Nicholas J. Hill

RECONNECTION AND ENERGETICS IN TWO-RIBBON FLARES: A REVISIT OF THE BASTILLE-DAY FLARE

We conduct a semi-quantitative analysis of two-ribbon flares to investigate the observational relationship between magnetic reconnection and energetics by revisiting the Bastille-day flare, particularly the UV and hard X-ray (HXR) observations. The analysis establishes that prominent UV emission is primarily produced by precipitating electrons that also produce HXRs. In addition, reconnection and subsequent energy release along adjacent field lines along the polarity inversion line (PIL) combined with elongated decay of UV emission may account for the observed extended UV ribbons whereas HXR sources with rapid decay appear mostly as compact kernels. Observations also show that HXR sources and UV brightenings exhibit an organized parallel motion along the magnetic PIL during the rise of the flare, and then the perpendicular expansion of UV ribbons dominate during the peak. With a 2.5 dimensional approximation with the assumed translational dimension along the PIL, we derive geometric properties of UV ribbons and infer the pattern of reconnection as with a varying magnetic guide field during reconnection. It is shown that HXR and UV emissions evolve in a similar way to reconnection rates determined by the perpendicular “motion.” The analysis suggests that a relatively strong guide field may be present during the rise of the flare, whereas particle acceleration and non-thermal energy release are probably more efficient with an enhanced reconnection rate with a relatively weak guide field. We discuss the role of the guide field in reconnection and particle energization, as well as novel observational experiments that may be conducted to shed new light on these issues.

Yttrium halide complexes of phosphine- and arsine oxides: synthesis, multinuclear NMR and structural studies

The reactions of YCl3.6H(2)O, YBr3.6H(2)O and YI3.8H(2)O with Ph3PO, Ph3AsO, Ph2MePO, Me3PO, Me3AsO, o-C6H4{P(O)Ph-2}(2), (ppO(2)) and Ph2P(O)CH2P(O)Ph-2 (dppmO(2)) have been examined in EtOH or Me2CO solution. Complexes isolated in the solid state include [YX2(Ph3PO)(4)]Z (X = Cl, Br or I; Z = X or PF6), [YX3(Ph2MePO)(3)], [YCl2(Ph2MePO)(4)]PF6, [YCl(Ph3PO)(5)][SbCl6](2), [Y(Me3PO)(6)]X-3, [YX2(Ph3AsO)(4)]X, [Y(Me3AsO)(6)]Cl-3 and [YCl2(L-L)(2)]Cl (L-L = ppO(2) or dppmO(2)) which were characterised by analysis, IR and multinuclear (H-1, P-31{H-1} and Y-89) NMR spectroscopy and conductance measurements. The X-ray crystal structures of [YCl2(Ph3PO)(4)]Cl.2.5EtOH.H2O, [YBr2(Ph3PO)(4)]PF6.Et2O and [Y(Me3PO)(6)]Br-3 are reported and discussed. The solution speciation (in CH2Cl2) in the various systems was examined by variable temperature multinuclear NMR spectroscopy. The Y-89 NMR chemical shifts show systematic trends with donor set which are described. No reaction between these ligands and YF3.1/2H(2)O was observed.

Radical Reactions of a Stable N-Heterocyclic Germylene: EPR Study and DFT Calculation

The first radical adducts of a stable N-heterocyclic germylene were investigated. Novel radical species were produced from a variety of precursors and studied by EPR spectroscopy. DFT (B3LYP) calculations of radical adducts of different (C, Si, Ge) unsaturated N-heterocyclic divalent species with phenoxyl radical show that in the radicals studied the unpaired electron is delocalized over the five-membered ring and the spin density on the central atoms decreases in the following order: C > Si > Ge. These trends can be understood in terms of zwitterionic structure of radical adducts.

Scandium halide complexes of phosphine- and arsine-oxides: synthesis, structures and 45Sc NMR studies

The reactions of ScCl(3)(.)6H(2)O, ScBr(3)(.)6H(2)O and Scl(3)(.)8H(2)O with Ph3PO, Ph3AsO, Ph2MePO, Me3PO and Me3AsO have been examined in EtOH or Me2CO solution. The new complexes [ScCl(Me3PO)(5)]Cl-2, [Sc(Me3PO)(6)]X-3 (X = Br or 1), [ScX,(Ph3PO)4]X (X = Cl, Br or 1), [ScX2(Ph3AsO)(4)]X, [Sc(Me3AsO)(6)]X-3 (X = Cl, Br or 1), [ScCl3(Ph2MePO)(3)] and [ScBr2(PhMePO)(4)]Br were isolated as solids and were characterised by analysis, IR and multinuclear (H-1, P-31{H}: and Sc-45) NMR spectroscopy and conductance measurements. The crystal structures of [ScBr2(Ph3PO)(4)]Br(.)1/2Et(2)O, [ScCl2(Ph3AsO)(4)]Cl and [Sc(Me3AsO)(6)]Br-3 are also reported. The solution speciation (in CH2Cl2 or MeNO2) in the various systems was examined by multinuclear NMR spectroscopy. The Sc-45 NMR chemical shifts and line widths show systematic trends with donor set and symmetry. which are described. No reaction between these ligands and ScF3.1/2H(2)O was observed.

Different electronic structure of phosphonyl radical adducts of N-heterocyclic carbenes, silylenes and germylenes: EPR spectroscopic study and DFT calculations

Stable N-heterocyclic carbenes and germylenes were allowed to react with a phosphonyl radical, (i-PrO)2(O)P˙ (7), generated by photolysis of [(i-PrO)2(O)P]2Hg. The products were identified by EPR spectroscopy. An unsaturated carbene (1) and germylene (3) react with 7 at the divalent atom to give unstable radical products (τ½ = 0.2 s). A benzo-annulated carbene (4) and a saturated germylene (6) react with 7 to give more active radicals. An unsaturated (2) and a saturated silylene (5) undergo rapid reaction (in the dark) with [(i-PrO)2(O)P]2Hg to yield unusual silyl phosphites. In these cases only secondary radicals were observed. DFT (PBE0/TZVP//B3LYP/6-31+G(d)) calculations of the radical adducts of the different (C, Si, Ge) unsaturated N-heterocyclic divalent species with the phosphonyl radical show that the unpaired electron is delocalized over the five-membered ring; the spin density on the central atoms decreases in the order C, 39% > Si, 14% > Ge, 2%. These trends can be understood in terms of a zwitterionic structure of the radical adducts. The calculations of the radical adducts of 4, 5 and 6 with 7 indicate larger spin density on the central atom, 47%, 58% and 42% on C, Si, Ge, respectively.

Homoleptic octahedral hexakis(trimethylphosphine oxide)lanthanide hexafluorophosphates, [Ln(Me3PO)6][PF6]3:: synthesis, structures and properties

The [Ln(Me3PO)(6)][PF6](3) (Ln = lanthanide except Pm) were prepared by reaction of LnCl(3) (.) nH(2)O with Me3PO and NH4PF6 in a 1:8:3 molar ratio in methanol. The complexes have been characterised by analysis, IR, H-1 and P-31 NMR spectroscopy and conductance measurements. The crystal structure of the complexes [Ln(Me3PO)(6)](PF6)(3) (Ln = Pr, Gd or Dy) have been determined and all contain the six-coordinate lanthanide cation in a close to octahedral geometry. Similar cations have been structurally characterised for Y (ICJ. Hill et al. Polyhedron 21 (2002) 445) and for the much smaller Sc.

Synthesis and molecular structures of dimeric assemblies of telluronium salts derived from o-C6H4(CH2TeMe)2 and PhMeTe

The ditelluroether, o-C6H4(CH2TeMe)(2) reacts with excess MeI in acetone to afford the bis(triorganotelluronium iodide), o-C6H4(CH2TeMe2I)(2), in high yield which has been characterised by H-1-, C-13{H-1}- and Te-125{H-1}-NMR spectroscopy, microanalysis and X-ray crystallography. The crystal structure of this species reveals a weakly associated dimer, assembled through a series of secondary (TeI)-I-... interactions to give a pseudo-cubane Te4I4 core, involving three-coordinate (pyramidal) iodine and six-coordinate (distorted octahedral) tellurium. The o-xylyl backbone units are oriented across the diagonal of two opposite faces of the cubane. This is the first crystallographic study of a triorganotelluronium halide salt derided from a ditelluroether, The crystal structure of PhTeMe2I shows a weakly associated mu(2)-diiodo bridged dimer, in this case with two-coordinate iodine and five-coordinate, distorted square pyramidal tellurium. The stereochemical activity of the Te-based lone pair is discussed for each system and the structures are compared with other related species.

Coordination networks derived from antimony(III) halide complexes with thio- and seleno-ether ligation

Antimony(III) halides form highly unusual infinite one- or two-dimensional networks when coordinated to dithio- or diseleno-ether ligands or macrocyclic selenoethers. The structures adopted are contrasted with those observed for related bismuth(III) species.

Synthesis and structural features of the first thallium(I) selenoether derivatives.

The first evidence for thallium(I) complexes involving selenoether ligands is presented, together with the structure determinations for the 1D chain species [T1[MeSe(CH2)3SeMe]]PF6 and the 3D network species [T1[MeSe(CH2)2SeMe]]PF6.

Facile routes to Alkyl-BIAN ligands

The Alkyl-BIAN ligands tert-Butyl-BIAN and 1-Adamantyl-BIAN have been synthesized and their structures have been determined by single-crystal X-ray diffraction along with that of the ZnCl2 complex of tert-Butyl-BIAN.