Synthetic and spectroscopic studies of platinum and gold sigma-acetylide complexes with conjugated arene ligands

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Exploring secondary bonding in p-block chemistry – an experimental study of [GeX 2 {o-C 6 H 4 (PMe 2 ) 2 }] using variable pressure single crystal X-ray diffraction

Secondary bonding interactions play a major role in governing the overall structures adopted. The low energy contributions from these weak interactions make structure prediction very difficult, hence there is a need for experimental techniques that contribute to understanding the interplay between different types of secondary bonding. Variable pressure single crystal X-ray diffraction studies on the homologous series, [GeX2{o-C6H4(PMe2)2}], X = Cl 1, Br 2, I 3, show that probing the different interfaces between layers of structural building blocks, rather than conventional molecular units, provides very valuable insights. 1 and 3 undergo a smooth compression as the pressure is increased, whereas a phase transition occurs for 2 at a pressure between 29 and 41 kbar. This is associated with an abrupt change in the β angle (from 111.33(2)° to 92.24(8)°). The structural consequences are most evident in the aromatic⋯aromatic layer interface. Below the phase transition there is an edge-to-face C–H⋯π arrangement (like 1), with the angle between the planes of adjacent rings of ~75°, whereas above the transition this interface has transformed to an offset-parallel face-to-face π–π stacking interaction (like 3). The GeX2⋯X2Ge interface undergoes a concomitant, but smoother compression with increasing pressure. 2 also has the highest void volume at ambient pressure (11.9%), and as expected the phase transition results in a structure with much more efficient packing. This, the first such study involving p-block coordination complexes, reveals the subtlety and complexity of the interplay between the different forms of weak, secondary (supramolecular) interactions present. The results indicate that this type of experimental study can provide valuable additional information to help guide crystal structure prediction by computational methods, an important and very challenging target

Niobium tetrahalide complexes with neutral diphosphine ligands

The reactions of NbCl4 with diphosphine ligands o-C6H4(PMe2)2, Me2PCH2CH2PMe2 or Et2PCH2CH2PEt2 in a 1:2 molar ratio in MeCN solution produced eight-coordinate [NbCl4(diphosphine)2]. [NbBr4(diphosphine)2] (diphosphine = o-C6H4(PMe2)2 or Me2PCH2CH2PMe2) were made similarly from NbBr4. X-ray crystal structures show that [NbCl4{o-C6H4(PMe2)2)2}] has a dodecahedral geometry but the complexes with dimethylene backboned diphosphines are distorted square antiprisms. The Nb-P and <P-Nb-P angles are very similar in the two types, but Nb-Cl distances are ~ 0.1Å longer in the square antiprismatic complexes. These paramagnetic (d1) complexes were also characterised by microanalysis, magnetic measurements, IR and UV-visible spectroscopy. Using a 1:1 molar ratio of NbCl4 : diphosphine (diphosphine = Me2PCH2CH2PMe2, Et2PCH2CH2PEt2, Cy2PCH2CH2PCy2 and Ph2PCH2CH2CH2PPh2) afforded [NbCl4(diphosphine)] and [NbBr4(Me2PCH2CH2PMe2)] was obtained similarly. These 1 : 1 complexes are unstable in solution, preventing X-ray crystallographic study, but based upon their diamagnetism, IR, UV-visible and 31P{1H} NMR spectra they are formulated as halide-bridged dimers [(diphosphine)X2Nb(μ-X)4NbX2(diphosphine)] with single Nb-Nb bonds and chelating diphosphines. The Nb(IV) complexes are prone to hydrolysis and oxidation in solution and the structures of the Nb(V) complexes [NbBr4(Me2PCH2CH2PMe2)2][NbOBr4(MeCN)] with a dodecahedral cation, and [{NbOCl3{Et2P(CH2)2PEt2}}2{μ-Et2P(CH2)2PEt2}] which contains seven-coordinate Nb(V) centres with a symmetrical diphosphine bridge are reported. The structure of niobium tetrabromide, conveniently made from NbCl4 and BBr3, is a chain polymer with edge-linked NbBr6 octahedra and alternating long and short Nb-Nb distances, the latter ascribed to Nb-Nb bonds

The Salivary Secretome of the Tsetse Fly Glossina pallidipes (Diptera: Glossinidae) Infected by Salivary Gland Hypertrophy Virus

Tsetse fly (Diptera; Glossinidae) transmits two devastating diseases to farmers (human African Trypanosomiasis; HAT) and their livestock (Animal African Trypanosomiasis; AAT) in 37 sub-Saharan African countries. During the rainy seasons, vast areas of fertile, arable land remain uncultivated as farmers flee their homes due to the presence of tsetse. Available drugs against trypanosomiasis are ineffective and difficult to administer. Control of the tsetse vector by Sterile Insect Technique (SIT) has been effective. This method involves repeated release of sterilized males into wild tsetse populations, which compete with wild type males for females. Upon mating, there is no offspring, leading to reduction in tsetse populations and thus relief from trypanosomiasis. The SIT method requires large-scale tsetse rearing to produce sterile males. However, tsetse colony productivity is hampered by infections with the salivary gland hypertrophy virus, which is transmitted via saliva as flies take blood meals during membrane feeding and often leads to colony collapse. Here, we investigated the salivary gland secretome proteins of virus-infected tsetse to broaden our understanding of virus infection, transmission and pathology. By this approach, we obtain insight in tsetse-hytrosavirus interactions and identified potential candidate proteins as targets for developing biotechnological strategies to control viral infections in tsetse colonies

Preparation and properties of cyclic and open-chain Sb/N-donor ligands

The preparations of both open-chain and cyclic mixed-donor Sb/N ligands, MeN(CH2-2-C6H4)2SbMe (1), MeN(CH2-2-C6H4SbMe2)2 (2), CH2{CH2N(Me)CH2-2-C6H4SbMe2}2 (3) and CH2{CH2N(Me)CH2-2-C6H4}2SbMe (4), are described via reaction of chlorostibines with dilithio-reagents, and their spectroscopic properties established. Air-stable stibonium derivatives of (3) and (4) have been isolated by treatment of the compounds with excess MeI, which leads to quaternisation at the Sb atoms exclusively. A crystal structure of a bis(stibonium) derivative of (3), [CH2{CH2N(Me)CH2-2-C6H4SbMe3}2]I2, reveals hypervalency at Sb through long-range Sb...N interactions (ca. 2.87 A), giving pseudo-five-membered rings fused to the aromatic rings, and distorted trigonal bipyramidal coordination at Sb. The coordinating properties of compounds (1) to (4) have been investigated through their reactions with Cu(I), Mn(I), Mo(0) and Pt(IV) reagents, and for (1) and (4) by reaction with Fe(0), giving [Fe(CO)4(L)]. The spectroscopic data (IR, 1H, 13C{1H}, 55Mn, 63Cu, 95Mo and 195Pt NMR), mass spectrometry and microanalyses for this series of complexes confirm that coordination occurs via the Sb donor atoms in all cases, with N-coordination only present in fac-[Mn(CO)3(2)](CF3SO3). Crystal structures of [Cu(2)2]BF4, [Mo(CO)4(2)] and [PtMe3I(2)] confirm the coordination modes, showing (2) functioning as a wide-angle bidentate distibine. The structures also show the amine N-donor atoms in the complexes are involved in a hypervalent SbN interaction (ca. 3.0 A) with one of the coordinated Sb atoms in each ligand, leading to significant differences in the conformations of the carbon backbones linking the Sb and N atoms. Reaction of Na3[RhCl6].12H2O with one mol equiv. of (2), (3) or (4) leads to the bis-ligand complex [RhCl2(2)2]Cl and the 1 : 1 Rh : L complexes [RhCl2(3)]Cl and [RhCl3(4)], both of which involve coordination via the Sb and N donor atoms.<br/

Effect of oxidative surface treatments on charge storage at titanium nitride surfaces for supercapacitor applications

The effects of surface oxidation on the capacitance of titanium nitride electrode surfaces, produced by reaction of titanium foils with ammonia, are examined. Thermal oxidation and electrochemical oxidation both increase the amount of redox active oxide at the surface, but electrochemical oxidation is found to be more successful in increasing the capacitance

Six- and eight-coordinate thio- and seleno-ether complexes of NbF5 and some comparisons with NbCl5 and NbBr5 adducts

The reaction of RS(CH(2))(2)SR (R = Me, Et or (i)Pr) with NbF(5) produces [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] which contain distorted eight-coordinate (dodecahedral) cations and octahedral anions, whereas RSe(CH(2))(2)SeR (R = Me or Bu(n)) form six-coordinate [(NbF(5))(2)(mu-RSe(CH(2))(2)SeR)]. Et(2)S and Me(2)Se (L) also form six-coordinate [NbF(5)(L)], but Me(2)S forms both [NbF(5)(Me(2)S)] and an eight-coordinate cation in [NbF(4)(Me(2)S)(4)][NbF(6)]. MeS(CH(2))(2)SMe forms eight-coordinate cations in [NbX(4){MeS(CH(2))(2)SMe}(2)][NbX(6)] (X = Cl or Br), but other complexes of the heavier halides including [NbX(5)(L)] and [(NbX(5))(2)(mu-L-L)] (L-L = RSe(CH(2))(2)SeR; o-C(6)H(4)(CH(2)SMe)(2) and o-C(6)H(4)(CH(2)SeMe)(2)) contain six-coordinate niobium. The very unstable [NbCl(5)(Me(2)Te)] was characterised spectroscopically, but all other attempts to form telluroether complexes resulted in decomposition, and NbI(5) was reduced even by thioethers. The complexes have been characterised by multinuclear NMR ((1)H, (19)F, (93)Nb, (77)Se or (125)Te), IR and UV/visible spectroscopy, and X-ray crystal structures are reported for [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] (R = Me, (i)Pr), [NbF(4)(Me(2)S)(4)][NbF(6)], [NbCl(5)(Me(2)Se)], [NbBr(5)(Me(2)S)], [(NbCl(5))(2){o-C(6)H(4)(CH(2)SMe)(2)}] and [(NbCl(5))(2){MeSe(CH(2))(2)SeMe}]. All the complexes are very moisture sensitive and the fluoride complexes decompose slowly with fluorination of the neutral ligand.<br/

Thio-, seleno- and telluro-ether complexes of aluminium(iii) halides:synthesis, structures and properties

The reaction of AlCl3 with Me2E (E = S, Se or Te) or nBu2E (E = Se or Te) in CH2Cl2 under rigorously anhydrous conditions gave the pseudo-tetrahedral complexes [AlCl3(R2E)]. The [AlX3(Me2E)] (X = Br or I, E = S; X = Br, E = Te) were made from toluene solution since attempted syntheses in CH2Cl2 resulted in substantial chloride incorporation. The synthesis of [(AlCl3)2{o-C6H4(CH2SEt)2}], in which the ligand bridges two tetrahedral aluminium centres, and of the six-coordinate trans-[AlX2{MeE(CH2)2EMe}2][AlX4] (X = Cl or Br, E = S, and X = Cl, E = Se) and cis-[AlI2{MeS(CH2)2SMe}2][AlI4] are reported. The tripodal thioether forms [AlCl3{MeC(CH2SMe)3}], which is a chain polymer with ?2-coordinated ligand and a tbp arrangement at Al(III). Chalcogenoether macrocycle complexes [AlCl3([9]aneS3)], [AlCl2([14]aneS4)][AlCl4] and [AlCl2([16]aneSe4)] [AlCl4] are also described. All complexes were characterised by microanalysis, IR and multinuclear NMR (1H, 27Al, 77Se or 125Te) spectroscopy as appropriate. In CH2Cl2 solution [AlCl3(Me2S)] with added Me2S forms [AlCl3(Me2S)2], and the [AlX2{MeS(CH2)2SMe}2][AlX4] exist as mixtures of cis and trans isomers which undergo rapid exchange at ambient temperatures. X-Ray crystal structures are reported for [AlCl3(Me2Se], [AlX3(Me2Te)] (X = Cl or Br), trans-[AlCl2{MeE(CH2)2EMe}2][AlCl4] (E = S or Se), cis-[AlI2{MeS(CH2)2SMe}2][AlI4], [AlCl3{MeC(CH2SMe)3}], and for the sulfonium salt [Me2SH][AlCl4]. The aluminium halide chalcogenoether chemistry is compared with the corresponding gallium and indium systems, and the relative Lewis acidities of the metals discussed. Attempts to use [AlCl3(nBu2E)] (E = Se or Te) as LPCVD reagents to form aluminium chalcogenide films were unsuccessful