Synthesis,structure, and 77Se NMR study of the (PPh4)2[Re6Se6Br8] complex

The octahedral cluster anion [Re₆Se₆Br₈]^2– was prepared by high-temperature synthesis from elementary substances in the presence of KBr. This cluster anion was isolated and structurally characterized by single-crystal X-ray diffraction analysis as the (PPh₄)₂[Re₆Se₆Br₈] complex (1). Refluxing of polymeric rhenium selenide bromide Re₆Se₆Br₆ in DMF in the presence of Bu₄NBr led to the cleavage of the Re—Br—Re bridges to form the complex (Bu₄N)₂[Re₆Se₆Br₈]. Comparative analysis of the interatomic distances in the octahedral rhenium(iii) selenide bromide clusters was carried out.     

Determination of 77Se-77Se and 77Se-13C J-coupling parameters for the clusters [Re5OsSe8(CN)6]3- and [Re4Os2Se8(CN)6]2-

We have investigated rarely observed 77Se J-couplings (spin-spin couplings) in the mixed-metal face-capped octahedral clusters [Re5OsSe8(CN)6]3- and [Re4Os2Se8(CN)6]2- at natural abundance. To the best of our knowledge, these are the first observations of Se-Se spin-spin interactions between mu3-Se sites, important for stereochemical assignments in hexarhenium analogues, Chevrel phase materials, and similar cluster materials. NMR techniques such as COSY, INADEQUATE, and 2D J-resolved spectroscopy have been used in conjunction to study these interactions. The two isomers (cis and trans) of [Re4Os2Se8(CN)6]2- were distinguishable, and selective isotopic labeling of [Re5OsSe8(CN)6]3- with 13CN ligands enabled resonances to be assigned by observing the 2J (Se-M-C) couplings. For [Re5OsSe8(CN)6]3-, two different 2J (Se-M-Se) couplings were measurable on a single cluster, and these are related to one another through spin-spin interactions across a face diagonal or along an edge of the cube of inner selenium ligands. A rigorous analysis based on combinatorial math has been invoked to assign the couplings on the basis of the probability of multiple-spin interactions. The face diagonal association is found to result in a J-coupling interaction larger in magnitude than that from coupling along an edge of the cube-information critical for making stereochemical assignments of selenium sites.     

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.     

Synthese und Kristallstrukturen von (PPh4)2[As2Se4Cl12] und (PPh4)2[As2Se4Br12]

Synthesis and Crystal Structures of (PPh₄)₂[As₂Se₄Cl₁₂] and (PPh₄)₂[As₂Se₄Br₁₂] The reaction of PPh₄Cl and As₂Se₃ with SOCl₂ or with chlorine in dichloromethane affords (PPh₄)₂[As₂Se₄Cl₁₂] with good yields. From PPh₄Br, As₂Se₃ and bromine the corresponding bromo compound was obtained. According to the X-ray crystal structure determinations both compounds are isotypic, crystallizing in the space group of P1 . In the anions two Se₂X₂ molecules are linked with two X^? ions forming an Se₄X₂ ring in chair conformation. Each X^?-ion is associated with an additional AsX₃ molecule (X = Cl, Br).     

Primitive cubic packing of anions in Cs4[Re6Te8(CN)6]· 2H2O and Ba2[Re6Te8(CN)6] · 12H2O crystals

Crystal structures of Cs₄[Re₆Te₈(CN)₆]·2H₂O (1) and Ba₂[Re₆Te₈(CN)₆]· 12H₂O (2) are determined. Crystals 1 are orthorhombic, a = 14,282(1), b = 12.910(1), c = 18.040(1) Å, V_cell = 3326.3(8) ų, space group Pbcn, Z = 4, d_calc = 5.715 g/cm³, R(F) = 0.0482 for 3193 F_hkl > 4σ(F). Crystals 2 are triclinic, a = 9.671(3), b = 9.697(4), c = 11.039(4) Å, α = 89.86(3), β = 72.34(3), γ = 82.46(3)°, V_cell = 977.2(6) ų, space group P1, Z = 1, d^calc = 4.733 g/cm³, R(F) = 0.0490 for 3226 F_hkl > 4σ(F). In both structures, the [Re₆Te₈(CN)₆]^4? anions form a distorted primitive cubic packing with distances between the centers 9.02-9.63 Å in 1 and 9.70-11.04 Å in 2. The Cs⁺ cations in 1 lie near the face centers of the cubes formed by the onions. In 2, cation pairs (Ba²⁺)₂ bonded to two solvate water molecules are formed; the pairs lie at the centers of the anion cubes. In structures 1 and 2, there are shortened contacts between the tellurium atoms belonging to the neighboring anions (3.75-4.09 and 3.95-4.22 Å, respectively).     

The 8 : 1 : 1 ternary hybrid framework in the system [EDT-TTF +][1,4-bis(iodoethynyl)benzene][Re6Se8(CN)6]4-: dual noncovalent expression of the octahedral halogen-bond hexa-acceptor nanonode

Complementary shapes of the neutral symmetrical halogen-bond bis-donor core and octahedral inorganic cluster core prevent halogen-bonded polymers developing in more than one direction, favouring further templating by conducting radical cation slabs and yielding an 8 : 1 : 1 phase formulation instead of n : 2 : 1, with a 2D net, or m : 3 : 1, with a pseudo-cubic architecture, which may in principle also be targeted.     

Mixing and decomposition behavior of {[4bmpy][Tf2N] + [emim][EtSO4]} and {[4bmpy][Tf2N] + [emim][TFES]} ionic liquid mixtures

Mixing ionic liquids (ILs) has been revealed as a useful way to finely tune the properties of IL-based solvents. The scarce available studies on IL mixtures have shown a quasi-ideal behavior of their physical properties. In this work, we have performed a thermophysical characterization of two binary IL mixtures, namely {4-methyl-N-butylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf₂N]) + 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO₄])} and {[4bmpy][Tf₂N] + 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate [emim][TFES]}. Both binary IL mixtures have been recently proposed as promising solvents in the (liquid + liquid) extraction of aromatic hydrocarbons from mixtures with alkanes. Densities, viscosities, refractive indices, thermal stability, and specific heats of the {[4bmpy][Tf₂N] + [emim][EtSO₄]} and {[4bmpy][Tf₂N] + [emim][TFES]} IL mixtures have been measured as a function of both temperature and composition. Dynamic viscosities, refractive indices, and thermal stability of the {[4bmpy][Tf₂N] + [emim][EtSO₄]} mixture have exhibited strong deviations from the ideality, in contrast with the quasi-ideal properties of the {[4bmpy][Tf₂N] + [emim][TFES]} mixture and the behavior of the imidazolium and pyridinium-based IL mixtures studied hitherto. The reliability of predictive methods of the thermophysical properties of the mixtures has also been evaluated.     

Reaktionen von Uranpentabromid Die Kristallstrukturen von PPh4[UBr6], PPh4 [UBr6] · 2CCl4, (PPh4)2[UBr6] · 4CH3CN und (PPh4)2[UO2Br4] · 2CH2Cl2

Reactions of Uranium Pentabromide. Crystal Structures of PPh₄[UBr₆], PPh₄[UBr₆] · 2CCl₄, (PPh₄)₂[UBr₆] · 4CH₃CN, and (PPh₄)₂[UO₂Br₄] · 2CH₂Cl₂ PPh₄[UBr₆] and PPh₄[UBr₆] · 2CCl₄ were obtained from UBr₅ · CH₃CN and tetraphenylphosphonium bromide in dichloromethane, the latter being precipitated by CCl₄. Their crystal structures were determined by X-ray diffraction. PPh₄[UBr₆]: 2101 observed reflexions, R = 0.090, space group C2/c, Z = 4, a = 2315.5, b = 695.0, c = 1805.2 pm, β = 96.38°. PPh₄[UBr₆] · 2CCl₄: 2973 reflexions, R = 0.074, space group P2₁/c, Z = 4, a = 1111.5, b = 2114.2, c = 1718.7 pm, β = 95.42°. Hydrogen sulfide reduces uranium pentabromide to uranium tetrabromide. Upon evaporation, bromide is evolved from solutions of UBr₅ with 1 or more then 3 mol equivalents of acetonitrile in dichlormethane yielding UBr₄ · CH₃CN and UBr₄ · 3CH₃CN, respectively. These react with PPh₄Br in acetonitrile affording (PPh₄)₂[UBr₆] · 4CH₃CN, the crystal structure of which was determined: 2663 reflexions, R = 0.050, space group P2₁/c, Z = 2, a = 981.8, b = 2010.1, c = 1549.3 pm, β = 98.79°. By reduction of uranium pentabromide with tetraethylammonium hydrogen sulfide in dichloromethane (NEt₄)₂[U₂Br₁₀] was obtained; (PPh₄)₂[U₂Br₁₀] formed from UBr₄ and PPh₄Br in CH₂Cl₂. Both compounds are extremely sensitive towards moisture and oxygen. The crystal structure of the oxydation product of the latter compound, (PPh₄)₂[U0₂Br₄]· 2 CH₂Cl₂, was determined: 2163 reflexions, R = 0.083, space group C2/c, Z = 4, a = 2006.3, b = 1320.6, c = 2042,5 pm, β = 98.78°. Mean values for the UBr bond lengths in the octahedral anions are 266.2 pm for UBr₆-, 276.7 pm for UBr₆^2? and 282.5 pm for UO₂Br₄^2?     

Synthesis and structures of new heteronuclear cluster complexes [PPh4][Fe4Rh3Se2(CO)16] and [PPh4]2[Fe3Rh4Te2(CO)15]

The reaction of the K₂[Fe₃Q(CO)₉] clusters (Q = Se or Te) with Rh₂(CO)₄Cl₂ under mild conditions is accompanied by complicated fragmentation of cores of the starting clusters to form large heteronuclear cluster anions. The [PPh₄][Fe₄Rh₃Se₂(CO)₁₆] and [PPh₄]₂[Fe₃Rh₄Te₂(CO)₁₅] compounds were isolated by treatment of the reaction products with tetraphenylphosphonium bromide. The structures of the products were established by X-ray diffraction. In both compounds, the core of the heteronuclear cluster consists of two octahedra fused via a common Rh₃ face. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 775–778, May, 2006.     

THE METASTABLE PARTIALLY POSITIVELY CHARGED Se6 MOLECULE: PREPARATION,CHARACTERISATION AND X-RAY CRYSTAL STRUCTURE OF [Ag2(Se6)(SO2)2][Sb(OTeF5)6]2, [Ag2Se6][AsF6]2 AND [AgSe6][Ag2(SbF6)3]

Reactions designed to give Se₆[Sb(OTeF₅)₆]₂ by the reaction of Se₂Br₂, 4Se, and 2Ag[Sb(OTeF₅)₆] lead to products that include [Ag₂(Se₆)(SO₂)₂][Sb(OTeF₅)₆]₂(1). The distorted cubic (Ag₂Se₆ ²⁺) _n consists of a Se₆ molecule bicapped by two silver cations (local D_3d sym.). Reactions of AgMX₆ (M = As, Sb) with selenium in liquid SO₂ yielded crystals of [Ag₂Se₆][AsF₆]₂ (2) and [AgSe₆][Ag₂(SbF₆)₃] (3). Both salts contain stacked arrays of [AgSe₆]⁺ half-sandwich cationic units. [Ag₂Se₆][AsF₆]₂ in addition contains stronger, linear Se─Ag─Se horizontal linkages between the vertically stacked cationic columns. [AgSe₆][Ag₂(SbF₆)₃] features a remarkable three-dimensional [Ag₂(SbF₆)₃]^? anion held together by strong Sb─F···Ag contacts between component Ag⁺ and SbF₆ ^? ions. Hexagonal channels through this honeycomb-like anion are filled by the stacked [AgSe₆ ⁺]_x.     

Interdependence of redox state,hydrogen bonding,anion recognition and charge partition in crystals of (EDT-TTF-CONHMe)6 [Re6Se8(CN)6] (CH3CN)2(CH2Cl2)2

Neutral pi-conjugated molecules and their radical cations co-exist in [(EDT-TTF-CONHMe+*)4(EDT-TTF-CONHMe0)2] [Re6Se8(CN)6]4- (CH3CN)2(CH2Cl2)2 whose crystal structure reveals that, upon one-electron oxidation, an activation of the N-H and C-H hydrogen bond donor ability is coupled to a deactivation of the hydrogen bond acceptor character of the carbonyl oxygen atom: this is expressed in the supramolecular hydrogen bond pattern and, ultimately, into charge localisation and partition in the solid state.     

A new cyanobridged one-dimensional coordination polymer based on the octahedral rhenium cluster [Re6Se8(CN)6]4−: Synthesis and crystal structure of [{Cu(H2O)0.5(en)2} {Cu(en)2}Re6Se8(CN)6]·3H2O

The rhenium cluster complex [{Cu(H₂O)_0.5(en)₂} {Cu(en)₂} Re₆Se₈(CN)₆]·3H₂O has been obtained by the reaction of an aqueous solution of K₄[Re₆Se₈(CN)₆]·3.5H₂O with an aqueous solution of Cu(en)₂Cl₂ using cross diffusion through a gel. The structure of the compound has been characterized by a single-crystal X-ray diffraction method (a = 10.690(3) Å, b = 15.035(5) Å, c = 25.847(8) Å, V = 4154(2) ų, Z = 4, space group P2₁2₁2₁, R = 0.0651). Cluster anions [Re₆Se₈(CN)₆]^4? in the complex are connected with Cu²⁺ cations by cyano bridges resulting in zigzag chains. Coordination environment of cations is completed by ethylenediamine molecules. Additionally each cluster anion is coordinated by one terminal fragment {Cu(H₂O)_0.5(en)₂}.