Photo-and thermoresponsive N-salicylideneaniline derivatives: solid-state studies and structural aspects

Eight photo-and/or thermoresponsive salicylideneanilines were obtained by mechanosynthesis under solvent-free conditions and stabilized by external stimuli for their isolations in solid-state. Switching properties of these materials were investigated by various analytical techniques and spectroscopic data.

The crystal structure and characterization of a co-product in the synthesis of a Schiff base give evidence of its zwitterionic nature in the solid state

The zwitterionic form of a Schiff base in the solid state was found by the structural characterization of a coproduct and a mechanistic proposal of its formation.

Enantiopure Schiff bases of amino acid phenylhydrazides: impact of the hydrazide function on their structures and properties

New chiral Schiff bases have been synthesized and characterized with an important contribution from quantum chemical calculations at the DFT level of theory. They have been evaluated for their physical and biological properties.

Resonance-Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

Resonance-assisted hydrogen bonding (RAHB), a concept introduced by Gilli and co-workers in 1989, concerns a kind of intramolecular H-bonding strengthened by a conjugated π-system, usually in 6-, 8-, or 10-membered rings. This Review highlights the involvement of RAHB as a driving force in the synthesis of organic, coordination, and organometallic compounds, as a handy tool in the activation of covalent bonds, and in starting moieties for synthetic transformations. The unique roles of RAHB in molecular recognition and switches, E/Z isomeric resolution, racemization and epimerization of amino acids and chiral amino alcohols, solvatochromism, liquid-crystalline compounds, and in synthons for crystal engineering and polymer materials are also discussed. The Review can provide practical guidance for synthetic chemists that are interested in exploring and further developing RAHB-assisted synthesis and design of materials.

A structural, spectroscopic and theoretical study of an o-vanillin Schiff base derivative involved in enol-imine and keto-amine tautomerism

The potassium salt of the Schiff base derived from o-vanillin and taurine is involved in enol-imine (I) and keto-amine (II) tautomerism. Both tautomeric forms coexist in the crystal and they are stabilized by strong O–H⋯N and O⋯H–N intramolecular hydrogen bonds.

Two fluorescent Schiff base sensors for Zn2+: the Zn2+/Cu2+ion interference

While theenol-iminetautomer inL1exhibits Zn²⁺/Cu²⁺ion interference, theketo-enaminetautomer inL2recognizes only Zn²⁺.

Crystal structure of N-[(E)-(1,3-benzodioxol-5-yl)-methyl-idene]-4-chloro-aniline

In the title compound, C₁₄H₁₀ClNO₂, obtained by the condensation of 4-chloro­aniline and piperonal, the five-membered ring is almost planar (r.m.s. deviation = 0.023 Å) and the dihedral angle between the aromatic rings is 43.22 (14)°. In the crystal, a short O⋯Cl contact of 3.173 (2) Å is observed. The mol­ecules are arranged into corrugated (010) layers.

Structure investigation of intramolecular hydrogen bond in some substituted salicylaldehydes and 4-aminoantipyrine derivatives in solution and in the solid state

Seven imine derivatives obtained by condensation of appropriate aldehydes and salicylaldehydes with 4-aminoantipyrine were investigated in terms of intramolecular hydrogen bond structure. On the base of (1)H, (13)C and (15)N NMR measurements in solution and in the solid state we found out that all compounds which can form such structure exist as OH forms with strong H-bonds to nitrogen atom. The structure conclusions taken from NMR study were confirmed by pKa measurements. Surpassingly, the positions of protons in H-bridges only very slightly depend on the substituents in aldehyde used for condensation and on the phase (solution vs. solid state). The influence of antipyrine moiety seems to be the major factor defining H-bond structure.

Desmotropy, polymorphism, and solid-state proton transfer: four solid forms of an aromatic o-hydroxy Schiff base

The Schiff base derived from salicylaldehyde and 2-amino-3-hydroxypyridine affords a diversity of solid forms, two polymorphic pairs of the enol-imino (D1 a and D1 b) and keto-amino (D2 a and D2 b) desmotropes. The isolated phases, identified by IR spectroscopy, X-ray crystallography, and (13)C cross-polarization/magnetic angle spinning (CP/MAS) NMR spectroscopy, display essentially planar molecular conformations characterized by strong intramolecular hydrogen bonds of the O-H⋅⋅⋅N (D1) or N-H⋅⋅⋅O (D2) type. A change in the position of the proton within this O⋅⋅⋅H⋅⋅⋅N system is accompanied by substantially different molecular conformations and, subsequently, by divergent supramolecular architectures. The appearance and interconversion conditions for each of the four phases have been established on the basis of a number of solution and solvent-free experiments, and evaluated against the results of computational studies. Solid phases readily convert into the most stable form (D1 a) upon exposure to methanol vapor, heating, or by mechanical treatment, and these transformations are accompanied by a change in the color of the sample. The course of thermally induced transformations has been monitored in detail by means of temperature-resolved powder X-ray diffraction and infrared spectroscopy. Upon dissolution, all forms equilibrate immediately, as confirmed by NMR and UV/Vis spectroscopy in several solvents, with the equilibrium shifted far towards the enol tautomer. This study reveals the significance of peripheral groups in the stabilization of metastable tautomers in the solid state.

(E)-2-{[2-(2-Hy-droxy-ethyl-amino)-ethyl-imino]-meth-yl}phenol

The asymmetric unit of the title compound, C(11)H(16)N(2)O(2), contains two independent conformational isomers which show intra-molecular aromatic-imine O-H⋯N hydrogen bonds. In the crystal, neighboring mol-ecules are linked through inter-molecular aliphatic-aliphatic O-H⋯N, aliphatic-aromatic N-H⋯O and C-H⋯O inter-actions into hydrogen-bonded layers parallel to the ab plane.