The charge distribution in chromium(III) and iron(III) hexafluoride

Semi-empirical molecular orbital calculations were performed for CrF^3?₆ and FeF^3?₆. The method of calculation is derived from the HF SCF equations using approximations appropriate to the highly ionic transition metal halides. The results of these calculations are shown to be in better agreement than previous semis-empirical calculations with X-ray emission line shifts and atom charges and populations estimated from these shifts.     

Self consistent modified extended Hückel (SC-MEH) calculations on heavy metal systems. I. Platinum(II) tetragonal planar complexes with and without relativistic effects

The Self Consistent Modified Extended Hückel molecular orbital method had been applied to several square planar complexes of platinum (II). Calculations including both the limited 5d, 6s, 6p and extended 5s, 5p, 5d, 6s, 6p starting bases for platinum were made. It is shown that in PtCl ₄ ^2– both the nuclear quadrupole moment and minimum total energy vs. bond distance are calculated to be in good agreement with experiment, only with the extended platinum AO basis.Specific inclusion of relativistic parameters via a pseudo-relativistic approximation are shown to have a significant effect on the energy molecular energy levels, however no meaningful rationalization can be made without the simultaneous inclusion of ligand field parameters as well.Supported in part by a grant made available through the Cancer Association of Greater New Orleans. Use of the facilities of the Computer Research Center of the University of New Orleans is gratefully acknowledged.     

Systematic generation of random networks

This paper reports the computer generation of atomic models for amorphous tetrahedrally coordinated materials. Several approaches are used and their results are intercompared in terms of careful statistical studies on each structure. The best approach is capable of automatically building large models with no included voids or dangling bonds. The strain energies are minimized for each structure implying that they represent metastable equilibrium arrangements; the radial distribution functions are in excellent agreement with experimental data. The programs developed are capable of building models which vary systematically as measured by several parameters including the ratio of five to six membered rings and the average distortion of the tetrahedra formed by near neighbors.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

An olefin polyanion equivalent: A new olefin synthesis from triflones

α-Trifyl-dimethylsulfone (CF₃SO₂CH₂SO₂CH₃) is a reagent which allows successive polyalkylation of the two carbons with regiocontrol. The polyalkylated trifyl-sulfone then undergoes a Ramberg-Bäcklund reaction with loss of triflinate anion and extrusion of SO₂ to form an olefin. In synthetic terms the net structural change is equivalent to regiospecific alkylation of an olefin polyanion, =CC=.     

SCMEH-MO calculations on lanthanide systems. III. Ln(CO)6, Ln(OC)6 (Ln = Nd,Sm)

The SCMEH-MO method with average relativistic and spin-orbit effects has recently been applied to study the electronic structure and bonding in samarium pentamethylcyclopentadienyls. In this report the same approach has been utilized in studying the electronic structures of Nd and Sm hexacarbonyls. In contrast to the stable transition metal d-block carbonyls, these lanthanide carbonyls are found to be quite unstable. These findings are based on calculated electronic structures and bond energies. © 1996 John Wiley & Sons, Inc.     

Erratum: E.A. Boudreaux and E. Baxter, “More QR‐SCMEH‐MO calculations on group VIB transition metal molecules,M2 (M = Cr,Mo, W,Sg) valence and valence‐core effects,” International Journal of Quantum Chemistry(2004) 100(6)1170–1178

The original article to which this Erratum refers was published in International Journal of Quantum Chemistry (2004) 100(6) 1170–1178.     

Calculations of the strength of the polyethylene molecule

A theoretical determination of the elastic modulus, the breaking strength, and breaking strain is made for a single infinitely long molecule of polyethylene (CH₂)_∞. These results are compared with those of a similar calculation on a molecule of polyethylene with a side chain attached. It is found that the presence of a side chain weakens the molecule by approximately 17%.     

Calculations of bond dissociation energies. New select applications of an old method

Application of Sanderson's definition of electronegativity as stability ratios (SRs), which BE = [E(i) + E(DA)] (IC) + E(cov) had been applied in the past to a wide variety of organic and nontransitional metal inorganic compounds with very good success, has been revived, modified so as to be applied to any types of molecules, including those containing transition metals, lanthanides, and actinides. This paper is limited to a demonstration of the method which is applied to a few metal cyclopentadienyl compounds, plus specific emphasis on the U(III) metallocene (CpSiMe(3))(3)U-AlCp* recently prepared by Arnold and co-workers having no experimental bond energies available. It is shown that computed bond energies of pertinent metallocyclopentadieneyls are in excellent agreement with the available experimental data. Calculated bond energies for all essential bonds in the uranium metallocene cited above are provided together with a further analysis of the bonding and magnetic properties of this unique compound.