Synthesis, crystal structure, resistivity, and electronic structure of the U(V) quaternary polyselenide Ba8PdU2Se12(Se2)2

Abstract

a b s t r a c tA new quaternary uranium(V) selenide, Ba 8 PdU 2 Se 12 (Se 2 ) 2 , has been synthesized by reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the compound crystallizes in a new structure type with two formula units in space group D Pnnm 2h 12 -of the orthorhombic crystal system with cell constants of a ¼9.490(1), b ¼12.240(2), and c¼ 13.780(3) Å. Its crystal structure consists of ⎡ ⎣ ⎤ ⎦ PdU Se 2 12 12− units where U atoms are coordinated to six Se atoms in octahedral geometry and Pd atoms are coordinated to four Se atoms in square-planar geometry. These ⎡ ⎣ ⎤ ⎦ PdU Se 2 12 12− units are separated by Ba to result in a salt-like crystal structure. This compound also contains Se 2 2− dimers that are part of Ba coordination polyhedra. The formula charge balances as (Ba 2 þ ) 8 (Pd 2 þ )(U 5 þ ) 2 (Se 2 À ) 12 (Se 2 2− ) 2 . Theoretical calculations predict antiferromagnetic semiconducting behavior for this compound with a band gap of 1.6 eV. Temperature-dependent four-probe resistivity measurements on single crystal confirm the semiconducting nature with an activation energy of 0.18(1) eV.

Synthesis and Crystal Structure of Cs2U2(P2Se9)(Se2)2

“…However, the U–Se distances in Cs 2 U 2 (P 2 Se 9 )(Se 2 ) 2 (data collection, 100 K) are smaller than those in the rubidium analogue Rb 2 U 2 (P 2 Se 9 )(Se 2 ) 2 (data collection, 293 K)where U was assigned a +5 oxidation state. This structure of Cs 2 U 2 (P 2 Se 9 )(Se 2 ) 2 also contains two distinct Se 2 2– species having distances of 2.403(1) and 2.409(1) Å, in good agreement with the corresponding distances in Ba 8 PdU 2 Se 12 (Se 2 ) 2 [2.392(1) and 2.407(1) Å], Cs 2 Th 2 (P 2 Se 9 )(Se 2 ) 2 [2.404(2) and 2.409(2) Å], and Rb 2 U 2 (P 2 Se 9 )(Se 2 ) 2 [2.411(4) and 2.413(4) Å] . These distances are slightly longer than the single Se bonds found in Ba 3 ThSe 3 (Se 2 ) 2 [2.374(1) and 2.377(1) Å], KU 2 SbSe 8 [2.356(5) to 2.375(4) Å], USe 3 (2.361 Å), KAuSe 5 [2.362(1) to 2.343(1) Å], Cs 4 Ge 2 Se 8 (2.350 Å), CsAuSe 3 (2.384 Å), and RbPdCu(Se 2 )(Se 3 ) [2.338(2) Å] .…”

Synthesis and Characterization of Ba2Ag2Se2(Se2)

“…The Se1 and Se4 atoms of the superstructure form Se1–Se4 dimers, i.e., Se 2 2– units. The Se1–Se4 distance of 2.378(2) Å is in good agreement with the single Se–Se bond distances found in orthorhombic CuSe [2.341(1) Å], KAuSe 5 [2.362(1)–2.343(1) Å], Cs 4 Ge 2 Se 8 [2.350(1) Å], CsAuSe 3 [2.384(1) Å], Ba 8 PdU 2 Se 12 (Se 2 ) 2 [2.392(1) and 2.407(1) Å], Cs 2 U 2 P 2 Se 9 (Se 2 ) 2 [2.403(1) and 2.409(1) Å], and Ba 3 ThSe 3 (Se 2 ) 2 [2.374(1) and 2.377(1) Å] …”

“…57 The Se1 and Se4 atoms of the superstructure form Se1−Se4 dimers, i.e., Se 2 2− units. The Se1−Se4 distance of 2.378(2) Å is in good agreement with the single Se−Se bond distances found in orthorhombic CuSe [2.341(1) Å], 58 KAuSe 5 [2.362(1)− 2.343(1) Å], 59 Cs 4 Ge 2 Se 8 [2.350(1) Å], 60 CsAuSe 3 [2.384(1) Å], 61 Ba 8 PdU 2 Se 12 (Se 2 ) 2 [2.392(1) and 2.407(1) Å], 62 Cs 2 U 2 P 2 Se 9 (Se 2 ) 2 [2.403(1) and 2.409(1) Å], 63 and Ba 3 ThSe 3 (Se 2 ) 2 [2.374(1) and 2.377(1) Å]. 46 Ba atoms in the superstructure of Ba 2 Ag 2 Se 2 (Se 2 ) are surrounded by eight Se atoms (two each of the Se1, Se2, Se3, and Se4 atoms) with Ba−Se distances ranging from 3.323(1) to 3.403(1) Å.…”

Synthesis, Crystal Structure, Theoretical, and Resistivity Study of BaUSe3

“…Examples of such compounds are AAn 2 Q 6 (An = Th, U, Np; Q = S, Se, and Te), 7−9 CsUTe 6 , 10 MU 8 Q 17 (M = transition metals, Q = S, Se), 11,12 MUQ 3 (M = Sc, Fe; Q = S, Se), 13,14 AMUQ 3 , 15,16 AMNpS 3 (M = Cu, Ag), 17 A 2 M 4 U 6 Q 17 (M = Pd, Pt), 18 A 2 M 3 UQ 6 (M = Pd, Pt), 19 ATiU 3 Te 9 , 20 Cs 2 Hg 2 USe 5 , 21 and AZrUTe 5 . 10,22 Recently, we have focused on the syntheses of new alkalineearth (Ak) metal containing actinide chalcogenides, such as Ba 2 AnS 2 (S 2 ) 2 (An = U, Th), 23 Ba 3 ThSe 3 (Se 2 ) 2 , 24 BaUS 3 , 25 AkAn 2 Q 5 (Ak = Ca, Sr, Ba, or Pb; An = U, Th; Q = S, Se, Te), 26,27 BaUTe 6 , 28 BaAnTe 4 (An = Th, U), 28 Ba 4 UQ 6 (Q = S, 25 Se 29 ), Ba 3 MUQ 6 (M = Mn, Fe, Ag; Q = S, Se), 29,30 Ba 2 MAnTe 7 (M = Ti, Cr; An = Th, U), 31 Ba 8 PdU 2 Se 12 (Se 2 ) 2 , 32 Ba 2 Cu 4 USe 6 , 33 and Ak 2 CuAnQ 5 . 33,34 These Ak-based compounds often show new structure types, and hence their crystal chemistry is different from their alkali-metal counterparts.…”

“…Recently, we have focused on the syntheses of new alkaline-earth (Ak) metal containing actinide chalcogenides, such as Ba 2 AnS 2 ­(S 2 ) 2 (An = U, Th), Ba 3 ThSe 3 ­(Se 2 ) 2 , BaUS 3 , AkAn 2 Q 5 (Ak = Ca, Sr, Ba, or Pb; An = U, Th; Q = S, Se, Te), , BaUTe 6 , BaAnTe 4 (An = Th, U), Ba 4 UQ 6 (Q = S, Se), Ba 3 MUQ 6 (M = Mn, Fe, Ag; Q = S, Se), , Ba 2 M­AnTe 7 (M = Ti, Cr; An = Th, U), Ba 8 Pd­U 2 Se 12 ­(Se 2 ) 2 , Ba 2 Cu 4 ­USe 6 , and Ak 2 Cu­AnQ 5 . , These Ak-based compounds often show new structure types, and hence their crystal chemistry is different from their alkali-metal counterparts. Here, we present the synthesis and characterization of the new ternary compound, BaUSe 3 , obtained by an exploratory study of the ternary Ba/U/​Se system.…”