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Amide-based organic cage cavities are, in principle, ideal enzyme active site mimics. Yet, cage-promoted organocatalysis has remained elusive, in large part due to synthetic accessibility of robust and functional scaffolds. Herein, we report the acyl transfer catalysis properties of robust, hexaamide cages in organic solvent. Cage structural variation reveals that esterification catalysis with an acyl anhydride acyl carrier occurs only in bifunctional cages featuring internal pyridine motifs and two crucial antipodal carboxylic acid groups. 1 H NMR data and X-ray crystallography show that the acyl carrier is rapidly activated inside the cavity as a covalent mixed-anhydride intermediate with an internal hydrogen bond. Michaelis-Menten (saturation) kinetics suggest weak binding ( K M = 0.16 M) of the alcohol pronucleophile close to the internal anhydride. Finally, activation and delivery of the alcohol to the internal anhydride by the second carboxylic acid group forms ester product and releases the cage catalyst. Eyring analysis indicates a strong enthalpic stabilization of the transition state (5.5 kcal/mol) corresponding to a rate acceleration of 10 4 over background acylation, and an ordered, associative rate-determining attack by the alcohol, supported by DFT calculations. We conclude that internal bifunctional organocatalysis specific to the cage structural design is responsible for the enhancement over the background reaction. These results pave the way for organic-phase enzyme mimicry in self-assembled cavities with the potential for cavity elaboration to enact selective acylations.

A series of mixed ligand, photoluminescent organometallic Ir(III) complexes have been synthesized to incorporate substituted 2-phenyl-1 H -naphtho[2,3- d ]imidazole cyclometalating ligands. The structures of three example complexes were categorically confirmed using X-ray crystallography each sharing very similar structural traits including evidence of interligand hydrogen bond contacts that account for the shielding effects observed in the 1 H NMR spectra. The structural iterations of the cyclometalated ligand provide tuning of the principal electronic transitions that determine the visible absorption and emission properties of the complexes: emission can be tuned in the visible region between 550 and 610 nm and with triplet lifetimes up to 10 μs. The nature of the emitting state varies across the series of complexes, with different admixtures of ligand-centered and metal-to-ligand charge transfer triplet levels evident. Finally, the use of the complexes as photosensitizers in triplet-triplet annihilation energy upconversion (TTA-UC) was investigated in the solution state. The study showed that the complexes possessing the longest triplet lifetimes showed good viability as photosensitizers in TTA-UC. Therefore, the use of an electron-withdrawing group on the 2-phenyl-1 H -naphtho[2,3- d ]imidazole ligand framework can be used to rationally promote TTA-UC using this class of complex.

A series of ligands based upon a 1,3-diimino-isoindoline framework have been synthesized and investigated as pincer-type (N ∧ N ∧ N) chelates for Pt(II). The synthetic route allows different combinations of heterocyclic moieties (including pyridyl, thiazole, and isoquinoline) to yield new unsymmetrical ligands. Pt( L 1-6 )Cl complexes were obtained and characterized using a range of spectroscopic and analytical techniques: 1 H and 13 C NMR, IR, UV-vis and luminescence spectroscopies, elemental analyses, high-resolution mass spectrometry, electrochemistry, and one example via X-ray crystallography which showed a distorted square planar environment at Pt(II). Cyclic voltammetry on the complexes showed one irreversible oxidation between +0.75 and +1 V (attributed to Pt 2+/3+ couple) and a number of ligand-based reductions; in four complexes, two fully reversible reductions were noted between -1.4 and -1.9 V. Photophysical studies showed that Pt( L 1-6 )Cl absorbs efficiently in the visible region through a combination of ligand-based bands and metal-to-ligand charge-transfer features at 400-550 nm, with assignments supported by DFT calculations. Excitation at 500 nm led to luminescence (studied in both solutions and solid state) in all cases with different combinations of the heterocyclic donors providing tuning of the emission wavelength around 550-678 nm.

Integrating symmetry-reducing methods into self-assembly methodology is desirable to efficiently realise the full potential of molecular cages as hosts and catalysts. Although techniques have been explored for metal organic (coordination) cages, rational strategies to develop low symmetry organic cages remain limited. In this article, we describe rules to program the shape and symmetry of organic cage cavities by designing edge pieces that bias the orientation of the amide linkages. We apply the rules to synthesise cages with well-defined cavities, supported by evidence from crystallography, spectroscopy and modelling. Access to low-symmetry, self-assembled organic cages such as those presented, will widen the current bottleneck preventing study of organic enzyme mimics, and provide synthetic tools for novel functional material design., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Six iridium(iii) complexes of the general form [Ir(C^N) 2 (N^N)]X (where C^N = cyclometalating ligand; N^N = disubstituted 2,2'-bipyridine), and incorporating alkyl chains of differing lengths (C8, C10, C12), have been synthesised and characterised. The complexes have been characterised using a variety of methods including spectroscopies (NMR, IR, UV-Vis, luminescence) and analytical techniques (high resolution mass spectrometry, cyclic voltammetry, X-ray diffraction). Two dodecyl-functionalised complexes were studied for their behaviour in aqueous solutions. Although the complexes did not possess sufficient solubility to determine their critical micelle concentrations (CMC) in water, they were amenable for use as emissive dopants in a N -methyl C12 substituted imidazolium salt microemulsion carrier system with a CMC = 36.5 mM. The investigation showed that the metal doped microemulsions had increased CMCs of 40.4 and 51.3 mM and luminescent properties characterised by the dopant., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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 ( λ em = 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)]PF 6 (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.

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 cm 2  V -1  s -1 for the 8-AGNR., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Two substituted phosphonium tetrahydoxidohexaoxidopentaborate(1-) salts, [ i PrPPh 3 ][B 5 O 6 (OH) 4 ]·3.5H 2 O ( 1 ) and [MePPh 3 ][B 5 O 6 (OH) 4 ]·B(OH) 3 ·0.5H 2 O ( 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 m 2 /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 H 2 O/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 i Pr groups oriented towards the pentaborate(1-)/H 2 O 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.

We report the first NMR and X-ray diffraction (XRD) structures of an unusual 13/11-helix (alternating i, i+1 {NH-O=C} and i, i+3 {C=O-H-N} H-bonds) formed by a heteromeric 1 : 1 sequence of α- and δ-amino acids, and demonstrate the application of this framework towards catalysis. Whilst intramolecular hydrogen bonds (IMHBs) are the clear driver of helix formation in this system, we also observe an apolar interaction between the ethyl residue of one δ-amino acid and the cyclohexyl group of the next δ-residue in the sequence that seems to stabilize one type of helix over another. To the best of our knowledge this type of additional stabilization leading to a specific helical preference has not been observed before. Critically, the helix type realized places the α-residue functionalities in positions proximal enough to engage in bifunctional catalysis as demonstrated in the application of our system as a minimalist aldolase mimic., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Cyclic porphyrin oligomers have been studied as models for photosynthetic light-harvesting antenna complexes and as potential receptors for supramolecular chemistry. Here, we report the synthesis of unprecedented β,β-directly linked cyclic zinc porphyrin oligomers, the trimer ( CP3 ) and tetramer ( CP4 ), by Yamamoto coupling of a 2,3-dibromoporphyrin precursor. Their three-dimensional structures were confirmed by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and single-crystal X-ray diffraction analyses. The minimum-energy geometries of CP3 and CP4 have propeller and saddle shapes, respectively, as calculated using density functional theory. Their different geometries result in distinct photophysical and electrochemical properties. The smaller dihedral angles between the porphyrin units in CP3 , compared with CP4 , result in stronger π-conjugation, splitting the ultraviolet-vis absorption bands and shifting them to longer wavelengths. Analysis of the crystallographic bond lengths indicates that the central benzene ring of the CP3 is partially aromatic [harmonic oscillator model of aromaticity (HOMA) 0.52], whereas the central cyclooctatetraene ring of the CP4 is non-aromatic (HOMA -0.02). The saddle-shaped structure of CP4 makes it a ditopic receptor for fullerenes, with affinity constants of (1.1 ± 0.4) × 10 5 M -1 for C 70 and (2.2 ± 0.1) × 10 4 M -1 for C 60 , respectively, in toluene solution at 298 K. The formation of a 1:2 complex with C 60 is confirmed by NMR titration and single-crystal X-ray diffraction.

The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: [C(NH 2 ) 2 (NHMe)][B 5 O 6 (OH) 4 ]·H 2 O ( 1 ), [C(NH 2 ) 2 (NH{NH 2 })][B 5 O 6 (OH) 4 ] ( 2 ), [C(NH 2 ) 2 (NMe 2 )][B 5 O 6 (OH) 4 ] ( 3 ), [C(NH 2 )(NMe 2 ) 2 ][B 5 O 6 (OH) 4 ] ( 4 ), [C(NHMe)(NMe 2 ) 2 ][B 5 O 6 (OH) 4 ]·B(OH) 3 ( 5 ), and [TBDH][B 5 O 6 (OH) 4 ] ( 6 ) (TBD = 1,5,7-triazabicyclo [4.4.0]dec-5-ene). Compounds 1 - 6 were prepared as crystalline salts from basic aqueous solution via self-assembly processes from B(OH) 3 and the appropriate substituted cation. Compounds 1 - 6 were characterized by spectroscopic (NMR and IR) and by single-crystal XRD studies. A thermal (TGA) analysis on compounds 1 - 3 and 6 demonstrated that they thermally decomposed via a multistage process to B 2 O 3 at >650 °C. The low temperature stage (<250 °C) was endothermic and corresponded to a loss of H 2 O. Reactant stoichiometry, solid-state packing, and H-bonding interactions are all important in assembling these structures. An analysis of H-bonding motifs in known unsubstituted guanidinium salts [C(NH 2 ) 3 ] 2 [B 4 O 5 (OH) 4 ]·2H 2 O, [C(NH 2 ) 3 ][B 5 O 6 (OH) 4 ]·H 2 O, and [C(NH 2 ) 3 ] 3 [B 9 O 12 (OH) 6 ] and in compounds 1 - 6 revealed that two important H-bonding R 2 2 (8) motifs competed to stabilize the observed structures. The guanidinium cation formed charge-assisted pincer cation-anion H-bonded rings as a major motif in [C(NH 2 ) 3 ] 2 [B 4 O 5 (OH) 4 ]·2H 2 O and [C(NH 2 ) 3 ] 3 [B 9 O 12 (OH) 6 ], whereas the anion-anion ring motif was dominant in [C(NH 2 ) 3 ][B 5 O 6 (OH) 4 ]·H 2 O and in compounds 1 - 6 . This behaviour was consistent with the stoichiometry of the salt and packing effects also strongly influencing their solid-state structures.

Crystal structures described as concomitant triclinic (I) and monoclinic (II) polymorphs of meso-(E,E)-1,1'-[1,2-bis(4-chlorophenyl)ethane-1,2-diyl]bis(phenyldiazene) [Mohamed et al. (2016). Acta Cryst. C72, 57-62] have been re-investigated. The published model for II was distorted due to forcing the symmetry of space group C2/c on an incomplete structure model. It is shown here to be a likely three-component superposition of S,S and R,R enantiomers with a lesser amount of the meso form. A detailed analysis of how the improbable distortion in the published model aroused suspicion and the subsequent construction of undistorted chemically and crystallographically plausible alternatives having the symmetry of Cc and C2/c is presented. For the sake of completeness, an improved model for the triclinic P-1 structure of the meso isomer I, revised to include a minor disorder component, is also given.

A series of 2-phenylquinoxaline ligands have been synthesised that introduce either CF 3 or OCF 3 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 (λ em =603-620 nm; Φ em ≤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 (Φ UC 5.9-14.1 %) were observed and shown to be strongly influenced by the ligand structure in each case., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

V-Shaped porphyrin dimers, with masked p- phenylene bridges, undergo efficient oxidative coupling to form meso - meso linked cyclic porphyrin oligomers. Reductive aromatization unmasks the p -phenylenes, increasing the strain. Oxidation then fuses the porphyrin dimers, providing a nanoring with curved walls. The strain in this macrocycle bends the p -phenylene and fused porphyrin dimer units (radii of curvature of 11.4 and 19.0 Å, respectively), but it does not significantly alter the electronic structure of the fused porphyrins.

Bis-terdentate (N^N^N) ligands coordinated to Cr(III) yield complexes that display near-IR emission under aerated solvent conditions at room temperature.

Treatment of a κ 1 -P-monodentate bicyclic diphosphane iridium(III) complex with a labile gold(I) precursor afforded an unusual Ir III /Au I complex in which the P-P single bond has been cleaved. This reaction was cleanly reversed upon addition of tertiary phosphine. Carbon-carbon bond activation, across neighbouring P 2 C 2 N rings of the coordinated bicyclic diphosphane, occurred upon thermolysis of the Ir III /Au I complex.

The self-assembly and self-organization of water molecules are relevant in many fields of research. When water spontaneously reacts with 2,2,6,6-tetra-methyl-piperidine (TMP) to form colourless and crystalline discrete needles, only in the exact ratio of 2:1, it is important to understand the phenomenon. Single-crystal X-ray and neutron diffraction data have unveiled that TMP self-assembles around columns of water molecules, and as such, the resulting adduct may be described as a series of molecular water pipes., (© Ian R. Butler et al. 2022.)

The synthesis of six N , N '-substituted thiourea ligands (L1a-L3b) was achieved in two steps. A corresponding extensive series of Cu(I), Cu(II), Ni(II) and Zn(II) complexes (1-24) with varying formulations were synthesised from these ligands by the reaction of a 1 : 1 or a 1 : 2 mixture of Cu(II), Ni(II) and Zn(II) perchlorate or chloride salts. Complexes 1-24 have been comprehensively characterised by mass spectrometry, elemental analysis, UV-vis., IR, and 1 H and 13 C{ 1 H} NMR spectroscopies where applicable. The X-ray crystal structures were obtained for eight examples: [(L1a) 2 Cu]ClO 4 (1), [(L1c) 2 Zn](ClO 4 ) 2 (4), [(L2a) 2 Cu]ClO 4 (6), [(L2c) 2 Ni](ClO 4 ) 2 (7), [(L1b) 2 Cu](ClO 4 ) (15), [(L1b)CuCl] (16), [(L4) 2 CuCl 2 ] (19) and [(L3b)CuClO 4 ] (21). These studies reveal that L1c and L2c represent ligands that have undergone cleavage during reaction with the metal salt; L4 represents an intramolecular rearrangement ( via a Hugershoff reaction) of L2b; and in most cases Cu(II) is reduced to Cu(I) during the ligand reaction. The X-ray crystal structures also reveal that 1, 4, 6, 15 and 16 are monometallic species in the solid state; that Cu(I) in 1, 6, 15 and 16 and Zn(II) in 4 are arranged in a distorted tetrahedral geometry; that Cu(I) in 21 adopts a trigonal planar geometry; and that in 7 and 19 the Ni(II) and Cu(II) centres, respectively, possess square planar geometry. Preliminary studies on the biological activity (using the Malaria Sybr Green I Fluorescence assay) of the thiourea containing complexes suggests that the d 10 complexes, and increased ligand stoichiometries, may afford higher potency.

Two ligands based upon a 2,6-disubstituted pyridine bridge introduce bis-quinoxalinyl units in a fashion that yields analogues to the archetypal terdentate ligand, 2,2':6',2''-terpyridine. The ligands were synthesised from the key intermediate 2,6-bis(bromoacetyl)pyridine: a new, high-yielding route is described for this reagent. Two ligand variants (differentiated by H/Me substituents on the quinoxaline ring) were explored as coordinating moieties for iridium(iii) in the development of luminescent complexes. Computational studies (DFT approaches employing B3LYP, B3LYP/LANL2DZ, and M062X/LANL2DZ levels) were used to investigate the geometric and coordination mode preferences of the new ligands and two possibilities arose from theoretical investigations: [Ir(N^N^N) 2 ] 3+ and [Ir(N^N^C) 2 ] + , with the former predicted to be more energetically favourable. Upon synthesis and isolation of the Ir(iii) complexes, X-ray crystallographic studies revealed coordination spheres that were cyclometalated, the structures both showing a [Ir(N^N^C) 2 ]PF 6 arrangement. Further spectroscopic characterization via NMR confirmed the ligand arrangements in the complexes, and photophysical studies, supported by DFT, showed that a mixture of metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT) character is likely to contribute to the emission features of the complexes, which phosphoresce orange-red ( λ em = 580-618 nm). The emission wavelength was influenced by the substituents on the quinoxaline ring (H vs. Me), thereby implying further tuneability is possible with future ligand iterations., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

During the racemization of a novel pharmaceutical spiro-cyclic imidazole-amine compound, namely, 6'-bromo- N -(6'-bromo-4-meth-oxy-4''-methyl-3' H -di-spiro[cyclo-hexane-1,2'-indene-1',2''-imidazol]-5''-yl)-4-meth-oxy-4''-methyl-3' H -di-spiro-[cyclo-hexane-1,2'-indene-1',2''-imidazol]-5''-imine, C 36 H 41 Br 2 N 5 O 2 , two impurities were isolated. These impurities were clearly dimers from mass spectroscopic analysis, however single-crystal diffraction characterization was required for the assignment of stereochemistry. The single-crystal diffraction results revealed subtly different structures to those proposed, due to an unexpected proton transfer. The dimers contain four stereocentres, but two of primary inter-est, and are centrosymmetric, so after careful structure refinement and close inspection it was possible to unambiguously assign the stereochemistry of both the homochiral [( S ),( S )- and ( R ),( R )-] and the heterochiral [( S ),( R )- and ( R ),( S )-] compounds., (© Blade et al. 2021.)

A series of ligands have been synthesized based upon a polysubstituted 2-phenylquinoxaline core structure. These ligands introduce different combinations of fluorine and methyl substituents on both the phenyl and quinoxaline constituent rings. The resultant investigation of these species as cyclometalating agents for Ir(III) gave cationic complexes of the form [Ir(C^N) 2 (bipy)]PF 6 (where C^N = cyclometalating ligand; bipy = 2,2'-bipyridine). X-ray crystallographic studies were conducted on four complexes and each revealed the expected distorted octahedral geometry based upon a cis -C,C and trans -N,N ligand arrangement at Ir(III). Supporting computational studies predict that each of the complexes share the same general descriptions for the frontier orbitals. TD-DFT calculations suggest MLCT contributions to the lowest energy absorption and a likely MLCT/ILCT/LLCT nature to the emitting state. Experimentally, the complexes display tunable luminescence across the yellow-orange-red part of the visible spectrum (λ em = 579-655 nm).

Porous Liquids (PLs) are a new class of material that possess both fluidity and permanent porosity. As such they can act as enhanced, selective solvents and may ultimately find applications which are not possible for porous solids, such as continuous flow separation processes. Type II PLs consist of empty molecular hosts dissolved in size-excluded solvents and to date have mainly been based on hosts that have limited chemical and thermal stability. Here we identify Noria, a rigid cyclic oligomer as a new host for the synthesis of more robust Type II PLs. Although the structure of Noria is well-documented, we find that literature has overlooked the true composition of bulk Noria samples. We find that bulk samples typically consist of Noria ( ca. 40%), a Noria isomer, specifically a resorcinarene trimer, "R3" ( ca. 30%) and other unidentified oligomers ( ca. 30%). Noria has been characterised crystallographically as a diethyl ether solvate and its 1 H NMR spectrum fully assigned for the first time. The previously postulated but unreported R3 has also been characterised crystallographically as a dimethyl sulfoxide solvate, which confirms its alternative connectivity to Noria. Noria and R3 have low solubility which precludes their use in Type II PLs, however, the partially ethylated derivative Noria-OEt dissolves in the size-excluded solvent 15-crown-5 to give a new Type II PL. This PL exhibits enhanced uptake of methane (CH 4 ) gas supporting the presence of empty pores in the liquid. Detailed molecular dynamics simulations support the existence of pores in the liquid and show that occupation of the pores by CH 4 is favoured. Overall, this work revises the general accepted composition of bulk Noria samples and shows that Noria derivatives are appropriate for the synthesis of more robust Type II PLs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The reaction between differently substituted borasiloxanes and 2,5-bis(3-pyridylethynyl)thiophene provided the first example of luminescent borasiloxane-based chiral helices held together by N-B bonds. The starting building blocks and the helices were fully characterized, and the nature of the N-B bond rationalized by means of theoretical calculations.

Six substituted ligands based upon 2-(naphthalen-1-yl)quinoline-4-carboxylate and 2-(naphthalen-2-yl)quinoline-4-carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating ligands for Ir III , yielding complexes of the form [Ir(C^N) 2 (bipy)]PF 6 (where C^N=cyclometallating ligand; bipy=2,2'-bipyridine). X-ray crystallographic studies on three examples demonstrate that the complexes adopt a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed. Intraligand torsional distortions are evident in all cases. The Ir III complexes display photoluminescence in the red part of the visible region (668-693 nm), which is modestly tuneable through the ligand structure. The triplet lifetimes of the complexes are clearly influenced by the precise structure of the ligand in each case. Supporting computational (DFT) studies suggest that the differences in observed triplet lifetime are likely due to differing admixtures of ligand-centred versus MLCT character instilled by the facets of the ligand structure. Triplet-triplet annihilation upconversion (TTA-UC) measurements demonstrate that the complexes based upon the 1-naphthyl derived ligands are viable photosensitisers with upconversion quantum efficiencies of 1.6-6.7 %., (© 2020 Wiley-VCH GmbH.)

Molecular self-assembly is the spontaneous association of simple molecules into larger and ordered structures 1 . It is the basis of several natural processes, such as the formation of colloids, crystals, proteins, viruses and double-helical DNA 2 . Molecular self-assembly has inspired strategies for the rational design of materials with specific chemical and physical properties 3 , and is one of the most important concepts in supramolecular chemistry. Although molecular self-assembly has been extensively investigated, understanding the rules governing this phenomenon remains challenging. Here we report on a simple hydrochloride salt of fampridine that crystallizes as four different structures, two of which adopt unusual self-assemblies consisting of polyhedral clusters of chloride and pyridinium ions. These two structures represent Frank-Kasper (FK) phases of a small and rigid organic molecule. Although discovered in metal alloys 4,5 more than 60 years ago, FK phases have recently been observed in several classes of supramolecular soft matter 6-11 and in gold nanocrystal superlattices 12 and remain the object of recent discoveries 13 . In these systems, atoms or spherical assemblies of molecules are packed to form polyhedra with coordination numbers 12, 14, 15 or 16. The two FK structures reported here crystallize from a dense liquid phase and show a complexity that is generally not observed in small rigid organic molecules. Investigation of the precursor dense liquid phase by cryogenic electron microscopy reveals the presence of spherical aggregates with sizes ranging between 1.5 and 4.6 nanometres. These structures, together with the experimental procedure used for their preparation, invite interesting speculation about their formation and open different perspectives for the design of organic crystalline materials.

The preparation of a range of amino acid derived guanidine organocatalysts is reported together with their application to the Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene, achieving a maximum ee of 56%. Some insight into the mechanism was sought by using X-ray crystallography and a detailed study of the intra- and intermolecular hydrogen bonding is reported., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

A series of heteroleptic, neutral iridium(III) complexes of the form [Ir(L) 2 (N^O)] (where L = cyclometalated 2,3-disubstituted quinoxaline and N^O = ancillary picolinate or pyrazinoate) are described in terms of their synthesis and spectroscopic properties, with supporting computational analyses providing additional insight into the electronic properties. The 10 [Ir(L) 2 (N^O)] complexes were characterized using a range of analytical techniques (including 1 H, 13 C, and 19 F NMR and IR spectroscopies and mass spectrometry). One of the examples was structurally characterized using X-ray diffraction. The redox properties were determined using cyclic voltammetry, and the electronic properties were investigated using UV-vis, time-resolved luminescence, and transient absorption spectroscopies. The complexes are phosphorescent in the red region of the visible spectrum (λ em = 633-680 nm), with lifetimes typically of hundreds of nanoseconds and quantum yields ca. 5% in aerated chloroform. A combination of spectroscopic and computational analyses suggests that the long-wavelength absorption and emission properties of these complexes are strongly characterized by a combination of spin-forbidden metal-to-ligand charge-transfer and quinoxaline-centered transitions. The emission wavelength in these complexes can thus be controlled in two ways: first, substitution of the cyclometalating quinoxaline ligand can perturb both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital levels (LUMO, Cl atoms on the ligand induce the largest bathochromic shift), and second, the choice of the ancillary ligand can influence the HOMO energy (pyrazinoate stabilizes the HOMO, inducing hypsochromic shifts).

The synthesis of a number of pentaborate(1-) salts from cations arising from N -substituted α,α-, α,β-, and α,γ-diaminoalkanes has been attempted in aqueous solution from B(OH) 3 and the appropriate diammine in a 10:1 ratio. Despite relatively mild work-up conditions the pentaborate(1-) salts prepared were not always as anticipated and the following compounds were isolated in good yield: [Me 2 NH(CH 2 ) 2 NHMe 2 ][B 5 O 6 (OH) 4 ] 2 ( 1 ), [Et 2 NH(CH 2 ) 2 NHEt 2 ][B 5 O 6 (OH) 4 ] 2 ( 2 ), [Et 2 NH 2 ][B 5 O 6 (OH) 4 ] ( 3 ), [Me 2 NH 2 ][B 5 O 6 (OH) 4 ] ( 4 ), [Me 2 NH(CH 2 ) 3 NHMe 2 ][B 5 O 6 (OH) 4 ] 2 ( 5 ), [Et 2 NH(CH 2 ) 3 NHEt 2 ][B 5 O 6 (OH) 4 ] 2 ( 6 ), [Me 3 NCH 2 CH=CH 2 ][B 5 O 6 (OH) 4 ] ( 7 ), and [Me 3 N(CH 2 ) 3 NMe 3 ] [B 5 O 6 (OH) 4 ] 2 . 0.5H 2 O ( 8 ). The tetraborate(2-) salt, [Me 3 N(CH 2 ) 2 NMe 3 ][B 4 O 5 (OH) 4 ] . 2B(OH) 3 . 2H 2 O ( 9 ) was obtained in moderate yield (41%) from a 3:1 reaction of B(OH) 3 with [Me 3 N(CH 2 ) 2 NMe 3 ](OH) 2 . All compounds were characterized by spectroscopy ( 1 H, 11 B, 13 C NMR and IR) and thermal gravimetric analysis (TGA). BET analysis on materials derived thermally from selected samples ( 1 , 2 , 6 , 7 ) all had porosities of < 1 m 2 /g, demonstrating that they were non-porous. Single-crystal XRD structures were obtained for 2 , 3 , 7 , 8 and 9 and all contain extensive H-bonded polyborate lattices.

The alkyl chain carrying ligands N,N-di(pyridin-2-yl)butanamide (LC4) and N,N-di(pyridin-2-yl)decanamide (LC10) were combined with NCS- co-ligands to form the neutral heteroleptic Fe(ii) complexes trans-[FeII(LC4)2(NCS)2] (1C4) and trans-[FeII(LC10)2(NCS)2] (1C10). Variable temperature crystallographic studies revealed that 1C4 is in the orthorhombic space group Pna21 between 85-200 K whereas 1C10 is in the monoclinic space group P21/c between 85-140 K. The average Fe-N bond lengths suggest that at 85 K 1C4 contains LS Fe(ii) centres; however, the ca. 0.18 Å increase in the average Fe-N bond lengths between 85 and 120 K suggests a spin-transition to the HS state occurs within this temperature interval. 1C10 contains LS Fe(ii) centres between 85 and 105 K. Upon warming from 105 to 140 K the average Fe-N bond lengths increase by ca. 0.19 Å, which suggests a spin-transition to the HS state. Solid-state magnetic susceptibility measurements showed that 1C4 undergoes semi-abrupt spin-crossover with T1/2 = 127.5 K and a thermal hysteresis of ca. 13 K whereas, 1C10 undergoes an abrupt spin-crossover with T1/2 = 119.0 K, and is also accompanied by thermal hysteresis of ca. 4 K. The crystallographic and magnetic data show that the length of the complex's alkyl chain substituents can have a large impact on the structure of the crystal lattice as well as a subtle effect on the T1/2 value for thermal spin-crossover.

A family of mono- and ditopic hydroxamic acids has been employed in the synthesis and structural and physical characterisation of discrete (0D) and (1- and 2-D) extended network coordination complexes. Examples of the latter include the 1-D coordination polymer {[Zn(ii)(L 3 H) 2 ]·2MeOH} n (5; L 3 H 2 = 2-(methylamino)phenylhydroxamic acid) and the 2-D extended network {[Cu(ii)(L 2 H)(H 2 O)(NO 3 )]·H 2 O} n (5; L 2 H 2 = 4-amino-2-(acetoxy)phenylhydroxamic acid). The 12-MC-4 metallacrown [Cu(ii) 5 (L 4 H) 4 (MeOH) 2 (NO 3 ) 2 ]·3H 2 O·4MeOH (7) represents the first metal complex constructed using the novel ligand N-hydroxy-2-[(2-hydroxy-3-methoxybenzyl)amino]benzamide (L 4 H 3 ). Variable temperature magnetic susceptibility studies confirm strong antiferromagnetic exchange between the Cu(ii) centres in 7. Coordination polymer 5 shows photoluminescence in the blue region (λ PL ∼ 421-450 nm) with a bathochromic shift of the emission (∼15-30 nm) from solution to the solid state.

Two new cobalt bis-iminopyridines, [Co(DDP)(H2O)2](NO3)2 (1, DDP = cis-[1,3-bis(2-pyridinylenamine)] cyclohexane) and [Co(cis-DDOP)(NO3)](NO3) (2, cis-DDOP = cis-3,5-bis[(2-Pyridinyleneamin]-trans-hydroxycyclohexane) electrocatalyse the 4-proton, 4-electron reduction of acetonitrile to ethylamine. For 1, this reduction occurs in preference to reduction of protons to H2. A coordinating hydroxyl proton relay in 2 reduces the yield of ethylamine and biases the catalytic system back towards H2.

Traditionally small-molecule crystallographers have not usually observed or recognized significant radiation damage to their samples during diffraction experiments. However, the increased flux densities provided by third-generation synchrotrons have resulted in increasing numbers of observations of this phenomenon. The diversity of types of small-molecule systems means it is not yet possible to propose a general mechanism for their radiation-induced sample decay, however characterization of the effects will permit attempts to understand and mitigate it. Here, systematic experiments are reported on the effects that sample temperature and beam attenuation have on radiation damage progression, allowing qualitative and quantitative assessment of their impact on crystals of a small-molecule test sample. To allow inter-comparison of different measurements, radiation-damage metrics (diffraction-intensity decline, resolution fall-off, scaling B -factor increase) are plotted against the absorbed dose. For ease-of-dose calculations, the software developed for protein crystallography, RADDOSE -3 D , has been modified for use in small-molecule crystallography. It is intended that these initial experiments will assist in establishing protocols for small-molecule crystallographers to optimize the diffraction signal from their samples prior to the onset of the deleterious effects of radiation damage.

Here we report a family of bis-amide receptors for anion binding that contain carboxylic acid groups vicinal to the amide function. Deprotonation of the carboxylic acids decreases the acidity of amide NHs, switching on the anion binding ability of the deprotonated receptors with selectivity for fluoride complexation. The proposed systems represent a unique example of anionic receptors able to bind anions via H-bonding.

A series of cationic, dihydroimidazolinium-functionalized 1,8-naphthalimide fluorophores have been isolated as their hexafluorophosphate salts, [HL]PF 6 . These pro-ligands react with [AuCl(tht)] in the presence of base to form N-heterocyclic carbene (NHC) complexes, [AuCl(L)]. Two X-ray structures represent a pro-ligand and complex pairing: the latter reveals the two-coordinate linear geometry of the NHC-Au(i) species, as well as intermolecular interactions supported by both ligand π-π stacking and a weak aurophilic interaction of 3.3205(6) Å. The luminescence properties of the pro-ligands and complexes are dominated by the ICT character of the substituted fluorophore at ca. 500 nm, which is further modulated via functionalization at the 4-position of the naphthalimide. Cytotoxicity assessments were performed for all [HL]PF 6 and [AuCl(L)] species against LOVO, MCF-7, A549 and PC3 cell lines; added lipophilicity seems to correlate with increased cytotoxicity. Confocal fluorescence microscopy was undertaken on a selected [HL]PF 6 and [AuCl(L)] species and showed that the intracellular distribution is dependent upon the specific ligand structure. More detailed co-localisation studies show that selected examples present a predominant lysosomal staining pattern. FLIM studies exemplified the applicability of these probes, and secondly suggest that fluorescence lifetime could be used to provide information on the integrity of the complex and thus liberation of gold in a biological environment.

Previous employment of the ligands 2-methoxy-6-[(methylimino)methyl]phenol (L 1 H) and 2-methoxy-6-[(phenylimino)methyl]phenol (L 2 H) has resulted in the self-assembly of pseudo metallocalix[6]arene complexes of general formulae: [M 7 (μ 3 -OH) 6 (L x ) 6 ](NO 3 ) y (M = Ni(ii), x = 1, y = 2 (1) and Co(ii/iii), x = 2, y = 3 (2)). Extrapolating upon this work, we report the coordination chemistry of ligands 2-methoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol (L 3 H), 2-[(benzylimino)methyl]-6-methoxyphenol (L 4 H), 2-[(benzylamino)methyl]-6-methoxyphenol (L 5 H) and 2-[(benzylamino)methyl]-4-bromo-6-methoxyphenol (L 6 H), whose structures are modifications of ligands L 1-2 H. These ligands are employed in the synthesis and characterisation of the dimetallic complex [Ni(ii) 2 (L 3 ) 3 (H 2 O)](NO 3 )·2H 2 O·3MeOH (3); the monometallic complexes [Ni(ii)(L 4 ) 2 ] (4) and [Co(iii)(L 4 ) 3 ]·H 2 O·MeOH (5a); and the tetranuclear pseudo metallocalix[4]arene complexes: [(NO 3 )⊂Co(ii) 4 (μ 3 -OH) 2 (L 5 ) 4 (H 2 O) 2 ](NO 3 )·H 2 O (6), [(NO 3 )⊂Ni(ii) 4 (μ 3 -OH) 2 (L 5 ) 4 (H 2 O) 2 ](NO 3 )·H 2 O (7) and [Ni(ii) 4 (μ 3 -OH) 2 (L 6 ) 4 (NO 3 ) 2 ]·MeCN (8). The tetrametallic 'butterfly' core topologies in 6-8 are discussed with respect to their structural and topological relationship with their heptanuclear [M 7 ] (M = Co(ii), Ni(ii)) pseudo metallocalix[6]arene ancestors (1 and 2).

A new aryl-imido polyoxometalate non-linear optical chromophore (POMophore) with a diphenylamino donor group attains the highest β zzz, 0 value (196 × 10 -30 esu by Hyper-Rayleigh Scattering, HRS), and best transparency/non-linearity trade off yet for such materials. Stark spectroscopic and DFT investigation of this compound, plus NMe 2 and carbazole analogues, show that its high performance results from a combination of strongly dipolar electronic transitions, and strong electronic communication across the π-system.

Three novel fluorescent aminophosphine ligands have been synthesised that incorporate napthyl (L1), pyrenyl (L2) and anthraquinone (L3) chromophores into their structures. The ligands react with [AuCl(tht)] (tht = tetrahydrothiophene) to give neutral complexes of the form [AuCl(L1-3)]. Solid state, X-ray crystallographic data was obtained for the anthraquinone derivative, [AuCl(L3)], and showed a distorted linear coordination geometry at Au(i). The packing structure also revealed a number of intermolecular π-π interactions that involve the anthraquinone and phenyl units of the aminophosphine ligand. 31P NMR spectroscopic data revealed δP values of +42.2 (L1), +42.1 (L2) and +26.1 (L3) ppm, which shifted downfield upon coordination to Au(i) to +64.6, +64.7, and +55.8 ppm, respectively. Supporting TD-DFT studies were able to reproduce the structure and 31P NMR chemical shifts of [AuCl(L3)] as well as rationalise the HOMO-LUMO compositions. Photophysical studies showed that the appended fluorophore dominates the absorption and emission properties for the ligands and complexes, with the anthraquinone derivatives showing visible emission at ca. 570 nm which was attributed to the intramolecular charge transfer character of the phosphinoaminoanthraquinone fragment.

A series of substituted 2-phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometallated iridium(III) complexes. The electronic and redox properties of the complexes were investigated through experimental (including time-resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emissions in the visible region that are attributed to metal to ligand charge-transfer transitions. The different substitution patterns of the ligands induce variations in these parameters. Time-dependent DFT studies support these assignments and show that there is likely to be a strong spin-forbidden contribution to the visible absorption bands at λ=500-600 nm. Calculations also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitisers in triplet-triplet annihilation upconversion experiments by using 9,10-diphenylanthracene as the acceptor; the methylated variants performed especially well with impressive upconversion quantum yields of up to 39.3 %., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Starting from (η 5 -acetylcyclopentadienyl)(η 4 -tetraphenylcyclobutadiene)cobalt(I), highly enantioselective (99 % ee) (S)-CBS catalysed ketone reduction followed by stereospecific alcohol-azide exchange, azide reduction and dimethyllation gave (R)-(η 5 -α-N,N-dimethylaminoethylcyclopentadienyl)(η 4 -tetraphenylcyclobutadiene) cobalt(I) (Arthurs' amine). This underwent highly diastereoselective cyclopalladation to give di-μ-acetate-bis-(R)-[(η 5 -(S p )-2-(α-N,N-dimethylaminoethyl)cyclopentadienyl, 1-C, N)(η 4 -tetraphenylcyclobutadiene)cobalt(I)]dipalladium, and highly diastereoselective lithiation to give (R)-(η 5 -(S p )-1-(α-N,N-dimethylaminoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η 4 -tetraphenylcyclobutadiene)cobalt(I) (PPCA) following the addition as electrophile of chlorodiphenylphosphine. This PN-ligand was converted into (R)-(η 5 -(S p )-1-(α-dicyclohexylphosphinoethyl)-2-(diphenylphosphino)cyclopentadienyl)(η 4 -tetraphenylcyclobutadiene)cobalt(I), a PP-ligand (Rossiphos), by stereospecific amine-phosphine exchange using HPCy 2 . These air-stable P-N and P-P complexes are the first examples of a new class of bulky planar chiral ligands for application in asymmetric catalysis., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A siloxane-based hexacarboxylic acid (L1-H 6 ) has been prepared and applied in MOF construction. L1-H 6 itself crystallizes as an unusual interpenetrated 3D hydrogen-bonded framework. Reaction of L1-H 6 with Zn(ii) gave IMP-18 - a 3D MOF incorporating Si-O-Si functionality. Cleavage of L1-H 6 gives a silanol-based triacid which is shown to give a coordination polymer (IMP-19) with Zn(ii).

A first-generation machine-assisted approach towards the preparation of hybrid ligand/metal materials has been developed. A comparison of synthetic approaches demonstrates that incorporation of both flow chemistry and microwave heating can be successfully applied to the rapid synthesis of a range of new phenyl-1H-pyrazoles (ppz) substituted with electron-withdrawing groups (-F, -CF 3 , -OCF 3 , and -SF 5 ). These, in turn, can be translated into heteroleptic complexes, [Ir(ppz) 2 (bipy)]BF 4 (bipy=2,2'-bipyridine). Microwave-assisted synthesis for the Ir III complexes allows isolation of spectroscopically pure species in less than 1 h of reaction time starting from IrCl 3 . All of the new complexes have been characterised photophysically (including nanosecond time-resolved transient absorption spectroscopy), electrochemically, and by TD-DFT studies. The complexes exhibit ligand-dependent, tuneable, green-yellow luminescence (500-560 nm), with quantum yields in the range 5-15 %., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The non-metal cation pentaborate(1-) salt [ p -H 2 NC 6 H 4 CH 2 NH 3 ][B 5 O 6 (OH) 4 ]·1/2H 2 O ( 1 ) was synthesised from B(OH) 3 and p -H 2 NC 6 H 4 CH 2 NH 2 and crystallized from aqueous solution. Compound 1 was characterized by thermal (TGA/DSC), spectroscopic (IR, NMR) and single-crystal X-ray diffraction methods and it was found to crystallize in the non-centrosymmetric point group P 2 1 . Powder SHG measurements on 1 and some related alkylammonium pentaborate salts, [NH 3 CMe 2 (CH 2 OH)][B 5 O 6 (OH) 4 ], [NH 3 CMe(CH 2 OH) 2 ][B 5 O 6 (OH) 4 ] and [NH 3 CHMeCH 2 OH][B 5 O 6 (OH) 4 ], a substituted imidazolium salt, [1,2,3-Me 3 C 3 H 2 N 2 ][B 5 O 6 (OH) 4 ], a substituted piperidinium salt, [(CH 2 ) 5 NH(CH 2 CH 2 OH)][B 5 O 6 (OH) 4 ], and a substituted pyrrolidinium salt, [ S -(+)-2-(HOCH 2 )C 4 H 7 NH 2 ][B 5 O 6 (OH) 4 ], were determined. Compound 1 and all compounds, except [1,2,3-Me 3 C 3 H 2 N 2 ][B 5 O 6 (OH) 4 ], showed some weak SHG activity with SHG efficiencies of 0.1-0.2 relative to that of KH 2 PO 4 (KDP)., (© The Author(s) 2017.)

Single-crystal semiconductors have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. Inorganic single crystals are typically grown from a melt using time-consuming and energy-intensive processes. Organic semiconductor single crystals, however, can be grown using solution-based methods at room temperature in air, opening up the possibility of large-scale production of inexpensive electronics targeting applications ranging from field-effect transistors and light-emitting diodes to medical X-ray detectors. Here we demonstrate a low-cost, scalable spray-printing process to fabricate high-quality organic single crystals, based on various semiconducting small molecules on virtually any substrate by combining the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the sheer force generated by the spray droplets' impact onto the antisolvent's surface. This method demonstrates the feasibility of a spray-on single-crystal organic electronics.

The study of ternary systems is interesting because it introduces the concept of molecular preference/competition into the system where one molecule may be displaced because the association between the other two is significantly stronger. Current definitions of a tertiary system indicate that solvent molecules are excluded from the molecule count of the system and some of the latest definitions state that any molecule that is not a solid in the parent form at room temperature should also be excluded from the molecule count. In the structure of the quinoline adduct hydrate of tryptaminium 3,5-dinitrobenzoate, 3C 10 H 13 N 2 + ·3C 7 H 3 N 2 O 6 - ·2C 9 H 7 N·2H 2 O, the asymmetric unit comprises multiple cation and anion species which are conformationally similar among each type set. In the crystal, a one-dimensional hydrogen-bonded supramolecular structure is generated through extensive intra- and inter-unit aminium N-H...O and N-H...N, and water O-H...O hydrogen bonds. Within the central-core hydrogen-bonding associations, conjoined cyclic R 4 4 (10), R 5 3 (10) and R 4 4 (12) motifs are generated. The unit is expanded into a one-dimensional column-like polymer extending along [010]. Present also in the crystal packing of the structure are a total of 19 π-π interactions involving both cation, anion and quinoline species [ring-centroid separation range = 3.395 (3)-3.797 (3) Å], as well as a number of weak C-H...O hydrogen-bonding associations. The presence of the two water molecules in the crystal structure is considered to be the principal causative factor in the low symmetry of the asymmetric unit.

Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.

Nine tris-urea receptors (L(1)-L(9)) have been synthesised and shown to coordinate to a range of anionic guests both by (1)H NMR titration techniques and single crystal X-ray structural analysis. The compounds have been shown to be capable of mediating the exchange of chloride and nitrate and also chloride and bicarbonate across POPC or POPC : cholesterol 7 : 3 vesicle bilayer membranes at low transporter loadings. An interesting dependency of anion transport on the nature of the cation is evidence to suggest that a M(+)/Cl(-) cotransport process may also contribute to the release of chloride from the vesicles.

Ligands based upon 4-carboxamide-2-phenylquinoline derivatives have been synthesised with solubilising octyl hydrocarbon chains and tethered aromatic chromophores to give naphthyl (), anthracenyl () and pyrenyl () ligand variants, together with a non-chromophoric analogue () for comparison. (1)H NMR spectroscopic studies of the ligands showed that two non-interchangeable isomers exist for and while only one isomer exists for and . Supporting DFT calculations on suggest that the two isomers may be closely isoenergetic with a relatively high barrier to exchange of ca. 100 kJ mol(-1). These new ligands were cyclometalated with Pt(ii) to give complexes [Pt()(acac)] (acac = acetylacetonate). The spectroscopically characterised complexes were studied using multinuclear NMR spectroscopy including (195)Pt{(1)H} NMR studies which revealed δPtca. -2785 ppm for [Pt()(acac)]. X-ray crystallographic studies were undertaken on [Pt()(acac)] and [Pt()(acac)], each showing the weakly distorted square planar geometry at Pt(ii); the structure of [Pt()(acac)] showed evidence for intermolecular Pt-Pt interactions. The UV-vis. absorption studies show that the spectral profiles for [Pt()(acac)] are a composite of the organic chromophore centred bands and a broad (1)MLCT (5d → π*) band (ca. 440 nm) associated with the complex. Luminescence studies showed that complexes [Pt()(acac)] are dual emissive with fluorescence characteristic of the tethered fluorophore and long-lived phosphorescence attributed to (3)MLCT emission. In the case of the pyrenyl derivative, [Pt()(acac)], the close energetic matching of the (3)MLCT and (3)LCpyr excited states led to an elongation of the (3)MLCT emission lifetime (τ = 42 μs) under degassed solvent conditions, suggestive of energy transfer processes between the two states.

Reaction of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline with [Cp*IrCl2]2 in benzonitrile with KPF6 and NaOH gave (η(5)-(S)-2-(4-(1-methylethyl))oxazolinylcyclopentadienyl)(η(5)-pentamethylcyclopentadienyl)iridium(iii) hexafluorophosphate (68%). This transformation of an iron-based into an iridium-based metallocene proceeds via the rearrangement, with loss of cyclopentadienyliron, of an intermediate cationic ferrocenyliridacycle.