Luminescent Pt(II) Complexes Using Unsymmetrical Bis(2-pyridylimino)isoindolate Analogues.

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(L1-6)Cl complexes were obtained and characterized using a range of spectroscopic and analytical techniques: 1H and 13C 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 Pt2+/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(L1-6)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.

Alkyl chain functionalised Ir(iii) complexes: synthesis, properties and behaviour as emissive dopants in microemulsions.

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.

Halogen bonding with carbon: directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures.

Carbon, although the central element in organic chemistry, has been traditionally neglected as a target for directional supramolecular interactions. The design of supramolecular structures involving carbon-rich molecules, such as arene hydrocarbons, has been limited almost exclusively to non-directional π-stacking, or derivatisation with heteroatoms to introduce molecular assembly recognition sites. As a result, the predictable assembly of non-derivatised, carbon-only π-systems using directional non-covalent interactions remains an unsolved fundamental challenge of solid-state supramolecular chemistry. Here, we propose and validate a different paradigm for the reliable assembly of carbon-only aromatic systems into predictable supramolecular architectures: not through non-directional π-stacking, but via specific and directional halogen bonding. We present a systematic experimental, theoretical and database study of halogen bonds to carbon-only π-systems (C-I⋯πC bonds), focusing on the synthesis and structural analysis of cocrystals with diversely-sized and -shaped non-derivatised arenes, from one-ring (benzene) to 15-ring (dicoronylene) polycyclic atomatic hydrocarbons (PAHs), and fullerene C60, along with theoretical calculations and a systematic analysis of the Cambridge Structural Database. This study establishes C-I⋯πC bonds as directional interactions to arrange planar and curved carbon-only aromatic systems into predictable supramolecular motifs. In >90% of herein presented structures, the C-I⋯πC bonds to PAHs lead to a general ladder motif, in which the arenes act as the rungs and halogen bond donors as the rails, establishing a unique example of a supramolecular synthon based on carbon-only molecules. Besides fundamental importance in the solid-state and supramolecular chemistry of arenes, this synthon enables access to materials with exciting properties based on simple, non-derivatised aromatic systems, as seen from large red and blue shifts in solid-state luminescence and room-temperature phosphorescence upon cocrystallisation.

2-(Thienyl)quinoxaline derivatives and their application in Ir(III) complexes yielding tuneable deep red emitters.

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.

Chirality: a key parameter in chemical probes.

Many small molecule bioactive and marketed drugs are chiral. They are often synthesised from commercially available chiral building blocks. However, chirality is sometimes incorrectly assigned by manufacturers with consequences for the end user ranging from: experimental irreproducibility, wasted time on synthesising the wrong product and reanalysis, to the added cost of purchasing the precursor and resynthesis of the correct stereoisomer. Further on, this could lead to loss of reputation, loss of funding, to safety and ethical concerns due to potential in vivo administration of the wrong form of a drug. It is our firm belief that more stringent control of chirality be provided by the supplier and, if needed, requested by the end user, to minimise the potential issues mentioned above. Certification of chirality would bring much needed confidence in chemical structure assignment and could be provided by a variety of techniques, from polarimetry, chiral HPLC, using known chiral standards, vibrational circular dichroism, and x-ray crystallography. A few case studies of our brushes with wrong chirality assignment are shown as well as some examples of what we believe to be good practice.

An Experimental and Theoretical Insight into I2 /Br2 Oxidation of Bis(pyridin-2-yl)Diselane and Ditellane.

The reactivity between bis(pyridin-2-yl)diselane o Py2 Se2 and ditellane o Py2 Te2 (L1 and L2, respectively; o Py=pyridyn-2-yl) and I2 /Br2 is discussed. Single-crystal structure analysis revealed that the reaction of L1 with I2 yielded [(HL1+ )(I- )⋅5/2I2 ]∞ (1) in which monoprotonated cations HL1+ template a self-assembled infinite pseudo-cubic polyiodide 3D-network, while the reaction with Br2 yielded the dibromide Ho PySeII Br2 (2). The oxidation of L2 with I2 and Br2 yielded the compounds Ho PyTeII I2 (3) and Ho PyTeIV Br4 (6), respectively, whose structures were elucidated by X-ray diffraction analysis. FT-Raman spectroscopy measurements are consistent with a 3c-4e description of all the X-Ch-X three-body systems (Ch=Se, Te; X=Br, I) in compounds 2, 3, Ho PyTeII Br2 (5), and 6. The structural and spectroscopic observations are supported by extensive theoretical calculations carried out at the DFT level that were employed to study the electronic structure of the investigated compounds, the thermodynamic aspects of their formation, and the role of noncovalent σ-hole halogen and chalcogen bonds in the X⋅⋅⋅X, X⋅⋅⋅Ch and Ch⋅⋅⋅Ch interactions evidenced structurally.

N=8 Armchair Graphene Nanoribbons: Solution Synthesis and High Charge Carrier Mobility.

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.

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam): A Novel Precursor of Calcium Oxalate Coating for Carbonate Stone Substrates.

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam), synthesized from O-methyl-N-(pyridin-2-ylmethyl)oxamate, was spectroscopically and structurally characterized and assayed as a novel precursor for the protection and consolidation of carbonate stone substrates. An in-depth characterization of treated and untreated biomicritic limestone and white Carrara marble samples was carried out by means of SEM microscopy, X-ray powder diffraction, helium pycnometry, determination of water transport properties, and pull-off tests. The improved solubility (1.00 M, 16.5% w/w) of the title compound with respect to ammonium oxalate (0.4 M, 5% w/w) results in the formation of a thicker protective coating of calcium oxalate (CaOx) dihydrate (weddellite) on marble and biomicrite samples after the treatment with 5% and 12% w/w water solutions, producing a reduction in the stone porosity and increased cohesion. Theoretical calculations were carried out at the DFT level to investigate both the electronic structure of the N-(pyridin-2-ylmethyl)oxamate anion and the hydrolysis reaction leading from AmPicOxam to CaOx.

A systematic study of the interplay between guest molecule structure and intermolecular interactions in crystalline sponges.

Utilization of the crystalline sponge {[(ZnI2)3(tpt)2·x(solvent)]n} method has enabled characterization of a novel family of synthetic organic oils. The systematic structural differences and diversity of functional groups offered by 13 related molecular adsorbates provide a detailed quantitative understanding of the relationship between the guest structure, its conformation, and the type of intermolecular interactions adopted with neighbouring guests and the host framework. This analysis is extended to assess the connection of these factors to the resulting quality indicators for a particular molecular structure elucidation.

Synthesis and Structural Characterization of Copper Complexes Containing "R-Substituted" Bis-7-Azaindolyl Borate Ligands.

The coordination chemistry of scorpionate ligands based on borates containing the 7-azaindole heterocycle is relatively unexplored. Thus, there is a requirement to further understand their coordination chemistry. This article outlines the synthesis and characterization of a family of complexes containing anionic flexible scorpionate ligands of the type [(R)(bis-7-azaindolyl)borohydride]- ([RBai]-), where R = Me, Ph or naphthyl. The three ligands were coordinated to a series of copper(I) complexes containing a phosphine co-ligand to form the complexes, [Cu(MeBai)(PPh3)] (1), [Cu(PhBai)(PPh3)] (2), [Cu(NaphthBai)(PPh3)] (3), [Cu(MeBai)(PCy3)] (4), [Cu(PhBai)(PCy3)] (5) and [Cu(NaphthBai)(PCy3)] (6). Additional copper(II) complexes, namely, [Cu(MeBai)2] (7) and [Cu(PhBai)2] (8), were obtained during attempts to obtain single crystals from complexes 4 and 2, respectively. Complexes 7 and 8 were also prepared independently from CuCl2 and two equivalents of the corresponding Li[RBai] salt alongside an additional complex, namely, [Cu(NaphthBai)2] (9). The copper(I) and copper(II) complexes were characterized using spectroscopic and analytical methods. Furthermore, a crystal structure was obtained for eight of the nine complexes. In all cases, the boron-based ligand was found to bind to the metal centers via a κ3-N,N,H coordination mode.

ß,ß-Directly Linked Porphyrin Rings: Synthesis, Photophysical Properties, and Fullerene Binding.

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 ß,ß-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) × 105 M-1 for C70 and (2.2 ± 0.1) × 104 M-1 for C60, respectively, in toluene solution at 298 K. The formation of a 1:2 complex with C60 is confirmed by NMR titration and single-crystal X-ray diffraction.

Hydroxypyridine/Pyridone Interconversions within Ruthenium Complexes and Their Application in the Catalytic Hydrogenation of CO2.

Reaction of a new ligand 6-DiPPon (6-diisopropylphosphino-2-pyridone) with 0.5 equiv of [RuCl2(p-cymene)]2 resulted in the formation of a mixture of [RuCl2(p-cymene)(κ1-P-6-DiPPon)]2 (1) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]Cl ([2]Cl) (where 6-DiPPin = 6-diisopropylphosphino-2-hydroxypyridine). The ratio between the two products can be controlled by the nature of the solvent. The similar reaction between 6-DiPPon and [RuCl2(p-cymene)]2 in the presence of AgOTf and Na[BArF24] (where BArF24 = [{3,5-(CF3)2C6H3}4B]-) resulted in the formation of the complexes [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]OTf, ([2]OTf) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]BArF24 ([2]BArF24), respectively. Reactions between complex [2]Cl, [2]OTf, or [2]BArF24 and a base (either DBU or NaOMe) resulted in the deprotonation of the hydroxyl functional group to form a novel neutral orange-colored dearomatized complex, 3. The identity of complex 3 was confirmed as [RuCl(p-cymene)(κ2-P,N-6-DiPPon*)], where 6-DiPPon* is the anionic species (6-diisopropylphosphino-2-oxo-pyridinide), which contains the deprotonated moiety. The new 6-DiPPon ligand and its corresponding air stable half-sandwich derivative ruthenium complexes 1, [2]OTf, [2]BArF24, and 3 were all isolated in good yields and fully characterized by spectroscopic and analytical methods. The interconversions between the neutral and anionic forms of the ligands 6-DiPPon, 6-DiPPin, and 6-DiPPon* offer the potential for novel secondary sphere interactions and proton shuttling reactivity. The consequences for this have been explored in the activation of H2 and the subsequent catalytic hydrogenations of CO2 into formate salts in the presence of a base.

Structural (XRD) Characterization and an Analysis of H-Bonding Motifs in Some Tetrahydroxidohexaoxidopentaborate(1-) Salts of N-Substituted Guanidinium Cations.

The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: [C(NH2)2(NHMe)][B5O6(OH)4]·H2O (1), [C(NH2)2(NH{NH2})][B5O6(OH)4] (2), [C(NH2)2(NMe2)][B5O6(OH)4] (3), [C(NH2)(NMe2)2][B5O6(OH)4] (4), [C(NHMe)(NMe2)2][B5O6(OH)4]·B(OH)3 (5), and [TBDH][B5O6(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 B2O3 at >650 °C. The low temperature stage (<250 °C) was endothermic and corresponded to a loss of H2O. 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(NH2)3]2[B4O5(OH)4]·2H2O, [C(NH2)3][B5O6(OH)4]·H2O, and [C(NH2)3]3[B9O12(OH)6] and in compounds 1-6 revealed that two important H-bonding R22(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(NH2)3]2[B4O5(OH)4]·2H2O and [C(NH2)3]3[B9O12(OH)6], whereas the anion-anion ring motif was dominant in [C(NH2)3][B5O6(OH)4]·H2O 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.

Fluorine-based Zn salan complexes.

We synthesised and characterised the racemic and chiral versions of two Zn salan fluorine-based complexes from commercially available materials. The complexes are susceptible to absorbing H2O from the atmosphere. In solution (DMSO-H2O) and at the millimolar level, experimental and theoretical studies identify that these complexes exist in a dimeric-monomeric equilibrium. We also investigated their ability to sense amines via19F NMR. In CDCl3 or d6-DMSO, strongly coordinating molecules (H2O or DMSO) are the limiting factor in using these easy-to-make complexes as chemosensory platforms since their exchange with analytes requires an extreme excess of the latter.

Strained Porphyrin Tape-Cycloparaphenylene Hybrid Nanorings.

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.

Chiral Co3Y Propeller-Shaped Chemosensory Platforms Based on 19F-NMR.

Two propeller-shaped chiral CoIII3YIII complexes built from fluorinated ligands are synthesized and characterized by single-crystal X-ray diffraction (SXRD), IR, UV-vis, circular dichroism (CD), elemental analysis, thermogravimetric analysis (TGA), electron spray ionization mass spectroscopy (ESI-MS), and NMR (1H, 13C, and 19F). This work explores the sensing and discrimination abilities of these complexes, thus providing an innovative sensing method using a 19F NMR chemosensory system and opening new directions in 3d/4f chemistry. Control experiments and theoretical studies shed light on the sensing mechanism, while the scope and limitations of this method are discussed and presented.

FeIII in the high-spin state in dimethylammonium bis[3-ethoxysalicylaldehyde thiosemicarbazonato(2-)-κ3O2,N1,S]ferrate(III).

The synthesis and crystal structure (100 K) of the title compound, [(CH3)2NH2][Fe(C10H11O2N3S)2], are reported. The asymmetric unit consists of an octahedral [FeIII(L)2]- fragment, where L2- is 3-ethoxysalicylaldehyde thiosemicarbazonate(2-), and a dimethylammonium cation. Each L2- ligand binds with the thiolate S, the imine N and the phenolate O atoms as donors, resulting in an FeIIIS2N2O2 chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis positions, and mutually trans N atoms. The FeIII ion is in the high-spin state at 100 K. The variable-temperature magnetic susceptibility measurements (5-320 K) are consistent with the presence of a high-spin FeIII ion with D = 0.83 (1) cm-1 and g = 2.

Organometallic Platinum(II) Photosensitisers that Demonstrate Ligand-Modulated Triplet-Triplet Annihilation Energy Upconversion Efficiencies.

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.

Synthesis and crystal structures of two related Co and Mn complexes: a celebration of collaboration between the universities of Dakar and Southampton.

We report the synthesis and structures of two transition-metal complexes involving 2-(2-hy-droxy-phen-yl)benzimidazole (2hpbi - a ligand of inter-est for its photoluminescent applications), with cobalt, namely, bis-[µ-2-(1H-1,3-benzo-diazol-2-yl)phenolato]bis-[ethanol(thio-cyanato)-cobalt(II)], [Co2(C13H9N2O)2(NCS)2(C2H6O)2], (1), and manganese, namely, bis-[µ-2-(1H-1,3-benzo-diazol-2-yl)phenolato]bis-{[2-(1H-1,3-benzo-diazol-2-yl)phenolato](thio-cyanato)-mang-an-ese(III)} dihydrate, [Mn2(C13H9N2O)4(NCS)2]·2H2O, (2). These structures are two recent examples of a fruitful collaboration between researchers at the Laboratoire de Chimie de Coordination Organique/Organic Coordination Chemistry Laboratory (LCCO), University of Dakar, Senegal and the National Crystallography Service (NCS), School of Chemistry, University Southampton, UK. This productive partnership was forged through meeting at Pan-African Conferences on Crystallography and quickly grew as the plans for the AfCA (African Crystallographic Association) developed. This article therefore also showcases this productive partnership, in celebration of the IUCr's 75 year anniversary and the recent inclusion of AfCA as a Regional Associate of the IUCr.

Scale-up and optimization of the synthesis of dual CBP/BRD4 inhibitor ISOX-DUAL.

ISOX-DUAL is a dual inhibitor of CBP/p300 (IC50 = 0.65 µM) and BRD4 (IC50 = 1.5 µM) bromodomains, and a useful chemical probe for epigenetic research. Aspects of the published synthetic route to this compound and its analogues are small-scale, poor-yielding or simply unamenable to scale-up without optimization. Herein we describe the development of a refined synthesis that circumvents the challenges of the original report, with notable improvements to several of the key synthetic transformations. Moreover, a general Suzuki Miyaura protocol for the late stage installation of alternative dimethyl-isoxazole acetyl-lysine (KAc) binding motifs is presented.