Ungewöhnliche lineare, oligomere Anionen [Ga_nSe_2n+2]^{(n + 4)}- (n =2,4,6) in festen Selenogallaten des Cäsiums

Abstract

The crystal structures of the ternary selenogallates Cs 6 Ga 2 Se 6 , Cs 8 Ga 4 Se 10 , €8x003686,4 and CsGaSe 2 -I are characterized by the existence of linear oligimeric and polymeric anions [Ga n Se 2n+2 ] (,I+4)_ (« = 2,4,6, oo). These anions consist of edge sharing GaSe 4 -tetrahedra and show systematic geometrical variations of distances and angles which correlate with the degree of oligomerisation. In connection with the geometrical variations remarkable space filling changes are observed. Preliminary transmission measurements with small single crystals of the air sensitive compounds show an optical band gap of about 3 eV. A significant shift of the optical band gap to higher energies is observed and can be correlated with the length of the oligomeric anions and qualitative arguments about the chemical bonding in them. Einleitung

Synthesis, Crystal Structure, and Physical Properties of Two Polymorphs of CsGaSe2, and High-Temperature X-ray Diffraction Study of the Phase Transition Kinetics

“…Both distances and angles are in good agreement with comparable compounds. − ,− The bond lengths differ slightly from the sum of the ionic radii, d (Ga 3+ –Se 2– ) ∼ 2.5 Å. Four GaSe 4 tetrahedra share common corners to build Ga 4 Se 10 supertetrahedra.…”

“…The angles ∠(Se–Ga–Se) range from 100.48(1)° to 115.67(2)°. Both distances and angles are in good agreement with comparable compounds. − ,− The bond lengths are slightly smaller than the sum of the ionic radii d (Ga 3+ –Se 2– ) ∼ 2.5 Å. Each GaSe 4 tetrahedron is connected to two adjacent tetrahedra by common edges, resulting in an infinite anionic chain ∞ 1 [GaSe 2 – ] running along [001].…”

“…All previously known compounds in the system cesium, gallium, and selenium contain infinite one-dimensional selenogallate anions. The phases Cs 6 Ga 2 Se 6 , Cs 8 Ga 4 Se 10 , and Cs 10 Ga 6 Se 14 feature edge-sharing dimeric, tetrameric, and hexameric selenogallate units. Cs 2 Ga 2 Se 5 and CsGaSe 3 contain polychalcogenide units Se 2 2– , and consist of infinite anionic chains ∞ 1 [Ga 2 Se 3 (Se 2 ) 2– ] and ∞ 1 [Ga 2 Se 2 (Se 2 ) 2 2– ], respectively.…”

(Cs6Cl)6Cs3[Ga53Se96]: A Unique Long Period-Stacking Structure of Layers Made from Ga2Se6 Dimers via Cis or Trans Intralayer Linking

“…Each Ga atom is 4-fold-coordinated in a distorted tetrahedral sphere with the Ga–Se distance varying from 2.367(2) to 2.448(2) Å (Figure b). These distances are consistent with those of 2.349–2.528 Å in Cs 8 Ga 4 Se 10 , 2.363–2.451 Å in BaGa 4 Se 7 , and 2.386–2.411 Å in Ba 3 CsGa 5 Se 10 Cl 2 …”

In Situ X-ray Diffraction Study of the Thermal Decomposition of Selenogallates Cs2[Ga2(Se2)2–xSe2+x] (x = 0, 1, 2)

“…The crystal structures of CsGaSe 3 , Cs 2 Ga 2 Se 5 , and CsGaSe 2 - mC 16 , feature polymeric, anionic chalcogenogallate chains ∞ 1 [Ga 2 ( Q 2 ) 2– x Q 2+ x 2– ] ( Q = S, Se; x = 0, 1, 2) like the analogous sulfides, see Figure . CsGaSe 2 crystallizes in two polymorphic modifications with CsGaSe 2 - mC 16 being the high-temperature polymorph and CsGaSe 2 - mC 64 being the low-temperature polymorph .…”