Powerful Templating Effect in Rb/Pd/Se_x Promoted by Crown Ether-like [Rb(Se₈)]⁺ Coordination. Formation of Rb₂[Pd(Se₄)₂]·Se₈:  A Layered Pd Polyselenide with “Encapsulated” Eight-Membered Selenium Rings

Abstract

A novel layered Rb−Pd polyselenide has been synthesized by methanothermal reaction of Pd2+ with Se x 2- (from Se2- + Se) in the presence of Rb2CO3. Rb2[Pd(Se4)2]·Se8 (I) reveals a unique structure with infinite [Pd(Se4)2]2- sheet polyanions acting as a host for neutral Se8 rings. The black shiny rectangular crystals of Rb2[Pd(Se4)2]·Se8 are insoluble in H2O and common organic solvents. The compound crystallizes in the noncentrosymmetric space group P4̄b2 (No. 117) with a = 12.6748(8) Å, c = 6.9273(7) Å, Z = 2, and V = 1112.9(2) Å3. The [Pd(Se4)2]2- sheet anion contains Pd2+ ions with a distorted square planar coordination geometry to four terminal Se atoms of Se4 2- chains. The cocrystallized neutral Se8 rings have a crown-like conformation as known from the elemental Se8 forms. Through coordination to Rb+ ions they build [Rb(Se8)+] n “cationic chains” running in the c direction. Rb2[Pd(Se4)2]·Se8 therefore differs fundamentally from its “neighboring” alkali metal Pd polyselenides, K2PdSe10 and Cs2PdSe8, which each possess a three-dimensional structure with two interpenetrating [Pd(Se x )2]2- frameworks. Optical spectroscopic data and the thermal stability of the compound are discussed.

In‐Between Complex and Cluster: A 14‐Vertex Cage in [Ag2Se12]2+

“…For comparison, the energetic differences between Se 6 , Se 8 , and Se 12 were also calculated with M052X/aug-cc-pVTZ-PP (see Table 1 a,b) that is known to deliver very accurate thermochemical values. [23] The calculated Gibbs energy difference between the rings Se 6 , Se 8 , and Se 12 does not depend on the method and is less than 3 kJ mol À1 per Se atom in the gas phase; the most favored ring at room temperature is Se 8 .…”

“…[1] For Se, the stability of the allotropes increases from Se 7 < Se 6 < Se 8 < Se 1 . Although being structurally related to crown ethers, only a few examples of chalcogen rings coordinated to a metal ion exist, including [Ag n (Se 6 )] n+ (n = 1, 2), [2,3] [M(S 8 ) n ] + (M = Cu; [4] Ag [5] ), [Cu(S 12 )] + , [Cu(S 8 )-(S 12 )] + . [6] All of these cations are partnered with weakly coordinating anions (WCA).…”

“…[6] All of these cations are partnered with weakly coordinating anions (WCA). [7] Related salts containing almost non-interacting cationic stacks are [Rb(Se 8 ) + ] 1 [8] and [Rb(Se 6 ) 2 + ] 1 . [9] The neutral selenium complexes [PdX 2 -(Se 6 )] [10] (X = Cl, Br), [(AgI) 2 Se 6 ], [11] [Re 2 I 2 (CO) 6 (Se 7 )], [12] and [Rh 2 (Se 9 )Cl 6 ] [13] complete this series.…”

Zwischen Komplex und Cluster: Ein 14‐eckiger Käfig in [Ag2Se12]2+

“…B. [Ag n (Se 6 )] n+ (n = 1, 2), [2,3] [M(S 8 ) n ] + (M = Cu; [4] Ag [5] ), [Cu(S 12 )] + und [Cu(S 12 )(S 8 )] + . [6] All diese Kationen liegen gepaart mit schwach koordinierenden Anionen (WCA) vor.…”

“…[6] All diese Kationen liegen gepaart mit schwach koordinierenden Anionen (WCA) vor. [7] Verwandte Salze, die fast wechselwirkungsfreie kationische Ketten enthalten, sind [Rb(Se 8 ) [8] und [Rb(Se 6 ) 2 + ] 1 . [9] Vervollständigt wird die Reihe mit neutralen Selenkomplexen wie [PdX 2 (Se 6 )] (X = Cl, Br), [10] [(AgI) 2 Se 6 ], [11] [Re 2 I 2 (CO) 6 (Se 7 )] [12] und [Rh 2 (Se 9 )Cl 6 ].…”