Long-range ordered magnetic structures in Li2MnSiO4and Li2CoSiO4

The lithium orthosilicates Li2MnSiO4 and Li2CoSiO4 have been synthesized by solid state reaction and characterized using X-ray powder diffraction (XRD), magnetic susceptibility measurement, heat capacity and neutron powder diffraction (NPD). The monoclinic Li2MnSiO4 and orthorhombic Li2CoSiO4 compound were found to be antiferromagnetically ordered below Neel temperature = ~12 K and ~13 K respectively. The ordered magnetic structures of both compounds have been solved for the first time using low temperature neutron diffraction data. The magnetic structure of Li2CoSiO4 can be described as antiferromagnetic quasi-layers stacked along the a-axis. The ordered magnetic moments of the Co2+ and Mn2+ are aligned perpendicularly and obliquely to the distorted closed-packed layers of oxygen atoms and the values, 2.9 bohr magneton and 4.6 Bohr magneton, are close to the expected values for d7 Co2+ and d5 Mn2+, respectively. The origin of these complex magnetic structures will be discussed in terms of super-superexchange interactions among the transition metal ions, mediated by bridging SiO4 tetrahedra. Figure 1: Magnetic sublattices in Li2CoSiO4 (left) and Li2MnSiO4 (right) with respect to crystal structure. Blue, yellow, and light and dark green show the M, Si, and Li1 and Li2 sites in Pbn21 Li2CoSiO4 and P21/n Li2MnSiO4.

Kinetic Studies of Reduction of Tris-(1,1,1,5,5,5-hexafluoroacetylacetonato) ruthenium(III) in Methanol, Ethanol and Propanol

The complex tris-(1,1,1,5,5,5-hexafluoroacetylacetonato-) ruthenium(III), hereafter referred to as Ru(hfacac)3, has been synthesized. Ultraviolet and visible spectroscopic measurements of the complex in ethanol revealed three prominent absorption bands at 287, 374 and 525 nm with molar absorptivity coefficients of 4.113, 3.885 and 3.59 respectively. Magnetic susceptibility measurements between 78 and 296 K revealed the complex to assume a low spin configuration of e0t2g5and an oxidation state of +3 as inferred from a value of 1.92 Bohr magneton. Kinetic investigation of the reduction of the complex in methanol, ethanol and propanol indicate the reduction to proceed in the order methanol > ethanol > propanol. The energies of activation of the reduction in methanol and ethanol were found to be 85.4 and 108 kJ/mol respectively.