Cadmium(II) thio‐ and selenocyanate complexes of 3,3′‐bis(1,2,4‐triazol‐4‐yl)‐1,1′‐biadamantane,a ligand designed with an `extended nanodiamond' aliphatic platform

In the structures of the Cd^II pseudohalide coordination polymer poly[[diaquabis[μ₂‐3,3′‐bis(1,2,4‐triazol‐4‐yl)‐1,1′‐biadamantane‐κ²N¹:N^1′]cadmium(II)] dithiocyanate dihydrate], {[Cd(C₂₄H₃₂N₆)₂(H₂O)₂](NCS)₂·2H₂O}_n, (I), and the isomorphous selenocyanate analogue, {[Cd(C₂₄H₃₂N₆)₂(H₂O)₂](NCSe)₂·2H₂O}_n, (II), the Cd^II cations occupy inversion centres and have octahedral CdN₄O₂ environments, completed by four N atoms of the organic ligands [Cd—N = 2.316 (2) and 2.361 (2) Å for (I), and 2.313 (3) and 2.372 (3) Å for (II)] and two trans‐coordinated aqua ligands [Cd—O = 2.3189 (15) Å for (I) and 2.323 (2) Å for (II)]. In each compound, the ligand displays a bidentate N¹:N^1′‐bridging mode, connecting the metal centres at a distance of 14.66 Å into two‐dimensional nets of (4,4)‐topology, while the uncoordinated thio(seleno)cyanate anions reside inside the net cavities. Hydrogen bonding between the water molecules, anions and 1,2,4‐triazole N atoms supports the tight packing, with an interlayer distance of 6.09 Å.     

A new adamantanecarboxylate coordination polymer: poly[[(μ3‐adamantane‐1,3‐dicarboxylato)aquadioxidouranium(VI)] monohydrate]

The title compound, {[U(C₁₂H₁₄O₄)O₂(H₂O)]·H₂O}_n, is the first actinide complex featuring adamantanecarboxylate ligands. The metal ion possesses a pentagonal–bipyramidal UO₇ coordination involving two axial oxide ligands [U—O = 1.732 (5) and 1.764 (5) Å] and five equatorial O atoms [U—O = 2.259 (5)–2.494 (4) Å] of aqua and carboxylate ligands. The latter display pseudo‐chelating and bridging coordination modes of the carboxylate groups that are responsible for the generation of the centrosymmetric discrete uranium–carboxylate [UO₂(μ‐RCOO)₂UO₂] dimers [U...U = 5.5130 (5) Å] and their connection into one‐dimensional chains. Hydrogen bonding involving two coordinated and two solvent water molecules [O...O = 2.719 (7)–2.872 (7) Å] yields centrosymmetric (H₂O)₄ ensembles and provides noncovalent linkage between the coordination chains to generate a three‐dimensional network structure.     

Peculiar All‐Metal σ‐Aromaticity of the [Au2Sb16]4− Anion in the Solid State

Gas‐phase clusters are deemed to be σ‐aromatic when they satisfy the 4n+2 rule of aromaticity for delocalized σ electrons and fulfill other requirements known for aromatic systems. While the range of n values was shown to be quite broad when applied to short‐lived clusters found in molecular‐beam experiments, stability of all‐metal cluster‐like fragments isolated in condensed phase was previously shown to be mainly ascribed to two electrons (n=0). In this work, the applicability of this concept is extended towards solid‐state compounds by demonstrating a unique example of a storable compound, which was isolated as a stable [K([2.2.2]crypt)]⁺ salt, featuring a [Au₂Sb₁₆]^4? cluster core possessing two all‐metal aromatic AuSb₄ fragments with six delocalized σ electrons each (n=1). This discovery pushes the boundaries of the original idea of Kekulé and firmly establishes the usefulness of the σ‐aromaticity concept as a general idea for both small clusters and solid‐state compounds.     

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the Förster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot–porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism.     

Simultaneous thermal and contraction/expansion analyses of cast iron solidification process

Journal of Thermal Analysis and Calorimetry - Simultaneous thermal and contraction/expansion analysis of hypoeutectic grey (lamellar graphite) and ductile (nodular graphite) cast irons...     

Sulfanyl chloride induced heterocyclization of N-(pyrazolyl)styrylacetamides

Heterocyclization of N-(pyrazol-3-yl)styrylacetamides with arenesulfenyl chlorides yields the corresponding tetrahydrofuran-2-iminium perchlorates isolable after chromatography as trans-5-aryl-4-(arylthio)tetrahydrofuran-2-ones and 5-aryl-4-(arylthio)-1-(pyrazol-3-yl)pyrrolidin-2-ones, with the latter predominating. N-(Pyrazol-4-yl)styrylacetamides react under analogous conditions to give 5-aryl-4-(arylthio)-1-(pyrazol-4-yl)pyrrolidin-2-ones, 4-aryl-3-(arylthio)-4-chloro-N-(1-methylpyrazol-4-yl)butanamides, and tetrahydrofuran-2-iminium perchlorates which, when chromatographed, produce 5-aryl-4-(arylthio)dihydrofuran-2(3H)-ones and 4-aryl-3-(arylthio)-4-methoxy-N-(1-methyl-1H-pyrazol-4-yl)butanamides.     

Fused 1,2‐Dithioles. Part VII

The 1,2‐dithiolosultam derivative 14 was obtained from the (α‐bromoalkylidene)propenesultam derivative 9 (Scheme 1). Regioselective cleavage of the two ester groups (→ 1b or 2b ) allowed the preparation of derivatives with different substituents at C(3) in the dithiole ring (see 27 and 28 ) as well as at C(6) in the isothiazole ring (see 17 – 21 ; Scheme 2). Curtius rearrangement of the 6‐carbonyl azide 21 in Ac₂O afforded the 6‐acetamide 22 , and saponification and decarboxylation of the latter yielded ‘sulfothiolutin’ ( 30 ). Hydride reductions of two of the bicyclic sultams resulted in ring opening of the sultam ring and loss of the sulfonyl group. Thus the reduction of the dithiolosultam derivative 14 yielded the alkylidenethiotetronic acid derivative 33 (tetronic acid=furan‐2,4(3H,4H)‐dione), and the lactam‐sultam derivative 10 gave the alkylidenetetramic acid derivative 35 (tetramic acid=1,5‐dihydro‐4‐hydroxy‐2H‐pyrrol‐2‐one) (Scheme 3). Some of the new compounds ( 14, 22, 26 , and 30 ) exhibited antimycobacterial activity. The oxidative addition of 1 equiv. of [Pt(η²‐C₂H₄)L₂] ( 36a , L=PPh₃; 36b , L=1/2 dppf; 36c , L=1/2 (R,R)‐diop) into the S? S bond of 14 led to the cis‐(dithiolato)platinum(II) complexes 37a – c . (dppf=1,1′‐bis(diphenylphosphino)ferrocene; (R,R)‐diop={[(4R,5R)‐2,2‐demithyl‐1,3‐dioxolane‐4,5‐diyl]bis(methylene)}bis[diphenylphosphine]).     

Order-Unity 13C Nuclear Polarization of [1-13C]Pyruvate in Seconds and the Interplay of Water and SABRE Enhancement

Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) is investigated to achieve rapid hyperpolarization of ¹³C₁ spins of [1-¹³C]pyruvate, using parahydrogen as the source of nuclear spin order. Pyruvate exchange with an iridium polarization transfer complex can be modulated via a sensitive interplay between temperature and co-ligation of DMSO and H₂O. Order-unity ¹³C (>50 %) polarization of catalyst-bound [1-¹³C]pyruvate is achieved in less than 30 s by restricting the chemical exchange of [1-¹³C]pyruvate at lower temperatures. On the catalyst bound pyruvate, 39 % polarization is measured using a 1.4 T NMR spectrometer, and extrapolated to >50 % at the end of build-up in situ. The highest measured polarization of a 30-mM pyruvate sample, including free and bound pyruvate is 13 % when using 20 mM DMSO and 0.5 M water in CD₃OD. Efficient ¹³C polarization is also enabled by favorable relaxation dynamics in sub-microtesla magnetic fields, as indicated by fast polarization buildup rates compared to the T₁ spin-relaxation rates (e. g., ∼0.2 s⁻¹ versus ∼0.1 s⁻¹, respectively, for a 6 mM catalyst-[1-¹³C]pyruvate sample). Finally, the catalyst-bound hyperpolarized [1-¹³C]pyruvate can be released rapidly by cycling the temperature and/or by optimizing the amount of water, paving the way to future biomedical applications of hyperpolarized [1-¹³C]pyruvate produced via comparatively fast and simple SABRE-SHEATH-based approaches.     

Properties of aromaticity indices based on the one-electron density matrix

Proper normalization of two previously published indices yields aromaticity measures that, when computed within the Hückel molecular orbital (HMO) approximation, closely match the topological resonance energies per pi electron of aromatic annulenes and their ions. The normalized indices, which quantify aromaticity of individual rings in polycyclic systems, are equally applicable to homocyclic and heterocyclic compounds and can be readily computed from 1-matrices calculated at any level of electronic structure theory. However, only the index ING, derived from the Giambiagi formula, produces proper ordering of aromaticities of heterocyclic compounds, provided it is calculated from all-electron wavefunctions in conjunction with the atoms in molecule (AIM) partitioning. Its values are shown to be strongly affected by electron correlation effects. Because of its apparent inability to distinguish between anti- and nonaromatic systems, ING should only be employed for aromatic species.     

Two new "onium" fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: structures and spectroscopic properties

Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions.