ABSTRACT
New nitridosilicates Ca(3)Sm(3)[Si(9)N(17)] and Ca(3)Yb(3)[Si(9)N(17)] were synthesized from the reactions of the pure metals (calcium and samarium/ytterbium) with silicon diimide "Si(NH)(2) " in a radio-frequency (rf) furnace at temperatures of up to 1650 °C. These isotypic compounds crystallize in the cubic space group P4(-)3m (no. 215) with lattice parameters a=739.50(3) pm; V=0.4044(1) nm(3); Z=1; wR(2) =0.029 (240 diffraction data, 26 parameters) for Ca(3)Sm(3)[Si(9)N(17)] and a=730.20(2) pm; V=0.3893(1) nm(3); wR(2) =0.039 (387 diffraction data, 27 parameters) for Ca(3)Yb(3)[Si(9)N(17)]. The new structure type of Ca(3)RE(3)[Si(9)N(17)] (RE=Sm, Yb) consists of two independent infinite networks, each of which have an expanded sphalerite (ZnS) topology in which the positions of the Zn and S atoms are replaced by voluminous [N([4])(SiN(3))(4)] units and [Si(5)N(16)] supertetrahedra, respectively, thereby displaying twofold interpenetration. As well, a structural description of Ca(3)Yb(3)[Si(9)N(17)], its thermal stability, and magnetic properties, as well as UV/Vis, IR, and Raman spectra, are presented.
ABSTRACT
The ternary iron arsenide BaFe2As2 becomes superconducting by hole doping, which was achieved by partial substitution of the barium site with potassium. We have discovered bulk superconductivity at T{c}=38 K in (Ba1-xKx)Fe2As2 with x approximately 0.4. The parent compound BaFe2As2 crystallizes in the tetragonal ThCr2Si2-type structure, which consists of (FeAs);{delta-} iron arsenide layers separated by Ba2+ ions. BaFe2As2 is a poor metal and exhibits a spin density wave anomaly at 140 K. By substituting Ba2+ for K+ ions we have introduced holes in the (FeAs);{-} layers, which suppress the anomaly and induce superconductivity. The T{c} of 38 K in (Ba0.6K0.4)Fe2As2 is the highest in hole doped iron arsenide superconductors so far. Therefore, we were able to expand this class of superconductors by oxygen-free compounds with the ThCr2Si2-type structure.
ABSTRACT
High-resolution X-ray diffraction data, in conjunction with DFT(B3LYP) quantum calculations, have been used in a QTAIM analysis of the charge density in the trimethylenemethane (TMM) complex Fe(eta(4)-C[CH(2)](3))(CO)(3). The agreement between the theoretical and experimental topological properties is excellent. Only one bond path is observed between the TMM ligand and the Fe atom, from the central C(alpha) atom. However, much evidence, including from the delocalization indices and the source function, suggests that there is a strong chemical interaction between the Fe and C(beta) atoms, despite the formal lack of chemical bonding according to QTAIM.
