MgCuAl₂-type Intermetallics REPdCd₂(RE = Ce, Pr, Nd, Sm)

Abstract

The cadmium-rich intermetallic compounds REPdCd 2 (RE = Ce, Pr, Nd, Sm) were obtained by high-frequency melting of the elements in sealed niobium ampoules and subsequent annealing in muffle furnaces. The REPdCd 2 phases crystallize with the orthorhombic MgCuAl 2 -type structure, space group Cmcm. The structure of NdPdCd 2 was refined from single-crystal X-ray diffractometer data: a = 421.9(3), b = 995.4(7), c = 834.5(6) pm, wR = 0.0286, 451 structure factors, 16 variables. The palladium and cadmium atoms build up a three-dimensional [PdCd 2 ] network (281 -283 pm Pd-Cd; 298 -335 pm Cd-Cd) in which the neodymium atoms fill cavities. They are connected to the [PdCd 2 ] network via shorter Nd-Pd bonds of 286 pm.

Magnesium and Cadmium in Covalently‐Bonded Lonsdaleite Networks: Synthesis, Structure, and Bonding of AETMg2 and SrTCd2 (AE = Ca, Sr; T = Pd, Ag, Pt, Au)

“…The diffractometer data sets of SrPdMg 2 and SrPdCd 2 showed C centered orthorhombic lattices and the systematic extinctions were compatible with space group Cmcm (MgCuAl 2 type1,2) in accordance with our earlier work on the RET Mg 2 and RE PdCd 2 phases 13,15. Consequently, the atomic parameters of NdPdCd 2 15 were taken as starting parameters and the two structures were refined using SHELXL‐9735,36 (full‐matrix least‐squares on F 2 ) with anisotropic atomic displacement parameters for all atoms. As a check for the correct composition (defects were observed for several MgCuAl 2 phases), the occupancy parameters were refined in a separate series of least‐squares cycles.…”

“…The palladium and cadmium atoms build up a three‐dimensional [PdCd 2 ] polyanionic network with Pd–Cd distances of 283 and 284 pm, longer than the sum of the covalent radii of 269 pm 37. A similar range of Pd–Cd distances is observed in isotypic NdPdCd 2 (281–283 pm) 15. The Cd–Cd distances within the cadmium substructure of SrPdCd 2 vary from 314 to 329 pm.…”

“…The platinum atoms build up the three‐dimensional network of distorted tetrahedra. (iii) The rare earth ( RE ) based magnesium compounds RET Mg 2 ( RE = La, Pr, Nd; T = Ni, Pd, Pt)12,13 as well as the cadmium intermetallics RE PdCd 2 ( RE = La, Ce, Pr, Nd, Sm) and PrNi 0.951 Cd 2 14,15 are further examples for magnesium and cadmium on the covalently bonded tetrahedral network.…”

Magnetic phase separation in the EuPdSn2ground state

“…hexagonal diamond), which can be easily evidenced when the relationship with the hexagonal CaIn 2 phase is considered. 39–41 Although covalent bonds were often described within such substructures, further interactions among the constituents make the bonding scenarios much more complicated. 33–35 According to the Pearson's crystal database, 42 only eight stannides show the MgCuAl 2 -type structure and the chemical bonding was analyzed for five of them: CaTSn 2 (T = Rh, Pd, Ir) 21 and AEIrSn 2 (AE = Sr, Ba).…”