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Hexacoordinate silicate and germanate linkers supporting high negative charges have been prepared and applied as building blocks for anionic MOF frameworks with lanthanide metal-based nodes. The SiO6/GeO6 centred linkers [Et3NH]2[H3L-Si/Ge] [H3L-Si/Ge = tris(3,4-diolato-benzoic acid) silicate/germanate] were initially prepared and characterised, with the germanate ligand demonstrating excellent water stability. A series of rare earth MOFs (IMP-33-Sc and IMP-34-Ln, Ln = Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were then synthesised under hydrothermal conditions using H3L-Ge. Both IMP-33-Sc and IMP-34-Ln exhibit (3,6)-connected networks with the same flu-3,6-C2/c topology, however, whereas IMP-33-Sc contains trimetallic nodes, IMP-34-Ln nodes are bimetallic, thus leading to a higher anionic network charge of 4− in IMP-34-Ln (vs. 1− in IMP-33-Sc). The terbium based MOF IMP-34-Tb exhibits characteristic luminescent properties and is shown to be selectively quenched by Pb2+ ions in aqueous solutions through a dynamic quenching process. A strong linear relationship between the fluorescence intensity and Pb2+ concentration in the range of 0.01–4 mM makes it a promising sensor for aqueous Pb2+ ions. [ABSTRACT FROM AUTHOR]

N-alkylated C2-symmetric amino acid amide derivatives were shown to catalyse the Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene, achieving a maximum ee of 44%. The corresponding trifluoroacetic acid salts also catalysed the aldol reaction between 4-nitrobenzaldehyde and hydroxyacetone, leading to the formation of predominantly syn-aldol products in up to 55% ee. Aspects of the solvent dependence of the aldol reaction and the H-bonding of the catalyst were investigated. [ABSTRACT FROM AUTHOR]

Several tetrahydroxidohexaoxidopentaborate(1-) salts of N-substituted diimidazolium cations or N-substituted dipyrrolidinium cations linked through N-C6-N chains have been synthesized and characterized spectroscopically (NMR, IR) and by single-crystal XRD studies: [R(NC3H3N)(CH2)6(NC3H3N)R][B5O6(OH)4]2·xH2O (R = Me, x = 0 (1); R = Et, x = 3 (2); [Me(NC3H3N)(CH2(C6H4)CH2)(NC3H3N)Me][B5O6(OH)4]2 (3), [(C4H8N)(R)(CH2)6(R)(NC4H8)][B5O6(OH)4]2·xB(OH)3 (R = Me, x = 0 (4, two polymorphs); R = Et, x = 0 (5); R = Bu, x = 4 (6); R = allyl, x = 0 (7)). Representative samples (1 and 7) were also characterized by thermal (TGA/DSC) studies; compounds are thermally decomposed to B2O3 in air. Numerous anion-anion H-bonding interactions are present in the solid-state structures of 1–5 and 7 as giant anionic networks. Unusually, in 6 there are no R22(8) anion-anion interactions as the co-crystallized B(OH)3 bridges between all pentaborate anions. H-bonding interactions in 1–7 have been examined using Etter graph set analysis; C(8), C33(18), R22(8), R22(12) and R44(12) motifs have been identified. [ABSTRACT FROM AUTHOR]

The synthesis and characterisation of eleven different 2-(thienyl)quinoxaline species that incorporate different points of functionality, including at the thiophene or quinoxaline rings, are described. These species display variable fluorescence properties in the visible region (λem = 401–491 nm) depending upon the molecular structures and extent of conjugation. The series of 2-(thienyl)quinoxaline species were then investigated as cyclometalating agents for Ir(III) to yield [Ir(C^N)2(bipy)]PF6 (where C^N = the cyclometalated ligand; bipy = 2,2′-bipyridine). Eight complexes were successfully isolated and fully characterised by an array of spectroscopic and analytical techniques. Two Ir(III) examples were structurally characterised in the solid state using single crystal X-ray diffraction; both structures confirmed the proposed formulations and coordination spheres in each case showing that the thiophene coordinates via a Ir–C bond. The photophysical properties of the complexes revealed that each complex is luminescent under ambient conditions with a range of emission wavelengths observed (665–751 nm) indicating that electronic tuning can be achieved via both the thienyl and quinoxaline moieties. [ABSTRACT FROM AUTHOR]

Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky barrier in device performance. Here, we demonstrate the first solution synthesis of 8‐AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor‐made polymer precursor into 8‐AGNRs was validated by FT‐IR, Raman, and UV/Vis‐near‐infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho[1,2,3,4‐ghi]perylene derivatives (1 and 2) as subunits of 8‐AGNR, with a width of 0.86 nm as suggested by the X‐ray single crystal analysis. Low‐temperature scanning tunneling microscopy (STM) and solid‐state NMR analyses provided further structural support for 8‐AGNR. The resulting 8‐AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical‐pump TeraHertz‐probe spectroscopy revealed charge‐carrier mobility in the dc limit of ∼270 cm2 V−1 s−1 for the 8‐AGNR. [ABSTRACT FROM AUTHOR]

Two substituted phosphonium tetrahydoxidohexaoxidopentaborate(1-) salts, [iPrPPh3][B5O6(OH)4]·3.5H2O (1) and [MePPh3][B5O6(OH)4]·B(OH)3·0.5H2O (2), were prepared by templated self-assembly processes with good yields by crystallization from basic methanolic aqueous solutions primed with B(OH)3 and the appropriate phosphonium cation. Salts 1 and 2 were characterized by spectroscopic (NMR and IR) and thermal (TGA/DSC) analysis. Salts 1 and 2 were thermally decomposed in air at 800 °C to glassy solids via the anhydrous phosphonium polyborates that are formed at lower temperatures (<300 °C). BET analysis of the anhydrous and pyrolysed materials indicated they were non-porous with surface areas of 0.2–2.75 m2/g. Rhe recrystallization of 1 and 2 from aqueous solution afforded crystals suitable for single-crystal XRD analyses. The structure of 1 comprises alternating cationic/anionic layers with the H2O/pentaborate(1-) planes held together by H-bonds. The cationic planes have offset face-to-face (off) and vertex-to-face (vf) aromatic ring interactions with the iPr groups oriented towards the pentaborate(1-)/H2O layers. The anionic lattice in 2 is expanded by the inclusion of B(OH)3 molecules to accommodate the large cations; this results in the formation of a stacked pentaborate(1-)/B(OH)3 structure with channels occupied by the cations. The cations within the channels have vf, ef (edge-to-face), and off phenyl embraces. Both H-bonding and phenyl embrace interactions are important in stabilizing these two solid-state structures. [ABSTRACT FROM AUTHOR]

Six disubstituted ligands based upon 2‐(2′‐pyridinyl/pyrazinyl)quinoline‐4‐carboxylic acids have been synthesised, solvent‐free, in one step from a range of commercially available isatin derivatives. These species behave as ancillary chelating ligands for Ir(III) complexes of the form [Ir(C^N)2(N^N)]PF6 (where C^N=cyclometalating ligand; N^N=2‐(2′‐pyridinyl/pyrazinyl)quinoline‐4‐carboxylic acids). An X‐ray crystallographic study on one complex shows a distorted octahedral geometry wherein a cis‐C,C and trans‐N,N coordination mode is observed for the cyclometalating ligands. DFT calculations predicted that variations in N^N ligand from 2,2′‐bipyridine to L1–6 should localise the LUMO on to the Ln ligand and that the complexes are predicted to display MLCT/LLCT character. All complexes displayed luminescence in the deep red part of the visible region (674–679 nm) and emit from triplet states, but with little apparent tuning as a function of L1–6. Further time‐resolved transient absorption spectroscopy supports the participation of these triplet states to the excited state character. [ABSTRACT FROM AUTHOR]

A series of 2‐phenylquinoxaline ligands have been synthesised that introduce either CF3 or OCF3 electron‐withdrawing groups at different positions of the phenyl ring. These ligands were investigated as cyclometalating reagents for platinum(II) to give neutral complexes of the form [Pt(C^N)(acac)] (in which C^N=cyclometalating ligand; acac=acetyl acetonate). X‐ray crystallographic studies on three examples showed that the complexes adopt an approximate square planar geometry. All examples revealed strong Pt−Pt linear contacts of 3.2041(6), 3.2199(3) and 3.2586(2) Å. The highly coloured complexes display efficient visible absorption at 400–500 nm (ϵ ≈5000 M−1 cm−1) and orange red photoluminescent characteristics (λem=603–620 nm; Φem ≤37 %), which were subtly tuned by the ligand. Triplet emitting character was confirmed by microsecond luminescence lifetimes and the photogeneration of singlet oxygen with quantum efficiencies up to 57 %. Each complex was investigated as a photosensitiser for triplet–triplet annihilation energy upconversion using 9,10‐diphenylanthracene as the annihilator species: a range of good upconversion efficiencies (ΦUC 5.9–14.1 %) were observed and shown to be strongly influenced by the ligand structure in each case. [ABSTRACT FROM AUTHOR]