BaCu6P2 and BaCu6As2 — two compounds with a periodic intergrowth of ThCr2Si2 and Cu structure-type segments

Experimental and Theoretical Studies on the Crystal Structure of Ternary Copper Arsenides A2Cu3As3 (A = Sr, Eu)

“…The Cu1-As2 bond length of 2.461 Å still falls into a reasonable range, whereas the distance between the Cu1-Cu1 pair is abnormally short (2.375 Å) compared with those of other copper arsenide analogues, for example, 2.559 to 2.978 Å in BaCu 6 As 2 . [26] The solved structure results in the composition Eu 2 Cu 4 As 2 , which is also significantly different from those suggested by the EDX measurements, that is, Eu 2 Cu 3 As 3 and Sr 2 Cu 3 As 3 (Supporting Information). In another attempt, this position was refined with an As1 atom, and the resultant formula was Eu 2 Cu 2 As 4 , which is isotypic to the CeNiSi 2 structure.…”

“…However, the coordination environment of Cu1 seems very unusual: it adopts a planar triangular coordination fashion with short bonds to two Cu1 atom and one As2 atom. The Cu1–As2 bond length of 2.461 Å still falls into a reasonable range, whereas the distance between the Cu1–Cu1 pair is abnormally short (2.375 Å) compared with those of other copper arsenide analogues, for example, 2.559 to 2.978 Å in BaCu 6 As 2 . The solved structure results in the composition Eu 2 Cu 4 As 2 , which is also significantly different from those suggested by the EDX measurements, that is, Eu 2 Cu 3 As 3 and Sr 2 Cu 3 As 3 (Supporting Information).…”

“…The probable reason is that the Cu 3d orbitals are not usually in strict closed‐shell configurations. In some cases, Cu–Cu interactions should even be counted . Owing to their complex crystal structures, the magnetic properties of these phases are also interesting.…”

“…In some cases, Cu-Cu interactions should even be counted. [26] Owing to their complex crystal structures, the magnetic properties of these phases are also interesting. Ferromagnetism was demonstrated for the euro-4.2552(6)/4.2096(5) Å for the Sr-and Eu-containing compounds, respectively.…”

“…The A–Cu–Pn ternary system (A = alkaline‐earth or rare‐earth metal, Pn = P, As) constitutes a huge family, and the relevant structural units are very flexible . In addition to the compounds based on simple CuPn 4 tetrahedra such as CaCu 2 As 2 and BaCu 2 As 2 , other copper‐rich or clathrate‐like analogues with very complex anions such as Ba 8 Cu 18– x As 10 and Eu 7 Cu 44 As 23 are also commonly seen, and the electrons in these compounds cannot be counted by the octet rule.…”