Measurement of gamow-teller strength for 176Yb --> 176Lu and the efficiency of a solar neutrino detector

We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem.     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

Tetravalent cerium carbene complexes

The tetravalent organometallic cerium complex [CeL4] is readily accessible from the oxidation of the trivalent [CeL3], L=a bidentate N-heterocyclic carbene alkoxide ligand, [C{(NPri)CHCHN}CH2CMe2O]. The [CeL4] complex should behave like the [UL4] analogue, but the two complexes show significantly different structures, highlighting the differences between 4f and 5f metals.     

Functionalised saturated-backbone carbene ligands: yttrium and uranyl alkoxy-carbene complexes and bicyclic carbene-alcohol adducts

A new and modular route to bidentate ligands that combines an alkoxide with a saturated backbone N-heterocyclic carbene (NHC) is presented. The bi(heterocyclic) compounds are formally the addition product of a saturated NHC and the alcohol group of the N-functionalised arm. Using these compounds, the synthesis and structural characterisation of the first electropositive metal complexes of saturated N-heterocyclic carbenes has been achieved, and examples structurally characterised for the yttrium(III) and the uranyl [UO(2)](2+) cations.     

Organometallic Cerium Complexes from Tetravalent Coordination Complexes

The use of tetravalent cerium alkoxides, nitrates, and triflates was studied as a direct route to [Ce^IV(carbene)] complexes. Protonolysis reactions between 1H‐imidazolium‐ or imidazoline (=4,5‐dihydro‐1H‐imidazole)‐containing alkoxide proligands HL (L=OCMe₂CH₂[1‐C(NCHCHNⁱPr)]) and HL^S (L^S=OCMe₂CH₂[1‐C(NCH₂CH₂NⁱPr)]) and Ce^IV tert‐butoxide, triflate, and nitrate compounds were studied to target [Ce^IV(N‐heterocyclic carbene)] complexes (of unsaturated and saturated carbenes, resp.). Instead, tetravalent cerium imidazolium [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL)Ce(O^tBu)₃], or imidazolinium adducts [(O^tBu)₃Ce(μ‐O^tBu)₂(μ‐HL^S)Ce(O^tBu)₃] were isolated. However, the salt metathesis of cerium triflate with KL provided a simple route to [CeL₄], which was significantly improved if an external oxidant, benzoquinone, was included in the mixture to maintain oxidation‐state integrity. Likewise, the salt metathesis of cerium triiodide with KL and added benzoquinone provided a straightforward route to [CeL₄].     

Breakup of 8B and the 7Be(p, γ)8B reaction

The calculated rate of events in some of the existing solar neutrino detectors is directly proportional to the rate of the ⁷Be(p, γ)⁸B reaction measured in the laboratory at low energies. However, the low-energy cross sections of this reaction are quite uncertain as various measurements differ from each other by 30–40%. The Coulomb dissociation process which reverses the radiative capture by the dissociation of ⁸B in the Coulomb field of a target, provides an alternate way of accessing this reaction. While this method has several advantages (like large breakup cross sections and flexibility in the kinematics), the difficulties arise from the possible interference by the nuclear interactions, uncertainties in the contributions of the various multipoles and the higher order effects, which should be considered carefully. We review the progress made so far in the experimental measurements and theoretical analysis of the breakup of ⁸B and discuss the current status of the low-energy cross sections (or the astrophysical S-factor) of the ⁷Be(p, γ)⁸B reaction extracted therefrom. The future directions of the experimental and theoretical investigations are also suggested. Work supported by EPSRC, UK, grant nos J/95867 and L/94574.     

Facile bismuth-oxygen bond cleavage, C-H activation, and formation of a monodentate carbon-bound oxyaryl dianion, (C₆H₂(t)Bu₂-3,5-O-4)²⁻

The Bi(3+) (N,C,N)-pincer complex Ar'BiCl(2) (1) [Ar' = 2,6-(Me(2)NCH(2))(2)C(6)H(3)], reacts with 2 equiv of KOC(6)H(3)Me(2)-2,6 and KOC(6)H(3)(i)Pr(2)-2,6 by ionic metathesis to form the anticipated bis(aryloxide) complexes Ar'Bi(OC(6)H(3)Me(2)-2,6)(2) (2) and Ar'Bi(OC(6)H(3)(i)Pr(2)-2,6)(2) (3), respectively. However, the analogous reaction with 2 equiv of KOC(6)H(3)(t)Bu(2)-2,6 forms HOC(6)H(3)(t)Bu(2)-2,6 and a dark-orange complex containing only one aryloxide-derived ligand bound via a Bi-C and not a Bi-O linkage. This complex is formulated as Ar'Bi(C(6)H(2)(t)Bu(2)-3,5-O-4) (4), a product of para C-H bond activation. Structural, spectroscopic, and DFT studies and a comparison with the protonated analogue [Ar'Bi(C(6)H(2)(t)Bu(2)-3,5-OH-4)][BPh(4)] (5), which was obtained by treatment of 4 with [HNEt(3)][BPh(4)], suggest that 4 contains an oxyaryl dianion. Complex 4 represents a fully characterizable product of a bismuth-mediated C-H activation and rearrangement of the type postulated in catalytic SOHIO processes.     

Bismuth coordination chemistry with allyl, alkoxide, aryloxide, and tetraphenylborate ligands and the {[2,6-(Me2NCH2)2C6H3]2Bi}+ cation

A series of bis(aryl) bismuth compounds containing (N,C,N)-pincer ligands, [2,6-(Me(2)NCH(2))(2)C(6)H(3)](-) (Ar'), have been synthesized and structurally characterized to compare the coordination chemistry of Bi(3+) with similarly sized lanthanide ions, Ln(3+). Treatment of Ar'(2)BiCl, 1, with ClMg(CH(2)CH═CH(2)) affords the allyl complex Ar'(2)Bi(η(1)-CH(2)CH═CH(2)), 2, in which only one allyl carbon atom coordinates to bismuth. Complex 1 reacts with KO(t)Bu and KOC(6)H(3)Me(2)-2,6 to yield the alkoxide Ar'(2)Bi(O(t)Bu), 3, and aryloxide Ar'(2)Bi(OC(6)H(3)Me(2)-2,6), 4, respectively, but the analogous reaction with the larger KOC(6)H(3)(t)Bu(2)-2,6 forms [Ar'(2)Bi][OC(6)H(3)(t)Bu(2)-2,6], 6, in which the aryloxide ligand acts as an outer sphere anion. Chloride is removed from 1 by NaBPh(4) to form [Ar'(2)Bi][BPh(4)], 5, which crystallizes from THF in an unsolvated form with tetraphenylborate as an outer sphere counteranion.     

Calcium-mediated intramolecular hydroamination catalysis

The calcium-catalyzed intramolecular hydroamination of alkenes and alkynes is reported. The beta-diketiminato complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}-Ca{N(SiMe3)2}(THF)] affects catalytic cyclization of a range of aminoalkenes and aminoalkynes with activities that are broadly commensurate to those of established rare earth catalysts.