Predicting 9Be nuclear magnetic resonance chemical shielding tensors utilizing density functional theory

The structures of a series of beryllium containing complexes have been optimized at the B3LYP/6-31G(d) level and their (9)Be magnetic shielding values have been determined using B3LYP/6-311G+g(2d,p) and the gauge-including atomic orbital (GIAO) method. The calculated chemical shifts are in excellent agreement with experimental values. The performance of a variety of NMR methods (SGO, IGAIM, CSGT) were also examined but were found to be inferior to the GIAO method at the chosen level of theory employed. The theoretical method has been utilized to predict the beryllium chemical shifts of structurally characterized complexes for which no measured (9)Be NMR spectrum exists, and to investigate a literature complex with an unusual (9)Be NMR chemical shift. A new standard for beryllium NMR in nonaqueous solvents has been suggested.     

Chelated aluminum alkoxides

The present contribution will demonstrate that monomeric alkoxide compounds can be formed by the use of the Salen(tBu) ligand. These alkoxides, LAlOR (with L=Salen (tBu), R=Me (1), Salomphen(tBu), R=Me (3) and L=Salen(tBu), R=Et (4)) feature five-coordinate monomeric aluminum (Salen(tBu)=N,N-ethylenebis(3,5-di-tert-butylsalicylideneimine) and Salomphen(tBu)=N,N-(4,5-di-methyl)phenylenenebis(3,5-di-tert-butylsalicylideneimine). Crystallization of 1 from MeOH affords the six-coordinate complex, Salen(tBu)AlOMe(MeOH) (2). The manner in which these compounds may be obtained, as well as the structures of 2 and 4 will be described     

A new approach for the justification of ensembles in quantum statistical mechanics — II

The results of the first paper in this series are generalized to include spin, permutation symmetry, and time dependence. In particular, the question of time invariance of localness in the Heisenberg picture is discussed and it is conjectured that an operator that is initially local will remain local over time. In order to treat macroscopic systems, it is shown that the ensemble decomposition of the previous paper can be used to coarsegrain configuration space. Finally, a physical interpretation of the ensemble decomposition in terms of redundant macroscopic information is used to give a derivation of the generalized microcanonical average.This work was supported in part by research grants from the National Science Foundation and the U.S. Public Health Service. Some of the material in this paper is contained in a doctoral dissertation submitted by the author to the University of Oregon (1969).     

Critical voltage of a mesoscopic superconductor

We study the influence of a voltage-driven nonequilibrium of quasiparticles on the properties of short mesoscopic superconducting wires. We employ a numerical calculation based upon the Usadel equation. Going beyond linear response, we find a nonthermal energy distribution of the quasiparticles caused by the applied bias voltage. It is demonstrated that this nonequilibrium drives the system from the superconducting state to the normal state, at a current density far below the critical depairing current density.     

Enhancement of second harmonic generation efficiency: Growth and characterization of magnesium(II)-doped tetrakis(thiourea)nickel(II) chloride crystals

The influence of magnesium doping on the properties of tetrakis(thiourea)nickel(II) chloride crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy. The incorporation of Mg(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Lattice parameters are determined by single crystal XRD analysis. The thermogravimetric and differential thermal analysis studies reveal the purity of the materials and no decomposition is observed up to the melting point. The crystal is further characterized by Kurtz powder technique and dielectric studies.     

Electroexcitation of the first excited state in K

Electroexcitation of the first excited state in ³⁹K has been studied in the momentum transfer region of 0.8–2.5 fm⁻¹. Separation of the longitudinal and transverse form-factor components has been obtained. The longitudinal form factor has been analyzed model-independently. A B (M1) value for this l-forbidden transition was also obtained. Presently available theoretical predictions are unable to reproduce the B(M1) value or the transverse form-factor data.     

Controlling the transport of cations through permselective mesoporous alumina layers by manipulation of electric field and ionic strength

The electric field-driven transport of ions through supported mesoporous gamma-alumina membranes was investigated. The influence of ion concentration, ion valency, pH, ionic strength, and electrolyte composition on transport behavior was determined. The permselectivity of the membrane was found to be highly dependent on the ionic strength. When the ionic strength was sufficiently low for electrical double-layer overlap to occur inside the pores, the membrane was found to be cation-permselective and the transport rate of cations could be tuned by variation of the potential difference over the membrane. The cation permselectivity is thought to be due to the adsorption of anions onto the pore walls, causing a net negative immobile surface charge density, and consequently, a positively charged mobile double layer. The transport mechanism of cations was interpreted in terms of a combination of Fick diffusion and ion migration. By variation of the potential difference over the membrane the transport of double-charged cations, Cu2+, could be controlled accurately, effectively resulting in on/off tunable transport. In the absence of double-layer overlap at high ionic strength, the membrane was found to be nonselective.