Zvjezdana Cimerman

The Schiff bases of salicylaldehyde and aminopyridines as highly sensitive analytical reagents

The analytical applicability of heteroaromatic Schiff bases, 2-(3-pyridylmethyliminomethyl)phenol (compound 1), 2-(2-pyridyliminomethyl)phenol (compound 2), 2-(2-amino-3-pyridyliminomethyl)phenol (compound 3), N,N′-bis(salicylidene)-2,3-pyridinediamine (compound 4), N,N′-bis(salicylidene)-2,6-pyridinediamine (compound 5) and 2-(2-amino-4-methox-ymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (compound 6), was proved. The investigation included a study of the characteristics that are essential for solvent extraction and for the spectrophotometric and spectrofluorimetric determinations of copper. Despite structural similarities, the investigated Schiff bases exhibited different behaviour in solution. Compounds 2–5 adopted predominantly the enolimino form in most solvents, whereas compound 1 was partially present as ketoamine in the solutions of polar solvents. Compound 6 was found to be the tautomeric mixture of cyclic diamine and enolimine in most solvents. All the investigated Schiff bases were capable of quantitatively extracting transition metals into chloroform. In the case of Cu(II), compound 4 proved to be an effective extractant in the range 5 <pH < 12, compounds 1 and 6 were effective in the range 6 <pH < 12, whereas compounds 2, 3 and 5 were effective only in the alkaline medium above pH 9. The spectrophotometric determination of Cu(II) after extraction was very sensitive and selective with regard to Cd(II) and Pb(II). Highest sensitivity was achieved with compound 4 (ϵ430 = 2.1 × 104 mol−1 1 cm−1). This characteristic was favourable compared to other well-known copper reagents. Since the fluorescence of Schiff bases was quenched by Cu(II), Mn(II), Fe(III), Ni(II) and Cr(III), the sensitivity as well as the selectivity were further enhanced using the spectrofluorimetric procedure. Additional advantages of these compounds to other reagents for copper(II) are simple preparation and a detailed knowledge of their equilibria.

Structural and spectroscopic characteristics of aroylhydrazones derived from nicotinic acid hydrazide

Abstract Aroylhydrazones derived from salicylaldehyde, o-vanillin and nicotinic acid hydrazide have been synthesized and characterized on the basis of NMR, IR and UV/Vis spectral data. The crystal and molecular structure of N′-salicylidene-3-pyridinecarbohydrazide has been determined by X-ray diffraction.

Tautomeric and protonation equilibria of Schiff bases of salicylaldehyde with aminopyridines

Abstract The equilibria of the Schiff bases of salicylaldehyde with 2-aminopyridine, 2,3-diaminopyridine, 2,6-diaminopyridine and 3-aminomethylpyridine were studied by means of spectroscopic methods. In non-polar solvents enolimines were predominantly present. In polar solvents rapid tautomeric interconversion of enolimines to ketoamines as well as slow hydrolysis were noted. The tendency to tautomeric interconversion was significant in the case of 2-(3-pyridylmethylimi-nomethyl)phenol, whereas in the case of other Schiff bases it was very low. The corresponding tautomeric constants were estimated in a variety of solvents on the basis of UV spectral data. The protonation constants of all compounds were determined in methanol/water mixtures by the spectrophotometric method and discussed with respect to their structural characteristics and solvent properties.

Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV–VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV–VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ϕ=80%) led to aggregation of the cationic molecules. Using the UV–VIS absorption data, a corresponding dimerization constant was evaluated.

The structure and tautomeric properties of 2-(3-pyridylmethyliminomethyl)phenol☆

Abstract The structure and properties of 2-(3-pyridylmethyliminomethyl)phenol have been determined by X-ray crystallography, NMR, UV and IR spectroscopy and compared with the characteristics of the Schiff bases derived from salicylaldehyde and aminopyridines. Crystal data: C13H12N2O, Mr = 212.250, monoclinic, space group P21/n, a = 10.49(1) A, b = 9.002(4) A, c = 12.42(1) A, β = 109.10(4)°, V = 1109(2) A3, Z = 4, Dx = 1.271 g cm−3, Mokα (λ = 0.71073 A), μ = 0.8 cm−1, F(000) = 448, T = 297 K, R = 0.049, RW = 0.053 for 886 reflections with I 2σ(I). Bond distances and bond angles are similar to those of 2-(pyridyliminomethyl)phenols. In the title molecule the dihedral angle between the pyridine and benzene least-squares planes is 89.9(2)°. There is an intramolecular O1H … N1 hydrogen bond of 2.572(5) A. In solutions of polar solvents tautomeric interconversion of the Schiff base into the ketoamine is observed. Corresponding equilibrium constants are estimated in a variety of solvents on the basis of UV spectral data.

Structure and spectroscopic characteristics of Schiff bases of salicylaldehyde with 2,3-diaminopyridine

Abstract The Schiff bases 2-amino-3-salicylideneaminopyridine ( 1 ) and 2,3-bis(salicylideneamino)pyridine (bimorphous, 2a and 2b ) were prepared and characterized by X-ray crystallography and by IR and NMR spectrometry. ( 1 ) C 12 H 11 N 3 O, M r = 213.240, monoclinic, space group P 2 1 / c , a = 12.00(2), b = 6.594(3), c = 14.06(2) A, β = 104.90(8)°, V = 1075(2) A 3 , Z = 4, D x = 1.317 g cm −3 , λ(Mo Kα) = 0.71073 A, μ = 0.82 cm −1 , F (000) = 448, T = 295 K, R = 0.047, R w = 0.028 for 886 reflections with I –σ( I ). ( 2a ) C 19 H 15 N 3 O 2 , M r = 317.348 monoclinic, space group P 2 1 , a = 6.202(3), b = 17.622(7), c = 14.724(8) A, β = 91.85(3)°, V = 1608(1) A 3 , Z = 4 (two crystallographically independent molecules A and B ), D x = 1.311 g cm −3 , λ(Mo Kα) = 0.71073 A, μ = 0.816 cm −1 , F (000) = 664, T = 295 K, R = 0.058, R w = 0.034 for 972 reflections with I > 3σ( I ). The angle between the benzene and the pyridine ring is 51.5(2)° in 1 , whereas in 2a the corresponding angles are 51.1(4)° in molecule A and 51.8(4)° in molecule B . Molecules of 1 are connected in pairs by two centrosymmetric hydrogen bonds NH⋯N Py of 3.024(5)A. Intermolecular bonding of 1 does not take place in CHCl 3 solution. No evidence was found in the IR and NMR spectra for tautomeric interconversion of 1 and 2 into the ketoamine or for cyclization of 2 into the cyclic diamine.

STRUCTURAL CHARACTERISTICS OF N,N'-BIS(SALICYLIDENE)-2,6-PYRIDINEDIAMINE

Abstract The Schiff base N , N ′-bis(salicylidene)-2,6-pyridinediamine has been synthesized and characterized in the solid state and in solution using X-ray analysis, IR, UV/Vis and NMR spectroscopy. Crystal data: C 19 H 15 N 3 O 2 , M r =317.34, monoclinic, space group P2 1 /c, a =19.313(5), b =5.854(2), c =14.957(6) A, β =110.45(2)°, V =1584.4(9) A 3 , Z =4, R =0.049, R w =0.095 for 3323 independent reflections with I >2 σ ( I ). There are two intramolecular hydrogen bonds O–H⋯N between the hydroxyl and imino groups of 2.564(3) and 2.633(3) A. The enolimino form is found in the solid state and is also the predominant tautomeric form in solution. A tendency of interconversion to ketoamine has been observed only in rather polar solvents, such as methanol and methanol/water mixtures and has been found to be very low: tautomeric constants K t =[ketoamine]/[enolimine] amount to 0.02 and 0.03 in methanol and methanol/water 4/1, respectively.© 1997 Elsevier Science B.V.

Fluoroionophores with phenanthridinyl units

Novel fluoroionophores bearing two (1) and one (2) fluorophoric 6-phenanthridinyl units attached by a short methylene spacer onto nitrogen atoms of 7,16-diaza- and aza-18-crown-6 rings have been prepared in high yields. The fluoroionophores exhibited the ability to signal binding of certain metal cations through the specific complexation induced shifts (CIS) of phenanthridine protons in 1H NMR spectra as well as by the large intensity enhancements in fluorescence spectra. The X-ray structure analysis of [1, K+(C2H4Cl2)] picrate complex revealed that K+ is nine-coordinated, using all donors from the diazacrown ring, one chlorine atom from 1,2-dichloroethane solvent molecule and both nitrogen donors from syn-oriented phenanthridine units.

Structure and Spectroscopic Characteristics of N,N′-bis(2-Hydroxy-3-methoxyphenylmethylidene)2,6-pyridinediamine

The Schiff base N,N′-bis(2-hydroxy-3-methoxyphenylmethylidene)-2,6-pyridinediamine has been synthesized and characterized in the solid state and in solution using X-ray analysis, IR, UV/Vis, and NMR spectroscopy. Crystal data: C21H19N3O4, Mr = 377.39, orthorhombic, space group Pnc2, a = 4.9288(8), b = 8.8873(19), c = 20.870(5) Å, V = 914.19(20) Å3, Z = 2, R = 0.0387, Rw = 0.0530, 1845 independent reflections, 778 with I > 2σ(I). There are two intramolecular hydrogen bonds O—H-N between the hydroxyl and imino groups of 2.622(3) Å. The enolimine form is found in the solid state and is also the predominant tautomeric form in solution. Comparison of the title compound with the structurally related N,N′-bis(salicylidene)-2,6-pyridinediamine and N,N′-bis(salicylidene)-2,3-pyridinediamine is given.