Showing papers by "Vieri Fusi published in 2003"

Ni(II), Cu(II), and Zn(II) Dinuclear Metal Complexes with an Aza−Phenolic Ligand: Crystal Structures, Magnetic Properties, and Solution Studies

Abstract: The basicity behavior and ligational properties of the ligand 2-((bis(aminoethyl)amino)methyl)phenol (L) toward Ni(II), Cu(II), and Zn(II) ions were studied by means of potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm-3). The anionic L-H- species can be obtained in strong alkaline solution; this species behaves as tetraprotic base (log K1 = 11.06, log K2 = 9.85, log K3 = 8.46, log K4 = 2.38). L forms mono- and dinuclear complexes in aqueous solution with all the transition metal ions examined; the dinuclear species show a [M2(L-H)2]2+ stoichiometry in which the ligand/metal ratio is 2:2. The studies revealed that two mononuclear [ML-H]+ species self-assemble, giving the dinuclear complexes, which can be easily isolated from the aqueous solution due to their low solubility. This behavior is ascribed to the fact that L does not fulfill the coordination requirement of the ion in the mononuclear species and to the capacity of the phenolic oxygen, as phenolate, to bridge two meta...

Molecular Switch Triggered by Solvent Polarity: Synthesis, Acid–Base Behavior, Alkali Metal Ion Complexation, and Crystal Structure

Abstract: The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1′-bis(2-phenol) groups as side-arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1±0.1 K, I=0.15 mol dm−3). The anionic H−1L− species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K1=11.22, log K2=9.45, log K3=7.07, log K4=5.08), and binds alkali metal ions to form neutral [MH−1L] complexes with the following stability constants: log KLi=3.92, log KNa=3.54, log KK=3.29, log KCs=3.53. The arrangement of the acidic protons in the H−1L− species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen-bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H−1L)]⋅CH3CN complex (space group P21/c, a=12.805(1), b=20.205(3), c=14.170(2) A, β=100.77(1)°, V=3601.6(8) A3, Z=4, R=0.0430, wR2=0.1181), obtained using CH2Cl2/CH3CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.

New ligand bearing preorganized binding side-arms interacting with ammonium cations: Synthesis, conformational studies and crystal structure

Abstract: The synthesis and characterization of the new tetraazamacrocycle 4-(N),10-(N)-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) is reported. L shows two 3-(hydroxy)-1-(carbonylmethylen)-2(1H)-pyridinone moieties as side-arms of a tetra-aza-macrocyclic base. The key coupling of side-arms was studied and the most significant results were obtained by activating the 3-(benzyloxy)-1-(carboxymethyl)-2(1H)-pyridinone as pentafluorophenol ester. The acid–base properties of L and its capability to interact with simple ammonium cations were investigated by potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm−3). Protonated species of L can bind NH4+ or primary ammonium cations such as MeNH3+ discriminating them from secondary or tertiary ammonium cations such as Me2NH2+ or Me3NH+ which are not bound in aqueous solution. 1 H and 13C NMR spectra showed the existence in solution of two conformers on the NMR time scale due to the rotational restriction of the two N–CO groups. The activation parameters were determined by dynamic variable-temperature NMR analysis.Molecular dynamics calculations gave results in agreement with the experimental data for both conformation and ammonium-binding studies, underlining that the transformation of the two secondary amines of the macrocyclic base to amide functions, forces the side-arms to remain fixed in position, almost face to face and thus to be preorganized to interact with other species. The crystal structure of the [HL]Cl·8H2O species shows the high number of preorganized hydrogen bond sites capable, in this case, of interacting directly with five H2O molecules.