Amine- and phosphine-borane adducts: new interest in old molecules.

A compendium of phase change enthalpies published in 2010 is updated to include the period 1880–2015. Phase change enthalpies including fusion, vaporization, and sublimation enthalpies are included for organic, organometallic, and a few inorganic compounds. Part 1 of this compendium includes organic compounds from C1 to C10. Part 2 of this compendium, to be published separately, will include organic and organometallic compounds from C11 to C192. Sufficient data are presently available to permit thermodynamic cycles to be constructed as an independent means of evaluating the reliability of the data. Temperature adjustments of phase change enthalpies from the temperature of measurement to the standard reference temperature, T = 298.15 K, and a protocol for doing so are briefly discussed.

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2015. Part 1. C1-C10

Ab initio STO-3G molecular orbital theory has been used to calculate energy-optimized Si-O bond lengths and angles for molecular orthosilicic and pyrosilicic acids. The resulting bond length for orthosilicic acid and the nonbridging bonds for pyrosilicic acid compare well with Si-OH bonds observed for a number of hydrated silicate minerals. Minimum energy Si-O bond lengths to the bridging oxygen of the pyrosilicic molecule show a close correspondence with bridging bond length data observed for the silica polymorphs and for gas phase and molecular crystal siloxanes when plotted against the SiOSi angle. In addition, the calculations show that the mean Si-O bond length of a silicate tetrahedron increases slightly as the SiOSi angle narrows. The close correspondence between the Si-O bond length and angle variations calculated for pyrosilicic acid and those observed for the silica polymorphs and siloxanes substantiates the suggestion that local bonding forces in solids are not very different from those in molecules and clusters consisting of the same atoms with the same coordination numbers. An extended basis calculation for H4SiO4 implies that there are about 0.6 electrons in the 3d-orbitals on Si. An analysis of bond overlap populations obtained from STO-3G* calculations for H6Si2O7 indicates that Si-O bond length and SiOSi angle correlations may be ascribed to changes in the hybridization state of the bridging oxygen and (d – p) π-bonding involving all five of the 3d AO's of Si and the lone-pair AO's of the oxygen. Theoretical density difference maps calculated for H6Si2O7 show a build-up of charge density between Si and O, with the peak-height charge densities of the nonbridging bonds exceeding those of the bridging bonds by about 0.05 e A−3. In addition, atomic charges (+1.3 and −0.65) calculated for Si and O in a SiO2 moiety of the low quartz structure conform reasonably well with the electroneutrality postulate and with experimental charges obtained from monopole and radial refinements of diffraction data recorded for low quartz and coesite.

Ab initio calculated geometries and charge distributions for H 4 SiO 4 and H 6 Si 2 O 7 compared with experimental values for silicates and siloxanes

Durch die vor einigen Jahren gefundene photochemische Reaktion von n- und π-Donatoren mit Metallcarbonylen oder deren Derivaten kann man ein breites Spektrum neuer Metallcarbonyl-Derivate herstellen, welche thermisch nicht oder nur mit schlechten Ausbeuten zu erhalten sind. — Praparative Verfahren werden beschrieben. An ausgewahlten Beispielen wurde der Reaktionsmechanismus dieser photochemisch induzierten Substitutionsreaktionen aufgeklart und versucht, einen Einblick in die Polaritat der Metall-Liganden-Bindung zu erhalten. — Dieser Beitrag soll einen Uberblick uber die in letzter Zeit auf diesem Gebiet erschienenen Arbeiten geben.

Photochemische Substitutionen an Metallcarbonylen und deren Derivaten

F.G.A. Stone

Papers

Vinyl Derivatives of the Metals. I. Synthesis of Vinyltin Compounds

The Relative Stabilities of Some Molecular Addition Compounds of Boron.

Chemistry of the metal carbonyls—IX: Diene complexes of iron

Vinyl Derivatives of the Metals. VI. Preparation, Properties and Some Reactions of Trivinyl Compounds of Group V Elements1,2

The chemistry of silicon involving probable use of d-type orbitals