Tm_2.22Co₆Sn₂₀and TmLi₂Co₆Sn₂₀stannides as disordered derivatives of the Cr₂₃C₆structure type

Abstract

A new ternary dithulium hexacobalt icosastannide, Tm2.22Co6Sn20, and a new quaternary thulium dilithium hexacobalt icosastannide, TmLi2Co6Sn20, crystallize as disordered variants of the binary cubic Cr23C6 structure type (cF116). 48 Sn atoms occupy sites of m.m2 symmetry, 32 Sn atoms sites of .3m symmetry, 24 Co atoms sites of 4m.m symmetry, eight Li (or Tm in the case of the ternary phase) atoms sites of -3 symmetry and four Tm atoms sites of m3m symmetry. The environment of one Tm atom is an 18-vertex polyhedron and that of the second Tm (or Li) atom is a 16-vertex polyhedron. Tetragonal antiprismatic coordination is observed for the Co atoms. Two Sn atoms are enclosed in a heavily deformed bicapped hexagonal prism and a monocapped hexagonal prism, respectively, and the environment of the third Sn atom is a 12-vertex polyhedron. The electronic structures of both title compounds were calculated using the tight-binding linear muffin-tin orbital method in the atomic spheres approximation (TB-LMTO-ASA). Metallic bonding is dominant in these compounds, but the presence of Sn-Sn covalent dumbbells is also observed.

Thulium nickel/lithium distannide, TmNi1−xLixSn2(x= 0.035)

“…The ability of lithium atoms to partially substitute the atoms of transition metals was previously observed by us while studying solid solutions RELi x Cu 2-x Si 2 and RELi x Cu 2-x Ge 2 (Pavlyuk et al, 1993). The ordered substitution of transition metals by lithium is observed for Tm 2.22 Co 6 Sn 20 and TmLi 2 Co 6 Sn 20 stannides (Stetskiv et al, 2013). The ability of lithium atoms to occupy the same crystallographic position as the atoms of transition metal was observed previously while studying compounds RELiGe with the ZrNiAl-type (Pavlyuk et al, 1991 andBodak, 1992a), RE 3 Li 2 Ge 3 with Hf 3 Ni 2 Si 3 -type (Pavlyuk & Bodak, 1992b) and…”

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)

“…The large, highly symmetric cubic unit cell of Th 6 Mn 23 contains one Th site (Wyckoff position 24 e ) and four Mn sites (2 × 32 f , 24 d , and 4 a ). Since its discovery, the chemistry within this structure type has proven rich and varied, as shown in the wide array of binary, ternary, and quaternary derivatives that have been discovered so far . This structure type also features a sizeable void at Wyckoff position 4 a .…”

“…The compounds found within this structure type need not conserve the 6:23 stoichiometric ratio, and in fact, a wide array of unique chemical formulae are known (Table S1, Supporting Information) . Such diverse stoichiometries, e.g.…”

The Ce2Li0.39Ni1.61Si2structure as a new derivative of the AlB2family

“…The ability of Li atoms to partially substitute transition metal atoms was observed previously by us while studying solid solutions RELi x Cu 2-x Si 2 and RELi x Cu 2-x Ge 2 (Pavlyuk et al, 1993), TbLi 1-x Zn x Sn 2 (Stetskiv et al, 2012) and TmNi 1-x Li x Sn 2 (Stetskiv et al, 2013a), and ternary phases Li 2-x Ag 1+x In 3 (Chumak et al, 2013) and Li 18 Cu 15 Al 7 (Dmytriv et al, 2010). The ordered distribution of transition-metal and Li atoms in separate crystallographic sites was indicated for the TmLi 2 -Co 6 Sn 20 phase, which crystallizes as a derivative variant of the binary cubic Cr 23 C 6 structure type (Stetskiv et al, 2013b). The Li atoms occupy the same crystallographic positions as the transition-metal atoms in previously studied ternary phases RELiGe with the ZrNiAl structure type (Pavlyuk et al, 1991;Pavlyuk & Bodak, 1992a) and RE 3 Li 2 Ge 3 with the Hf 3 Ni 2 Si 3 structure type (Pavlyuk & Bodak, 1992b).…”