Induction of Λ-helicity in a zinc complex with an alanine-appended aminopyridine ligand

The crystal structure of tris[dimethyl 5-({1-[(pyridin-2-yl-κN)carbamoyl-κO]ethyl}carbamoyl)benzene-1,3-dicarboxylate]zinc(II) dinitrate acetonitrile trisolvate, [Zn(C19H19N3O6)3](NO3)2·3CH3CN or [Zn(L)3](NO3)2·3CH3CN, (1), has been determined by single-crystal X-ray diffraction. The neutral ligand L coordinates to the Zn2+ cation in a bidentate fashion via the pyridine N atom and an amide O atom, forming a six-membered chelate ring. The Λ-helical chirality of the Zn2+ coordination sphere is induced by pendant L-alanine residues through stacking interactions between the arene groups of two coordinated ligands, assisted by a hydrogen bond between amide groups bonded to the stacked arene rings. The third ligand is coordinated to the Zn2+ cation by the same six-membered chelate ring, but in the opposite direction with respect to the analogous chelate rings of the first two coordinated ligands. Besides ionic interactions between [ZnL 3]2+ complexes and NO3 − anions, several types of hydrogen bonds and intermolecular stacking interactions contribute to the stability of the solid-state phase.

Crystal structure of poly[(μ3-4-amino-1,2,5-oxadiazole-3-hydroxamato)thallium(I)]

The title compound represents the thallium(I) salt of a substituted 1,2,5-oxadiazole, [Tl(C3H3N4O3)] n , with amino- and hydroxamate groups in the 4- and 3- positions of the oxadiazole ring, respectively. In the crystal, the deprotonated hydroxamate group represents an intermediate between the keto/enol tautomers and forms a five-membered chelate ring with the thallium(I) cation. The coordination sphere of the cation is augmented to a distorted disphenoid by two monodentately binding O atoms from two adjacent anions, leading to the formation of zigzag chains extending parallel to the b axis. The cohesion within the chains is supported by π–π stacking [centroid–centroid distance = 3.746 (3) Å] and intermolecular N—H...N hydrogen bonds.

Dibromido[N-(1-diethylamino-1-oxo-3-phenylpropan-2-yl)-N′-(pyridin-2-yl)imidazol-2-ylidene]palladium(II) dichloromethane monosolvate

In the molecule of the title N,N′-disubstituted imidazol-2-ylidene palladium(II) complex, [PdBr2(C21H24N4O)]·CH2Cl2, the palladium(II) atom adopts a slightly distorted square-planar coordination (r.m.s. deviation = 0.0145 Å), and the five-membered chelate ring is almost planar [maximum displacement = 0.015 (8) Å]. The molecular conformation is enforced by intramolecular C—H...Br hydrogen bonds. In the crystal, complex molecules and dichloromethane molecules are linked into a three-dimensional network by C—H...O and C—H...Br hydrogen bonds.

On the preferences of five-membered chelate rings in coordination chemistry: insights from the Cambridge Structural Database and theoretical calculations

We illustrate, combining experimental and theoretical results, that the five-membered chelate ring is able to adapt itself to a great variety of metal ions.

Investigation of nitro–nitrito photoisomerization: crystal structures of trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato}(pyridine/4-methylpyridine)nitrocobalt(III)

The reaction cavities of the nitro groups in the title compounds, trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-κ4 O,N,N′,O′}(nitro-κN)(pyridine-κN)cobalt(III), [Co(C16H14N2O2)(NO2)(C5H5N)], (I), and trans-{2,2′-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-κ4 O,N,N′,O′}(4-methylpyridine-κN)(nitro-κN)cobalt(III), [Co(C16H14N2O2)(NO2)(C6H7N)], (II), have been investigated to reveal that the intermolecular CMe—H...O(nitro) contacts in (II) are unfeasible for the nitro–nitrito photochemical linkage isomerization process. In (I), there are two independent complexes showing similar conformations, and the central five-membered chelate ring of the tetradentate salen ligand adopts the same absolute configuration. This is the result of pseudo-spontaneous resolution, since the configuration of the five-membered chelate ring may frequently be reversed in solution. In the crystals of (I) and (II), the molecules are linked into three-dimensional networks by C—H...O hydrogen bonds.

Supramolecular architectures sustained by arene-C–H…π(quasi-chelate ring) interactions in the crystal structures of copper(I) complexes

A review of the crystallographic literature is presented whereby structures featuring a quasi-six-membered chelate ring of the type {CuCl…HNCS} were evaluated for the presence of intermolecular C–H…π(quasi-chelate) interactions. These are shown to stabilise crystal structures leading to zero-, one-, two- and even three-dimensional architectures. Details of these interactions are described and a comparison to analogous interactions formed intramolecularly has been made. The C–H…π(quasi-chelate) interactions in these structures occur in one-third of structures where such contacts can potentially form.