H-C-SiH3: direct generation and spectroscopic identification of ethylidene's cousin

Ground-state triplet silaethylidene, generated directly by the reaction of 3P carbon atoms with silane under matrix isolation conditions in solid Ar (10-12 K), has been thoroughly characterized by the EPR and IR spectra of both the parent and perdeuterated isotopologs. A theoretical anharmonic vibrational analysis based on a CCSD(T)/cc-pVTZ complete quartic force field gave remarkable agreement with the experimental IR fundamentals, generally within 10 cm-1 and without any empirical scaling of the ab initio frequencies. Silaethylidene exhibits a Cs minimum with a H-C-Si angle near 153 degrees , but the barrier to H-C-Si linearity (C3v symmetry) is only 0.24 kcal mol-1. This minuscule barrier can be surmounted by zero-point vibrations, as evident from the EPR data. The triplet stabilizing effect of the electropositive SiH3 group amounts to about 15 kcal mol-1.     

The dependence of 13C-1H coupling constants on CCC bond angles

The relationship between one-bond ¹³C-¹H coupling constants and internuclear CCC bond angles (_n) in hydrocarbons of the type R₂CH₂ is best approximated by a quadratic expression.     

A semilinear elliptic equation with a mild singularity at u = 0: Existence and homogenization

In this paper we consider singular semilinear elliptic equations whose prototype is the following

$\{\begin{array}{cc}?divA(x)Du=f(x)g(u)+l(x)\hfill & \text{in}\mathrm{\Omega },\hfill \\ u=0\hfill & \text{on}?\mathrm{\Omega },\hfill \end{array}$

where Ω is an open bounded set of ${\mathbb{R}}^N,N\ge 1$, $A\in L^{\infty }{(\mathrm{\Omega })}^{N\times N}$ is a coercive matrix, $g:[0,+\infty [\to [0,+\infty ]$ is continuous, and $0\le g(s)\le \frac{1}{s^{\gamma }}+1$ for every $s>0$, with $0<\gamma \le 1$ and $f,l\in L^r(\mathrm{\Omega })$, $r=\frac{2N}{N+2}$ if $N\ge 3$, $r>1$ if $N=2$, $r=1$ if $N=1$, $f(x),l(x)\ge 0$ a.e. $x\in \mathrm{\Omega }$.We prove the existence of at least one nonnegative solution as well as a stability result; we also prove uniqueness if $g(s)$ is nonincreasing or “almost nonincreasing”.Finally, we study the homogenization of these equations posed in a sequence of domains ${\mathrm{\Omega }}^{\epsilon }$ obtained by removing many small holes from a fixed domain Ω.     

Synthese und Kristallstruktur des gemischt‐valenten Komplexes [Sn2I3(NPPh3)3]

Synthesis and Crystal Structure of the Mixed Valent Complex [Sn₂I₃(NPPh₃)₃] The mixed valent phosphoraneiminato complex [Sn₂I₃(NPPh₃)₃] ( 1 ) was prepared by the reaction of the tin(II) complex [SnI(NPPh₃)]₂ with sodium in tetrahydrofuran. 1 crystallizes with two formula units of THF to form yellow, moisture sensitive single crystals, which were characterized by a crystal structure determination. 1 · 2 THF: Space group P2₁/c, Z = 4, lattice dimensions at –80 °C: a = 1964.5(2), b = 1766.0(2), c = 2058.6(2) pm; β = 118.33(1)°, R = 0.052. 1 forms dimeric molecules in which the tin atoms are linked by two nitrogen atoms of two (NPPh₃^–) groups to form a planar Sn₂N₂ four‐membered ring. The Sn^IV atom is additionally coordinated by a terminal iodine atom and by a terminal (NPPh₃^–) group, whereas the Sn^II atom is additionally coordinated by two iodine atoms forming a ψ trigonal‐bipyramidal surrounding.     

Enthalpies of formation of solid cobalt-tellurium alloys

The enthalpies of formation of solid Co?Te alloys were determined at room temperature with an isoperibol solution calorimeter of the submarine type. Co?Te alloys and mechanical mixtures of the pure components were dissolved in separate experiments in a saturated hydrochloric acid (8.000n)—bromine mixture and the enthalpies of formation obtained by difference. For the NiAs-type β-phase ΔH _f ^o(N_Te)=(4.079–15.017N _Te) kcal·g-atom^?1 and for the marcasitetype γ-phase ΔH _f ^o(N _Te)=(3.787–14.400N _Te) kcal·g-atom^?1. Combining these results with data from the literature integral thermodynamic properties of solid Co—Te alloys were calculated at room temperature and at 600°C.     

On the successive minima of a bounded star domain

Sunto. è dato nel seguente capoverso

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Dedicated to Max Dehn.