Monofluoride Bridged, Binuclear Metallacycles of First Row Transition Metals Supported by Third Generation Bis(1-pyrazolyl)methane Ligands: Unusual Magnetic Properties

The reaction of M(BF4)2•xH2O, where M is Fe, Co, Cu, and Zn, and the bitopic, bis(pyrazolyl)methane ligand m-[CH(pz)2]2C6H4, Lm, where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M2(μ-F)(μ-Lm)2](BF4)3 complexes. In contrast, a similar reaction of Lm with Ni(BF4)2•6H2O yields dibridged [Ni2(μ-F)2(μ-Lm)2](BF4)2. The solid state structures of seven [M2(μ-F)(μ-Lm)2](BF4)3 complexes, with M = Fe, Co, Cu, and Zn, indicate that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear M–F–M bridging arrangement in five of the complexes, or with a slightly bent Cu–F–Cu bridge in two of the complexes. NMR results indicate that [Zn2(μ-F)(μ-Lm)2](BF4)3 retains its dimeric structure in solution. The [Ni2(μ-F)2(μ-Lm)2](BF4)2 complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe2(μ-F)(μ-Lm)2](BF4)3 and [Co2(μ-F)(μ-Lm)2](BF4)3 complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of –10.4 and –0.67 cm–1, respectively; there is no observed long-range magnetic order. Three different solvates of [Cu2(μ-F)(μ-Lm)2](BF4)3 are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of –600 cm–1 or more negative. Mössbauer spectra indicate that [Fe2(μ-F)(μ-Lm)2](BF4)3 exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II)

Engineering for the ATLAS SemiConductor Tracker (SCT) End-cap.

The ATLAS SemiConductor Tracker (SCT) is a silicon-strip tracking detector which forms part of the ATLAS inner detector. The SCT is designed to track charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC) at CERN at an energy of 14 TeV. The tracker is made up of a central barrel and two identical end-caps. The barrel contains 2112 silicon modules, while each end-cap contains 988 modules. The overall tracking performance depends not only on the intrinsic measurement precision of the modules but also on the characteristics of the whole assembly, in particular, the stability and the total material budget. This paper describes the engineering design and construction of the SCT end-caps, which are required to support mechanically the silicon modules, supply services to them and provide a suitable environment within the inner detector. Critical engineering choices are highlighted and innovative solutions are presented – these will be of interest to other builders of large-scale tracking detectors. The SCT end-caps will be fully connected at the start of 2008. Further commissioning will continue, to be ready for proton-proton collision data in 2008