Chromium chains as polydentate fluoride ligands for actinides and group IV metals.

The reactions of {Cr6} horseshoe chains {[nPr2NH2]3[Cr6F11(O2CtBu)10]}2, 1 and precursors of actinides and group IV metals led to a series of ring complexes [nPr2NH2][Cr7TiF6O2(O2CtBu)16], 2, [nPr2NH2][Cr6Ti2F5O3(O2CtBu)16], 3, [Cr6ThF7(O2CtBu)15 (Me2SO)], 4, [(nPr2NH2)2(Cr6Th2F12(O2CtBu)16)], 5 and [nPr2NH2][Cr6U2O2F8(O2CtBu)16(Me2SO)], 6. X-ray structure studies indicate that the {Cr6} chains maintain their structures in these complexes, acting as polydentate fluoride ligands. Their static magnetic properties were measured and fitted by isotropic exchange Hamiltonian. In accordance with 1, the magnetic exchanges between CrIII are antiferromagnetic, while the exchange interactions can be modified by the tetravalent metals. For compound 6, ferromagnetic exchanges JCr-U and JU-U are obtained. EPR spectra of compounds 2-5 were measured at Q band and were simulated. The spectrum of 2 has the same profile as {Cr7Cd} and {Cr7Zn} rings with a ground state S = 3/2. 3, 4 and 5 give similar EPR spectra with S = 0 ground states.

Enhanced Photosensitive Schottky Diode Behavior of Pyrazine over 2-Aminopyrimidine Ligand in Copper(II)-Phthalate MOFs: Experimental and Theoretical Rationalization.

Two novel Cu(II)-based metal-organic frameworks [C40H34Cu2N6O18 (1) and C20H18CuN2O10 (2)] have been synthesized using 2-aminopyrimidine or pyrazine ligands and phthalate ion and characterized spectroscopically and by X-ray single-crystal diffraction. Both 1 and 2 show electrical conductivity and photosensitivity, evidencing their potentiality in optoelectronic device applications. Experimental and theoretical investigations revealed that the electrical conductivity under irradiation of visible light increases compared to that under dark condition (photosensitive Schottky barrier diode behavior), especially in complex 2. Both 1 and 2 have been successfully applied in technologically challenging thin-film active devices.

Axial stereocontrol in tropos dibenz[c,e]azepines: the individual and cooperative effects of alkyl substituents.

6,7-Dihydro-5H-dibenz[c,e]azepines, a class of secondary amine incorporating a centre-axis chirality relay, can be prepared from N-(2-bromobenzyl)-N-(1-arylalkyl)methanesulfonamides via Pd-catalysed intramolecular direct arylation, and methylated at C(7) via the 5,7-trans diastereoselective addition of methylmagnesium bromide to the derived N-benzylazepinium tetraphenylborate. Using these methods, the 4,5-dimethylated and 4,5,7-trimethylated homologues 13 and 14 were obtained and shown by 1H NMR spectroscopy to be axially biased in opposite senses, as defined by the respective pseudoaxial or pseudoequatorial orientation of the 5-substituent in the preferred conformers, while retaining their tropos nature (the Arrhenius activation energy, EA, for the conformational exchange process in 14 was estimated to be 57 kJ mol-1 using 2D-EXSY NMR spectroscopy at 233-248 K). These results serve to illustrate how substituent effects might be exploited in new designs of bridged biaryl ligand in which tropos dynamics operate in combination with a pre-existing axial stereochemical bias.

Halogen bonding in a series of Br(CF2)nBr-DABCO adducts (n = 4, 6, 8).

Halogen bonding (XB) is a highly-directional class of intermolecular interactions that has been used as a powerful tool to drive the design of crystals in the solid phase. To date, the majority of XB donors have been iodine-containing compounds, with many fewer involving brominated analogues. We report the formation of adducts in the vapour phase from a series of dibromoperfluoroalkyl compounds, BrCF2(CF2)nCF2Br (n = 2, 4, 6), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Single-crystal X-ray diffraction studies of the colourless crystals identified 1,4-diazabicyclo[2.2.2]octane-1,4-dibromoperfluorobutane (1/1), C4Br2F8·C6H12N2, (I), 1,4-diazabicyclo[2.2.2]octane-1,6-dibromoperfluorohexane (1/1), C6Br2F12·C6H12N2, (II), and 1,4-diazabicyclo[2.2.2]octane-1,8-dibromoperfluorooctane (1/1), C8Br2F16·C6H12N2, (III), each of which displays a one-dimensional halogen-bonded network. All three adducts exhibit N...Br distances less than the sum of the van der Waals radii, with butane analogue (I) showing the shortest N...Br halogen-bond distances yet reported between a bromoperfluorocarbon and a nitrogen base [2.809 (3) and 2.818 (3) Å], which are 0.58 and 0.59 Šshorter than the sum of the van der Waals radii.

An Extensive Family of Heterometallic Titanium(IV)-Metal(III) Rings with Structure Control through Templates.

A family of heterometallic [Cat][Tix MO(x+1 )(O2 Ct Bu)2x+2 ] rings is reported where Cat=a secondary or tertiary alkyl ammonium ion, x=7, 8 or 9, and M=FeIII , GaIII , CrIII , InIII and AlIII . The structures are regular polygons with eight, nine or ten vertices with each edge bridged by an oxide and two pivalates. The size of the ring formed is controlled by the alkylammonium cation present. In each case a homometallic by-product is found [Cat][Tix O(x+1 )(O2 Ct Bu)2x-1 ].

Transition metal-free, visible-light mediated synthesis of 1,10-phenanthroline derived ligand systems.

A broad range of 1,10-phenanthroline substrates was efficiently C-H functionalised, providing rapid, gram-scale access to substituted heteroaromatic cores of broad utility. Furthermore, this C-H functionalisation pathway was extended to the synthesis of previously inaccessible, ultra-soluble, 2,9-bis-triazinyl-1,10-phenanthroline (BTPhen) ligands for advanced nuclear fuel cycles.

Heterodimers of heterometallic rings.

Nine new complexes are reported involving linked heterometallic rings; one ring is designed as a ligand for the second, and the compounds produced can be regarded as molecular prototypes for implementing quantum gates featuring two subtly different qubits.

Exploring electronic effects on the partitioning of actinides(iii) from lanthanides(iii) using functionalised bis-triazinyl phenanthroline ligands.

The first examples of 4,7-disubstituted 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzo-triazin-3-yl)-1,10-phenanthroline (CyMe4-BTPhen) ligands are reported herein. Evaluating the kinetics, selectivity and stoichiometry of actinide(iii) and lanthanide(iii) radiotracer extractions has provided a mechanistic insight into the extraction process. For the first time, it has been demonstrated that metal ion extraction kinetics can be modulated by backbone functionalisation and a promising new CHON compliant candidate ligand with enhanced metal ion extraction kinetics has been identified. The effects of 4,7-functionalisation on the equilibrium metal ion distribution ratios are far more pronounced than those of 5,6-functionalisation. The complexation of Cm(iii) with two of the functionalised ligands was investigated by TRLFS and, at equilibrium, species of 1 : 2 [M : L] stoichiometry were observed exclusively. A direct correlation between the ELUMO-EHOMO energy gap and metal ion extraction potential is reported, with DFT studies reaffirming experimental findings.

Synthesis and reactions of N-heterocycle functionalised variants of heterometallic {Cr7Ni} rings.

Here we present a series of linked cage complexes of functionalised variants of the octametallic ring {Cr7Ni} with the general formula [(n)Pr2NH2][Cr7NiF8(O2C(t)Bu)15(O2CR)], where HO2CR is a N-heterocycle containing carboxylic acid. These compounds are made by reacting [(n)Pr2NH2][Cr7NiF8(O2C(t)Bu)15(O2CR)] with a variety of simple metal salts and metal dimers. The carboxylic acids studied include iso-nicotinic acid, 3-(4-pyridyl)acrylic acid and 4-pyridazine carboxylic acid. These new linked cage complexes have been studied structurally and the study highlights the versatility of functionalised {Cr7Ni} as a Lewis base ligand. As {Cr7Ni} is a putative molecular electron spin qubit this work contributes to our understanding of the chemistry that might be required to assemble molecular spin qubits.

Halogen-bonded adduct of 1,2-dibromo-1,1,2,2-tetrafluoroethane and 1,4-diazabicyclo[2.2.2]octane.

Halogen bonding is an intermolecular interaction capable of being used to direct extended structures. Typical halogen-bonding systems involve a noncovalent interaction between a Lewis base, such as an amine, as an acceptor and a halogen atom of a halofluorocarbon as a donor. Vapour-phase diffusion of 1,4-diazabicyclo[2.2.2]octane (DABCO) with 1,2-dibromotetrafluoroethane results in crystals of the 1:1 adduct, C2Br2F4·C6H12N2, which crystallizes as an infinite one-dimensional polymeric structure linked by intermolecular N...Br halogen bonds [2.829 (3) Å], which are 0.57 Šshorter than the sum of the van der Waals radii.

Correction: perfluoropropenyl-containing phosphines from HFC replacements.

Correction for 'Perfluoropropenyl-containing phosphines from HFC replacements' by Alan K. Brisdon et al., Dalton Trans., 2015, DOI: 10.1039/c5dt02043c.

Perfluoropropenyl-containing phosphines from HFC replacements.

A series of new perfluoropropenyl-containing phosphines of the type R3-nP(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, iPr, n = 1, 2; R = tBu, n = 2) have been prepared from the reaction of the hydrofluoroolefin Z-CF3CF[double bond, length as m-dash]CFH (HFO-1225ye) with base and the appropriate chlorophosphine, while reaction with Cl2PCH2CH2PCl2 gave (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, the first example of a bidentate perfluoroalkenyl-containing phosphine. An alternative route to these phosphines based on the room- or low-temperature deprotonation of CF3CF2CH2F (HFC-236ea) gives mainly the E-isomer, but also a small amount of the Z-isomer, the ratio of which depends on the reaction temperature. All of the phosphines could be readily oxidised with either H2O2 or urea·H2O2, and the phosphine selenides R3-nP(Se)(E-CF[double bond, length as m-dash]CFCF3)n (R = Ph, n = 1,2; R = iPr, n = 1; R = tBu, n = 2) were also prepared. The steric and electronic properties of these ligands were determined based on their platinum(ii), palladium(ii) and molybdenum carbonyl complexes. The crystal structures of (CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2, (CF3CF[double bond, length as m-dash]CF)2P(O)CH2CH2P(O)(CF[double bond, length as m-dash]CFCF3)2, iPr2P(Se)(CF[double bond, length as m-dash]CFCF3)2, trans-[PtCl2{Ph(3-n)P(E-CF[double bond, length as m-dash]CFCF3)n}2] (n = 1 or 2), trans-[PdCl2{R2P(E-CF[double bond, length as m-dash]CFCF3)}2] (R = Ph, iPr) and [Mo(CO)4{(CF3CF[double bond, length as m-dash]CF)2PCH2CH2P(CF[double bond, length as m-dash]CFCF3)2}] are reported.

Antibacterial activities of novel nicotinic acid hydrazides and their conversion into N-acetyl-1,3,4-oxadiazoles.

Synthesis of a series of novel N-acylhydrazones of nicotinic acid hydrazides 3a-j via condensation of nicotinic acid hydrazide 1 with the corresponding aldehydes and ketones is described. The series 3a-j was evaluated for in vitro antibacterial activity against two gram negative (Pseudomonas aeruginosa and Klebsiella pneumoniae) and two gram positive (Streptococcus pneumoniae and Staphylococcus aureus) bacteria. The zone of inhibition was measured using the disk diffusion method, and in vitro minimum inhibitory concentration indicating that compounds 3a and 3e were effective against P. aeruginosa with MICs of 0.220 and 0.195 µg respectively.

A Star of David catenane.

We describe the synthesis of a [2]catenane that consists of two triply entwined 114-membered rings, a molecular link. The woven scaffold is a hexameric circular helicate generated by the assembly of six tris(bipyridine) ligands with six iron(II) cations, with the size of the helicate promoted by the use of sulfate counterions. The structure of the ligand extension directs subsequent covalent capture of the catenane by ring-closing olefin metathesis. Confirmation of the Star of David topology (two rings, six crossings) is provided by NMR spectroscopy, mass spectrometry and X-ray crystallography. Extraction of the iron(II) ions with tetrasodium ethylenediaminetetraacetate affords the wholly organic molecular link. The self-assembly of interwoven circular frameworks of controlled size, and their subsequent closure by multiple directed covalent bond-forming reactions, provides a powerful strategy for the synthesis of molecular topologies of ever-increasing complexity.

A detailed study of the magnetism of chiral {Cr7M} rings: an investigation into parametrization and transferability of parameters.

Compounds of general formula [Cr7MF3(Etglu)(O2C(t)Bu)15(Phpy)] [H5Etglu = N-ethyl-d-glucamine; Phpy = 4-phenylpyridine; M = Zn (1), Mn (2), Ni (3)] have been prepared. The structures contain an irregular octagon of metal sites formed around the penta-deprotonated Etglu(5-) ligand; the chirality of N-ethyl-d-glucamine is retained in the final product. The seven Cr(III) sites have a range of coordination environments, and the divalent metal site is crystallographically identified and has a Phpy ligand attached to it. By using complementary experimental techniques, including magnetization and specific heat measurements, inelastic neutron scattering, and electron paramagnetic resonance spectroscopy, we have investigated the magnetic features of this family of {Cr7M} rings. Microscopic parameters of the spin Hamiltonian have been determined as a result of best fits of the different experimental data, allowing a direct comparison with corresponding parameters found in the parent compounds. We examine whether these parameters can be transferred between compounds and compare them with those of an earlier family of heterometallic rings.

A synthetic approach to novel carvotacetone and antheminone analogues with anti-tumour activity.

A synthetic approach to analogues of the terpenoid natural product antheminone A is described which employs (-)-quinic acid as starting material. A key conjugate addition step proved to be unpredictable regarding its stereochemical outcome however the route allowed access to two diastereoisomeric series of compounds. The results of biological assay of the toxicity of the target compounds towards non-small-cell lung cancer cell line A549 are reported.

Rings and threads as linkers in metal-organic frameworks and poly-rotaxanes.

Coordination polymers and metal-organic rotaxane frameworks are reported where the organic linker is replaced by functionalised inorganic clusters that act as bridging ligands.

Studies of hybrid organic-inorganic [2] and [3]rotaxanes bound to Au surfaces.

Hybrid organic-inorganic [2]- and [3]rotaxanes have been synthesised, and their ability to bind to Au surfaces studied; the length of the tethering group is found to control how the supramolecular assembly binds to the surface and we find that [2]rotaxanes show improved stability over previous studies of simple inorganic rings.

Molecular amino-phosphonate cobalt-lanthanide clusters.

The use of 1-amino-1-cyclohexyl phosphonic acid, a functionalised phosphonate, leads to the synthesis of two new structural types for 3d-4f phosphonate cages with unusual structural cores and which show high magnetocaloric effects.