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.     

Synthesis,spectroscopic and crystal field studies on some azido-chromium(III)-pyridine complexes

The new complexes mer-Cr(py)₃(N₃)₃, NaCr(py)₄(N₃)₄, KCr(py)₄(N₃)₄, and RbCr(py)₃(N₃)₄ (py = pyridine) have been prepared. Infrared (4000-50 cm⁻¹) and diffuse reflectance spectra (region 300-77 K) of powdered samples have been measured and discussed on bases of the known structures of these complexes. Single crystal absorption spectra for the mer-complex were obtained in the temperature range from 300 to 10 K revealing extensive vibronic structure associated with the ²E_g(O_h) and ²T_1g(O_h) electronic origins. Crystal field calculations were used to assign the bands in the vibronic region and to obtain estimates for the crystal field and Racah parameters for this class of substances. The parameters found for the mer-complex at 10 K are 10 Dq = 17906 cm⁻¹, B = 387 cm⁻¹ and C = 3381 cm⁻¹.     

Vibrational spectroscopic study of the structure of Ti(III) organometallic compounds

Conclusions A full interpretation was carried out for the vibrational spectra of TiR₃, where R= -CH₂C₆H₅, -CH₂C(CH₃)₂C₆H₅, and-CH₂Si(CH₃)₃. The absorption bands for the Ti-C bonds were delineated. A dimeric structure was established for the compounds studied with a Ti-Ti bond, whose band lies at 230–280 cm^–1. There is an interaction of the titanium atom with the -carbon atom of the ligand for the Ti(III) benzyl and neophyl derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2736–2739, December, 1987.     

Steric effects control the structure of the solvated lanthanum(III) ion in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution. An EXAFS and large-angle X-ray scattering study

The structure of the solvated lanthanum(III) ion has been determined in aqueous, dimethyl sulfoxide, and N,N'-dimethylpropyleneurea solution by means of the EXAFS and large-angle X-ray scattering (LAXS) techniques. The close agreement between the EXAFS spectra of solid nonaaqualanthanum(III) trifluoromethanesulfonate and of an aqueous lanthanum(III) perchlorate solution shows that the hydrated lanthanum(III) ion in aqueous solution most probably has the same structure as in the solid, i.e., nine water molecules coordinated in a tricapped trigonal prismatic configuration. The data analysis from EXAFS and LAXS measurements of the aqueous solution resulted in the La-O bond distances 2.52(2) and 2.65(3) A to the water molecules in the prism and the capping positions, respectively. The LAXS study shows a second hydration sphere consistent with approximately 18 water molecules at 4.63(2) A. The EXAFS spectra of solid octakis(dimethyl sulfoxide)lanthanum(III) trifluoromethanesulfonate and a dimethyl sulfoxide solution of this salt are also similar. The data analysis of EXAFS and LAXS measurements assuming eight-coordination around lanthanum yielded an La-O bond distance of 2.50(2) A, and an La...S distance of 3.70(3) A, giving an La-O-S angle of 133(2) degrees. The EXAFS data of an N,N'-dimethylpropyleneurea solution of lanthanum(III) trifluoromethanesulfonate gave the La-O bond distance 2.438(4) A and the La...C distance 3.41(2) A, which correspond to an La-O-C angle of 131(2) degrees. The La-O bond distance is consistent with seven-coordination around lanthanum, on the basis of the variation of the ionic radii of the lanthanum(III) ion with different coordination numbers.     

Copper(II) complex with thienyltrifluoroacetylacetone and dimethyl sulfoxide: Synthesis and crystal structure

A new copper(II) complex with thienyltrifluoroacetone (Tfa) and dimethyl sulfoxide (DMSO), Cu(Tfa)₂DMSO, was synthesized, and its X-ray diffraction analysis was carried out. The crystals were triclinic: a = 9.4496(5), b = 10.5075(6), c = 11.9160(6) Å, α = 82.600(1)°, β = 84.116(1)°, γ = 77.904(1)°, V = 1143.8(1) ų, space group P $ \bar 1 $ , Z = 2, ρ_calcd = 1.696 mg/m³, R = 0.0700. The environment of the copper atom was formed by four oxygen atoms of two thienyltrifluoroacetylacetone molecules and one oxygen atom of DMSO.     

Synthesis,crystal structures and spectroscopic studies of praseodymium(III) malonate complexes

Reactions of malonic acid (H₂mal) with PrCl₃·6H₂O afforded the known complex [Pr₂(mal)₃(H₂O)₆]_n (1), and compounds [Pr₂(mal)₃(H₂O)₆]_n·2nH₂O (2·2nH₂O), [PrCl(mal)(H₂O)₃]_n·0.5nH₂O (3·0.5nH₂O) and [Pr(mal)(Hmal)(H₂O)₃]_n·nH₂O (4·nH₂O) using various reaction ratios, reaction media (H₂O, MeOH) and pH values. Analogous reactions with CeCl₃·7H₂O afforded compounds [Ce₂(mal)₃(H₂O)₆]_n (5), [CeCl(mal)(H₂O)₃]_n·nH₂O (6·nH₂O) and [Ce(mal)(Hmal)(H₂O)₃]_n·nH₂O (7·nH₂O). Compounds 2·2nH₂O and 3·0.5nH₂O were characterized by X-ray crystallography, and 4–7 by microanalytical and spectroscopic data. The malonate(-2) ligand adopts three different coordination modes in the structures of 1–3, i.e., the μ₂-κO:κO′:κO″ and the μ₄-κ²O:κO′:κ²O″:κO? in 1 and 2 leading to a 3D network structure, and the μ₃-κ²O:κO′:κ²O″:κO? in 3 promoting an 1D structure. The thermal decomposition of 1 and 3·0.5nH₂O was monitored by TG/DTA and TG/DTG measurements. The structural features of 1–3 are discussed in terms of known malonato(-2) Ln^III and Ca^II complexes. The bioinorganic chemistry relevance of our results is discussed.     

Iron(III) hetero-ligand complexes containing 1,10-phenanthroline derivatives, chloride and dimethyl sulfoxide: synthesis, characterization, crystal structure determination and luminescent properties

[Fe(Me-phen)Cl₄][Me-phen·H] (1) and [Fe(Cl-phen)Cl₄][Cl-phen·H] (2) complexes were prepared from the reactions of FeCl₃·6H₂O with 5-methyl-1,10-phenanthroline (Me-phen) and 5-chloro-1,10-phenanthroline (Cl-phen), respectively, in a 0.1 M aqueous solution of HCl. Stepwise addition of dimethyl sulfoxide to the solution of 1 in methanol results in a mixed ligand complex, [Fe(Me-phen)Cl₃(DMSO)] (3). Complex 3 was also prepared by two other methods. The reaction of a methanol solution of [Fe(Me-phen)Cl₄][Me-phen·H] (1) with [Fe(DMSO)₄Cl₂][FeCl₄] in 1:6 ratio led to 3. Complex 3 was also prepared from the reaction of 5-methyl-1,10-phenanthroline with [Fe(DMSO)₄Cl₂][FeCl₄] in 1:1 ratio in methanol. The three complexes were characterized by IR, UV–Vis, ¹H NMR and luminescence spectroscopy and their structures were studied by the single-crystal diffraction method. Calculation methods were employed to study the isomerization of (3) in solution.     

The solvation of the dioxouranium(VI) ion by dimethyl sulfoxide

The species UO₂(DMSO) ₅ ²⁺ is shown from¹H NMR studies to be the predominant dioxouranium(VI) species existing in dilute anhydrous acetonedimethyl sulfoxide (DMSO) solutions, and this result is compared with data reported for the analogous water-acetone-dimethyl sulfoxide system. Complete line-shape analyses of exchange-modified¹H NMR line shapes indicate that the mechanism for DMSO exchange on UO₂(DMSO) ₅ ²⁺ is probably of theD orI _D type. A typical set of rate parameters arek _ex (260°K) =273±14 sec^–1, H ^#=38.9±0.5 kJ-mole^–1, and S ^#=–47.5±1.8 J-^oK^–1-mole^–1 for a solution in which [UO₂(DMSO)₅ ²⁺], [DMSO], and [d ₆ acetone] are, respectively, 0.01155, 0.0875, and 13.00 moles-dm^–3.     

Synthesis,X-ray crystal structure,and properties of antipyrinium perchlorates,hexakis(antipyrine)thulium- and hexakis(antipyrine)ytterbium perchlorates. Quantum-chemical studies of ligands protonation

Protonation of the bioactive ligand-antipyrine (AP, 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one) has been considered, the crystal packing specific features for the protonated antipyrine perchlorate compounds ([APH]ClO₄ · H₂O (1, 2) and [AP₂H]ClO₄ (3, 4)), as well as the crystal structure particularities for [Tm(AP)₆](ClO₄)₃ (5) and [Yb(AP)₆](ClO₄)₃ (6) have been elucidated. The protonation ability—complex formation ability relationship has been revealed for a number of organic ligands. Quantum-chemical calculations (DFT) and comparison with the experimental data allowed aligning some organic ligands in a row according to their ability to be protonated and to be incorporated into the inner coordination sphere of the complex.     

Salicylic acid derivatives form stable complexes with scandium(III) ion in aqueous solution

The stability constants of 5-nitrosalicylic acid (5-NSA) and 5-sulfosalicylic acid (5-SSA) complexes of Sc(III) were determined by potentiomeric pH titration. ML and ML2 type first and second complexes were observed in the solutions of 5-NSA and 5-SSA with Sc(III) at 25 degrees C in I=0.1 M ionic medium. The stability constants of Sc(III)-5NSA and Sc(III)-5SSA systems were also investigated by spectrophotometry to determine the stoichiometries of the complexes formed in the reactions. Our results showed that Sc(III)-5SSA complexes are more stable than the Sc(III)-5NSA complexes in aqueous solutions.     

Vibrational spectroscopy and dynamics of azide ion in ionic liquid and dimethyl sulfoxide water mixtures

Steady-state and time-resolved infrared spectroscopy of the azide (N(3)-) anion has been used to characterize aqueous mixtures both with the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]) and with dimethyl sulfoxide (DMSO). In the DMSO-water mixtures, two anion vibrational bands are observed for low water mole fractions (0 > X(w) > 0.25), which indicates a heterogeneous ion solvation environment. The band at 2000 cm(-1) observed for neat DMSO does not shift but decreases in amplitude as the amount of water is increased. Another band appears at slightly higher frequency at low X(w) (=0.05). As the amount of water is increased, this band shifts to higher frequency and becomes stronger and is attributed to azide with an increasing degree of hydration. At intermediate and high X(w), a single band is observed that shifts almost linearly with water mole fraction toward the bulk water value. The heterogeneity is evident from the infrared pump-probe studies in which the decay times depend on probe frequency at low mole fraction. For the azide spectra in IL-water mixtures, a single azide band is observed for each mole fraction mixture. The azide band shifts almost linearly with mole fraction, indicating nearly ideal mixing behavior. As with the DMSO-water mixtures, the time-resolved IR decay times are probe-frequency-dependent at low mole fraction, again indicating heterogeneous solvation. In both the DMSO and IL mixtures with water, the relaxation times are slower than would be expected from ideal mixing, suggesting that vibrational relaxation of azide is more sensitive than its vibrational frequency to the solvent structure. The results are discussed in terms of preferential solvation and the degree to which the azide shift and vibrational relaxation depend on the degree of water association in the mixtures.     

Single ion and dimerization studies of the Al(III) ion in aqueous solution

Aqueous trivalent aluminum (Al) ions and their oligomers play important roles in diverse areas, such as environmental sciences and medicine. The geometries of octahedral Al(H(2)O)(6)(3+) and tetrahedral Al(OH)(4)(-) species have been studied extensively. However, structures of intermediate hydrolysis products of the Al(III) ion, such as the penta-coordinated Al(OH)(2+) species, which exists at pH values ranging from 3.0 to 4.3, and their mode of formation have been poorly understood. Here, we present that a trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) structure is formed in aqueous solution and how this monomeric species dimerizes to a dinuclear [(H(2)O)(4)Al(OH)(2)Al(H(2)O)(4)](4+) complex in aqueous solution. The Gibbs free energy change calculations indicate that the formation of the dinuclear complex is preferred over the existence of two single trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) species in aqueous solution. This study captures the solution dynamics and proton transfer in the oligomerization reactions of penta-coordinated Al(OH)(2+) species in aqueous solution.     

Synthesis,crystal structure,spectroscopic, and biological studies on Cu(II) complexes of N,O donor dimethyl isoxazole Schiff bases

Cu(II) complexes with Schiff bases DMIIMP, DMIIMBD, DMIIMBP, DMIIMCP, DMIIMMP, and DMIIMNP (see Introduction for definitions) are derived from condensation of 3,4-dimethyl 5-amino-isoxazole with salicylaldehyde and substituted salicylaldehydes. The newly synthesized ligands were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra, and elemental analysis. The Cu(II) complexes were characterized by IR, UV-Vis, ESR, elemental analysis, magnetic moments, thermogram, DTA, and single crystal analysis. The complexes have general formula [M(L)₂]. The Schiff bases are bidentate coordinating through the azomethine nitrogen and phenolic oxygen of salicylaldehydes. Based on the analytical and spectral data, four-coordinate geometry is assigned for all the complexes. ESR and single crystal analysis suggests square planar geometry for all complexes. [Cu(DMIIMP)₂] crystallizes in the orthorhombic system. Antimicrobial studies of Schiff bases and their metal complexes show significant activity with the metal complexes showing more activity than corresponding Schiff bases. Cytotoxicity of the copper complexes on human cervical carcinoma cells (HeLa) was measured using the Methyl Thiazole Tetrazolium assay.     

Investigations on the structure of dimethyl sulfoxide and acetone in aqueous solution

Aqueous solutions of dimethyl sulfoxide (DMSO) and acetone have been investigated using neutron diffraction augmented with isotopic substitution and empirical potential structure refinement computer simulations. Each solute has been measured at two concentrations-1:20 and 1:2 solute:water mole ratios. At both concentrations for each solute, the tetrahedral hydrogen bonding network of water is largely unperturbed, though the total water molecule coordination number is reduced in the higher 1:2 concentrations. With higher concentrations of acetone, water tends to segregate into clusters, while in higher concentrations of DMSO the present study reconfirms that the structure of the liquid is dominated by DMSO-water interactions. This result may have implications for the highly nonideal behavior observed in the thermodynamic functions for 1:2 DMSO-water solutions.     

Ambidentate coordination of dimethyl sulfoxide in rhodium(III) complexes

The two dimethyl sulfoxide solvated rhodium(III) compounds, [Rh(dmso-κO)(5)(dmso-κS)](CF(3)SO(3))(3) (1 & 1* at 298 K and 100 K, respectively) and [Rh(dmso-κO)(3)(dmso-κS)(2)Cl](CF(3)SO(3))(2) (2), crystallize with orthorhombic unit cells in the space group Pna2(1) (No. 33), Z = 4. In the [Rh(dmso)(6)](3+) complex with slightly distorted octahedral coordination geometry, the Rh-O bond distance is significantly longer with O trans to S, 2.143(6) ? (1) and 2.100(6) ? (1*), than the mean Rh-O bond distance with O trans to O, 2.019 ? (1) and 2.043 ? (1*). In the [RhCl(dmso)(5)](3+) complex, the mean Rh-O bond distance with O trans to S, 2.083 ?, is slightly longer than that for O trans to Cl, 2.067(4) ?, which is consistent with the trans influence DMSO-κS > Cl > DMSO-κO of the opposite ligands. Raman and IR absorption spectra were recorded and analyzed and a complete assignment of the vibrational bands was achieved with support by force field calculations. An increase in the Rh-O stretching vibrational frequency corresponded to a decreasing trans-influence from the opposite ligand. The Rh-O force constants obtained were correlated with the Rh-O bond lengths, also including previously obtained values for other M(dmso)(6)(3+) complexes with trivalent metal ions. An almost linear correlation was obtained for the MO stretching force constants vs. the reciprocal square of the MO bond lengths. The results show that the metal ion-oxygen bonding of dimethyl sulfoxide ligands is electrostatically dominated in those complexes and that the stretching force constants provide a useful measure of the relative trans-influence of the opposite ligands in hexa-coordinated Rh(III)-complexes.