Ru9Zn7Sb8: a structure with a 2 × 2 × 2 supercell of the half-Heusler phase

The title compound Ru(9)Zn(7)Sb(8) was synthesized via a high-temperature reaction from the elements in a stoichiometric ratio, and its structure was solved by a single-crystal X-ray diffraction method. The structure [cubic, space group Fm3m, Pearson symbol cF96, a = 11.9062(14) ? (293 K), and Z = 4] adopts a unique 2a(hh) × 2a(hh) × 2a(hh) supercell of a normal half-Heusler phase and shows abnormal features of atomic coordination against the Pauling rule. The formation of this superstructure was discussed in light of the valence electron concentration per unit cell. It is a metallic conductor [ρ(300 K) = 16 μΩ·m], and differential scanning calorimetry revealed that Ru(9)Zn(7)Sb(8) undergoes a transformation at 1356(1) K and melts, by all indications, congruently at 1386 K. At room temperature, its thermal conductivity is about 3 W/m·K, which is only one-quarter of that of most normal half-Heusler phases. Ru(9)Zn(7)Sb(8) as well as its analogues of iron-, cobalt-, rhodium-, and iridium-containing compounds are expected to serve as a new structure type for exploring new thermoelectric materials.     

Does CH prefer a C2v rather than a Cs structure?

The closely related C_s ( 1 ) and C_2v ( 3 ) structures of CH have been reinvestigated at many ab initio levels using MP2/6-31G** and MP2/6-311 + + G(2df, 2pd) geometries. The largest basis sets employed were 6-311G(3df, 2p), 6-311 + + G(3df, 3pd), and the Dunning “correlation consistent” polarized triple-split valence basis set (cc-pVTZ). Electron correlation was probed at the MP4 level, but the QCISD method was also used with the largest basis sets. While electron correlation favors 3 over 1 by about 2 kcal/mol, the correlated relative energies with all basis sets employed range from 0.36–1.03 kcal/mol in favor of 1 . The best estimate of this difference, 0.86 kcal/mol, is essentially identical with the (scaled) zero-point energy difference, 0.84 kcal/mol, favoring 3 over 1 . These results indicate that 1 and 3 have almost exactly the same energy at 0 K. Our best value for the dissociation energy of CH is 42.0 kcal/mol [QCISD(T)/6-311 + + G(3df, 3pd)//MP2(fu)/6-311 + + G(2df, 2pd), corrected to 298 K], which agrees very well with the experimental value. © 1992 by John Wiley & Sons, Inc.     

{[Ag2 (μ-dppm)2 (μ-TCNQ)2](TCNQ)}, a charge transfer compound derived from a donor with a metal–metal bond

Reaction of AgNO3, dppm (bis(diphenylphosphino)methane), and TCNQ in molar ratio of 1 : 1 : 1 produced an acceptor–donor silver compound {[Ag₂(dppm)₂ (µ-TCNQ)₂](TCNQ)}, 1. In the structure, determined by X-ray crystallography, two silver atoms are triply-bridged by two dppm ligands and metal–metal bond to form a dimer; the distance between two Ag is 3.1753(8) Å. Compound 1 was studied by IR and UV/Vis/NIR spectroscopy, exhibiting an intervalence transfer transition at λ = 1286 nm, and also is photoluminescent (λ_max = 537 and 654 nm) at room temperature.     

Access to a stable Si2N2 four-membered ring with non-Kekulé singlet biradical character from a disilyne

The reactions of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of trans- and cis-3,3',5,5'-tetramethylazobenzenes produced a Si(2)N(2) four-membered ring biradicaloid [RSi(μ-NAr)(2)SiR] 2 (R = Si(i)Pr[CH(SiMe(3))(2)](2), Ar = 3,5-Me(2)C(6)H(3)), which was isolated as air- and moisture-sensitive dark purple crystals. Compound 2 displays no EPR signal, and the molecular structure of 2 was characterized by NMR spectroscopy and X-ray crystallography, revealing that 2 has a planar centrosymmetric Si(2)N(2) four-membered ring. The Si1-Si1' distance is 2.63380(9) ?, and there is no bond interaction between the Si1 and Si1' atoms of 2. The reactions of 2 with methanol and carbon tetrachloride show that 2 has both closed-shell and radical-type reactivity.     

EuPtSn2 – A Stannide with Sn2 Dumbbells in a Three-dimensional [PtSn2]2– Polyanion

EuPtSn₂ was obtained by melting of the elements in a sealed tantalum ampoule followed by an annealing sequence for crystal growth. The EuPtSn₂ sample was studied through its Guinier powder pattern and the structure was refined from single-crystal X-ray diffractometer data: CeRhSn₂ type, Cmcm, a = 472.05(3), b = 1724.19(12), c = 957.36(7) pm, wR₂ = 0.0388, 879 F² values and 30 variables. The platinum and tin atoms build up a three-dimensional [PtSn₂]^2– polyanionic network which consists of distorted PtSn₅ square pyramids (265–278 pm Pt–Sn) and Sn₂ dumbbells with 281 and 299 pm Sn–Sn distances. The structural relationship with DyRhGe₂ and Ce₃Pt₄Ge₆ is discussed. EuPtSn₂ shows Curie–Weiss behavior with an experimental magnetic moment of 7.78(1) μ_B / Eu, indicating stable divalent europium. This is corroborated by ¹⁵¹Eu Mössbauer spectroscopy. Antiferromagnetic ordering is detected below 3.4 K. Specific heat measurements confirm the magnetic ordering and indicate a second phase transition through a clear λ-type signal at 7.3 K which might be associated with a structural distortion.     

Synthesis and Structure of a New Polymorph Ba_2CuSi_2O_7

1INTRODUCTIONTheuniqueelectronicpropertiesofcopperoxidesandoxyhalideshaveattractedmuchattentionduetotheirpotentialapplicationsassupercon-ductors,catalysts,luminescentmaterialsandp-typetransparentconductors[1].Inanefforttoexplorenewframeworkstructuresofmixed-metaloxyha-lidessuchasCuAgOCl,wehaveobtainedanewpolymorphofthebariumdicopperdisilicate,b-Ba2CuSi2O7.Inthispaper,wewillreportthesolid-statesynthesisandcrystalstructureofthisnewphaseanddiscussthedifferencesbetweenthestructuresofb-Ba2C…     

Dimorphism in a 2,2′,2″-terpyridyl compound

Chloro-(2,2,2-terpyridine)platinum(II) chloride dihydrate, [Pt(terpy)Cl]Cl · 2H₂O, crystallizes from aqueous EtOH (1:1) as a yellow dimorph, but from dilute (1 M) HCl as its less stable red dimorph. X-ray powder photography shows that, above 100 °C, the red form converts into the yellow form.     

Et2SnCl2 · H2O and the Trigonal–Bipyramidal Transition State of a SN2 Reaction

Abstract

The title compound Et₂SnCl₂ · H₂O was prepared and characterized by IR-spectroscopy and single crystal X-ray diffraction, showing the typical trigonal bipyramidal structure of a S_N2 transition state with the water molecule in an axial position.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

GRAPHICAL ABSTRACT     

Crystal Structure of a New Allotropic Form of trans-Pd(Creat)2Cl2·2H2O

Pd(creat)₂Cl₂·2H₂O crystallizes in space group P&1macr; with a= 7.257(2), b= 8.159(2), c= 14.640(2) Å, f =73.97(2), g =77.0(1), u =72.22(2)°, Z=2, and represents a new allotropic form of this compound. Pd atoms have planar fourfold coordination of N and Cl atoms in trans configuration. Creatinine moieties are coordinated to the Pd atoms via endocyclic N atoms and their essential planarity causes significant delocalization of electron density. The structure is stabilized by a system of weak hydrogen bonds involving interstitial water molecules and creatinine amino-groups.     

μ-XAFS of a single particle of a practical NiO(x)/Ce2Zr2O(y) catalyst

μ-XAFS analysis using an X-ray μ-beam (1000 nm (h) × 800 nm (v)) was successfully carried out on a single particle of a practical catalyst NiO(x)/Ce(2)Zr(2)O(y) (0 ≤x≤ 1, 7 ≤y≤ 8). The oxidation state and local coordination structure of the NiO(x)/Ce(2)Zr(2)O(y) particle were characterized by Ni K-edge μ-XANES and μ-EXAFS, which showed the catalytically active and inactive phases of a single catalyst particle.     

Bioconjugation of the estrogen receptor hERα to a quantum dot dye for a controlled immobilization on a SiO2 surface

We investigated the immobilization of the estrogen receptor hER(α) on silanized SiO(2) surfaces for biosensor applications. The conjugation of the estrogen receptor hER(α) to the quantum dot dye QD655 was achieved. In order to obtain an optimal immobilization of the estrogen receptor hER(α) on the functionalized SiO(2) surface, the bioconjugate hER(α)-QD655 (Rcpt-qd655) solution was prepared with a higher molar ratio of 10-15 between the QDs and the receptors. A blue laser with an excitation wavelength of 405 nm was used for photoluminescence spectroscopy (PL) investigations to monitor the bioconjugate Rcpt-qd655 immobilization on the silanized SiO(2) surfaces with three different functional groups, namely NH(2), -COO(-), and -SH. Several wash processes were applied to remove the excess receptors from the surface after the immobilization. A Fourier transform infrared spectroscopy (FTIR) was used to control the biofilm background after each wash of the receptor-coated surface which allows the optimization of the immobilization protocol. In order to test its stability a quartz crystal microbalance (QCM) was employed and the receptor density was calculated. Finally the optimal biolayer (silane film+hER(α) receptor) was tested for measurements of 17?-estradiol (E2) with a concentration of 1 μM in waterish solution. The measurement concept outlined in [L. Rebohle et al., Vacuum 83 (2009) 24-28] was applied. The whole system was investigated by PL, which exhibits two color signals, namely from the receptor and the detected E2 molecules.     

Self-assembly snapshots of a 2 × 2 copper(I) grid

Self-assembled 2 × 2 grids have been characterised as high-fidelity species produced when the correct stoichiometric ratios are met, but rarely are the individual steps leading to and from their formation characterised. Here, we present such a study using equilibrium-restricted factor analysis to model a set of UV–vis spectra starting from a bis-bidentate ligand to the assembly of a 2 × 2 grid complex upon titration with 1 equiv. of [Cu(MeCN)₄](PF₆) and to disassembly upon further titration. Intermediate species [CuL₂]⁺, [Cu₂L₃]²⁺, [Cu₃L₂]³⁺ and [Cu₂L]²⁺ are evidenced along the assembly and disassembly pathways. Complementary ¹H NMR titrations are consistent with the rich set of complexes and equilibria involved. Given the nature of the assembly process, the assembly is entropy driven and likely enthalpy driven as well. The disassembly process is both enthalpy and entropy driven according to the standard free energy values derived from the modelling of the spectrophotometric titration data.     

Oxidation of alkanols with a CeIII—LiBr—H2O2 system

Russian Chemical Bulletin -     

Synthesis and Crystal Structure of a Novel (2:2) Macrocyclic Thiocarbohydrazone

Thiocarbohydrazoneshavebeentestedasantindcrobialandantitumouragentsandwidelyusedinanalyticalchemistry'-'.Ontheotherhand,thechemistryofmacrocycliccompoundshasattTactedcontinuousinterestformanyyears.Thiocarbohydrazide,HZN'N'HC(S)NHN'Hz,anditsSchiffbasecomplexesconstitUteintersstingligandsystemsbecauseoftheavailbilityofseveralpotentialdonorsites,inwhichthioketo-thioenoltautomerismispossible.Significantly,theyareabletoformbothmono-andbinuclearcomplexesbydifferentmethods3-6.Withtheaimofdesign…     

Stereospecific [2 + 2]-cross-photocycloaddition in a supramolecular donor–acceptor complex

A bis(propylammonium) derivative of (E)-4-(4-mercaptostyryl)pyridine, which was synthesized for the first time, forms a highly stable bimolecular complex with a bis(18-crown-6 ether) derivative of (E)-stilbene in solution owing to ditopic coordination via hydrogen bonds. The complex formation results in much faster deactivation of the excited states of both compounds, which is explained by photoinduced electron transfer from the stilbene derivative to the styrylpyridinium dye. Despite this, the complexed olefins undergo [2?+?2]-cross-photocycloaddition upon selective excitation of the dye to afford solely the syn-cycloadduct. The retro-photocycloaddition occurs readily upon UV irradiation of the cycloadduct and leads to the initial bimolecular complex.     

A Palladium-mediated DNA Base Pair of a β-C-Nucleoside Possessing a 2-Aminophenol as the Nucleobase

Abstract

An approach we have used in this study for the incorporation of metal ions into DNA, is the direct modification of a DNA base itself, turning it into a metal-chelating nucleobase wherein two nucleobases are paired through metal coordination. Herein we report the X-ray crystal structure of a synthetic intermediate 6 for the aminophenol bearing nucleoside 3 and its metal coordination properties with Pd²⁺. The anomeric configuration of the nucleoside was unequivocally determined to be β-form by the X-ray analysis of 6; the structure has been resolved by direct methods (S1R97) and expanded using Fourier techniques (DIRDIF94) using 2628 independent reflections with I>2.00 [sgrave](I) and 425 parameters. Final R (R_w) was 0.037 (0.043): orthorhombic, space group P2₁2₁2₁ (#19) with a=16.562(1) Å, b=16.933(1) Å, c=11.205(1) Å, and V=3142.2(4) ų; D_c =1.369g/cm³ for Z=4, and molecular weight 647.65. This result is consistent with the tentative assignment by our previous ¹H NOE differentiation experiments. Detailed ¹H NMR studies showed that the nucleoside forms a stable 2:1 complex with Pd²⁺ with concomitant deprotonation of its phenolic proton. Although there are two possible structures (cis or trans) for the square-planar Pd²⁺ complex, the ratio of cis to trans was approximately 1:1. The electrospray ionization time-of-flight mass spectrum of the complex also provided clear evidence for the 2:1 complexation.     

Embedding a Planar Hypercoordinate Carbon Atom into a [4n+2] π-System

Through delicate tuning of the electronic structure, we report herein a rational design of seventeen new putative global minimum energy structures containing a planar tetra- or pentacoordinate carbon atom embedded in an aromatic hydrocarbon. These structures are the result of replacing three consecutive hydrogen atoms of an aromatic hydrocarbon by less electronegative groups, forming a multicenter σ-bond with the planar hypercoordinate carbon atom and participating in the π-electron delocalization. This strategy that maximizes both mechanical and electronic effects through aromatic architectures can be extended to several molecular combinations to achieve new and diverse compounds containing planar hypercoordinate carbon centers.     

Synthesis and Crystal Structure of a Cu^2＋ Supramolecular Complex [Na2Cu（BTA）2（H2O）8]·H2O with a Three-dimensional Network Structure

A three-dimensional Cu^2＋ supramolecular complex [Na2Cu（BTA）2（H2O）8]·H2O 1 （H2BTA = bistetrazolylamine） was synthesized by reacting the aqueous solution of CuSO4·5H2O and H2BTA under stirring. The crystal structure of 1 was determined by single-crystal X-ray diffraction. The result indicates that 1 crystallizes in triclinic, space group P1, with a = 7.0518（2）, b = 12.2692（2）, c = 13.8583（3） A, α = 115.7260（10）,β = 93.2440（10）, γ = 98.3610（10）°, Mr = 573.90, V= 1059.01（4） A^3, Z = 2, De= 1.800 g·cm^-3,μ（MoKα） = 1.155 mm^-l, F（000） = 586.0, S = 1.074, the final R = 0.0273 and wR = 0.0744 for 4334 observed reflections with I 〉 2σ（I）. The Cu^2＋ ion is five-coordinated with a N4O1 donor set with r = 0.153 according to the method of Addison et al. And the Na^＋ ions form an infinite main chain through bridging O atoms from coordinated water molecules. In 1, a three-dimensional supratnolecular network is formed by O-H….O, O-H…N, N-H…O and N-H…N hydrogen bonds.