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M Micheloni

Publications and source records attributed to M Micheloni.

4 recordsLinked to original sources
PubMed2001

Addition of small molecules by Zn(II) and Cu(II) dinuclear complexes obtained by an amino-phenolic ligand. Crystal structures of the dinuclear zinc complex assembling butanolate and azide anions.

The coordination properties of the ligand 2,6-bis-[[bis-(2-aminoethyl)-amino]methyl]-phenol (L) toward the zinc ion were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)). L forms mono- and dinuclear complexes with zinc; the stable dinuclear complexes are practically the only existing species using L/Zn(II), molar ratio of 1:2. In these species, each dien subunit binds one zinc ion, while the phenolate moiety bound to both ions allows the two metal centers to be in close proximity with an incomplete coordination environment. The role of this metal-metal distance in binding secondary ligands was investigated for the dinuclear systems 2Zn/L and 2Cu/L by potentiometric (298.1 +/- 0.1 K, I = 0.15 mol dm(-3)) and NMR experiments in aqueous and methanol solution with a series of small guests having nitrogen donor atoms. The coordination sphere of the two metals was completed by adding 1 equiv of only those guests, which showed at least two contiguous donor atoms or two lone pairs on the same atom, to exactly fit the metal-metal distance without modifying the metal cluster. To do this, the imidazole molecule which shows the highest addition constants to the [M(2)H(-1)L](3+) species probably forms a mu-1,1-amino. These results are in agreement with the two crystal structures reported herein [Zn(2)(H(-1)L)(CH(3)CH(2)CH(2)CH(2)O)](ClO(4))(2) (space group P2(1)nb, a = 11.483(5), b = 14.166(5), c = 18.279(5) A, V = 2973(19) A(3), Z = 4, R = = 0.0701, wR2 = 0.1611) and [Zn(2)(H(-1)L)N(3)](ClO(4))(2) (space group C 2/c, a = 14.460(3), b = 12.814(3), c = 14.875(3) A, beta = 105.35(2) degrees, V = 2658(10) A(3), Z = 4, R = 0.0783, wR2 = 0.1806). In fact, these structures display a butanolate or azide guest linked to both Zn(II) ions of the dinuclear complex, resulting in a mu-1,1-oxo and mu-1,1-azido bridge, respectively.

Journal Article↗
PubMed2000

Polyamine macrocycles incorporating a phenolic function: their synthesis, basicity, and coordination behavior toward metal cations. Crystal structure of a binuclear nickel complex.

The synthesis and characterization of two new polyazamacrocycles, 1,4,7,10-tetraaza[12](2,6)phenolphane (L1) and 1,4,7,10,13-pentaaza[15](2,6)phenolphane (L2), are reported. Both ligands incorporate the 2,6-phenolic unit within the cyclic framework. The basicity behavior and the ligational properties of L1 and L2 toward Ni(II), Zn(II), and Cu(II) were determined by means of potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I = 0.15 mol dm-3). UV spectra were used to understand the role of the phenolic function in the stabilization of the cations. L1 and L2 behave as pentaprotic bases under the experimental conditions used. The UV spectra showed that the deprotonation of the phenolic function occurs at low pH values for both ligands, giving rise to the simultaneous presence of positive and (one) negative charges on the macrocycle. While L1 forms only mononuclear complexes, L2 can also form binuclear species with all the metal ions investigated. In the mononuclear species of both ligands, one nitrogen atom close to the phenol remains unbound. The UV spectra revealed that the phenol, bridging the two metal ions in phenolate form, plays an important role in the stabilization of the binuclear complexes of L2. The coordination sphere of the two metals is completed by adding a secondary ligand such as water molecules or OH-, in any case preferring substrates able to bridge the two close metal ions. These results are confirmed by the crystal structure of [Ni2(C16H28ON5)(H2O)2Cl2]Cl.H2O.CH3OH (space group P21/a, a = 14.821(5) A, b = 10.270(4) A, c = 17.663(6) A, beta = 108.87(3) degrees, V = 2544(2) A3, Z = 4, R1 = 0.0973, wR2 = 0.2136). This structure displays a Ni(II) binuclear complex of L2 in which the phenolic oxygen and a chlorine ion bridge the two close Ni(II) ions.

Journal Article↗