, K2B10H10, and K2B12H12.

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Abstract: Flexible metal-organic frameworks (MOFs) exhibit large potential as next-generation materials in areas such as gas sensing, gas separation and mechanical damping. By using a mixed metal approach, we report how the stimuli reponsive phase transition of flexible pillared-layered MOFs can be tuned over a wide range. Different Cu2+ to Zn2+ metal ratios are incorporated into the materials by using a simple solvothermal approach. The properties of the obtained materials are probed by differential scanning calorimetry and CO2 sorption measurements, revealing stimuli responsive behaviour as a function of metal ratio. Pair distribution functions derived from X-ray total scattering experiments suggest a distortion of the M2 paddlewheel as a function of the Cu content. We rationalize these phenomena by the different distortion energies of Cu2+ and Zn2+ ions to deviate from the square pyramidal structure of the relaxed paddlewheel node.Our work follows on from the large interest in tuning and understanding the materials properties of flexible MOFs, highlighting the large number of parameters that can be used for the targeted manipulation and design of properties of these fascinating materials.

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Abstract: [FeFe]-hydrogenases contain strongly electronically coupled diiron [2Fe]H and tetrairon [Fe4–S4]H clusters, and thus much recent effort has focused on the chemistry of diiron-dithiolate biomimics with appended redox-active ligands. Here we report on the synthesis and electrocatalytic activity of Fe2(CO)4(μ-edt)(κ2-bpcd) (2) in which the electron-acceptor 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) acts as a surrogate of the [Fe4–S4]H sub-cluster. The complex is prepared in low yield but has been fully characterised, including a crystallographic study which shows that the diphosphine adopts a basal-apical coordination geometry in the solid state. Cyclic voltammetry shows that 2 undergoes four reduction events with DFT studies confirming that the first reduction is localised on the low-lying π* system of the diphosphine ligand. The addition of the second electron furnishes a triplet dianion that exhibits spin density distributed over the diphosphine and diiron subunits. Protonation at the Fe–Fe bond of the triplet dianion furnishes the corresponding bridging hydride as the thermodynamically favoured species that contains a reduced bpcd ligand. Complex 2 functions as a catalyst for proton-reduction at its second reduction potential, in contrast to the related 2,3-bis(diphenylphosphino)maleic anhydride (bma) complex, Fe2(CO)4(μ-pdt)(κ2-bma) (1), which shows similar electrochemical behaviour but is not catalytically active. The difference in chemical behaviour is attributed to greater stability of the 4-cyclopenten-1,3-dione platform in 2 as compared to the maleic anhydride ring of the bma ligand in 1 following the uptake of the second electron. Thus protonation of the Fe–Fe bond in the 22− affords a species which is stable enough to undergo a further reduction–protonation event, unlike the bma ligand whose maleic anhydride ring undergoes deleterious C–O bond scission upon protonation or reaction with adventitious moisture. DFT studies, however, suggest that electron-transfer from the diphosphine to the diiron centre is not significant, probably due to their poor redox levelling. Thus, while the diphosphine is readily reduced, the added electron is apparently not utilised in proton-reduction and hence cannot truly be considered as an [Fe4–S4]H surrogate.

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Abstract: Hydrothermal crystallisation of CeO2 from aqueous sodium hydroxide solution at 240 °C using CeCl3·7H2O in the presence of hydrogen peroxide with addition of either SbCl3 or SbCl5 yields polycrystalline samples of antimony-containing ceria directly from solution. Powder X-ray diffraction shows a contraction of the cubic lattice parameter with increasing Sb content, and also a broadening of Bragg peaks, from which Scherrer analysis yields crystallite domain sizes of 5–20 nm. Scanning transmission electron microscopy provides consistent results with observation of highly crystalline particles of a few nm in diameter. X-ray absorption near edge structure spectroscopy at the Ce LIII- and Sb K-edges reveals the presence of Ce4+ and Sb5+ in the solids. To balance charge the presence of co-included Na is proposed, corroborated by elemental analysis. The general chemical formula of the materials can thus be written as (Ce1−xSbx)1−yNayO2−δ (where x < 0.4 and y ≥ x/3). Sb K-edge extended X-ray absorption fine structure spectroscopy of the substituted ceria samples shows that the local structure of Sb resembles that in NaSbO3, where six-coordinate metal sites are found, but with evidence of a longer interatomic correlation due to surrounding Ce/Sb atoms in the fluorite structure; this implies that the Sb is displaced from the ideal eight-coordinate site of the fluorite structure. This structural distortion gives materials that are unstable under reducing conditions, coupled by the ease of reduction to elemental antimony, which is extruded leading to phase separation.

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Abstract: Heteroleptic [Cu(P^P)(N^N)][PF6] complexes, where N^N is a halo-substituted 2,2′-bipyridine (bpy) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) have been synthesized and investigated. To stabilize the tetrahedral geometry of the copper(I) complexes, the steric demands of the bpy ligands have been increased by introducing 6- or 6,6′-halo-substituents in 6,6′-dichloro-2,2′-bipyridine (6,6′-Cl2bpy), 6-bromo-2,2′-bipyridine (6-Brbpy) and 6,6′-dibromo-2,2′-bipyridine (6,6′-Br2bpy). The solid-state structures of [Cu(POP)(6,6′-Cl2bpy)][PF6], [Cu(xantphos)(6,6′-Cl2bpy)][PF6]·CH2Cl2, [Cu(POP)(6-Brbpy)][PF6] and [Cu(xantphos)(6-Brbpy)][PF6]·0.7Et2O obtained from single crystal X-ray diffraction are described including the pressure dependence of the structure of [Cu(POP)(6-Brbpy)][PF6]. The copper(I) complexes with either POP or xantphos and 6,6′-Cl2bpy, 6-Brbpy and 6,6′-Br2bpy are orange-to-red emitters in solution and yellow-to-orange emitters in the solid state, and their electrochemical and photophysical properties have been evaluated with the help of density functional theory (DFT) calculations. The emission properties are strongly influenced by the substitution pattern that largely affects the geometry of the emitting triplet state. [Cu(POP)(6,6′-Cl2bpy)][PF6] and [Cu(xantphos)(6,6′-Cl2bpy)][PF6] show photoluminescence quantum yields of 15 and 17%, respectively, in the solid state, and these compounds were tested as luminophores in light-emitting electrochemical cells (LECs). The devices exhibit orange electroluminescence and very short turn-on times (<5 to 12 s). Maximum luminance values of 121 and 259 cd m−2 for [Cu(POP)(6,6′-Cl2bpy)][PF6] and [Cu(xantphos)(6,6′-Cl2bpy)][PF6], respectively, were achieved at an average current density of 100 A m−2. External quantum efficiencies of 1.2% were recorded for both complexes.