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

Abstract

Abstract. The alkaline earth metal compounds AETMg 2 and AETCd 2 (AE = Ca, Sr; T = Pd, Ag, Pt, Au) were synthesized by inductionmelting (or in muffle furnaces) of the elements in sealed niobium ampoules. The new phases were characterized by powder X-ray diffraction. The structures of SrPdMg 2 and SrPdCd 2 were investigated by Xray diffraction on single crystals: MgCuAl 2 type, Cmcm, a = 436.42(4), b = 1130.1(1), c = 820.54 (7)

CaTMg2 and CaTCd2 (T =Rh, Pd, Pt) with YPd2Si-type Structure

“…1. Similar to the MgCuAl 2 -type phases [8,10], for CaPdMg 2 we also observe formation of a pronounced lonsdaleiterelated (hexagonal diamond) magnesium substructure. The Mg-Mg distances range from 306 to 327 pm, in close agreement with the average Mg-Mg distance of 320 pm in hcp magnesium [46].…”

“…We can thus expect substantial Mg-Mg bonding. In the magnesium substructures of the MgCuAl 2 -type phases one observes much longer Mg-Mg distances and larger anisotropy in Mg-Mg bonding [8].…”

“…In Fig. 2 we present cut-outs of the CaIn 2 [50], CaPdMg 2 , CaRhIn 2 [51], and SrPdMg 2 structures [8]. For each compound one layer of puckered hexagons and one Ca, CaPd, CaRh, and SrPd layer are shown.…”

“…Even more interesting is the result that MgCuAl 2 -type compounds are formed with two different alkaline earth elements, as shown by the synthesis of AETMg 2 (AE = Ca, Sr; T = Pd, Ag, Pt, Au) and isotypic SrT Cd 2 compounds [8]. To give an example, the magnesium atoms in CaAuMg 2 build up the orthorhombically distorted tetrahedral network, and the calcium atoms fill the typical cation position.…”

EuPtSn2 – A Stannide with Sn2 Dumbbells in a Three‐dimensional [PtSn2]2– Polyanion

“…Besides aluminides, gallides, indides, and thallides (isoelectronic but with distinctly different atomic / covalent radii), networks also form with magnesium and cadmium, e.g. SrPdMg 2 or LaNiCd 2 with a much lower electron count. The indides RE NiIn 2 ( RE = Ce, Pr, Nd, Sm, Gd) do not exactly meet the geometrical requirements for a MgCuAl 2 type structure.…”