Thermodynamic and spectroscopic studies of lanthanides(III) complexation with polyamines in dimethyl sulfoxide

The thermodynamic parameters of complexation of Ln(III) cations with tris(2-aminoethyl)amine (tren) and tetraethylenepentamine (tetren) were determined in dimethyl sulfoxide (DMSO) by potentiometry and calorimetry. The excitation and emission spectra and luminescence decay constants of Eu3+ and Tb3+ complexed by tren and tetren, as well as those of the same lanthanides(III) complexed with diethylenetriamine (dien) and triethylenetetramine (trien), were also obtained in the same solvent. The combination of thermodynamic and spectroscopic data showed that, in the 1:1 complexes, all nitrogens of the ligands are bound to the lanthanides except in the case of tren, in which the pendant N is bound. For the larger ligands (trien, tren, tetren) in the higher complexes (ML2), there was less complete binding by available donors, presumably due to steric crowding. FT-IR studies were carried out in an acetonitrile/DMSO mixture, suitably chosen to follow the changes in the primary solvation sphere of lanthanide(III) due to complexation of amine groups. Results show that the mean number of molecules of DMSO removed from the inner coordination sphere of lanthanides(III) is lower than ligand denticity and that the coordination number of the metal ions increases with amine complexation from approximately 8 to approximately 10. Independently of the number and structure of the amines, linear trends, similar for all lanthanides, were obtained by plotting the values of DeltaGj degrees, DeltaHj degrees, and TDeltaSj degrees for the complexation of ethylenediamine (en), dien, trien, tren, and tetren as a function of the number of amine metal-coordinated nitrogen atoms. The main factors on which the thermodynamic functions of lanthanide(III) complexation reactions in DMSO depend are discussed.     

Proton magnetic resonance studies of tautomerism in substituted pyrimidines

Studies of line width and chemical shift vs. temperature for amide and hydroxyl proton magnetic resonance signals from: barbituric acid, dialuric acid, parabanic acid, alloxan and alloxan monohydrate dissolved in anhydrous dimethyl sulfoxide-d₆ are reported. The behavior of the amide signals shows that, between 20 and 65°C, none of the compounds listed exhibits lactim-lactam tautomerism. The amide proton resonance in uracil has also been investigated. The signal is a closely spaced, equal intensity, doublet due to the non-equivalence of H(1) and H(3). Again, no evidence of tautomerism is observed. Activation energies for the hydroxyl resonances in dialuric acid and alloxan monohydrate indicate hydrogen bonding between solute and solvent. The results of simple LCAO-MO calculations are in accord with the experimental conclusions concerning tautomeric equilibria.     

Proton magnetic resonance studies of 8-hydroxyquinoline derivatives

The PMR spectra of 8-hydroxyquinoline and eighteen derivatives have been obtained at 220 MHz. For several of the compounds, PMR spectra have not been reported previously. The use of 220-MHz frequency considerably facilitates the interpretation of spectra from such complex derivatives as 2-(2'-pyridyl) and 2-(2'-thienyl)-8-hydroxyquinoline.     

Change in the reactivity of N-vinylsuccinimide after complexation with dimethyl sulfoxide

The influence of dimethyl sulfoxide on the copolymerization kinetics and the reactivity parameters of N-vinylsuccinimide was studied. It was shown that, owing to the complexation of monomer molecules with dimethyl sulfoxide molecules, the relative activities of monomers are changed. The electron structures of N-vinylsuccinimide and dimethyl sulfoxide molecules and the molecule geometry was considered, and a complexation mechanism was proposed. The Alfrey–Price Q-e parameters of N-vinylsuccinimide during the complexation were analyzed. The causes of the change in the reactivity of monomer were revealed.     

Proton magnetic resonance studies of actinomycin-related peptides containing N-methyl groups

The PMR spectra of several cyclic and acyclic dipeptide derivatives representing portions of the actinomycin structure have been studied. In the spectra of the acyclic compounds temperature-dependent duplicity resulted from the equilibration of conformers possessing cis and trans peptide bonds. The lanthanide shift reagent Eu(FOD)₃ was utilized to distinguish N-methyl groups in the two conformations and observations were made on the steric dependence of the observed shifts. The origin of the wide variation in chemical shift of N-methylvalyl α-protons is discussed in relation to the conformation of actinomycin.     

The resonance Raman effect of uranyl chloride in dimethyl sulfoxide

A study was carried out of the resonance Raman scattering spectra of uranyl chloride (UO2Cl2) in dimethyl sulfoxide ((CH3)2SO) (DMSO) under laser excitation of the UO2(2+) ion in resonance with the 1sigma(g)+ --> 1phi(g) Laport-forbidden f-f electronic transitions span from 530 to 450 nm by using ten output lines of the argon-ion laser at room temperature. The resonance Raman excitation profile of the totally symmetric stretching vibrational mode of uranyl observed at 832 cm(-1) is presented and analyzed in terms of transform theory within the non-Condon model to give relatively good agreement with experimental results. The disagreement between the experimental data and the calculated resonance Raman excitation profile, at the long-wave part of the the 1sigma(g)+ --> 1phi(g) electronic transitions, may be referred to interference between the weak scattering from the neighboring forbidden electronic states (1delta(g)) and strong preresonance scattering from allowed electronic states at higher levels. An amount of change in the experimental resonance Raman excitation profile of the uranyl-DMSO system depends considerably upon the ligands (L) bound to the uranyl group. Elongation of the U-O equilibrium bond length resulting from the 1sigma(g)+ --> 1phi(g) electronic transitions is related to the magnitude of the change in the excitation profile of UO2L2 (L = NO3, CH3COO, Cl) type uranyl compounds in (DMSO).     

The resonance Raman effect of uranyl formate in dimethyl sulfoxide

The resonance Raman scattering spectra of uranyl formate (UO(2)(HCOO)(2)) in dimethyl sulfoxide ((CH(3))(2)SO, DMSO) have been measured under laser excitation of the uranyl ion in resonance with the 1Sigma(g)(+)-->(1)Phi(g) Laport forbidden f-f electronic transitions (ranging from 510 to 450 nm) by using ten output lines with wavelength ranging from 528.7 to 454.5 nm of the argon-ion laser at room temperature. The observed resonance excitation profile resembles the vibronic structure of the electronic absorption spectrum (ABS) but does not completely superimpose on it. Such a discrepancy is quantitatively explained by the interference effect, which occurs noticeably in the UO(2)L(2) (L=NO(3), CH(3)COO, Cl or HCOO)-DMSO system. Transform theory that makes use of the electronic ABS of the resonant electronic state has been applied to predict the Raman excitation profile (REP) of the uranyl totally symmetric stretching vibrational mode. Comparing the experimental REP with the transform theory prediction, it is found that the resonance Raman intensities of this stretching mode depend mainly on the vibronic interaction (non-Condon effect) in excited electronic states. Reliable value of the nuclear displacement on going the 1Sigma(g)(+)-->(1)Phi(g) electronic transition and the amount of charge transferred from the ligand to uranium of uranyl ion both in the ground and excited states are obtained. Elongation of the U-O equilibrium bond length due to the electronic transition is related to the magnitude of the change in the excitation profile, and has linear relation to the change in the amount of charge transferred from the ligand to uranium of uranyl ion in UO(2)L(2) type uranyl compounds in DMSO.     

Proton and boron-11 magnetic resonance studies of some potassium tetraarylborates

Proton and boron-11 magnetic resonance spectra for several potassium para-substituted tetraarylborate compounds [KB(C₆H₄-pX)₄, where X is H, OCH₃, CH₃, Br, Cl, F, CF₃] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para-substituent. Additionally, the boron-11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para-substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions.     

The resonance Raman effect of dicaesium uranyl tetrachloride in dimethyl sulfoxide

The resonance Raman scattering spectra of dicaesium uranyl tetrachloride (Cs2UO2Cl4) in dimethyl sulfoxide ((CH3)2SO) have been measured under laser excitation of the uranyl ion in resonance with the 1sigma(g)+ --> 1phi(g) Laport-forbidden f-f electronic transitions (520-450 nm) by using 10 output lines of the argon-ion laser at room temperature. The excitation profile of the totally symmetric stretching vibrational mode of uranyl observed at 830 cm(-1) is presented and analyzed in terms of the transform methods which are able to formally bypass multimode complexities. The non-Condon model (generalized B, C-terms of scattering) gives a relatively good agreement with the resonance excitation profile of experiment. Reliable value of the nuclear displacement on going the 1sigma(g)+ --> 1phi(g) electronic transition and the amount of charge transferred from the ligand to uranium of uranyl ion both in the ground and excited states are obtained. It is found that the average number of ligands coordinated equatorically to the central uranium atom affects on the amount of charge transferred from the ligand to uranium, especially in the electronic excited state. As increasing the average number of ligands, the amount of charge transferred from the ligand to uranium increases in the ground state, while in the electronic excited state, the charge transferred decreases.     

Proton nuclear magnetic resonance and infra-red studies of the outer-sphere hydration of pentane-2,4-dionato metal complexes in benzene solution

Studies of hydrogen bonding between water and bis(pentane-2,4-dionato)-beryllium(II) (Be(acac)₂), bis(3-methylpentane-2,4-dionato)-beryllium(II) (Be(Meacac)₂), and tris(pentane-2,4-dionato)cobalt(III) (Co(acac)₃) have been undertaken in [²H]₆-benzene solution using¹H NMR and infra-red spectroscopy. Equilibrium constants for 1:1 water-metal complex hydrates, and approximate enthalpies and entropies of reaction, have been measured from the¹H NMR data. The equilibrium constants are larger for Co(acac)₃ than for the Be(II) complexes, in line with previous data for the partition of these chelates between water and aliphatic hydrocarbon solvents.