Mihaela-Diana Şerb

The whole range of hydrogen bonds in one crystal structure: neutron diffraction and charge-density studies of N,N-dimethylbiguanidinium bis(hydrogensquarate).

N,N-Dimethylbiguanidinium bis(hydrogensquarate) features an impressive range of hydrogen bonds within the same crystal structure: neighbouring anions aggregate to a dianionic pair through two strong O-H···O interactions; one of these can be classified among the shortest hydrogen bonds ever studied. Cations and anions in this organic salt further interact via conventional N-H···O and nonclassical C-H···O contacts to an extended structure. As all these interactions occur in the same sample, the title compound is particularly suitable to monitor even subtle trends in hydrogen bonds. Neutron and high-resolution X-ray diffraction experiments have enabled us to determine the electron density precisely and to address its properties with an emphasis on the nature of the X-H···O interactions. Sensitive criteria such as the Laplacian of the electron density and energy densities in the bond-critical points reveal the incipient covalent character of the shortest O-H···O bond. These findings are in agreement with the precise geometry from neutron diffraction: the shortest hydrogen bond is also significantly more symmetric than the longer interactions.

Synthesis and Characterization of Archetypal Ladder-Like Dibutyloxotin Cluster Derived from Sterically Encumbered 4-[( E )-2-(4-hydroxy-5-methylphenyl)-1-diazenyl]benzoate

Reaction of Bu2SnO with 4-[(E)-2-(4-hydroxy-5-methylphenyl)-1-diazenyl]benzoic acid in toluene yielded a tetranuclear tin cluster {[Bu2Sn(O2CC6H4(N=N(C6H3-4-OH-5-CH3))-p)]2O}2·2EtOH (1). The complex 1 was characterized using IR spectroscopy, NMR, elemental analysis and single-crystal X-ray diffraction. The compound is a centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complex containing a planar Sn4O2 core in which two μ3-oxo O-atoms connect an Sn2O2 ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination: syn–syn O, O′-bridging and mono atomic bridge. In the complex, the geometry around the tin atoms is distorted trigonal bipyramidal with an additional longer Sn···O contact.

Biguanide and squaric acid as pH-dependent building blocks in crystal engineering

In solutions containing biguanides and squaric acid, the pH value allows to control the outcome of crystallization. From N,N-dimethylbiguanide, N-phenylbiguanide and N-o-tolylbiguanide 10 different salts have been obtained as a function of proton activity. The constituents in these ionic solids reflect the species present in solution: hydrogensquarate, still a strong acid, only occurs in crystals precipitated from acidic medium, and biguanidinium monocations prevail in precipitates from basic solutions. Within these limitations, polymorphs and hydrates of different stoichiometry have been encountered. The pH of the crystallization medium also affects the nature of close contacts. The shortest hydrogen bonds in the crystalline solids do not occur between ions of opposite charge; rather, pH matching leads to close O–H⋯O contacts between squarate and hydrogensquarate anions which can only coexist at pH < 4.

One‐ and two‐dimensional polymers from proline and calcium bromide

Reactions of calcium bromide with enantiopure and racemic proline in aqueous solution lead to two solids in which the zwitterionic amino acid acts as a bridging ligand between neighbouring cations. Depending on the chirality of the amino acid, topologically very different products are obtained. With racemic proline, bromide acts as a simple uncoordinated counter-anion for the cationic heterochiral chains in catena-poly[[aquacalcium(II)]-μ-aqua-μ3-DL-proline-μ2-DL-proline], {[Ca(C5H9NO2)2(H2O)2]Br2}n. In agreement with chemical intuition, only carboxylate and aqua O atoms coordinate the alkaline earth cation in a low-symmetry arrangement. In contrast, L-proline affords the two-dimensional network poly[dibromidobis(μ2-L-proline)calcium(II)], [CaBr2(C5H9NO2)2]n, with an unexpected CaBr2 unit in a more regular coordination sphere.

The weakly coordinating perchlorate group in bis(N,N'-dimethylethylenediamine-κ2N,N')bis(perchlorato-κO)copper(II) studied at 100, 250 and 400 K.

The crystal structure of the title compound, [Cu(ClO(4))(2)(C(4)H(12)N(2))(2)], (I), is reported at 100, 250 and 400 K. The Cu(II) cation in this complex is coordinated in a distorted octahedral mode characteristic of Jahn-Teller systems. The coordination of the perchlorate ligands via longer, and presumably weaker, axial Cu-O distances varies significantly as a function of temperature. One of the Cu-O distances increases between 100 and 250 K, and one of the Cu-O-Cl angles expands between 250 and 400 K. At all temperatures, the complex forms a two-dimensional N-H···O hydrogen-bond network in the (001) plane.

[rac-2-(1-Amino­eth­yl)phenyl-κ2C1,N](ethyl­endiamine-κ2N,N′)palladium(II) 3,5-dimethyl­benzoate

In the title compound, [Pd(C8H10N)(C2H8N2)](C9H9O2), the palladium ion is coordinated in a distorted square-planar fashion by the two N atoms from the chelating ethylenediamine group and by the N and a C atom of the deprotonated chiral amine. The resulting cationic complex and the 3,5-dimethylbenzoate anion are interconnected by N—H⋯O hydrogen bonds.

[rac-2-(1-Amino-eth-yl)phenyl-κC,N](ethyl-endiamine-κN,N')palladium(II) 3-methyl-benzoate monohydrate.

In the title compound, [Pd(C8H10N)(C2H8N2)](C8H7O2)·H2O, the palladium ion is coordinated in a distorted square-planar fashion by the two N atoms from the chelating ethylenediamine group and by the N and a C atom of the deprotonated chiral amine. The resulting cationic complex, the 3-methylbenzoate anion and the hydrate water molecule are interconnected by N—H⋯O and O—H⋯O hydrogen bonds.

Halogen bonds on demand: I...S contacts in cocrystals of trans‐bis(thiocyanato‐κN)tetrakis(4‐vinylpyridine‐κN)nickel(II) and 2,3,5,6‐tetrafluoro‐1,4‐diiodobenzene

Hydrogen bonds are considered a powerful organizing force in designing supramolecular architectures because they are directional, selective and reversible at room temperature. trans-Dithiocyanatotetrakis(4-vinylpyridine)nickel(II) is a popular host for the inclusion of small molecules and 2,3,5,6-tetrafluoro-1,4-diiodobenzene (TFDIB) represents a strong halogen-bond donor. These constituents cocrystallize in a 1:1 stoichiometry, [Ni(NCS)2(C7H7N)4]·C6F4I2, in the tetragonal space group I4₁/a. Both residues occupy special positions, i.e. the pseudo-octahedral Ni(II) complex is located on a twofold axis and the TFDIB molecule sits about a crystallographic centre of inversion. The components interact via a short S···I contact of 3.2891 (12) Å between the thiocyanate S atom of the host and the iodine substituent at the perhalogenated aromatic ring of the smaller guest molecule. This interaction meets the commonly accepted criteria for a halogen bond. Such halogen bonds to sulfur are significantly less common than to smaller electronegative atoms.

Pyridine-2,6-dicarboxaldehyde bis[(diphenylmethylidene)hydrazone].

The title compound, C33H25N5, belongs to the family of pyridine-2,6-dicarboxaldehyde Schiff bases which possess a terdentate coordinating site (–N=C–C=N–C–C=N–) similar to terpyridine derivatives. The dihedral angles between pairs of terminal rings are 69.67 (9) and 66.23 (9)°. The shortest distance between the centroids of aromatic rings in neighbouring molecules is 3.8080 (14) Å.

Triaqua­bis­[4-(meth­oxy­carbon­yl)benzoato-κO 1]zinc dihydrate

In the crystal structure of the title complex, [Zn(C9H7O4)2(H2O)3]·2H2O, the Zn atom and the apical aqua ligand are located on a crystallographic twofold axis, with the ZnII ion in a distorted square-pyramidal coordination geometry composed of five O atoms, two from the monodentate methylterephthalato group and three from water molecules. The resulting complex and the two hydrate water molecules are interconnected by O—H⋯O hydrogen bonds.