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)-amin o]methyl}-phenol (L) toward the zinc ion were determined by means of potent iometric 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 dinuclea r complexes are practically the only existing species using L/Zn(H), molar ratio of 1:2. In these species, each then 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 o f this metal-metal distance in binding secondary ligands was investigated f or 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 coordinatio n sphere of the two metals was completed by adding I equiv of only those gu ests, 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 t he metal cluster. To do this, the imidazole molecule which shows the highes t addition constants to the [M2H-1L](3+) species probably forms a mu -1,1-a mino. These results are in agreement with the two crystal structures report ed herein [Zn-2(H-1L)(CH3CH2CH2CH2O)](ClO4)(2) (space group P2(1)nb, a = 11 .483(5), b = 14.166(5), c = 18.279(5) Angstrom, V= 2973(19) Angstrom (3), Z = 4, R = = 0.0701, wR2 = 0.1611) and [Zn-2(H-1L)N-3](ClO4)(2) (space group C 2/c, a = 14.460(3), b = 12.814(3), c = 14.875(3) Angstrom, beta = 105.35 (2)degrees, V = 2658(10) Angstrom (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.