1,721,123 research outputs found
Group 13 and 14 coordination complexes and reagents for the electrodeposition of tin and lead from supercritical fluids
No full textSupercritical fluid electrodeposition is a new technique being developed that aims to deposit technologically important p-block materials at the nanoscale. This requires significant synthetic effort in precursor development, and investigations into fundamental p-block coordination chemistries, primarily through the use of neutral phosphine and arsine ligands, have been undertaken to aid the design process. The compounds synthesised have been characterised by microanalysis, IR spectroscopy and multinuclear NMR spectroscopy (1H, 11B, 19F, 31P{1H}, 27Al and 119Sn, where appropriate), while single crystal X-ray structure determinations have been performed for representative examples.AlX3 (X = Cl, Br, I) form both [AlX3(PMe3)] and [AlX3(PMe3)2] depending on the reagent stoichiometry employed. While all reported arsine complexes are four-coordinate, neutral diphosphine ligands show a preference for six-coordinate Al; the crystal structures of [AlCl2{o-C6H4(PR2)2}2][AlCl4] (R = Me, Ph) and [AlCl2{Me2P(CH2)2PMe2}2][AlCl4] are reported, along with [(AlCl3)2{?-R2P(CH2)2PR2}] (R = Me, Cy). The importance of solvent choice and hydrolysis in these systems is discussed. Steric and electronic effects are considered in comparing the behaviour of MX3 (M = Al, Ga, In) towards phosphines.A number of new phosphine complexes of BX3 (X = F, Cl, Br, I) have been synthesised, and [BF3(PMe3)] is crystallographically authenticated. Flexible diphosphine ligands yield bridging [(BX3)2{?-R2P(CH2)2PR2}] (R = Me, Et), while rigid chelating ligands produce the unusual ionic [BX2{o-C6H4(PMe2)2}]+ and [BCl2{o-C6H4(AsMe2)2}]+. The d(B–P) are consistent with the order of Lewis acidity being BI3 > BBr3 > BCl3 > BF3. The rare [B2F7]- ion is thought to drive the unexpected formation of [BF2{Ph2P(O)CH2P(O)Ph2}][B2F7].The effect of the weakly coordinating fluoroanions [BF4]- and [SiF6]2- on the coordination environments around Pb(II) in di- and tri-imine complexes is investigated, with several different coordination modes observed. A method is devised to synthesise some Pb(II) diphosphine complexes; the crystal structures of [Pb{o-C6H4(PMe2)2}(H2O)(SiF6)]·H2O and [Pb(L–L)(NO3)2] (L–L = Me2P(CH2)2PMe2, o-C6H4(PMe2)2) are reported, which reveal chelating diphosphines and intermolecular anion interactions, giving extended structures. Adventitious O2 forms the bridging ligand complex [Pb{Et2(O)P(CH2)2P(O)Et2}2(NO3)2].The well-defined and stable [NnBu4][SnX3] and [PPh4][PbX3] (X = Cl, Br, I) precursors are shown by cyclic voltammetry to give reproducible metal deposition and stripping peak features in CH2Cl2, with the reduction potential becoming more accessible Cl ? Br ? I. Good quality thin films of Sn and Pb can be electrodeposited from CH2Cl2 using these precursors, which are analysed by SEM, EDX and XRD. Subsequent work in the group has shown that [NnBu4][SnCl3] can be used to deposit 13 nm Sn nanowires from supercritical CH2F2, highlighting the potential of this versatile electrolyte system for future applications in p-block materials deposition at the extreme nanoscale, and device fabrication
Systematics of BX3 and BX2+ complexes (X = F, Cl, Br, I) with neutral diphosphine and diarsine ligands
Full text linkThe coordination chemistry of the neutral diphosphines, R2P(CH2)2PR2 (R = Me or Et) and o-C6H4(PR?2)2 (R? = Me or Ph), and the diarsine, o-C6H4(AsMe2)2, toward the Lewis acidic BX3 (X = F, Cl, Br, and I) fragments is reported, including several rare complexes incorporating BF3 and BF2+. The studies have revealed that the flexible dimethylene linked diphosphines form [(BX3)2{?-R2P(CH2)2PR2}] exclusively, confirmed by multinuclear NMR (1H, 11B, 19F{1H}, and 31P{1H}) and IR spectroscopy and microanalytical data. Crystallographic determinations of the four BX3 complexes with Et2P(CH2)2PEt2 confirm the 2:1 stoichiometry and, taken together with the spectroscopic data, reveal that the Lewis acid behavior of the BX3 fragment toward phosphine ligands increases in the order F ? Cl ? Br < I. The first diphosphine- and diarsine-coordinated dihaloboronium cations, [BX2{o-C6H4(EMe2)2}]+ (E = P, As), are obtained using the rigid, preorganized o-phenylene linkages. These complexes are characterized similarly, and the data indicate that the complexes with o-C6H4(AsMe2)2 are much more labile and readily decomposed than the phosphine analogues. X-ray crystallographic studies on [BX2{o-C6H4(PMe2)2}][BX4] (X = Cl, Br), [BI2{o-C6H4(PMe2)2}][I3], and [BCl2{o-C6H4(AsMe2)2}][BCl4] confirm the presence of distorted tetrahedral coordination at boron through a chelating diphosphine or diarsine and two X ligands, with d(B–P) revealing a similar increase in Lewis acidity down group 17. Comparison of d(B–P) and d(B–As) reveals an increase of ca. 0.08 Å from P to As. Reaction of BCl3 with the diphosphine dioxide Ph2P(O)CH2P(O)Ph2 gives the ligand-bridged dimer [(BCl3)2{Ph2P(O)CH2P(O)Ph2}], while using either BF3 gas or [BF3(SMe2)] gives a mixture containing both [(BF3)2{?-Ph2P(O)CH2P(O)Ph2}] and the unexpected difluoroboronium salt, [BF2{Ph2P(O)CH2P(O)Ph2}][B2F7] containing a chelating phosphine oxide. The structure of the latter was confirmed crystallographically
Phosphine complexes of aluminium(iii) halides – preparation and structural and spectroscopic systematics
No full textSix-coordinate pseudo-octahedral complexes trans-[AlX2(L–L)2][AlX4] (X = Cl, Br or I; L–L = o-C6H4(PMe2)2, Me2P(CH2)2PMe2) are produced from reaction of AlX3 with the diphosphine in CH2Cl2 (X = Cl) or toluene (X = Br or I) solution. Four-coordinate dimers [Cl3Al(?-L?–L?)AlCl3] (L?–L? = Me2P(CH2)2PMe2, Cy2P(CH2)2PCy2), and the tetrahedral cation [AlCl2{o-C6H4(PPh2)2}][AlCl4] were also obtained. Both four- and five-coordinate complexes [AlX3(PMe3)] and [AlX3(PMe3)2] could be isolated with PMe3 depending upon the ratio of reagents used. These extremely moisture sensitive complexes have been characterised by microanalysis, IR and multinuclear NMR (1H, 31P{1H} and 27Al) spectroscopy. X-ray crystal structures are reported for [AlCl2{o-C6H4(PMe2)2}2][AlCl4], [AlCl2{Me2P(CH2)2PMe2}2][AlCl4], [Cl3Al{?-Me2P(CH2)2PMe2}AlCl3], [Cl3Al{?-Cy2P(CH2)2PCy2}AlCl3], [AlCl3(PMe3)], [AlCl3(PMe3)2], and for the six-coordinate cation complex [AlCl2{o-C6H4(PPh2)2}2][AlCl4], although a bulk sample of the last could not be isolated. Tertiary arsines (AsPh3 or AsEt3) form only 1 : 1 complexes even with excess arsine present. The unstable [AlCl2{o-C6H4(AsMe2)2}][AlCl4] is also described, and shown to decompose rapidly in CH2Cl2 solution to form the diquaternised diarsine cation [o-C6H4(AsMe2)2(CH2)][AlCl4]2, which was fully characterised. Comparisons are drawn with the corresponding gallium(III) systems (Cheng et al., Inorg. Chem., 2007, 46, 7215–7223) and with AlX3 complexes of Group 16 ligands (George et al., Dalton Trans., 2014, 43, 3637–3648), and it is concluded that the differences between the Al and Ga systems reflect the higher Lewis acidity of aluminium(III) towards soft donor ligands
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Hexafluorosilicate and tetrafluoroborate coordination to lead(II) di- and tri-imine complexes – unusual fluoroanion coordination modes
No full textLead(II) tetrafluoroborate and hexafluorosilicate complexes with 2,2?-bipyridyl, 1,10-phenathroline and 2,2?:6?,2?-terpyridyl have been prepared from the ligand and lead salt in aqueous/MeCN. Crystal structures are reported for [Pb(bipy)2(SiF6)], [Pb(phen)2(SiF6)] and [Pb(bipy)2(BF4)2] which are dinuclear with each lead coordinated “cis” to the two diimines and with the bridging fluoroanions completing eight or nine-coordination. [Pb(phen)2(BF4)2] is eight-coordinate and mononuclear with “cis” diimines and two ?2-BF4? groups. [Pb(phen)2(H2O)2(SiF6)] is also mononuclear with a ?2-SiF62? group and two coordinated water molecules. Reaction of Pb(BF4)2 with 2,2?:6?,2?-terpyridyl gave only [Pb(terpy)3][BF4]2, but Pb(SiF6) produced [Pb(terpy)(H2O)(SiF6)], which is a chain polymer with bridging SiF62? groups and significant ?-stacking of the imine rings. The work has identified a number of coordination modes of the SiF62? anion, which has been little used in coordination chemistry but proves to be versatile and also stable (to decomposition/hydrolysis)
Additional data for Systematics of BX3 and BX2+ Complexes (X= F, Cl, Br, I) with Neutral Diphosphine and Diarsine Ligands
Full text linkADDITIONAL DATA for 'Systematics of BX3 and BX2+ Complexes (X= F, Cl, Br, I) with Neutral Diphosphine and Diarsine Ligands' by Jennifer Burt, James Emsley, William Levason, Gillian Reid and Iain Tinkler. It consists of the original spectra for all new compounds.</span
Haloplumbate salts as reagents for the non-aqueous electrodeposition of lead
No full textCyclic voltammetry experiments on the Pb(II) salts, [PPh4][PbX3] (X = Cl, Br, I) in CH2Cl2 solution ([PPh4]X supporting electrolyte) at a Pt disk electrode show reproducible nucleation and stripping features consistent with reduction to elemental Pb. The reduction potential shifts to less cathodic from Cl (?0.40 V) ? Br (?0.27 V) ? I (?0.19 V vs. Ag/AgCl), in line with the Pb–X bond strengths decreasing. Potentiostatic electrodeposition using [PPh4][PbCl3] in CH2Cl2 leads to growth of a thin film of crystalline Pb onto planar TiN electrodes, confirmed by SEM, EDX and XRD analysis. Electrodeposition under similar conditions onto a planar Au electrode leads to deposition of elemental Pb, accompanied by some alloying at the substrate/film interface, with XRD analysis confirming the formation of AuPb2 and AuPb3. Transferring the [PPh4][PbCl3] reagent into supercritical CH2F2 (17.5 MPa and 360 K) containing [PPh4]Cl led to very limited solubility of the Pb reagent; using [NnBu4]Cl as a supporting electrolyte caused an increase in solubility, although still lower than in liquid CH2Cl2. Cyclic voltammetry experiments (Pt disk) using this electrolyte also show voltammetry consistent with Pb deposition, however the low solubility of the lead salt in scCH2F2 meant that electrodeposition onto a planar TiN substrate was not possible
- …
