Rheniumselenidtelluride Re2SexTe5–x: Die Struktur von Re6Se8Te7

Rhenium Selenidetellurides Re₂Se_xTe_5–x: The Structure of Re₆Se₈Te₇ Well-crystallized rhenium selenidetellurides of the Re₂Te₅-type structure were prepared from the elements in evacuated sealed quartz glas tubes at 1 130 K within 14 d. The orthorhombic lattice parameters of the phases shrink with increasing selenium content from a = 1 304.9(1) ? 1 255.8(2) pm, b = 1 297.5(1) ? 1 260.0(2) pm, and c = 1 425.1(1) ? 1 408.2(1) pm. The phase width ends at composition Re₂Se_2.7Te_2.3. An X-ray structure analysis of a crystal of composition Re₆Se₈Te₇ was performed. Selenium and tellurium atoms differ structurally completely: Whereas the selenium atoms are separated within distorted octahedral [Re₆Se₈] clusters, the tellurium atoms form homonuclear bonded bicyclic [Te(Te₃)₂] units. They also link the clusters which are arranged according to the motif of a cubic closest packing.     

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.     

Balancing framework densification with charged, halogen-bonded-pi-conjugated linkages: [PPh4]2{[E-TTF-I2][Re6Se8(CN)6]} versus [PPh4]2[EDT-TTF-I]2{[EDT-TTF-I][Re6Se8(CN)6]}

The ionic character of a set of two redox linkages and strong, directional halogen bonding at the organic-inorganic interface compromise to produce two materials sharing a common two-dimensional net, eventually extended in a third dimension, although two of the six symmetrical halogen bond acceptors ultimately remain uninvolved as a result of charge densification.     

Synthesis and characterization of A4[Re6Q8L6]@SiO2 red-emitting silica nanoparticles based on Re6 metal atom clusters (A = Cs or K, Q = S or Se, and L = OH or CN)

Metal atom clusters constitute very promising candidates as luminophores for applications in biotechnology because they are nanosized entities offering robust luminescence in the near-infrared field (NIR). However, they cannot be used as prepared for biological applications because of potential toxic effects and quenching of the clusters' luminescence in aqueous media, and they therefore need to be dispersed in a biocompatible matrix. We describe herein the encapsulation of octahedral rhenium clusters, denoted as A(4)[Re(6)Q(8)L(6)] (A = Cs or K, Q = S or Se, and L = OH or CN), in silica nanoparticles by a water-in-oil microemulsion process, paying particular attention to the clusters' stability. The obtained A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles are 30 nm in size with good monodispersity and a perfectly spherical shape, as shown by scanning electron microscopy (SEM). The presence of cluster units inside the silica matrix was evidenced by scanning transmission electron microscopy in annular dark-field mode (ADF-STEM). From the point of view of their optical properties, the A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles show red and NIR emission under UV excitation, even when dispersed in water. The evolution of the structural and luminescence properties of clusters before and after encapsulation was followed by Raman and photoluminescence spectroscopy.     

PdCl2Se6 und PdBr2Se6, neue chalkogenreiche Komplexe von Palladium(II)-Halogeniden mit Se6-Gruppen als Liganden

PdCl₂Se₆ and PdBr₂Se₆, New Chalcogenrich Complexes of Palladium(II) Halides with Se₆ Groups as Ligands PdCl₂Se₆ und PdBr₂Se₆, chalcogenrich complexes of palladium halides with Se₆ groups as ligands have been prepared by reactions of Pd metal with melts of selenium and SeX₄ (X = Cl, Br) at 180°C in closed silica ampoules. The new compounds have been characterized by vibrational spectra and thermal analysis. The X-ray analysis of PdCl₂Se₆ showed a polymeric structure, built up by chains of linear PdX₂ groups connected by Se₆ groups in a chair conformation.     

Na6Si2Se8: Ein Perselenidosilicat

On Na₆Si₂Se₈, the First Perselenido Silicate The new compound Na₆Si₂Se₈ crystallizes in the monoclinic system, space group P2₁/c (No. 14) with lattice constants see ?Inhaltsübersicht”?. Two SiSe₄ tetrahedra are connected by a Se–Se covalent bond, forming a discrete [Si₂Se₈]^6? anion.     

A family of octahedral rhenium cluster complexes [Re6Q8(H2O)n(OH)6-n]n-4 (Q=S, Se; n=0-6): structural and pH-dependent spectroscopic studies

The conversions of hexahydroxo rhenium cluster complexes [Re6Q8(OH)6]4- (Q=S, Se) in aqueous solutions in a wide pH range were investigated by chemical methods and spectroscopic measurements. Dependences of the spectroscopic and excited-state properties of the solutions on pH have been studied in detail. It has been found that a pH decrease of aqueous solutions of the potassium salts K4[Re6Q8(OH)6].8H2O (Q=S, Se) results in the formation of aquahydroxo and hexaaqua cluster complexes with the general formula [Re6Q8(H2O)n(OH)6-n]n-4 that could be considered as a result of the protonation of the terminal OH- ligands in the hexahydroxo complexes. The compounds K2[Re6S8(H2O)2(OH)4].2H2O (1), [Re6S8(H2O)4(OH)2].12H2O (2), [Re6S8(H2O)6][Re6S6Br8].10H2O (3), and [Re6Se8(H2O)4(OH)2] (4) have been isolated and characterized by X-ray single-crystal diffraction and elemental analyses and infrared (IR) spectroscopy. In crystal structures of the aquahydroxo complexes, the cluster units are connected to each other by an extensive system of very strong hydrogen bonds between terminal ligands.     

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.     

A morphotropic series of the cluster complexes [Ln(DMF)8][Re6Q7Br7] (Q = S, Se): Synthesis, structure, and thermal transformations

The reactions of the octahedral anionic complexes [Re₆Q₇Br₇]^3? (Q = S, Se) with lanthanide bromides in DMF were studied. The reactions gave a series of compounds [Ln(DMF)₈][Re₆Q₇Br₇] (Q = S, Se) containing [Ln(DMF)₈]³⁺ complex cations. The compounds were studied by single-crystal and powder X-ray diffraction and thermal analyses. The crystal structures of [Ln(DMF)₈][Re₆S₇Br₇] with Ln = La (I), Ce (II), Nd (III), Eu (IV), and Lu (V) and [Ln(DMF)₈][Re₆Se₇Br₇] with Ln = La (VI), Ce (VII), Pr (VIII), and Lu (IX) were determined. It was found that [Ln(DMF)₈][Re₆Q₇Br₇] (Q = S, Se) can be divided into three structural groups: I, II, and VI (type A), VII (type B), and III–V, VIII, IX (type C). The complex [Pr(DMF)₈][Re₆Se₇Br₇] was found to crystallize in two polymorphous modifications with type B and C structures. Presumably, the morphotropic transitions in the [Ln(DMF)₈][Re₆Q₇Br₇] series (Q = S, Se) are mainly related to the change in the configuration of the [Ln(DMF)₈]³⁺ cations, resulting in a change in the packing motif of large complex ions in the crystals. The compounds [Ln(DMF)₈][Re₆Se₇Br₇] decompose according to a stepwise pattern, which suggests an intermediate formation of the complexes [Ln(DMF)₆][Re₆Se₇Br₇] (this was proved for Ln = Yb, Lu) with subsequent more extensive transformations, which affect also the cluster anion.     

(EDT-TTF-CONH2)6[Re6Se8(CN)6], a metallic Kagome-type organic-inorganic hybrid compound: electronic instability, molecular motion, and charge localization

(EDT-TTF-CONH2)6[Re6Se8(CN)6], space group R, was prepared by electrocrystallization from the primary amide-functionalized ethylenedithiotetrathiafulvalene, EDT-TTF-CONH2 (E(1/2)1 = 0.49 V vs SCE in CH3CN), and the molecular cluster tetraanion, [Re6Se8(CN)6]4- (E(1/2) = 0.33 V vs SCE in CH3CN), equipped with hydrogen bond donor and hydrogen bond acceptor functionalities, respectively. Its Kagome topology is unprecedented for any TTF-based materials. The metallic state observed at room temperature has a strong two-dimensional character, in coherence with the Kagome lattice symmetry, and the presence of minute amounts of [Re6Se8(CN)6](3-)* identified by electron spin spectroscopy. A structural instability toward a distorted form of the Kagome topology of lesser symmetry is observed at ca. 180 K. The low-temperature structure is associated with a localized, electrically insulating electronic ground state and its magnetic susceptibility accounted for by a model of uniform chains of localized S = 1/2 spins in agreement with the 100 K triclinic crystal structure and band structure calculations. A sliding motion, within one out of the three (EDT-TTF-CONH2)2 dimers coupled to the [Re6Se8(CN6)(3-)*]/[Re6Se8(CN6)4-] proportion at any temperature, and the electronic ground state of the organic-inorganic hybrid material are analyzed on the basis of ESR, dc conductivity, 1H spin-lattice relaxation, and static susceptibility data which qualify a Mott localization in [EDT-TTF-CONH2]6[Re6Se8(CN)6]. The coupling between the metal-insulator transition and a structural transition allows for the lifting of a degeneracy due to the ternary axis in the high temperature, strongly correlated metallic phase which, in turn, leads to Heisenberg chains at low temperature.     

Synthese,Kristallstruktur und spektroskopische Charakterisierung von Tetraphosphorhexaoxiddiselenid P4O6Se2

Synthesis, Crystal Structure, and Spectroscopic Characterization of Tetraphosphorus Hexaoxide Diselenide P₄O₆Se₂ P₄O₆Se₂ has been prepared by photochemical selenation of P₄O₆ with red selenium in CS₂ in presence of catalytical amounts of iodine. Isolation and single crystal growth were performed by fractional crystallization and subsequent sublimation. The compound crystallizes in the monoclinic space group P2₁/c (Nr. 14) with a = 11.473(2); b = 6.536(1); c = 11.796(2) Å; β = 90.06(1)°; Z = 4; R₁ = 0.030; wR² = 0.073. Within the limits of experimental error, the P₄O₆Se₂ molecules exhibit C_2v symmetry in the crystal. Bond lengths and angles within the molecule as well as the arrangement of the molecules within the crystal are discussed; IR-, Raman-, and ³¹P solution NMR data are reported.     

Synthese und Kristallstruktur von (PPh4)2Se6

Synthesis and Crystal Structure of (PPh₄)₂Se₆ (PPh₄)₂Se₆ has been prepared by the reaction of selenium with K₂Se₂ in dimethylformamide solution in the presence of K₃[Mn(CN)₆] and PPh₄Br, forming black crystal needles. According to the crystal structure determination the compound consists of PPh⁺₄ ions and chainlike hexaselenide ions. Space group P6 , Z = 2,4683 Observed unique reflections, R = 0.066. Lattice dimensions at ?90°C: a = 951.0, b = 1094.8, c = 2137.4 pm, α = 82.66°, β = 83.36°, γ = 89.96°.     

Cyclic Se6 and helical infinity1[Sex] as neutral ligands in the new compounds PdBr2Se6 and PdCl2Se8

PdBr2Se6 and PdCl2Se8 are two new compounds with cyclic Se6 coordinated to PdBr2 molecules and one-dimensional helical Sex chains coordinated to PdCl2 molecules. PdBr2Se6 is a black solid with a crystal structure similar, but not equal, to PdCl2Se6. It crystallizes in the space group P1 with the lattice constants a = 4.3946(8) A, b = 7.605(1) A, c = 7.992(2) A, alpha = 66.15(2) degrees , beta = 86.44(2) degrees , gamma = 80.90(2) degrees , and Z = 1 and can be handled in air like the deep red PdCl2Se8 which crystallizes in the orthorhombic space group Pbca with the lattice constants a = 9.609(2) A, b = 8.958(2) A, c = 13.799(3) A, and Z = 4. In PdBr2Se6, two cyclic Se6 molecules (chair conformation) are directly coordinated to Pd atoms, forming Pd(Se6)2Br2 groups. These are connected to one-dimensional chains via trans-standing Se atoms. In PdCl2Se8, the selenium substructure consists of helical chains with every fifth Se atom directly coordinated to the Pd atom of a PdCl2 group. Each PdCl2 group on the other hand connects two neighboring Sex helices. The type of Sex helix found for this compound is unique and differs from all other ones reported up to now including elemental alpha-Se. A reproducible twinning observed for PdBr2Se6 crystals in the course of the X-ray single-crystal investigations is checked by transmission electron microscopy in connection with details of the atomic arrangement. The Raman spectra of PdBr2Se6 and PdCl2Se8 are compared to Raman data of elemental Se modifications and give significant support for the Se6 and helical Sex to be neutral molecules. A discussion of the results of thermal analyses gives clear evidence that cyclic Se6 and helical Sex are considerably stabilized by bonding to the PdX2 molecules because the melting temperatures of the composite materials are significantly higher than the ones of the respective elemental modifications.     

Jahn-Teller distortion of the open-shell 23-electron chalcogenide rhenium cluster cores in crystals of the series, ([Re6Q8]3+(X-)6)3- (Q = S,Se; X = Cl,CN)

Comparison within the title [Re6Q8X6]4-/[Re6Q8X6]3- redox series of 14 precise crystal structures of the Re6 cluster cores at different low temperatures reveals that the one-electron oxidised, open-shell (23 electron) cores undergo a Jahn-Teller distortion of their parent 24 electron octahedral cores and that D4h and D2h forms may co-exist in the solid state.