Synthesis and characterization of Na2GdOPO4 and Na2LaOPO4

A new orthorhombic phase of previously reported orthorhombic Na2GdOPO4, sodium gadolinium oxyphosphate, was synthesized by solid state reactions starting with four different sets of chemicals at 1000 degrees C. The unit cell dimensions were calculated using its powder X-ray diffraction data and were found to be a = 14.709(6), b = 10.661(4) and c = 13.081(6) Angstrom and the space group is probably Pmm2 (No: 25). its monoclinic form was also obtained by further heating the orthorhombic phase at 1000 degrees C. The unit cell dimensions of the monoclinic form was found to be a = 14.719(5), b = 10.669(3), c = 13.091(5) Angstrom and beta = 92.274 degrees(2). Using the same procedure Na2LaOPO4 was also prepared the first time in this work through three sets of starting materials at 1000 degrees C. Na2LaOPO4 also crystallizes in the orthorhombic system with a = 13.657(5), b = 11.076(5), c = 6.730(3) Angstrom which seems to be isostructural with Na2GdOPO4 prepared before in our laboratory. The IR data of both Gd and La compounds agreed with the literature values. (C) 2000 Elsevier Science S.A. All rights reserved

[MU-BIS(DIALKYLPHOSPHINO)ALKANE]-BIS[PENTACARBONYLMETAL(0)] COMPLEXES OF THE GROUP-6B ELEMENTS - SYNTHESIS AND SPECTROSCOPIC STUDY

[mu-Bis(dialkylphosphino)alkane]-bis[pentacarbonylmetal(0)] complexes (CO)5MR2P(CH2)nPR2M(CO)5, (M: Cr, Mo, W; n: 1, 2, 3; R: CH3, C2H5, C6H5) were synthesized from the reaction of M(CO)5(CH3CN) with the appropriate ligand and characterized by means of IR and NMR (H-1, C-13, P-31) spectroscopy. Spectral data indicate that the complexes contain two identical M(CO)5 moieties linked to each other by the R2P(CH2)nPR2 ligand. Each metal atom has a pseudo-octahedral arrangement of the five CO ligands and one phosphorus atom

Magnetic properties of multiband U=infinity Hubbard model on anisotropic triangular and rectangular lattice strips

We study the dependence of the ground state spin of a multiband Hubbard model with infinite electron repulsion on anisotropic triangular and rectangular lattice strips on the model parameters. Considering the results of numerical calculations for the exact spectra of finite triangular lattice strips at different values of hopping integrals, we show the existence of a type of magnetic transitions with the jump of the ground state spin between minimal and maximal values. This transition is found only for special filling factors and when the lattice anisotropy parameter takes some critical value, which depends on the size of the lattice strip. Near this critical point two states with marginal values of the total spin, both of which can be a ground state before or after the transition, are locally stable against a few flips of spins. [S0163-1829(98)04241-6]

Structural studies of polypyrroles - II. A Monte Carlo growth approach to the branch formation

A simulation technique which is based on quantum mechanically generated probability distributions of alpha alpha, alpha beta and beta beta type linkages in polypyrroles is presented and applied for a statistical analysis of the growth process. The results show that the branching occur even at very short chains. The extent of the branching does not depend on the chain length and it is a slowly varying function of the temperature. At room temperatures, 20-25% deviations from the linearity is observed which is consistent with the experimental observations. (C) 1999 Elsevier Science S.A. All rights reserved

Effect of doping on the ground-state spin of stacked organometallic ferromagnets

The effective Hamiltonians that describe the low-lying energy states of some stacked organometallic ferromagnets with dopants have been derived. It is shown that the lattice stack with N unit cells and p conduction electrons has the ground-state spin S-0 = (N + p)/2 at p < N and S-0 less than or equal to (3N - p)/2 at N less than or equal to p < 2N. This means that the ferromagnetic ground state of metallocene-based donor-acceptor stack is unstable to the donor doping and is stable to the acceptor doping. (C) 1999 John Wiley & Sons, Inc