P. Barczyński

Luminescence studies of Eu(III) mixed ligand complexes

Abstract A series of europium(III) mixed ligand complexes, Ln/L/X based on pyridine carboxylic acid N-oxides, L, plus 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen), X, have been studied. The complexes were characterized using Eu luminescence (conventional and laser-induced) spectroscopy. A number of N-oxide ligand designs, including mono- and dicarboxylic acids and their derivatives (aryl-substituted), having various steric groups, have been tested with the main goal of optimizing the luminescence properties under various experimental conditions. Potentiometric titration of acid N-oxides have been carried out in aqueous solution in order to determine their p K a and the pH values, important for complexation conditions. Based on the Eu(III) luminescence lifetime measurements, hydration numbers of the Eu(III) complexes have been obtained, which evidenced the formation of binary EuL and EuL 2 complexes and mixed ligand EuL 2 X complexes. The results suggest that in ternary complex formation the steric requirement of the secondary ligand play an important role. The results of these studies lead us to achieve a better understanding of the factors, as aryl substituted groups (e.g. Br, NO 2 , NH 2 , CH 3 , OCH 3 ) and a kind of solvent, influencing the luminescence intensity and lifetime of the Eu(III) complexes studied.

Spectroscopic differences between molecular (O–H ⋯ N) and ionic pair (O–⋯ H–N+) hydrogen complexes

The centre of gravity (H) and chemical shifts (δH) of hydrogen-bonded protons in 55 complexes of pyridines with acetic acids have been measured in dichloromethane. If H and δH are plotted against the aqueous pKa values for protonation of these bases general scatter diagrams are obtained which may be resolved into separate trends for different acids. We noted that this behaviour is controlled by the equilibrium between the molecular complex and the ion pair. Strong overlap of the carbonyl and carboxy stretching bands of the molecular complex and the hydrogen-bonded ion pair leads in most cases to a single band. Characteristic variations of the bandwidth were found. A plot of δH against H can be resolved into a series of straight lines for molecular complexes, hydrogen-bonded ion pairs and their mixtures, respectively. A straight line for molecular complexes consists of data for the monomeric acids. The chemical shifts for N+–H proton of the ‘free’ pyridine cation was estimated from the line of protonated pyridines and compared with the calculated value.

Conductance studies of acid–base equilibria between 4-methoxy-2,6-dimethylpyridine N-oxide and trifluoroacetic acid in nitrobenzene

The conductance behaviour of solutions of the equimolar complex (BHA) of 4-methoxy-2,6-dimethylpyridine N-oxide (B) with trifluoroacetic acid (HA) has been studied over a wide range of concentration (10–5–10–2 mol dm–3) in pure nitrobenzene and with the addition of increasing amounts of free 4-methoxy-2,6-dimethylpyridine N-oxide or free trifluoroacetic acid. Using the Fuoss and Kraus linear relation F(Z)/Λ= 1/Λ∞+ΛCy2/[F(z)(Λ∞)2K], several apparent values of Λ∞ and K were obtained and constants of the equilibria affecting each other in a common reaction mixture were calculated: formation constants, Kf 109(AHB), K1+= 3.7 (BHBA), Kl–= 0.6 (AHAHB); homoconjugation constants, Kh+= 3.31 × 104[(BHB)+], Kh–= 1.37 × 105[(AHA)–], Khh–= 1.9 [(A)–(HA)2]; and dissociation constants, kc+= 1.21 × 10–3[(BHB)++ A–], Kd= 1.36 × 10–7(A–+ HB+); Kc–= 3.0 × 10–2[(AHA)–+ HB+]. Comparison with our earlier study of mixtures of 2,4,6-trimethylpyridine with trifluoroacetic acid shows that in both cases the stoichiometry of the chemical species is the same but the nature of the hydrogen bonds is different [e.g. in AHB, BHBA and (BHB)+]. The hydrogen bond is shown to be the major factor affecting the conductance of acid–base complexes.

Conductance studies of acid–base equilibria in 2,4,6-trimethylpyridinium trifluoroacetate in nitrobenzene

The conductance behaviour of solutions of 2,4,6-trimethylpyridinium trifluoroacetate (BHA) is presented over a wide range of concentration (10–5–10–2 mol dm–3) in pure nitrobenzene and with addition of increasing amounts of free trifluoroacetic acid or free 2,4,6-trimethylpyridine. Using the Fuoss and Kraus linear relation F(z)/Λc= 1/Λ∞+ΛcC0f2/F(z)(Λ∞)2K, several apparent Λ∞s and Ks were obtained. This and the previous IR studies allowed division of the plot of the conductivity vs. acid–base mole ratio into eight sections. The following equilibrium constants have been evaluated: formation constants, Kf= 1.3 × 107(BHA); homoconjugation constants, K–h= 1.07 × 105[(AHA)–]; K+h= 24.4 [(BHB)+]; and dissociation constants, Kd= 2.6 × 10–6(A–+ HB+); K–c= 7.4 × 10–2[(AHA)–+ HB+]; K+c= 5.8 × 10–5[(BHB)++ A–].The results show that: (a) complex formation is not complete in the stoichiometric mixture; (b) addition of acid or base leads to formation of 2 : 1 and 1 : 2 acid–base complexes and homoconjugated anions or cations, respectively. Species AHAHB and AHA– are more stable than BHBA and BHB+; (c) anions are more mobile than cations.

Interaction of 2,4,6-trimethylpyridine with some halogenocarboxylic acids in benzene and dichloromethane. Problem of stoicheiometry

The practical molal osmotic coefficients of 2,4,6-trimethylpyridine complexes with dichloroacetic and 2,2-dichloropropionic acid in benzene solutions over the concentration range 0.05–0.5 mol kg–1 were determined by vapour pressure osmometry (v.p.o.). The non-ideal behaviour of the investigated systems is interpreted on the basis of the stepwise aggregation model and the association constants are derived. 1H N.m.r. and i.r. spectra are reported for 2,4,6-trimethylpridine with dichloroacetic, 2,2-dichloropropionic, and trifluoroacetic acids with various acid-base ratios (2:1, 1.33:1, and from 1:1 to 1:10). Both the chemical shift of hydrogen-bonded protons and the continuous absorption in i.r. spectra are affected when an excess of base is added to the equimolar mixture of 2,4,6-trimethylpyridine with dichloroacetic and 2,2-dichloropropionic acids. The results can be rationalized in terms of formation of the following complexes: B ⋯ HA, B+ H ⋯ A–, (BHA)n, and B+H(A–⋯ HA). For trifluoroacetic acid the B+H(A–⋯ HA) complex is formed only when there is an excess of acid, while for dichlorocetic and 2,2-dichloropropionic acids the equilibrium can be completely shifted to the 1:1 complex only when there is a three-fold excess of base.

Influence of excess base and solvents on hydrogen bond and proton transfer in complexes between dichloroacetic acid and substituted pyridines

Abstract IR and 1H NMR spectra are reported for mixture of dichloroacetic acid and pyridines with various acid-base ratios (2:1, 1:1, and 1:4) in benzene and dichloromethane. Both the continuous absorption in IR spectra and the chemical shift of hydrogen bonded protons are affected when an excess of base is added to the equimolar mixture. The results can be explained by the incomplete reactions (e.g. 3-CN, 4-CN-, and 3-Br-pyridines), formation of B+H(A−⋯HA) complex (e.g. Pyridine and its methylderivatives) and homoconjugation (e.g. 4-NMe2-pyridine). The intensity variation of the continuous absorption and the chemical shift with solvent is very similar to that predicted by theory, and may provide evidence that the dipole of the hydrogen bond interacts with the reaction field from the environment. The centre of gravity, ν H, and the chemical shift, δH, is correlated with pKa and discussed with respect to the proton transfer reaction.

Structure and conformation of 2,3-diethoxycarbonyl-1-methylpyridinium iodide studied by NMR, FTIR, Raman, X-ray diffraction and DFT methods.

Computational and spectroscopic properties of 2,3-diethoxycarbonyl-1-methylpyridinium iodide, 1, were studied. The crystal structure of 1 was analyzed by X-ray diffraction. Molecular geometry of title compound has been calculated using the density functional theory (DFT) at B3LYP/6-311G(d,p) level of theory and was compared with the experimental data. Iodide anion interacts electrostatically with the positively charged pyridinium nitrogen atom and via weak CH⋯I(-) hydrogen bonds. In crystals the N-methyl and ethoxycarbonyl groups are disordered in two orientations. The structures of 2 (in vacuum), 3 (in CHCl3) and 4 (in DMSO) optimized by the B3LYP/6-311G(d,p) approach are different than that in crystal 1. The experimental (13)C and (1)H chemical shifts (δexp) of the investigated ester in CDCl3 and DMSO-d6 correlate linearly with GIAO/B3LYP/6-311G(d,p) magnetic isotropic shielding constants calculated according to the screening solvation model (COSMO), δexp=a+b σcalc. The FTIR and Raman spectra of the solid compound are consisted with the X-ray structure.

Quantum-chemical, NMR, FT IR, and ESI MS studies of complexes of colchicine with Zn(II)

AbstractColchicine is a tropolone alkaloid from Colchicinum autumnale. It shows antifibrotic, antimitotic, and anti-inflammatory activities, and is used to treat gout and Mediterranean fever. In this work, complexes of colchicine with zinc(II) nitrate were synthesized and investigated using DFT, 1H and 13C NMR, FT IR, and ESI MS. The counterpoise-corrected and uncorrected interaction energies of these complexes were calculated. We also calculated their 1H, 13C NMR, and IR spectra and compared them with the corresponding experimentally obtained data. According to the ESI MS mass spectra, colchicine forms stable complexes with zinc(II) nitrate that have various stoichiometries: 2:1, 1:1:1, and 2:1:1 with respect to colchichine, Zn(II), and nitrate ion. All of the complexes were investigated using the quantum theory of atoms in molecules (QTAIM). The calculated and the measured spectra showed differences before and after the complexation process. Calculated electron densities and bond critical points indicated the presence of bonds between the ligands and the central cation in the investigated complexes that satisfied the quantum theory of atoms in molecules. Graphical AbstractDFT, NMR, FT IR, ESI MS, QTAIM and puckering studies of complexes of colchicine with Zn(II).

Crystal structure and physical properties of 1-methyl-3-(carboxymethyl)benzimidazolium betaine·CuBr2 in crystal and water solution

A new Cu(II) carboxylate coordinating compound [1-methyl-3-carboxymethyl benzimidazolium betaine]2CuBr2 was synthesized and crystallized. The crystal has the triclinic symmetry P, with unit cell dimensions a = 7.9693, b = 8.4129, c = 9.1302 A, α = 68.058, β = 85.402 and γ = 71.258 deg. (Z = 1), and molecules stacked along the a-axis. Cu(II)-complexes are planar and four-coordinated with chromophore CuO2Br2, where two oxygen atoms belong to the carboxylate groups of two betaines acting as unidentate ligands. The compound was characterized by two-dimensional 1H and 13C NMR spectroscopy for the determination of the correlation between protons of a ligand molecule. NMR spectra confirm the coordination of Cu(II) ions and allow identification of H(2) proton as easily detached in basic conditions. FT-IR spectra confirm the unidentate coordination of the betaine carboxylate group. UV-Vis spectra show three bands in d–d-transition region. Energies of these transitions were used in the interpretation of the EPR results. From powder and single crystal EPR measurements the g-factors were determined as gx = 2.072, gy = 2.030, gz = 2.241. A non-typical g-factor sequence is a consequence of the orbital mixing in the ground state of Cu(II) complex of D2h symmetry. The g-factors were interpreted in terms of the Molecular Orbital (MO) theory which delivered the Cu(II) unpaired electron density delocalization onto the ligand molecules. A strong delocalization on betaine molecules via in-plane ground-state orbital was found and unexpectedly also via out-of plane orbital directed towards the non-coordinating oxygen of the betaine carboxylate group.

Human Body Fluid Ions In colchicine complexes ESI MS, MADLI MS, Spectroscopic, DFT Studies and Fungicidal Activity of colchicine complexes With Sodium, Potassium, Magnesium and calcium carbonates and Sulphates

Colchicine is an alkaloid characterised by good water solubility. After administration of colchicine as a medicine for example for the treatment of gout, colchicine probably forms some more or less stable structures with cations and/or anions present in human body fluid. The colchicine complexes with Na + , K + Mg 2+ and Ca 2+