Investigation of molecular structure and solvent/temperature effect on tautomerism in (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl]phenol, a new thermochromic Schiff base, by using XRD, FT-IR, UV-vis, NMR and DFT methods.

The molecular structure and the solvent/temperature effect on the tautomerism in a new Schiff base, (E)-4,6-dibromo-3-methoxy-2-[(p-tolylimino)methyl]phenol, were investigated using spectroscopic (NMR, UV-vis, FT-IR), crystallographic (XRD), computational (DFT and TD-DFT) methods and harmonic oscillator model of aromaticity (HOMA). The XRD, DFT and FT-IR results show that the compound exists in the phenol-imine form in the solid state. HOMA indices support the aromatic structure of the compound. DFT calculations were performed to understand proton transfer process and relatively close values were obtained for the energies of tautomers. UV-vis studies prove the solvent dependence of the tautomerism in the compound by revealing the existence of both phenol-imine and keto-amine forms in polar solvents and only the phenol-imine form in apolar solvent. The TD-DFT results for the electronic transitions lead to the same conclusion as the absorption spectra. 1H NMR and 13C NMR studies at room and low (-60 °C) temperatures indicate that the tautomeric equilibrium occurs rapidly in the compound. Therefore, it is difficult to observe two tautomers. However, the presence of tautomeric structures is clearly seen in acetone­d6, alternatively underlying the solvent and temperature dependence of tautomerism in the title compound.

Analysis of tautomeric equilibrium in (E)-4,6-dibromo-2-[(4-fluorophenylimino)methyl]-3-methoxyphenol compound.

In this study, the tautomeric equilibrium between the phenol-imine and keto-amine structural forms of (E)-4,6-dibromo-2-[(4-fluorophenylimino)methyl]-3-methoxyphenol compound has been investigated with experimental (XRD, UV-vis and NMR) and theoretical (DFT and TD-DFT) methods. The results clearly show that structural preference of the compound is definitely depended on its state. Namely, the compound exists in phenol-imine form in the solid state while one or both of these forms can be seen in solvent media. For example, the compound prefers phenol-imine form in benzene while both forms exist in EtOH and DMSO solvents. Coexistence of two forms has been quantified with NMR studies, giving a ratio of 11:9 for phenol and keto structures of the compound in acetone-d6 solvent.

Existence of a resonance hybrid structure as a result of proton tautomerism in (±)-(E)-4-bromo-2-[(2,3-dihydroxypropylimino) methyl]phenol racemate.

o-Hydroxy Schiff bases have two tautomers known as phenol-imine and keto-amine forms. In the present work, the tautomerism in (E)-4-Bromo-2-[(2,3-dihydroxypropylimino)methyl]phenol compound has been investigated by experimental (XRD, FT-IR and UV-vis) and computational (DFT and TD-DFT) methods. The X-ray diffraction (XRD) study reveals that the title compound favors a resonance hybrid structure of phenol-imine and keto-amine forms in the solid state rather than having these forms separately or jointly. Experimental UV-vis study of proton transfer process in solvent media (Benzene, DMSO and EtOH) shows the preference of phenol-imine form in benzene while both phenol-imine and keto-amine characteristics are present in EtOH and DMSO.

The prototropic tautomerism and substituent effect through strong electron-withdrawing group in (E)-5-(diethylamino)-2-[(3-nitrophenylimino)methyl]phenol.

The prototropic tautomerism in o-Hydroxy Schiff bases results in two forms called phenol-imine and keto-amine. The preference of a particular form by the compound changes in the solid and solvent media. The choice can also be regulated by a substituent with a different electron-donating or withdrawing group. In the present study, the above-mentioned factors are considered in the investigation of (E)-5-(diethylamino)-2-[(3-nitrophenylimino)methyl]phenol compound (an o-Hydroxy Schiff basis) by experimental (XRD, FT-IR and UV-vis) and computational (DFT and TD-DFT) methods. The results show that the title compound adopts only phenol-imine form in the solid and solvent media. This was attributed to the substituent effect through strong electron-withdrawing nitro group.

Bis(propane-1,3-diamine)-disaccharinatonickel(II).

In the title complex, [Ni(C(7)H(4)NO(3)S)(2)(C(3)H(10)N(2))(2)] or [Ni(sac)(2)(pen)(2)] (sac = saccharinate or 1,1,3-trioxo-2,3-dihydro-1λ(6,2)-benzothia-zol-2-ide and pen = propane-1,3-diamine), the Ni(II) ion sits on an inversion center, being coordinated by two N atoms of the sac ligands, which occupy trans positions, and four N atoms of the bidentate pen ligands to define a distorted octa-hedral geometry. The pen ligands chelate the metal ion, forming a six-membered ring which adopts a half-chair conformation, while the sac ligands adopt the most common coordination mode. The crystal packing is stabilized by N-H⋯O hydrogen bonds, which form a one-dimensional network along [010]. It is also supported by an N-H⋯S hydrogen bond between the amine group of the pen ligand and the sulfonyl group of the sac ligand.

Survey of conformational isomerism in (E)-2-[(4-bromophenylimino)methyl]-5-(diethylamino)phenol compound from structural and thermochemical points of view.

In this study, (E)-2-[(4-bromophenylimino)methyl]-5-(diethylamino)phenol compound was investigated by mainly focusing on conformational isomerism. For this purpose, molecular structure and spectroscopic properties of the compound were experimentally characterized by X-ray diffraction, FT-IR and UV-Vis spectroscopic techniques, and computationally by DFT method. The X-ray diffraction analysis of the compound shows the formation of two conformers (anti and eclipsed) related to the ethyl groups of the compound. The two conformers are connected to each other by non-covalent C-H⋯Br and C-H⋯π interactions. The combination of these interactions is resulted in fused R(2)(2)(10) and R(2)(4)(20) synthons which are responsible for the tape structure of crystal packing arrangement. The X-ray diffraction and FT-IR analyses also reveal the existence of enol form in the solid state. From thermochemical point of view, the computational investigation of isomerism includes three studies: the calculation of (a) the rate constants for transmission from anti or eclipsed conformations to transition state by using Eyring equation, (b) the activation energy needed for isomerism by using Arrhenius equation, (c) the equilibrium constant from anti conformer to eclipsed conformer by using the equation including the change in Gibbs free energy. The dependence of tautomerism on solvent types was studied on the basis of UV-Vis spectra recorded in different organic solvents. The results showed that the compound exists in enol form in all solvents except ethyl alcohol.

Single stranded helical chains of C-H⋯π interactions further connected by halogen-halogen interactions of type I to construct supramolecular structure of (E)-5-(diethylamino)-2-[(4-iodophenylimino)methyl]phenol compound.

In this study, (E)-5-(diethylamino)-2-[(4-iodophenylimino)methyl]phenol compound was investigated from the point of stacking interactions assembling the supramolecular network, conformational isomerism and tautomerism. For this purpose, X-ray diffraction, FT-IR and UV/Vis spectroscopic techniques were used, giving the following structural and spectroscopic properties of the compound: The title compound has two conformers (anti and eclipsed) in the crystal structure resulting from rotation about C-N single bond of ethyl group. Both conformers prefer enol form in the solid state, adopting E configuration about the CN double bond. The supramolecular architecture of the compound is constructed by two non-covalent interactions as C-H⋯π and halogen-halogen interactions. The repetition of C-H⋯π interactions is resulted in a single-stranded helical structure. The helical structures are further connected by C-I⋯I-C interactions of Type I to construct the two dimensional supramolecular network defined as (6,3)-net in Wells nomenclature. The title compound adopts both enol and keto forms in EtOH (a polar and protic solvent) while enol form is preferred in the solid state.

Probing the compound (E)-5-(diethylamino)-2-[(4-methylphenylimino)methyl]phenol mainly from the point of tautomerism in solvent media and the solid state by experimental and computational methods.

In this study, the molecular structure and spectroscopic properties of (E)-5-(diethylamino)-2-[(4-methylphenylimino)methyl]phenol were characterized experimentally by X-ray diffraction, FT-IR and UV-vis spectroscopic techniques and computationally by DFT method. It is concluded on the basis of X-ray diffraction and FT-IR analyses that the title compound exists in enol form in the solid state. UV-vis spectra of the title compound were recorded in different organic solvents to investigate the dependence of tautomerism on solvent types. The tautomerism-solvent relation was also studied by computational methods to have more insight on structural properties. The geometry optimization of the title compound in gas phase was performed by using DFT (B3LYP) method with 6-311G(d,p) basis set. The geometry optimizations in solvent media were carried out at the same theory level by the polarizable continuum model (PCM). In the calculation of excitation energies, TD-DFT calculations were carried out in both gas and solution phases. The computational investigation of non-linear optical properties indicates that the title compound has a good second order nonlinear optical property. The thermodynamic properties were obtained in the range of 100-500 K.

[N-(2-Hydroxy-ethyl)ethyl-enediamine]oxalatocopper(II).

In the title mononuclear copper(II) compound, [Cu(C(2)O(4))(C(4)H(12)N(2)O)], the Cu(II) ion has a slightly distorted square-pyramidal geometry, with a tridentate N-(2-hydroxy-ethyl)ethyl-enediamine (HydEt-en) and a bidentate oxalate (ox) ligand. The N atoms of the HydEt-en ligand and the O atoms of ox ligand form the basal plane, while the O atom of the ethanol group of the HydEt-en ligand is located in the axial position. The complex mol-ecules participate in a supra-molecular assembly through N-H⋯O and O-H⋯O hydrogen bonds between HydEt-en and ox ligands.

cis-Bis(butyl-amine-κN)bis-[sulfa-diazine(1-)-κN,N']copper(II) penta-hydrate.

In the title compound {systematic name: cis-bis-[4-amino-N-(pyrimidin-2-yl)benzene-sulfonamidato-κ(2)N,N']bis-(butyl-amine-κN)copper(II) penta-hydrate}, [Cu(C(10)H(9)N(4)O(2)S)(2)(C(4)H(11)N)(2)]·5H(2)O or [Cu(sdz)(2)(ba)(2)]·5H(2)O [ba is butyl-amine and sdz = sulfadiazine(1-)], the copper(II) cation is six-coordinated by four N atoms of two sulfadiazine ligands and two N atoms of butyl-amine ligands. The copper(II) ion and one of the water mol-ecules lie on twofold rotation axes. One of the butyl groups is disordered over two sites, with occupancies of 0.395 (8) and 0.605 (8). The geometry around the S atom is distorted tetra-hedral. The crystal structure involves inter-molecular N-H⋯N and N-H⋯O hydrogen bonds. N-H⋯N hydrogen bonds between sdz ligands lead to a sheet structure parallel to the ab plane.

Polymeric mu-cyano-dicyanonickelate(II)-mu-cyano-trans-bis[N-(2-hydroxyethyl)ethylenediamine]cadmium(II).

The title compound, catena-poly[[mu-cyano-1:2kappa(2)C:N-dicyano-1kappa(2)C-trans-bis[N-(2-hydroxyethyl)ethane-1,2-diamine-2kappa(2)N,N']cadmium(II)nickel(II)]-mu-cyano-1:2'kappa(2)C:N], [CdNi(CN)(4)(C(4)H(12)N(2)O)(2)], consists of alternating square-planar Ni(CN)(4) fragments, formally dianionic, and Cd(hydet-en)(2) moieties [hydet-en is N-(2-hydroxyethyl)ethylenediamine], with the two bridging cyanide ligands in a mutually trans disposition at the Ni atom and cis at the Cd atom. The resulting one-dimensional zigzag chain structure has the Ni atom on an inversion center, while the distorted octahedron centered on the Cd atom lies on a twofold axis. The polymer chains are connected into undulating sheets by weak interchain N-H...N, N-H...O and O-H...N hydrogen bonds, which are also present between successive sheets.