Gabriella Bombieri

Crystal structure and solution dynamics of the lutetium(III) chelate of DOTA

Abstract The X-ray structure of Na[Lu(DOTA)(H 2 O)]·4H 2 O consists of (−1) complex anions balanced by sodium cations. The ninecoordinate Lu(III) is linked to the four nitrogen and to four oxygen atoms of the macrocyclic ligand DOTA in a square antiprismatic arrangement with a coordinated water molecule in capping position. In aqueous solution the complex is present under two isomeric forms in the relative ratio of 10:1, as evaluated from the low temperature limiting 13C NMR spectrum. The variable temperature behavior is consistent with the presence of two dynamic processes. One exchanges enantiomeric pairs for both isomers and involves concerted conformational changes of the ethylenic groups of the macrocyclic ring and rotation of the acetate arms. The other corresponds to the interconversion between the two isomers. Complete line-shape analysis of the variable-temperature 13C NMR spectra of Lu-DOTA allowed a quantitative evaluation of the two processes. The enantiomerization is slower than the isomerization: the corresponding calculated free energies of activation are 65.9 ± 1.2, 62.7 ± 2.0 (exchange major ⇌ minor) and 58.7 ± 2.I kJ mol −1 (exchange minor ⇌ major), respectively.

Preparation and characterization of the first triscyclopentadienyl lanthanoid complexes containing two aliphatic nitrile ligands: Crystal and molecular structures of the isomorphous compounds Trans-bis(acetonitrile)tris(η5cyclopentadienyl)lanthanoid(III) (Ln = La, Ce, Pr). A successful confirmation of the solid ‘solid angle sum rule’

Abstract Systematic studies to arrive at some first examples of the sterically congested complex type Cp3Ln(NCR)2 (Cp = η5-C5H5, Ln = lanthanoid element) resulted in the preparation and detailed spectroscopic characterization of analytically pure representatives of this type with Ln = La, Ce and Pr, but not with Nd (R = CH3, and C2H5 for Ln = La only). The crystal and molecular structures of representatives of the isomorphous series Cp3Ln(NCCH3)2, (Ln = La, Ce, Pr) were determined from three-dimensional X-ray diffraction data. The compounds crystallize in the orthorhombic space group Pnca (standard group Pbcn) with: a = 14.940(3), b = 14.074(3), c = 8.596(2)A, Z = 4, R = 0.070, Rw = 0.079 for 1633 intensity data (La derivative, I); a = 14.906(3), b = 13.974(3), c = 8.502(2)A, R = 0.041, Rw = 0.047 for 1378 intensity data (Ce derivative, VII); a = 14.936(3), b = 13.986(3), c = 8.498(2)A, R = 0.031 for 1372 intensity data (Pr derivative, IX). According to the X-ray crystallographic results, the novel complexes are trigonal bipyramidally coordinated with three η5-bonded Cp rings in the equatorial plane (Ln—ring centre distances 2.62, 2.64 for La, 2.58, 2.59Afor Ce and 2.57, 2.57Afor Pr and two acetonitrile groups in the axial positions (Ln N 2.785 for La, 2.749 for Ce, 2.752 for Pr). The range of the distances in the three derivatives is in agreement with the trend in the crystal radii along the lanthanoid series. Pure 1:2 adducts involving any alkyl group larger than R = C2H5 could not be isolated. The relative stabilities of the novel Cp3Ln(NCR)2 systems, with respect to the decreasing ionic radius (i.e. from La to Nd) and to the variable space demanded by the group R, are in excellent accord with independent expectations based on the recently developed cone packing model (‘SAS-rule’) for f-element organometallics.

Non-ionic Ln(III) chelates as MRI contrast agents: Synthesis, characterisation and 1H NMR relaxometric investigations of bis(benzylamide)diethylenetriaminepentaacetic acid Lu(III) and Gd(III) complexes

Abstract The syntheses of the ligand bis(benzylamide)diethylenetriaminepentaacetic acid (BBA-DTPA) and its Gd(III) and Lu(III) complexes are reported. The solid state structure of Lu(III) BBA-DTPA was determined in a single crystal X-ray diffraction study. The lutetium ion adopts a mine-coordinate geometry, which is best described as a distorted tricapped prism. Eight coordination sites are occupied by the ligand (three nitrogen atoms, two carboxamide oxygens and three carboxylate oxygens) and the ninth site is occupied by the oxygen atom of a water molecule. The VT 13 C NMR spectra of Lu(III) BBA-DTPA are consistent with the presence of three isomers in solution. Water proton relaxation rates have shown that Gd(III) BBA-DTPA displays an analogous behaviour to that observed for other Gd(III) complexes of related bisamide derivatives of DTPA. The solubility of Gd(III) BBA-DTPA has been markedly improved by the presence of an excess of hydroxypropyl-β-cyclodextrin. The thermodynamic stability of the inclusion complex has been evaluated by measuring the proton relaxation enhancement upon addition of β-cyclodextrin.

Synthesis, chemical and electrochemical deprotonation reactions of aminocarbene complexes of palladium(II) and platinum(II). X-ray structure of {(PPh3)ClPt[μC,N]}2

Abstract The diaminocarbene complexes cis-Cl2(PPh3)Pt[ CN(Bu t )CH 2 CH 2 N H] (1) and cis-Cl2Pt[ CN(C 6 H 4 -p-OMe)CH 2 CH 2 N H]2 (2) have been prepared by reaction of the corresponding isocyanide derivatives with aziridine/ClCH2CH2NH3+Cl− and aziridine alone, respectively. The aminooxycarbene complex cis-Cl2Pt[ CN(C 6 H 4 -p-OMe)CH 2 CH 2 O ]2 (3) has been prepared by reaction of the bis-isocyanide derivative with 2-chloroethanol/n-BuLi. The dimeric complexes {(PPh3)BrPd[μ- CN(Me)CH 2 CH 2 N C,N]}2 (4), {(PPh3)ClPd[μ- CN (C6H4-p-OMe)CH2CH2NC,N]}2 (5), {(PPh3)ClPt[μ- CN(C 6 H 4 -p-OMe)CH 2 CH 2 N C,N]}2 (6) have been prepared by deprotonation reaction of the NH group of the corresponding mononuclear derivatives with n-BuLi. The X-ray structure of {(PPh3)ClPt[μ- COCH 2 CH 2 N C,N]}2 (7) is reported. The structural model was refined to R=0.055 (Rw=0.061) for 7442 independent reflections. Crystal data: triclinic, space group P , a=19.564(3), b=16.497(3), c=13.243(2) A, α=88.93(3), β=97.88(3), γ=91.97(3)° Z=4. The crystal contains two crystallographically independent dimer units and a disordered dichloroethane molecule. Each dimer is formed by two bridging carbene ligands which are coordinated to one platinum on one side via a PtN bond and to the second platinum via a PtC bond. The coordination geometry around each platinum atom is an irregular square with deviations in the tetrahedral direction of the bonded atoms. The anodic behaviour of these and related monocarbene, dicarbene or dinuclear dicarbene complexes has been studied by cyclic voltammetry and controlled potential electrolysis in aprotic media and shown to present irreversible oxidation waves commonly with a multi-electron character (up to four electrons) and involving liberation of protons (in a number similar to that of the transfered electrons) conceivably resulting from anodically induced NH or CH bond cleavage, the former at an amino group and the latter occurring at methylene groups activated by adjacent amino- or oxy-carbene moieties.

3,3′-Di [1,3-thiazolidine-4-one] system. VI. Structural and conformational studies on configurational isomers with antihistaminic activity

Abstract The stereochemistry of the 3,3′-(1,2-ethanediyl)bis[2-(3-fluorophenyl)-1,3-thiazolidine-4-one] configurational isomers ( 2R,2′R 2S,2′ S and 2R,2′S meso ) has been investigated by 1 H-NMR techniques in solution, by X-ray diffraction methods in the solid state and by quantum chemical methods as the free molecule. The racemic compound, which has antagonistic activity at both H 1 and H 2 receptors, is found to prefer a gauche conformation in CDCl 3 solution, in the solid state and in the free molecule. The inactive meso stereoisomer is centrosymmetric in the crystalline state with an antiperiplanar conformation of the ethylene chain, whereas in CDCl 3 solution it exists as a rapidly interconverting mixture of 3 rotamers. The free molecule presents 2 gauche and 1 anti -periplanar conformations (differing by 1.3–2.4 kcal/mol). Some relationships between stereochemistry and activity are discussed.

X-ray crystal structures and nuclear magnetic resonance spectra of macrocyclic complexes of neodymium(III) and europium(III)

Abstract The compounds of formula [M(CH3COO)2LI]Cl·4H2O, in which M is neo-dymium(III) or europium(III) and LI is a six-nitrogen-donor macrocyclic ligand (C22H26N6), have been investigated by single crystal X-ray diffraction, thermogravimetric analysis and nuclear magnetic resonance spectroscopy. The two compounds are isostructural and crystallize in the triclinic system, space group P 1 . The complex cations present in the crystal lattice consist of a 10-coordinate metal centre linked to the six nitrogen-donor atoms of the macrocyclic ligand and to two bidentate chelating acetates, situated on opposite sides of the macrocycle and staggered by approximately 90°; an ionic chloride balances the residual metal charge. The paramagnetic-shifted NMR spectra of the complexes were measured in various solvents, and confirm that the metal-macrocycle moieties remain undissociated. Also, the spectra depend on the counterions, showing that, on average, at least one of the labile acetate ligands is bound to the metal ion even in aqueous solution.

Synthesis, binding, and modeling studies of new cytisine derivatives, as ligands for neuronal nicotinic acetylcholine receptor subtypes.

The availability of drug affecting neuronal nicotinic acetylcholine receptors (nAChRs) may have important therapeutic potential for the treatment of several CNS pathologies. Pursuing our efforts on the systematic structural modification of cytisine and N-arylalkyl and N-aroylalkyl cytisines were synthesized and tested for the displacement of [(3)H]-epibatidine and [(125)I]-alpha-bungarotoxin from the most widespread brain nAChRs subtypes alpha(4)beta(2) and alpha(7), respectively. While the affinity for alpha(7) subtype was rather poor (K(i) from 0.4 to >50 microM), the affinity for alpha(4)beta(2) subtype was very interesting, with nanomolar K(i) values for the best compounds. The N-substituted cytisines were docked into the rat and human alpha(4)beta(2) nAChR models based on the extracellular domain of a molluscan acetylcholine binding protein. The docking results agreed with the binding data, allowing the detection of discrete amino acid residues of the alpha and beta subunits essential for the ligand binding on rat and human nAChRs, providing a novel structural framework for the development of new alpha(4)beta(2) selective ligands.

Polynuclear transition metal complexes. The reactivity of the new potentially binucleating ligand 2,6-diacetylpyridine-bis(1'-phthalazinylhydrazone) towards NiII, CuII and ZnII salts, and crystal and molecular structure of {bis[2,6-diacetylpyridine-bis(1-phthalazinylhydrazonato)nickel(II)]} dimethylformamide and water solvate

Abstract The interaction of the new, potentially binucleating, ligand 2,6-diacetylpyridine-bis(1′-phthalazinylhydrazone) (H 2 dapz), containing only nitrogen donor atoms, towards nickel(II), copper(II) and zinc(II) salts is reported. Depending on the nature of the counteranions, Ni II and Cu II ions selectively enter in one of the two ‘compartments’ present in the ligand. Analytical and spectroscopic characterizations of five series of mononuclear complexes [dapzM], [H 2 dapzMCl 2 ], [HdapzMCl], [(H 2 dapz) 2 M][ClO 4 ] 2 , [HdapzM][ClO 4 ], coming from reactions of metal acetates, metal chlorides and metal perchlorates, respectively, and the ligand in the bisdeprotonated, monodeprotonated and undeprotonated forms, are reported together with some interconversion reactions. Some tentative stereochemical assignments of these compounds are reported on the basis of their physicochemical properties. Different behaviour has been observed in the case of zinc(II) chloride and perchlorate. Crystal structure analysis on the bisdeprotonated complex [dapzNi] 2 , shows that the compound is dimeric, with the metal ions octahedrally coordinated into the upper compartment, and the pyridine nitrogens bridging the two nickel atoms.

Analysis, imitation and emulation of classical texts in the Hebrew Bible

Some uranyl complexes with triphenylphosphine and triphenylarsine oxides as ligands have been reinvestigated. The crystal structure of Dioxo-dinitratobis(triphenylarsineoxide) uranium(VI) has been determined by X-ray diffraction. The crystals are monoclinic with a = 11.09±0.04, b = 19.28±0.06, c = 10.88±0.04 A, β = 128° 10′±10′, Z = 2, space group P2 1 /c. Intensities of 921 independent reflections were obtained photographically with CuK α radiation. The structure was solved by three-dimensional Fourier syntheses and refined by was full-matrix least squares. The final R index 8.6%. The uranium atom is octacoordinated with two bidentate nitrate ions and two oxygens from ligands coordinated in the plane perpendicular to the uranyl group.

Synthesis, characterization and X-ray structure of [Pd(dppp)(H2O)(TsO)][TsO] (dppp = 1,3-bis(diphenylphosphino)propane; TsO = p-CH3C6H4SO3), a catalytic species in COC2H4 copolymerization

Abstract The title complex was prepared by reacting Pd(AcO) 2 first with dppp and then with TsOH·H 2 O in MeOH at r.t. It is highly active in COC 2 H 4 copolymerization in MeOH. It has been characterized by IR and 1 H and 31 P NMR spectroscopies. The X-ray structure consists of a packing of monomeric palladium cations and tosylate anions in the ratio 1:1. The palladium atom is in rather distorted square coordination.