Structural and thermodynamic aspects of hydration of Gd(iii) systems.

X-ray crystal structures of Gd(iii) and Lu(iii) aqua ions as well as their complexes with polyaminopolycarboxylates (EDTA, CDTA, EGTA, DTPA, DOTA) were determined: [Gd(H2O)9](CF3SO3)3, [Gd(H2O)8]Cl3·C10H20O5, [Lu(H2O)8]Cl3·C12H24O6·4H2O, [C(NH2)3][Gd(EDTA)(H2O)3], [C(NH2)3]2[Lu(EDTA)(H2O)2]ClO4·6H2O, [C(NH2)3][Lu(CDTA)(H2O)2]·6H2O, [C(NH2)3][Gd(EGTA)(H2O)]·2H2O, [C(NH2)2(N2H4)][Gd(HDTPA)(H2O)]·2H2O, Na[Gd(DOTA)(H2O)]·4H2O, and K2[Lu(DOTA)]Cl·4.6H2O. The weighted sums of UV absorption spectra of appropriate crystals were used to reproduce the spectra of the Gd(iii) aqueous solutions in the temperature range 276-363 K. It was shown that in aqueous solution the Gd(iii)-EGTA, Gd(iii)-DTPA and Gd(iii)-DOTA complexes exist as almost pure monohydrate [GdL(H2O)]n- species, while in the case of the Gd(iii) aqua ion, Gd(iii)-EDTA and Gd(iii)-CDTA systems the equilibria between variously hydrated species were found. The derived molar fractions of these species were used to determine the ΔG, ΔH and ΔS of hydration. It was shown that these thermodynamic functions may be derived not only from the spectra of the hypersensitive transitions, but from other f-f transitions as well. Next the ΔG, ΔH and ΔS values of hydration for the other Ln(iii)-EDTA systems (where Ln = Pr, Nd, Sm, Eu) were determined. It was found that the ΔG298 values of the dehydration reaction for Ln(iii)-EDTA complexes (where Ln = Pr, Nd, Sm, Eu, Gd, Ho, Er) were almost linearly dependent on the number of 4f electrons in the whole series of lanthanides. Moreover, it was shown that the point, where the ratio of [LnL(H2O)n] : [LnL(H2O)n-1] is equal to 1, shifts along the lanthanide series depending on the ligand denticity - the higher the ligand denticity, the farther the point of the equimolar ratio in the lanthanide series. The presented results are the first systematic experimental study on the thermodynamic description of the hydration equilibrium of Gd(iii) compounds.

The first example of ab initio calculations of f-f transitions for the case of [Eu(DOTP)]5- complex-experiment versus theory.

Crystal structures and photophysical properties (IR and UV-vis-NIR) of two compounds, [C(NH2)3]5[Eu(DOTP)]·12.5H2O and K5[Eu(DOTP)]·11H2O (DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylenephosphonic acid)), were determined. The DOTP ligand is bonded to Eu3+via four O and four N atoms, filling thus eight coordination sites of Eu3+. The experimental structures of two [K4Eu(DOTP)]- clusters were used as a starting point for theoretical ab initio calculations based on a multireference wavefunction approach. Positions of the energy levels of the 4f6 configuration of the Eu3+ ion have been calculated and compared with those derived from the experimental spectra. This enabled us to tentatively assign energy levels of the Eu3+ ion. The relationship between calculated energies of excited states and Eu-N and Eu-O bond lengths was discussed with respect to the nephelauxetic effect.

A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)(n)](-) complexes.

Two anionic complexes [Er(EDTA)(H2O)2](-) and [Er(EDTA)(H2O)3](-) were obtained in the form of the following compounds: [C(NH2)3]2[Er(EDTA)(H2O)2]ClO4·6H2O () and Na[Er(EDTA)(H2O)3]·5H2O (), respectively. The UV-vis-NIR absorption spectra of both monocrystals were measured at room temperature and at 4.2 K. The influence of the coordination number changes on intensities of the f-f transitions and the crystal field splitting of (2S+1)LJ multiplets are discussed. The weighted sum of molar absorption coefficients of f-f transitions in the spectra of and was used to reproduce the absorption bands of the Er(3+)-EDTA complex in aqueous solution. This approach allowed us to estimate that the complex in solution exists in 95% as the 8-coordinate [Er(EDTA)(H2O)2](-) species and in 5% as the 9-coordinate [Er(EDTA)(H2O)3](-) ones as well as to calculate the conditional hydration equilibrium constant (Kaqua) of the reaction: [Er(EDTA)(H2O)3](-) ↔ [Er(EDTA)(H2O)2](-) + H2O which is rather difficult to determine by using other methods. The Kaqua value was found to be 19 ± 1.

From structural properties of the EuIII complex with ethylenediaminetetra(methylenephosphonic acid) (H8EDTMP) towards biomedical applications.

Crystals of Eu(III) with ethylenediaminetetra(methylenephosphonic acid) (H(8)EDTMP) and with ethylenediaminetetraacetic acid (H(4)EDTA) have been synthesized in the same experimental conditions and their X-ray analyses have been performed. The EDTMP ligand wraps the Eu(III) ion in a fashion similar to its carboxylic analogue, EDTA, i.e. coordinating through two nitrogen atoms and four oxygen atoms in such a way that only one oxygen atom from each phosphonate group is bonded to the central ion. The coordination sphere is completed by two oxygen atoms of the bidentate carbonate anion in the case of the Eu(III)-EDTMP complex, whereas the inner sphere of the Eu(III)-EDTA crystal is completed by three water molecules. Spectroscopic studies (UV-Vis and (31)P NMR spectra) of Eu(III)-EDTMP solutions at controlled pH showed that the replacement of inner sphere water molecules and/or OH hydroxy groups by a carbonate anion in the Eu(III)-EDTMP complex at physiological pH results in the formation of [Eu(EDTMP)(CO(3))](7-) species which is thermodynamically stable and kinetically inert. The affinity of the carbonate anion towards the Eu(III)-EDTMP species was studied by analysis of f-f intensities and luminescence decay rates. The dissociation constant of the Eu(III)-EDTMP-carbonate complex was found to be approximately 43 mM. The presented results may be helpful in understanding the role played by the (153)Sm(III)-EDTMP complex known as Quadramet in the seeking of metastatic tissue in bones as well as possibly giving some premises for future ligand design of these types of complexes with lanthanide radionuclides.

Coordination ability of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) towards lanthanide(III) ions.

The proton and metal complex equilibria of trans-cyclohexane-1,2-diamine-N,N,N',N'-tetrakis(methylenephosphonic acid) (CDTP) with lanthanide(iii) ions, where Ln(III) = La(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Ho(III) and Lu(III) were studied. The stoichiometry, protonation and complex formation constants were determined by potentiometric titration at 25.0 degrees C and ionic strength of 0.1 mol dm(-3) (KCl). All metal ions form several species: [LnH4L]-, [LnH3L](2-), [LnH2L](3-), [LnHL](4-), [LnL](5-), [LnH(-1)L](6-) and [LnH(-2)L](7-) in the pH range between 2 and 11. The stability constants log beta(LnL) were found to be between 14.7 and 16.7. The studied complexes were also characterized by spectroscopic methods (31P NMR, UV-Vis absorption and emission spectroscopy). These studies allowed to reveal a distinct structural change of the Ln(III)-CDTP complex which occurs between protonated and hydroxy species in solutions at pH around 7.5. The major change is caused by the involvement of both nitrogen donors in the metal ion coordination occurring in ML species. The data obtained from UV-Vis spectroscopy allowed to draw conclusions about complex symmetry and to estimate a number of coordinated water molecules. The hydration number or more precisely the number of two OH oscillators was found to be approximately one in all species formed over the pH range between 5 and 10. The structure of the major hydroxy complex was supported by X-ray crystallographic data. The crystal structures of the Eu(III) and Tb(III) complexes clearly show that the CDTP ligand is coordinated to the Ln(III) ion by two nitrogen and four oxygen atoms in such a way that only one oxygen atom from each phosphonic group is placed in the lanthanide inner sphere. The monomeric complex anion is connected to a symmetry related ion through short hydrogen bonds formed by two hydroxy ions and one water molecule. In this way the two neighbouring anions form a quasi-dimer in which one of the Ln(III) ion is seven-coordinate (two N atoms, four O atoms and one hydroxy ion) and the other is eight-coordinate (two N atoms, four O atoms, one hydroxy ion and one water molecule).

Pentaaza macrocyclic ytterbium(III) complex and solvent controlled supramolecular self-assembly of its dimeric mu-eta 2:eta 2 peroxo-bridged derivatives.

The unprecedented template action of ytterbium ion in the synthesis of pentaaza macrocyclic Schiff bases is exemplified by isolation and definitive identification of the seven-coordinate pentagonal bipyramidal complex with the formula of [YbLCl(2)]ClO(4) (1), where L is 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene, providing the first example of crystallographically characterized pentaaza macrocyclic ytterbium complex. For the first time the spectrum of the (2)F(7/2) --> (2)F(5/2) transition has been obtained for a molecular complex of ytterbium with organic ligands in which all ligand-field components of the ground and excited state are well displayed at room temperature. This complex is capable of forming a dimeric peroxo Yb(2)(mu-eta(2):eta(2)-O(2))L(2)(4+) (2) derivative containing the biologically significant planar side-on doubly bidentate coordination mode of the peroxide. Inclusion of the appropriate solvent molecule into the crystal structure generates supramolecular architectures (2a-d) in which the solvent controlled self-assembly is observed. Spectral properties of these complexes were found to be very important and promising in the area of ytterbium physicochemistry.

Crystal Structure and Absorption Spectroscopy of a Neodymium(III) Complex with Triethylenetetraaminehexaacetic Acid, Na(3)[Nd(TTHA)].2.5NaClO(4).7.617H(2)O.

The crystal structure and absorption spectroscopy results of the Na(3)[Nd(TTHA)].2.5NaClO(4).7.617H(2)O compound are presented. The crystal structure of the complex was determined by X-ray analysis. Crystals are monoclinic, space group C2/c, with a = 38.446(8) Å, b = 10.552(2) Å, c = 25.796(5) Å, beta = 130.51(3) degrees, and Z = 4. The structure consists of monomeric (triethylenetetraaminehexaacetato)neodymate anions, perchlorate anions, sodium cations, and water molecules. The Nd(III) ion adopts a 10-coordinate geometry with six oxygen atoms and four nitrogen atoms from a ligand molecule, which is best described as a bicapped square antiprism. Absorption spectra of a single crystal were measured at room and liquid helium temperatures. Intensities of the f-f transitions were analyzed on the basis of Judd-Ofelt theory. The good correspondence between the spectra of [Nd(TTHA)](3)(-) in solution and in the single crystal suggests close similarity of both coordination polyhedra.