Redetermination of (acetonitrile-κN)dicarbon-yl(η(5)-cyclo-penta-dien-yl)iron(II) tetra-fluoridoborate

The crystal structure of the title compound, [Fe(C5H5)(CH3CN)(CO)2]BF4, of which only the coordinates of the non-H atoms of the cation have previously been reported [Fadel et al. (1979 [triangle]). Z. Anorg. Allg. Chem. 453, 98–106] has been redetermined. The FeII atom in the complex cation is coordinated by a cyclo­penta­dienyl ring, two carbonyl ligands and an acetonitrile mol­ecule displaying a three-legged piano stool structure. Three of the four F atoms of the BF4 − anion are disordered over two sets of sites, with a site-occupancy factor of 0.709 (10) for the major occupied site

(18-Crown-6)(trifluoro­methane­sulfonato)­sodium

The title compound, [Na(CF3O3S)(C12H24O6)], features a sodium cation that is coordinated by eight O atoms in an irregular hexa­gonal bipyramidal environment. The equatorial positions are occupied by the six O atoms of an 18-crown-6 ether ring. In the axial positions, there is one O atom of a trifluoro­methane­sulfonate anion and an ether O atom of a symmetry-equivalent crown ether ring. In this way, centrosymmetric dimers are formed

Tetra­aceto­nitrile­lithium tetra­iso­thio­cyanato­borate

The crystal structure of the title salt, [Li(CH3CN)4][B(NCS)4], is composed of discrete cations and anions. Both the Li and B atoms show a tetra­hedral coordination by four equal ligands. The aceto­nitrile and iso­thio­cyanate ligands are linear. The bond angles at the B atom are close to the ideal tetra­hedral value [108.92 (18)–109.94 (16)°], but the bond angles at the Li atom show larger deviations [106.15 (17)–113.70 (17)°]

Dichloridobis(di-tert-butylmethylphosphine oxide-[kappa]O)diphenyltin(IV)

The complete molecule of the title compound, [Sn(C6H5)2Cl2(C9H21OP)2], is generated by crystallographic inversion symmetry, the Sn atom is located on a special position of site symmetry \overline{1}. The Sn atom adopts an all-trans SnC2O2Cl2 octahedral geometry. As a consequence of the bulky substituents at the O atom, the P-O-Sn bond angle is 163.9 (3)°. Key indicators: single-crystal X-ray study; T = 173 K; mean σ(C–C) = 0.012 Å; R factor = 0.058; wR factor = 0.099; data-to-parameter ratio = 18.6

The OPAL Equation of State and Low Metallicity Isochrones

The Yale stellar evolution code has been modified to use the OPAL equation of state tables (Rogers 1994). Stellar models and isochrones were constructed for low metallicity systems ($-2.8 \le [Fe/H] \le -0.6$). Above M\sim 0.7\,\msun, the isochrones are very similar to those which are constructed using an equation of state which includes the analytical Debye-Huckel correction at high temperatures. The absolute magnitude of the main sequence turn-off (\mvto) with the OPAL or Debye-Huckel isochrones is about 0.06 magnitudes fainter, at a given age, than \mvto derived from isochrones which do not include the Debye-Huckel correction. As a consequence, globular clusters ages derived using \mvto are reduced by 6 -- 7\% as compared to the ages determined from the standard isochrones. Below M\sim 0.7\,\msun, the OPAL isochrones are systematically hotter (by approximately 0.04 in B-V) at a given magnitude as compared to the standard, or Debye-Huckel isochrones. However, the lower mass models fall out of the OPAL table range, and this could be the cause of the differences in the location of the lower main-sequences.Comment: to appear in ApJ, 8 pages LaTeX, uses aaspptwo.sty. Complete uuencoded postscript file (including figures) available from: ftp://ftp.cita.utoronto.ca/cita/chaboyer/papers/opal.u

Zener diode function generator requires no external reference voltage

Function generator utilizing parallel impedance networks with zener diodes produces functions which are discontinuous in slope. The function generated appears at the output of the parallel network in the form of a voltage varying in time