cis-Di­chloro­bis­(triethyl­arsine)­platinum(II) and cis-di­chloro­bis­(triethyl­phosphine)­platinum(II)

The crystal structure of cis-[PtCl₂(C₆H₁₅As)₂], (I), is isostructural with a previously reported structure of cis-[PtCl₂(C₆H₁₅P)₂], (II). A new polymorph of (II) is also reported here. Selected geometrical parameters in the arsine complex are Pt—Cl 2.3412 (12) and 2.3498 (13), Pt—As 2.3563 (6) and 2.3630 (6) Å, Cl—Pt—Cl 88.74 (5), As—Pt—As 97.85 (2), and Cl—Pt—As 171.37 (4) and 177.45 (4)°. Corresponding parameters in the phosphine complex are Pt—Cl 2.364 (2) and 2.374 (2), Pt—P 2.264 (2) and 2.262 (2) Å, Cl—Pt—Cl 85.66 (9), P—Pt—P 98.39 (7), and Cl—Pt—P 170.26 (7) and 176.82 (8)°.     

Tri­carbonyl­[1,1′,1′′-ethyl­idyne­tris­(pyrazole-κN2)]­rhenium(I) bromide and tri­carbonyl­[methyl­idyne­tris­(pyrazole-κN2)]­rhenium(I) iodide ethanol hemisolvate

The two title compounds, [Re(C₁₀H₁₀N₆)(CO)₃]Br and [Re(C₁₁H₁₂N₆)(CO)₃]I·0.5C₂H₆O, have slightly distorted octahedral geometries about the rhenium centers. The distortions result from the constraints of the η³-coordinated tris­(pyrazol-1-yl)­methane ligands in each case which reduce the N—Re—N bond angles well below the preferred value of 90° for facially disposed ligands at a six-coordinate metal center.     

Sodium thio­phenolate N,N,N′,N′-tetra­methyl­ethyl­enedi­amine

The title compound, Na⁺·C₆H₅S⁻·C₆H₁₆N₂, forms lipophilically wrapped infinite sodium chains along the a axis. Each sodium cation is coordinated by three thio­phenolate S atoms and two N centres of one tetra­methyl­ethyl­enedi­amine molecule.     

N,N′-(1,2-phenylene)bis­(pyridine-2-carboxamide) and N,N′-(1,2-cyclohexanediyl)bis(pyridine-2-carbox­amide) toluene hemisolvate

The crystal structures of N,N′-(1,2-phenyl­ene)­bis­(pyridine-2-carbox­amide), C₁₈H₁₄N₄O₂, (I), and N,N′-(1,2-cyclo­hexane­diyl)­bis­(pyridine-2-carbox­amide) have been determined, the latter compound as the toluene hemisolvate, C₁₈H₂₀N₄O₂·0.5C₇H₈, (II). In (I), the benzene ring is nearly coplanar with one of the pyridine rings and forms a dihedral angle of 59.4 (1)° with the other. However, in (II), the dihedral angle of the two pyridine rings is 70.0 (1)°.     

Phase transitions in n-alkyl­ammonium di­hydrogenphosphates and -arsenates and ferroelastic n-hexyl- and n-octyl­ammonium di­hydrogen­arsenate

-Hexyl­ammonium di­hydrogenarsenate, (C₆­H₁₆N)[AsO₂(OH)₂], and -octyl­ammonium di­hydrogenarsenate, (C₈H₂₀N)[AsO₂(OH)₂], are both ferroelastic at room temperature. The samples used in this study were not subjected to a phase transition after they had been crystallized. The structures are monoclinic (P2₁/n) and isostructural with the corresponding di­hydrogenphosphates. Each sample contained two domains and each structure was refined as a twin. There are strong hydrogen bonds between di­hydrogenarsenates and moderate hydrogen bonds between di­hydrogenarsenates and -alkyl­ammonium groups. The hydrogen-bond distances correspond well to those observed in the di­hydrogenphosphates. All the atoms except two H atoms exist in pairs linked by the lost symmetry operations derived from the prototypic space group P2/b2₁/n2₁/a. Each of these two different H atoms is involved in an asymmetric hydrogen bond between an oxy­gen pair. These oxy­gens are supposed to change their roles as hydrogen-bond donors and acceptors during the ferroelastic switching. The phase-transition sequences are affected by interactions between the neighbouring organic chains in the structure.     

trans-Bis(2-amino­pyridine-N)bis(O,O′-diiso­propyl di­thio­phosphato-S,S′)nickel(II)

In the title compound, [Ni(C₆H₁₄O₂PS₂)₂(C₅H₆N₂)₂], the coordination around the Ni atom, which lies on a crystallographic centre of symmetry, is octahedral with the S atoms from the di­thio­phosphate ligands occupying the equatorial positions, while the axial positions are occupied by the ring N atoms of the 2-amino­pyridine ligands. The mol­ecules form layers in the bc plane which are stacked in the direction of the a axis.     

Di­chloro­bis(4-methyl­pentan-2-onato-C4,O)­tin(IV) and bis(4-methyl­pentan-2-onato-C4,O)(2-thio­xo-1,3-di­thiole-4,5-di­thiol­ato-S,S′)­tin(IV) at 150 K

The structures of the ketotins determined here, [SnCl₂(C₆H₁₁O)₂] and [Sn(C₃S₅)(C₆H₁₁O)₂], respectively, along with that previously reported for [MeC(O)CH₂CMe₂]₂SnI₂, are compared with the structures of the analogous estertins [MeOC(O)CH₂CH₂]₂SnX₂. Pairwise comparison of the mean ketotin [estertin] Sn—X and Sn—O distances as Sn—X 2.4422 (4) [2.4054 (7) Å], 2.4970 (4) [2.471 (2) Å] and 2.8463 (4) [2.7788 (8) Å] and Sn—O 2.4926 (12) [2.528 (1) Å], 2.6110 (11) [2.629 (7) Å] and 2.435 (3) [2.525 (4) Å] (for X = Cl, S and I, respectively) clearly demonstrates the superior donor ability of the ketotin O atom in chelate formation.     

Hydro­gen bonds in the framework of bis{2-[bis(2-amino­ethyl)­amino]­ethanol}nickel(II) diperchlorate

The title molecule, [Ni(C₆H₁₇N₃O)₂](ClO₄)₂, possesses a crystallographic centre of symmetry at the Ni^II position. The coordination geometry around the Ni^II atom is distorted octahedral, consisting of six N atoms from two tripodal poly­amine ligands, while the ethanol O atoms of the ligands remain uncoordinated. The crystal packing shows two-dimensional layers and an infinite three-dimensional framework which is stabilized by a hydrogen-bonded network.     

Nucleophilic Substitution in 6-Chloro-2-(2-cyano­phenoxy)quinoxalines and Antibacterial Activity of Phenoxychloroquinoxaline Derivatives

Russian Journal of Organic Chemistry - Ullmann reaction of 2-[(6-chloroquinoxalin-2-yl)oxy]benzonitrile with 4-tert-butylphenol unexpect­edly afforded...     

5,6-Bis(2-pyridyl)-2,3-pyrazine­dicarbo­nitrile

The crystal structure of the title compound, C₁₆H₈N₆, contains two independent mol­ecules with no significant difference in their structures. The pyrazine ring makes dihedral angles of 36.7 (2) and 36.5 (3)° with the two pyridine rings in one mol­ecule, and 43.1 (2) and 38.4 (1)° in the other. The dihedral angles between the two pyridine rings are 58.2 (2) and 56.0 (2)°, respectively. The favoured orientation of the pyridine rings is such that their N atoms face each other.     

Di­methyl (1R,8R)-1,11,11-tri­methyl-2,3-di­aza­tri­cyclo­[6.2.1.02,6]­undeca-3,5-diene-4,5-di­carboxyl­ate,a chiral mol­ecule with an approximate centrosymmetric crystal structure

The crystal structure of the title compound, C₁₆H₂₂N₂O₄, has two independent chiral mol­ecules related by a pseudo-inversion centre. 14 of the 22 non-H atoms have a centrosymmetric counterpart within a tolerance of 0.17 Å. A search of the Cambridge Structural Database [Spring 2000; Allen & Kennard (1993). Chem. Des. Autom. News, 8 , 1, 31–37] shows at least 10% of the crystal structures reported in the literature with space group P2₁ and Z = 4 to be chiral compounds with a pseudo-P2₁/c packing.     

A metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid bis(pentafluorophenyl)(phenoxy)borane

A new strategy for the metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid Boron has been first identified. Bis(pentafluorophenyl)(phenoxy)borane was used as a catalyst for the polymerization reaction system. And polytetrahydrofuran with high molecular weight and narrow molecular weight distribution could be obtained. The proposed mechanism was studied by MALDI-TOF, ESI-MS and O-18 isotope labeling analyses as a metal-free coordination insert...     

(±)-3-(3-Oxo­cyclo­hexyl)­propionic acid: dual conformational selection and hydrogen bonding in an ɛ-keto acid

The asymmetric unit of the title compound, C₉H₁₄O₃, consists of two mol­ecules having conformations that differ by a rotation of 111.7 (5)° about the equatorial substituent bond, so that the side chains of the two species extend away from the ring in different directions. Each conformer forms centrosymmetric hydrogen-bonded acid-to-acid dimers with its own enantiomer [O⋯O = 2.681 (3) and 2.698 (4) Å]. There is an intermolecular C—H⋯O close contact involving the ketone group of one of the conformers.     

Triangular ruthenium acetate clusters containing the bis(pyridyl)propane ligand and their inclusion chemistry with β-cyclodextrin

The triruthenium carboxylate cluster [Ru₃O(OAc)₆(py)₂(bpp)]⁺ (OAc = acetate) containing the bridging 1,3-bis(4-pyridyl)propane (bpp) ligand, and its dimeric species [{Ru₃O(OAc)₆(py₂)}₂(μ-bpp)]²⁺ were synthesized in order to investigate their inclusion compounds with β-cyclodextrin (β-CD). Characterization of the complexes was carried out based on spectroscopic, electrochemical and spectroelectrochemical techniques, while the formation of inclusion complexes was evaluated using ¹H NMR/NOESY spectroscopy. Since bpp is a flexible ligand, a DFT study was carried out in order to characterize its conformational isomers and their possible role in the host–guest chemistry with β-CD. Instead of observing the formation of inclusion compounds with different stoichiometries, we observed the formation of 1:1 bpp/β-CD compounds in which the bpp ligand assumes different conformations. The assembly of polymetallic rotaxane species was successfully demonstrated by monitoring the ¹H NMR spectra of the monomeric cluster species in the presence of aquapentacyanoferrate(II) ions and β-CD.     

A nitronyl nitro­xide complex of ­nickel(II) with nitrate as a ligand

The complex cation in [4,5-di­hydro-4,4,5,5-tetra­methyl-2-(2-pyridyl-κN)­imidazol-1-oxyl 3-oxide-κO³](nitrato-κ²O,O′)(N,N,N′,N′-tetra­methyl-1,2-ethanedi­am­ine-κ²N,N′)­nickel(II) hexafluorophosphate dichloromethane solvate, [Ni(NO₃)(C₆H₁₆N₂)(C₁₂H₁₆N₃O₂)]PF₆·CH₂Cl₂, is the first example of a nitro­nyl nitro­xide complex of a transition metal ion having d electrons in which nitrate is coordinated as a bidentate ligand. Owing to the smaller steric requirement of NO₃⁻, the Ni—­O(nitro­xide) bond length [2.014 (2) Å] is remarkably shorter than that in the corresponding ­β-­diketonate complexes [2.052 (4)–2.056 (2) Å].     

Large tunneling effect on the hydrogen transfer in bis(μ-oxo)dicopper enzyme: a theoretical study

Type-III copper-containing enzymes have dicopper centers in their active sites and exhibit a novel capacity for activating aliphatic C-H bonds in various substrates by taking molecular oxygen. Dicopper enzyme models developed by Tolman and co-workers reveal exceptionally large kinetic isotope effects (KIEs) for the hydrogen transfer process, indicating a significant tunneling effect. In this work, we demonstrate that variational transition state theory allows accurate prediction of the KIEs and Arrhenius parameters for such model systems. This includes multidimensional tunneling based on state-of-the-art quantum-mechanical calculations of the minimum-energy path (MEP). The computational model of bis(μ-oxo)dicopper enzyme consists of 70 atoms, resulting in a 204-dimensional potential energy surface. The calculated values of E(a)(H) - E(a)(D), A(H)/A(D), and the KIE at 233 K are -1.86 kcal/mol, 0.51, and 28.1, respectively, for the isopropyl ligand system. These values agree very well with experimental values within the limits of experimental error. For the representative tunneling path (RTP) at 233 K, the pre- and post-tunneling configurations are 3.3 kcal/mol below the adiabatic energy maximum, where the hydrogen travels 0.54 ? by tunneling. We found that tunneling is very efficient for hydrogen transfer and that the RTP is very different from the MEP. It is mainly heavy atoms that move as the reaction proceeds from the reactant complex to the pretunneling configuration, and the hydrogen atom suddenly hops at that point.     

Bis(O,O′-diiso­propyl di­thio­phosphato-S,S′)(1,10-phenanthroline-N,N′)metal(II) complexes with cadmium(II) and iron(II)

The two title compounds, [M(C₆H₁₄O₂PS₂)₂(C₁₂H₈N₂)], where M = Cd^II and Fe^II, are isomorphous. Each compound has a crystallographic twofold axis of symmetry through the metal atom and the 1,10-phenanthroline mol­ecule. The central metal atom is coordinated to four S atoms from the two dithiophos­phate groups and two N atoms from the 1,10-phenanthroline ligand. The environment of the metal atom is a distorted octahedron.     

Synthesis and Characterization of 2,6-Bis(imino)phenoxy Cobalt Complexes

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Room-temperature monoclinic and low-temperature triclinic phase-transition structures of meso-octa­methyl­calix­[4]­pyrrole–di­methyl sulfoxide (1/1)

Crystals of the title complex, C₂₈H₃₆N₄·C₂H₆OS, undergo a phase transition between room temperature and 198 K, as determined by X-ray diffraction techniques. A monoclinic form is observed at room temperature, while a triclinic modification is found at 198 K, with Z′ changing from 1 to 2. Differential scanning calorimetry (DSC) of the calix­pyrrole–di­methyl sulfoxide complex revealed a series of phase changes between 273 and 243 K. The transition from the room-temperature monoclinic form to the low-temperature triclinic form is reversible, as determined by changes in the cell dimensions from remeasuring selected reflections at room temperature and at temperatures below 223 K. The uncomplexed calix­[4]­pyrrole mol­ecule shows no phase changes occurring between room temperature and 233 K, the low-temperature limit of the DSC.