Solvent-triggered stereoselectivity of α,α-cyclopropanation of amino acids in the Ni(ii) chiral coordination environment.

Experimental and DFT investigation of the α,α-cyclopropanation of amino acids via nucleophilic addition of the deprotonated glycine Ni(ii)-Schiff-base complex, containing the (S)-proline derivatives as an auxiliary chiral moiety, to alkyl α-bromoacrylates was performed. It was demonstrated that the predominant configuration of the newly formed α-stereocenter is (S), regardless of the solvent used but the smart choice of solvent allows high diastereoselectivity at the removed ß-stereocenter to be obtained, which commonly is rather rare. DFT analysis of the reaction path provides a rationale for the stereochemical outcome observed. The cyclopropanated complexes exhibit stereodependent redox activity, thus supporting that this is a general phenomenon inherent to this class of Ni Schiff-base derivatives, accounting for the influence of the peripheral groups in the metal coordination environment on the relative impact of different parts of the molecule in the frontier orbitals via conformational changes.

Carboxylate-phenolate tautomerism in 5-[(nitrophenyl)diazenyl]salicylate anions.

Aryldiazenyl derivatives of salicylic acid and their salts are used as dyes. In these structures, the carboxylate groups are engaged in short contacts with the cations and in hydrogen bonds with water molecules, if present. If both O atoms of the carboxylate group take part in such interactions, the negative charge is delocalized over the two atoms. In the absence of hydrogen bonds and contacts with cations, the negative charge is localized on one of the O atoms. In the crystal structures of tetramethylammonium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate and tetramethylammonium 2-hydroxy-5-[(E)-(2-nitrophenyl)diazenyl]benzoate, both C4H12N(+)·C13H8N3O5(-), all the interactions between the cations and anions are weak, and their effect on the geometry of the anions is negligible. Under these conditions, the 2-nitro-substituted anion is an almost pure phenol-carboxylate tautomer, whereas in the 4-nitro-substituted anion, the phenolic H atom is shifted towards the carboxylate group, and thus the structure of this anion is intermediate between the phenol-carboxylate and phenolate-carboxylic acid tautomeric forms. The probable formation of such an intermediate form is supported by quantum chemical calculations. Being the characteristic feature of this form, a short distance between the phenolic and carboxylate O atoms is observed in the 4-nitro-substituted anion, as well as in the structures of some 3,5-dinitrosalicylates reported in the literature.

Solutions of complex copper salts in low-transition-temperature mixture (LTTM).

The structure and properties of diethanolamine complexes of copper(ii) triflates dissolved in an excess of diethanolamine (DH2) were studied. The copper containing substance was found to be a solution of copper(ii) complex salt [Cu(2+)DH2(DH(-))]OTf(-) in LTTM composition [(DH2)4H(+)](OTf(-)), where LTTM = low-transition-temperature mixture, OTf(-) = triflate anion. According to the EXAFS data, the coordination number of copper(ii) atoms in solution does not exceed four. Addition of even negligible amounts of acid significantly changes DH2 volatility and decomposition conditions.

syn and anti conformations in 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoic acid and two related salts.

The crystal structures of 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoic acid, C13H9N3O5, (I), ammonium 2-hydroxy-5-[(E)-phenyldiazenyl]benzoate, NH4(+)·C13H9N2O3(-), (II), and sodium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate trihydrate, Na(+)·C13H8N3O5(-)·3H2O, (III), have been determined using single-crystal X-ray diffraction. In (I) and (III), the phenyldiazenyl and carboxylic acid/carboxylate groups are in an anti orientation with respect to each other, which is in accord with the results of density functional theory (DFT) calculations, whereas in (II), the anion adopts a syn conformation. In (I), molecules form slanted stacks along the [100] direction. In (II), anions form bilayers parallel to (010), the inner part of the bilayers being formed by the benzene rings, with the -OH and -COO(-) substituents on the bilayer surface. The NH4(+) cations in (II) are located between the bilayers and are engaged in numerous N-H···O hydrogen bonds. In (III), anions form layers parallel to (001). Both Na(+) cations have a distorted octahedral environment, with four octahedra edge-shared by bridging water O atoms, forming [Na4(H2O)12](4+) units.

Two polymorphs of 2-ethyl-3-hydroxy-6-methylpyridinium hydrogen N-acetyl-L-glutamate from powder diffraction data.

The title salt, C8H12NO(+)·C7H10NO5(-), crystallizes in two polymorphic modifications, viz. monoclinic (M) and orthorhombic (O). The crystal structures of both polymorphic modifications have been established from laboratory powder diffraction data. The crystal packing motifs in the two polymorphs are different, but the conformations of the anions are generally similar. In M, the anions are linked by pairs of hydrogen bonds of the N-H···O and O-H···O types into chains along the b-axis direction, and neighbouring molecules within the chain are related by the 21 screw axis. The cations link these chains via O-H···O and N-H···O hydrogen bonds into layers parallel to (001). In O, the anions are linked by O-H···O hydrogen bonds into helices along [001], and neighbouring molecules within the helix are related by the 21 screw axis. The neighbouring helical turns are linked by N-H···O hydrogen bonds. The cations link the helices via O-H···O and N-H···O hydrogen bonds, thus forming a three-dimensional network.

Zoledronic acid: monoclinic and triclinic polymorphs from powder diffraction data.

The crystal structures of the monoclinic and triclinic polymorphs of zoledronic acid, C5H10N2O7P2, have been established from laboratory powder X-ray diffraction data. The molecules in both polymorphs are described as zwitterions, namely 1-(2-hydroxy-2-phosphonato-2-phosphonoethyl)-1H-imidazol-3-ium. Strong intermolecular hydrogen bonds (with donor-acceptor distances of 2.60 Šor less) link the molecules into layers, parallel to the (100) plane in the monoclinic polymorph and to the (1-10) plane in the triclinic polymorph. The phosphonic acid groups form the inner side of each layer, while the imidazolium groups lie to the outside of the layer, protruding in opposite directions. In both polymorphs, layers related by translation along [100] interact through weak hydrogen bonds (with donor-acceptor distances greater than 2.70 Å), forming three-dimensional layered structures. In the monoclinic polymorph, there are hydrogen-bonded centrosymmetric dimers linked by four strong O-H...O hydrogen bonds, which are not present in the triclinic polymorph.

4-Chloro-2-[(E)-(4-nitro-phen-yl)diazenyl]phenol.

The title compound, C(12)H(8)ClN(3)O(3), in the crystalline state and in solution, exists in the azo form, as predicted by density functional theory (DFT) calculations. The mol-ecule is approximately planar [the dihedral angle between the rings is 1.83 (8)°], with the nitro group slightly twisted [13.4 (2)°] relative to the benzene ring. Translationally related mol-ecules form stacks along [010] with an inter-planar distance of 3.400 (2) Å. The hydroxy group forms an intramolecular hydrogen bond with the azo N atom.

4-[(E)-1-Naphthyl-diazen-yl]phenol.

The title compound (C. I. Solvent Yellow 8), C(16)H(12)N(2)O, crystallizes with two crystallographically independent mol-ecules in the asymmetric unit. The planarity of both mol-ecules is slightly distorted, the dihedral angles between the benzene ring and the naphthalene system being 9.04 (8) and 5.69 (3)°. In the crystal, O-H⋯N hydrogen bonds between the hydr-oxy groups and azo N atoms link the two symmetry-independent mol-ecules into a polymeric chain propagating in [001].

The twofold interpenetrated three-connected three-dimensional (10,3)-net in 2-aminoethene-1,1,2-tricarbonitrile.

In the crystal structure of the title compound, C5H2N4, each molecule is linked by N-H...N[triple-bond]C hydrogen bonds to four other molecules, thus forming a network that can be described as a twofold interpenetrated three-connected three-dimensional (10,3)-net. The interpenetrated nets are related by (010) translation. If only intermolecular hydrogen bonds are taken into account, these nets can be considered as independent. However, the interactions between the cyano groups from different nets indicate mutual assistance of the two nets during their formation.