Rafał Janicki

Charge density distribution in aminomethylphosphonic acid.

The experimental charge density distribution in aminomethylphosphonic acid has been determined from X-ray diffraction and its topological features have been analyzed. The results have shown that the P-O bonds are highly polarized, moreover the P-OH bond is weaker than the bonds to unprotonated O atoms. These facts have been confirmed by theoretical density functional theory (DFT) calculations, which have shown that the single, strongly polarized bonds within the phosphonate group are modified by hyperconjugation effects.

Enormous lattice distortion through an isomorphous phase transition in an organic–inorganic hybrid based on haloantimonate(III)

Bis(diisobutylammonium) octabromodiantimonate(III), [(i-C4H9)2NH2]2Sb2Br8, has been synthesized. The differential scanning calorimetric measurements indicate a reversible, first-order phase transition at 222/229 K (cooling/heating). The single crystal X-ray diffraction studies reveal that the phase transition is isomorphous and is accompanied by a huge distortion of the crystal lattice. By comparison of the crystal structures of [(i-C4H9)2NH2]2Sb2Br8 and [(i-C4H9)2NH2]2Sb2Cl8, an analogous mechanism of the phase transition of the former is proposed. The change of the electronic structure of the complex during the phase transition was analyzed by UV-vis spectroscopy. A low-frequency dielectric relaxation process appears over phase I (below the room temperature) and corresponds to the dynamics of dipolar diisobutylammonium cations. The detailed analysis of the molecular motions of the organic cations studied by means of proton magnetic resonance (1H NMR) in a wide temperature range indicates a leading role of the methyl groups in the relaxation mechanism. A variable-temperature investigation of the infrared spectra of [(i-C4H9)2NH2]2Sb2Br8 confirms, in turn, the influence of the diisobutylammonium cation dynamics on the molecular mechanism of the structural transformation at 229 K.

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.

Ferroelectricity in bis(ethylammonium) pentachlorobismuthate(III): synthesis, structure, polar and spectroscopic properties

A brief description of the thermal, structural and dielectric properties of bis(ethylammonium) pentachlorobismuthate(III) ferroelectric with Ps that equals to 1.4 μC cm−2 at 180 K is presented. This paper focuses in particular on the molecular mechanism of a phase transition that is related mainly to the deformation of the anionic sublattice confirmed by temperature-variable powdered UV-Vis spectroscopy.

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.

Stoichiometry of lanthanide(III) complexes with tripodal aminophosphonic ligands – a new solution to an old problem

The Eu3+ and Gd3+ complexes with an N-(methylene-2-pyridine)-N,N-di(methylenephosphonate) ligand (H4NP2py), an analogue of nitrilotri(methylphosphonic) acid (H6NTP), were synthesized and structurally characterized by X-ray single crystal diffraction. The determined crystal structures ([C(NH2)3]5[Ln(NP2py)2]·12H2O) are the first example of a monomeric Ln3+ complex encapsulated by two tripodal aminophosphonic ligands. Each of the NP2py anions coordinates to Ln3+ through two oxygen atoms from each monodentate phosphonic group, amine nitrogen and pyridine nitrogen atoms, filling thus 8 coordination sites of Ln3+. The luminescence properties of [C(NH2)3]5[Eu(NP2py)2]·12H2O crystals were studied and compared with those of Eu–NP2py complexes in solution. Speciation analysis of Ln–NP2py complexes (Ln : NP2py = 1 : 2), performed by luminescence and potentiometric methods, showed that both [Ln(NP2py)]− and [Ln(NP2py)2]5− species may exist in solution. However, the formation of the latter one occurs in alkaline solutions at pH as high as 8. By implementing the Specific Ion Interaction Theory (SIT) it was possible to calculate the thermodynamic stability constants of the [Eu(NP2py)]− and [Eu(NP2py)2]5− complexes. The corresponding log β0Eul and values are 16.3 ± 0.11 and 19.5 ± 0.15, respectively.

New aspects of coordination chemistry and biological activity of NTMP-related diphosphonates containing a heterocyclic ring

Two analogues of nitrilotris(methylene-phosphonic acid) (NTMP), namely L1 = N-(methylene-2-pyridine)-N,N,-di-(methylenephosphonate) and L2 = N-(methylene-1H-benzimidazol)-N,N,-di-(methylenephosphonate) in which one of the phosphonic arms was replaced by a heterocyclic moiety, pyridine and benzimidazole, were studied in terms of coordination chemistry towards transition (Cu2+, Ni2+, Zn2+) and alkaline-earth metal ions (Ca2+ and Mg2+) by means of potentiometry, UV-vis spectroscopy, mass spectrometry (ESI-MS), and isothermal titration calorimetry (ITC). The cytotoxicity of the ligands as well as their Zn2+, Ca2+ and Mg2+ complexes was tested against various cell lines (human melanoma A375 and human colon adenocarcinoma HT29) revealing a selective antitumor effect in vivo. Both of the ligands exhibit a potent inhibitory effect on tumor cell migration and experimental metastasis. Potentiometric and ESI-MS measurements have shown the existence of monomeric species only, without the presence of biscomplexes or polynuclear species. The conditional stability constants (log Kc) of the Zn2+, Ca2+, and Mg2+ complexes were determined independently by two methods for both of the studied ligands and are a first example of comprehensive potentiometry/ITC studies made for phosphonic acid complexation. No significant differentiation in coordination models for the studied set of metal ions was noticed; however, as expected due to the different metal ion natures, the complexes revealed dissimilar thermodynamic stability and behavior, depending on the metal ion and pH used. The possible structures of the complexes formed are discussed on the basis of spectroscopic and spectrometric results.

Unraveling the Ground State and Excited State Structures and Dynamics of Hydrated Ce3+ Ions by Experiment and Theory

The 4f-5d transition of Ce3+ provides favorable optical spectroscopic properties such as high sensitivity and quantum yield, making it a most important dopant for lanthanide-activated phosphors. A key for the design of these materials with fine-tuned color emission is a fundamental understanding of the Ce3+ ground state and excited state structures and the dynamics of energy transfer. Such data is also crucial for deriving coordination chemistry information on Ce3+ ions in different chemical environments directly from their optical spectra. Here, by combining 4f-5d absorption and luminescence spectroscopy and highly accurate quantum chemical electronic structure calculations, we study the interplay between the local structure of Ce3+ in aqueous solutions and in crystalline hydrates, the strengths of Ce-O/Cl interactions with aqua and chloride ligands, and the resulting absorption and luminescence spectra. Experimental and theoretical absorption spectra of [Ce(H2O)9]3+ and [Ce(H2O)8]3+ with defined geometries provide a means for analyzing the equilibrium between these species in aqueous solution as a function of temperature ( K(298) = 0.20 ± 0.03), while analyses of spectra of different aqua-chloro complexes reveal that eight-coordinate aqua-chloro complexes are present in solution at high chloride concentration. An intriguing feature in these systems concerns the large observed Stokes shifts, 5500-10 100 cm-1. By exploring the excited state potential energy surfaces with relativistic multireference calculations, we show that these shifts result from significant geometrical relaxation processes in the lowest 5d1 excited state. For [*Ce(H2O)8]3+ the relaxation gives shorter Ce-O bonds and a Stokes shift of ∼5500 cm-1, while for [*Ce(H2O)9]3+ the lowest 5d1 state results in a spontaneous dissociation of a water molecule and a Stokes shift of ∼10 100 cm-1. These findings are important for the understanding and optimization of luminescence properties of cerium complexes.

Eu(III) and Cm(III) tetracarbonates – in the quest for the limiting species in solution

The structural and spectroscopic properties of the compounds [C(NH2)3]5[Gd:M(CO3)4(H2O)]·0.75H2O (1) and [C(NH2)3]5[Y:M(CO3)4]·2H2O (2) (M = Eu, Cm) were determined. The crystals contain differently hydrated tetracarbonate complexes, [M(CO3)4(H2O)]5- and [M(CO3)4]5-, which were used as structural and spectroscopic models of Eu(iii) and Cm(iii) tetracarbonate species in aqueous solutions. The luminescence spectra of the crystals were used to establish the stoichiometry and stability of the limiting species of the aqueous Eu(iii) and Cm(iii) carbonate systems at different temperatures and in a broad range of ionic strengths. By implementing this method together with the Pitzer approach used for the description of highly concentrated systems, it was possible to determine the thermodynamic functions of the reaction [Eu(CO3)3]3- + CO32- ⇆ [Eu(CO3)4]5- under standard conditions for the first time (ΔH° = 31.4 ± 2 kJ mol-1 and ΔS° = 82 ± 10 J mol-1 K-1). The proposed model for Eu(iii) carbonates is consistent with the data recorded for the Cm(iii)-carbonate systems. The presented results are important not only from the point of view of environmental issues, but also for the coordination chemistry of f-elements in general.