Eu₂CuSe₃ Revisited by Means of Experimental and Quantum‐Chemical Techniques

Abstract

The bonding nature between chalcogenides and rare-earthelements is typically described as ionic in the spirit of the Zintl-Klemm formalism; yet, recent efforts showed that lanthanides also act as d-metals in transition-metal-post-transition-metalelement bonding. Hence, how can we describe the bonding nature between chalcogen and europium atoms, which have frequently acted as electron-donors like group-I/II-elements? To answer this question, we prototypically explored the electronic structure of Eu 2 CuSe 3 , which was obtained in considerable yields from solid-state reactions of the pure elements at 600°C.The crystal structure of Eu 2 CuSe 3 was determined based on Xray diffraction experiments and it is composed of diverse types of linear chains of selenium polyhedra enclosing the copper and europium atoms. These chains are condensed into 2 1 [EuCuSe 3 ] layers, which are separated by additional europium atoms. From analyses of the crystal structure and electronic structure of Eu 2 CuSe 3 , it is clear that there are two different europium valence states, whose nature controls if europium acts as an electron-donor like a group-I/II-element or as a dmetal.

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies

“…This contradicts the data obtained for the synthesized Eu +2 Eu +3 Cu +1 Se −2 3 , for which the structural type of Eu 2 CuS 3 with the cell parameters a = 10.773 (7) Å, b = 4.134(3) Å, c = 13.466(9) Å was established [31]. This compound was synthesized from elemental europium and selenium for about 400 h [31]. The resulting sample was contaminated by EuSe and an unidentified impurity.…”

“…Three structural types were predicted for EuLnCuSe 3 , namely KZrCuSe 3 (Ln = Nd-Lu, Y), BaLaCuS 3 (Ln = La-Pr) and NaCuTiS 3 for EuScCuSe 3 [32]. This contradicts the data obtained for the synthesized Eu +2 Eu +3 Cu +1 Se −2 3 , for which the structural type of Eu 2 CuS 3 with the cell parameters a = 10.773 (7) Å, b = 4.134(3) Å, c = 13.466(9) Å was established [31]. This compound was synthesized from elemental europium and selenium for about 400 h [31].…”

“…Two types of orthorhombic Pnma and one type of orthorhombic Cmcm crystal structures were revealed for EuLnCuSe3 (Figures 1 and 2). Compound EuLaCuSe3 belongs to the structural type Ba2MnS3, while compounds EuLnCuSe3 (Ln = Sm, Eu [31], Gd, Tb, Dy, Ho, Y) are isostructural to Eu2CuS3. These crystal structures have the same type of symmetry but differ in the system of bonds and coordination of Ln 3+ .…”

“…In the structure of EuLaCuSe3, the polyhedron EuSe7 is formed from two atoms of Se1 i , two atoms of Se1 ii , two atoms of Se2 i and one atom of Se3 (Table S4 in the Supplementary Materials) with all the Eu-Se distances being within the Two types of orthorhombic Pnma and one type of orthorhombic Cmcm crystal structures were revealed for EuLnCuSe 3 (Figures 1 and 2). Compound EuLaCuSe 3 belongs to the structural type Ba 2 MnS 3 , while compounds EuLnCuSe 3 (Ln = Sm, Eu [31], Gd, Tb, Dy, Ho, Y) are isostructural to Eu 2 CuS 3 . These crystal structures have the same type of symmetry but differ in the system of bonds and coordination of Ln 3+ .…”

“…Quaternary selenides, comprising copper and rare earth elements, are of particular interest due to a variety of different combinations of cations that enable the design of the structural type and band gap, as well as electrical and optical characteristics [1][2][3]8,[22][23][24][25][26][27][28][29][30][31][32][33]. Recent theoretical studies well predict thermoelectric properties of the copper-derived quaternary selenides [32,34,35], which are one of the promising alternatives to traditional thermoelectric materials.…”