Strukturänderungen bei der Reduktion von 9-(Diphenylmethyliden)fluoren mit Natrium-Metall zu Schichten (R2O)Na⊕-verknüpfter Kohlenwasserstoff-Dianionen

Structural Changes on Reduction of 9-(Diphenylmethylidene)fluorene by Sodium Metal to Sheets of (R₂O)Na⊕- Connected Hydrocarbon Dianions The single-crystal structure of 9-(diphenylmethylidene)fluorene (monoclinic, space group P2₁/n, Z = 4) proves a C?C bond length of 135 pm and a twisting of the two Ph rings out of the methylidene-fluorene plane by 70° and 83°. Its reduction in Et₂O solution by a Na mirror under Ar yields dark green crystals with a metallic luster. Their structure, determined in a N₂ flow cooled to 223 K (monoclinic, space group C2/c, Z = 4), reveals sheets of hydrocarbon dianions, connected by sodium(diethylether) links. The Na centers are sixfold coordinated as half-sandwiches to the fluorene benzo rings and threefold allylic to the Ph rings. In the dianion of 9-(diphenyl-methylidene)fluorene, the central C?C bond is stretched by 13 pm to 148 pm length, and the two molecular cyanine-like halves are twisted by 51° relative to each other. Both the contact-ion multiple structures as well as the structural changes on twofold reduction are discussed by way of comparison with literature examples and based on semiempirical calculations.     

Transient field measurements of g-factors for 24Mg AND 26Mg

The g-factors of the first-excited J^π = 2⁺ states of ²⁴Mg and ²⁶Mg have been measured with the ion-implantation perturbed angular correlation technique (IMPAC). The precession of the spins of nuclei recoiling into a magnetized iron backing is predominantly caused by the transient magnetic field for these very light and short-lived (τ_m ≈ 1 ps) nuclei. The transient field, which attains a value of 200 T for the Mg isotopes, is present only during the slowing-down of the recoiling nucleus and results in average precession angles of about 1.5 mrad. The experimental results are treated in the framework of the transient field theory of Lindhard and Winther. This yields g-factors of g = +0.42b ± 0.09 and g = +1.3 ± 0.3 for ²⁴Mg and ²⁶Mg, respectively. The results are compared with theoretical predictions and for ²⁴Mg also with a recent time-differential deorientation experiment.     

High energy final bands in Cu

We probe final energy bands of Cu in the kinetic energy range 20 eV ? E ?120 eV by angle resolved photoemission techniques. We observe deviations from free electron like behaviour in agreement with a LEED-type KKR calculation (Jepsen [5]). The lifetime broadening of the final bands at 60 eV kinetic energy is ～5 eV (FWHM).     

Large transient magnetic fields at high ion velocities in polarized iron

Nuclear spin precessions due to the transient magnetic field in polarized Fe have been measured as a function of the initial velocity of²⁸Si ions in the first-excited nuclear state. The transient field was found to increase linearly with the ion velocityv in the regionv/c=0.006–0.049. This is in contrast to the Lindhard and Winther model, which requires an inverse proportionality with ion velocity. Reanalysis of an earlier measurement on³⁰Si(2 ₁ ⁺ ) with the linear velocity dependence yields a reduced value for theg-factor ofg=0.37±0.12. Other available velocity-dependent data for²²Ne,⁵⁶Fe and¹⁹⁶Pt are consistent with a linear velocity dependence and suggest in addition a linear dependence on the nuclear charge Z of the moving ion. The increase of the transient field with recoil velocity can be explained semi-quantitatively by the capture of polarized Fe electrons into 1s and 2s vacancies in the moving ion. The velocity-dependent data and other discrepancies from the Lindhard and Winther model for¹⁶N,¹⁸O and very recently, for¹²C are also discussed in terms of the proposed microscopic model.     

Cationic rare-earth metal SALEN complexes

Complexes (Salpren(tBu,tBu))Y[N(SiHMe2)2](thf) and (SALEN(tBu,tBu))La[N(SiHMe2)2](thf) (SALEN(tBu,tBu) = Salcyc(tBu,tBu) and Salpren(tBu,tBu)) were prepared from Ln[N(SiHMe2)2]3(thf)2 and H2SALEN(tBu,tBu). The yttrium complex was characterized by X-ray crystallography revealing intrinsic solid-state structural features: the metal centre is displaced by 1.05 angstroms from the [N2O2] least squares plane of a highly bent Salpren(tBu,tBu) ligand (angle(Ph,Ph) dihedral angle of 80.4(1) degrees ) and is coordinated asymmetrically by the silylamide ligand exhibiting one significant Y---(HSi) beta-agostic interaction (Y-N1-Si1, 106.90(9) degrees; Y---Si1, 3.2317(6) angstroms). Complexes (SALEN(tBu,tBu))Ln[N(SiHMe2)2](thf)n (n = 1, Sc; n = 2, Y, La) react with ammonium tetraphenylborate to form the ion pairs [(SALEN(tBu,tBu))Ln(thf)n][BPh4]. The cationisation was proven by X-ray crystal structure analyses of [(Salpren(tBu,tBu))Sc(thf)2][B(C6H5)4].2(thf) and [(Salpren(tBu,tBu))Ln(thf)3][B(C6H5)4].4(thf) (Ln = Y, La), showing an octahedral and pentagonal-bipyramidal coordination geometry, respectively.