Crystal Chemistry of the New Families of Interstitial Compounds R₆Mg₂₃C (R = La, Ce, Pr, Nd, Sm, or Gd) and Ce₆Mg₂₃Z (Z = C, Si, Ge, Sn, Pb, P, As, or Sb)

Abstract

The crystal chemical features of the new series of compounds R6Mg23C with R = La-Sm or Gd and Ce6Mg23Z with Z = C, Si, Ge, Sn, Pb, P, As, or Sb have been studied by means of single-crystal and powder X-ray diffraction techniques. All phases crystallize with the cubic Zr6Zn23Si prototype (cF120, space group Fm3̅m, Z = 4), a filled variant of the Th6Mn23 structure. While no Th6Mn23-type binary rare earth-magnesium compound is known to exist, the addition of a third element Z (only 3 atom %), located into the octahedral cavity of the Th6Mn23 cell (Wyckoff site 4a), stabilizes this structural arrangement and makes possible the formation of the ternary R6Mg23Z compounds. The results of both structural and topological analyses as well as of LMTO electronic structure calculations show that the interstitial element plays a crucial role in the stability of these phases, forming a strongly bonded [R6Z] octahedral moiety spaced by zeolite cage-like [Mg45] clusters. Considering these two building units, the crystal structure of these apparently complex intermetallics can be simplified to the NaCl-type topology. Moreover, a structural relationship between RMg3 and R6Mg23C compounds has been unveiled; the latter can be described as substitutional derivatives of the former. The geometrical distortions and the consequent symmetry reduction that accompany this transformation are explicitly described by means of the Bärnighausen formalism within group theory.

Synthesis and structure determination of Ce6Cd23Te: a new chalcogen-containing member of theRE6Cd23T family (REis a rare-earth metal and T is a late group 14, 15 and 16 element)

“…The latter observation was backed up by similar findings for the RE 6 Mg 23 T series (Wrubl et al, 2016). The latter observation was backed up by similar findings for the RE 6 Mg 23 T series (Wrubl et al, 2016).…”

“…In addition to our previous report on the RE 6 Cd 23 T series of compounds, with RE being La-Nd, Sm, and Gd, and T being Sn, Pb, Sb, and Bi (Desroches & Bobev, 2017), the crystal ISSN 2053ISSN -2296 # 2017 International Union of Crystallography chemistry of the Mg-based RE 6 Mg 23 T counterparts has also been established (Wrubl et al, 2016), in addition to that of La 6 Mg 23 Si and Er 6 Zn 23 Ge (De Negri et al, 2009;Solohka et al, 2016). In addition to our previous report on the RE 6 Cd 23 T series of compounds, with RE being La-Nd, Sm, and Gd, and T being Sn, Pb, Sb, and Bi (Desroches & Bobev, 2017), the crystal ISSN 2053ISSN -2296 # 2017 International Union of Crystallography chemistry of the Mg-based RE 6 Mg 23 T counterparts has also been established (Wrubl et al, 2016), in addition to that of La 6 Mg 23 Si and Er 6 Zn 23 Ge (De Negri et al, 2009;Solohka et al, 2016).…”

Crystal Chemistry of RE6MgxCd23–xPb [0.6(1) ≤ x ≤ 3.2(1); RE = La and Ce]. New Mixed‐Metal Derivatives of the RE6Cd23T Phases (T = Group 14/15/16 Element)

“…From Figure , the presence of a non‐zero electronic density of states (DOS) at the Fermi level ( E F ) indicates an overall metallic character for the studied system, in line with previous observations of RE 6 Mg 23 T . Below the Fermi level, the Cd 5 p and La 5 d bands exhibit a great degree of overlap, which indicates some p–d hybridization between the two.…”

“…The title compounds adopt the same structure as RE 6 Mg 23 T and RE 6 Cd 23 T -localized covalent RE 6 T clusters within an extended metallic Cd sub-structure. [20][21][22] Thus, many of the structural descriptions given in our earlier work still apply, to which we refer the reader for a more exhaustive description. [21,22] To maintain consistency with our previous work, all present discussion also follow the f 2 edba Wyckoff scheme, with position 4b occupied by Pb.…”

“…[8,15] In the latter case, the four Mn 23 positions need not experience the same degree of mixed occupancy, and a more ordered distribution may be favored at certain sites due to electronic, magnetic, and/or volume effects. [15] Other literature findings suggest that the chemical make-up of the Mn 23 sub-structure greatly influences the compound's bulk properties, [6,[19][20][21][22] which may open ARTICLE the door for tuning of physical properties through substitutional chemistry.…”