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

Abstract

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.

End‐to‐End Thiocyanato‐Bridged Helical Chain Polymer and Dichlorido‐Bridged Copper(II) Complexes with a Hydrazone Ligand: Synthesis, Characterisation by Electron Paramagnetic Resonance and Variable‐Temperature Magnetic Studies, and Inhibitory Effects on Human Colorectal Carcinoma Cells

“…The UV absorption band observed at 385 for 1 , and 370 nm for 2 , is ascribed to the ligand–metal charge-transfer transition (LMCT) between the hydrazone ligand and cop per(II). [27, 28] The visible region of the spectrum for 1 displays a single broad band between 525 and 640 nm. These spectral features are consistent with the five-coordinate geometry of 1 .…”

Dibromido[N-propyl-N′-(2-pyridylmethylidene)ethane-1,2-diamine]zinc(II)

“…For background to the chemistry of Schiff base complexes, see: Ali et al (2008); Biswas et al (2008); Chen et al (2008); Darensbourg & Frantz (2007); Habibi et al (2007); Kawamoto et al (2008); Lipscomb & Strä ter (1996); Tomat et al (2007); Wu et al (2008); Yuan et al (2007). For related structures, see: Dapporto et al (2001); You & Zhu (2006).…”

Interactions, Transformations, and Bioavailability of Nano-Copper Exposed to Root Exudates

“…45 Within the mixture, binding between Cu 2+ and aromatic rings and π-stacking between different components in more complicated geometries may be possible, further contributing to the higher binding affinity. 37,44,46 Determination of nCu−SRE Thermodynamic Binding Parameters.…”