Cyclische Polyselenidoarsenate(III) und -antimonate(III): PPh4[Se5AsSe], PPh4[AsSe6–xSx], (PPh4)2[As2Se6] · 2 CH3CN und (PPh4)2[Se6SbSe]2

Cyclic Polyselenidoarsenates(III) and Polyselenidoantimonates(III): PPh₄[Se₅AsSe], PPh₄[AsSe_6–xS _x ], (PPh₄)₂[As₂Se₆] · 2 CH₃CN, and (PPh₄)₂[Se₆SbSe]₂ In acetonitrile, AsCl₃ and sodiumphenolate formed Cl₂AsOPh which then was reacted with PPh₄Se₅ and finally with Na₂Se to yield PPh₄[Se₅AsSe]. With Na₂S instead of Na₂Se, PPh₄[AsSe_6–xS_x] was obtained; the sulfur contents increased with increasing reaction temperature and time (x = 0.21 to 1.09). With PPh₄Se₂ instead of PPh₄Se₅, (PPh₄)₂[1,4-As₂Se₆] · 2 CH₃CN and PPh₄[Se₅AsSe] were the products. With SbCl₃ instead of AsCl₃, (PPh₄)₂[Se₆SbSe]₂ formed. PPh₄[Se₅AsSe] can also be produced from As₂Se₃, PPh₄Br, Na₂Se and selenium in acetonitrile. The crystal structure of PPh₄[SeAsSe₅] is isotypic with PPh₄[S₅AsS] (X-ray structure analysis with 2414 observed reflexions, R = 0.038). The Se₅AsSe^– ion consists of a six-membered AsSe₅ ring in chair conformation, and the As atom has an additional terminal Se atom. The compounds PPh₄[AsSe_6–xS_x] have the same crystal structures, with sulfur atoms taking all selenium positions at random, but with a preference for the terminal position. The anion in (PPh₄)₂[As₂Se₆] · 2 CH₃CN also has a six-membered ring structure in chair conformation, with two arsenic atoms in positions 1 and 4. The centrosymmetric anion in (PPh₄)₂[Se₆SbSe]₂ consists of a central Sb₂Se₂ ring, and a Se₆ ligand is bonded in a chelating manner to each Sb atom (X-ray structure analysis with 2669 observed reflexions, R = 0.099). ⁷⁷Se-NMR spectra are reported.     

[Re5(μ-H)4(CO)20]− and [Re5(μ-H)5(CO)20], Two Isolobal Analogues of Cyclopentane

The first five-membered rings of metal atoms connected by M–M or M-H-M bonds only have been obtained by a Re₂+Re₃ condensation in which a polyhydride acts as a bridging bidentate ligand toward a coordinatively unsaturated fragment (see scheme below). In spite of the octahedral coordination of the Re centers, the Re₅ rings display conformations (twisted and envelope) comparable with those observed for organic five-membered rings of tetrahedral carbon atoms.     

Synthesen und Strukturen neuer amido- und imidoverbrückter Cobaltcluster: [Li(THF)2]3[Co3(μ2-NHMes)3Cl6] (1), [Li(DME)3]2[Co18(μ4-NPh)3(μ3-NPh)12Cl3] (2), [Li(DME)3]2[Co6(μ4-NPh)(μ2-NPh)6(PPh2Et)2] (3) und [Li(THF)4][Co8(μ3-NPh)6(μ2-NPh)3(PPh3)2] (4)

Syntheses and Crystal Structures of new Amido- und Imidobridged Cobalt Clusters: [Li(THF)₂]₃[Co₃(μ₂-NHMes)₃Cl₆] (1), [Li(DME)₃]₂[Co₁₈(μ₄-NPh)₃(μ₃-NPh)₁₂Cl₃] (2), [Li(DME)₃]₂[Co₆(μ₄-NPh)(μ₂-NPh)₆(PPh₂Et)₂] (3), and [Li(THF)₄][Co₈(μ₃-NPh)₆(μ₂-NPh)₃(PPh₃)₂] (4) The reactions of cobalt(II)-chloride with the lithium-amides LiNHMes and Li₂NPh leads to an amido-bridged multinuclear complex [Li(THF)₂]₃[Co₃(μ₂-NHMes)₃Cl₆] ( 1 ) as well as to the imido-bridged cobalt cluster [Li(DME)₃]₂[Co₁₈(μ₄-NPh)₃(μ₃-NPh)₁₂Cl₃] ( 2 ). In the presence of tertiary phosphines two imido-bridged cobalt clusters [Li(DME)₃]₂[Co₆(μ₄-NPh)(μ₂-NPh)₆(PPh₂Et)₂] ( 3 ) and [Li(THF)₄][Co₈(μ₃-NPh)₆(μ₂-NPh)₃(PPh₃)₂] ( 4 ) result. The structures of 1 – 4 were characterized by X-ray single crystal structure analysis.     

Synthesis and Structural Characterization of [Cu20Se4(μ3‐SePh)12(PPh3)6] and [Ag(SePh)]∞

Reaction of lithium phenylselenothiolate, generated in situ from the reductive cleavage of PhSe‐SiMe₃ with alkyl lithium reagents and insertion of elemental sulfur, with triphenylphosphine solubilized CuCl affords the molecular cluster complex [Cu₂₀Se₄ (μ₃‐SePh)₁₂(PPh₃)₆] ( 1 ). The analogous reaction with AgCl yields the extended structure [Ag(SePh)]_∞ ( 2 ) in which an infinite layer of Ag^I atoms is capped on either side by μ₄‐SePh ligands. 1: space group P¯1, a = 17.9510(6), b = 18.1712(7), c = 31.4311(11) Å, a = 78.098(2), β = 82.905(2), γ = 70.012(2)°. 2: space group C2/c, a = 5.8762(6), b = 7.2989(7), c = 29.124(2) Å, β = 95.790(3)°.     

Cobalt Chalcogenide Clusters. Synthesis,Characterization and DFT Calculations of [Co4Se2(CO)10] and [Co4Te2(CO)11]. Crystal Structure of [Co8Se4(CO)16(μ‐dppa)2]

The reactions of [Co₂(CO)₈] with E(SiMe₃)₂ (E = Se, Te) in CH₂Cl₂ result in the formation of the compounds [Co₄Se₂(CO)₁₀]> ( 1 ) and [Co₄Te₂(CO)₁₁] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ₄‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ₂‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph₂PC≡CPPh₂ (dppa), the reaction of [Co₂(CO)₈] with Se(SiMe₃)₂ leads to the formation of [Co₈Se₄(CO)₁₆(μ‐dppa)₂] ( 3 ). During the reaction two molecules of [Co₂(CO)₈] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ₃‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups.