Host-guest assembly of ligand systems for metal ion complexation. Synergistic solvent extraction of copper(II) and silver(I) by 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane in combination with carboxylic acids.
Host-guest formation between 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclodecane (1) and lipophilic organic carboxylic acids in chloroform has been investigated and the effect of such ligand assembly on the solvent extraction of copper(II) and silver(I) has been probed. NMR titration experiments in the absence of a metal ion confirm the formation of weak 1:1 and 1:2 (macrocycle:carboxylic acid) assemblies in CDCl(3) between 1 and palmitic (hexadecanoic) acid or 4-tert-butylbenzoic acid while difunctional salicylic acid showed a 1 [ratio] 2 interaction that is somewhat stronger. The interaction between the former two acids and the tetra-N-benzylated macrocycle is significantly less than that reported previously for its non-substituted parent, cyclam; a result that likely reflects the presence of the less-basic, more sterically hindered tertiary nitrogens in 1 relative to the secondary nitrogens present in cyclam. Carboxylic acid-containing assemblies of this type have been used as extractants in a series of solvent extraction (water/chloroform) experiments. From both previous observations as well as from entropy considerations, it was anticipated that the use of a host-guest assembly of the above type for metal-ion complexation might contribute to enhanced metal ion binding (and concomitant enhanced metal ion extraction). Such behaviour is postulated to arise from the components of the coordination sphere being, at least in part, assembled for complex formation. In accord with this, the use of the ligand assembly involving palmitic acid/macrocycle 1 was found to lead to enhanced (synergistic) extraction of copper(II) at a metal ion concentration of 10(-3) mol dm(-3) while, for silver(I), synergism was somewhat marginal at this concentration but was clearly apparent under related conditions when the silver concentration was reduced to 10(-4) mol dm(-3). Similar behaviour towards silver was also observed when 4-tert-butylbenzoic acid was substituted for palmitic acid, while the use of salicylic acid resulted in enhanced (synergistic) extraction at both metal ion concentrations.
Synthesis, characterization, electrochemical behaviour and X-ray crystal structures of nickel(II) complexes with a N2O4 donor set macrocyclic Schiff base ligand
Abstract Two nickel(II) complexes of [1 + 1] macrocyclic Schiff base ligand (L) have been prepared by cyclocondensation reactions between 1,3-diamino-2-propanol and 2-[3-(2-formylphenoxy)-2-hydroxypropoxy] benzaldehyde, using NiX 2 (X = Br, and I) salts as template agents, and characterized by elemental analyses, IR, molar conductivity and electronic spectra in both solid and solution states. The single-crystal X-ray diffractions of the complexes are also reported that contain nickel(II) ion in a distorted octahedral geometry coordination of N 2 O 3 X (X = Br, I and NO 3 ). In all complexes the ligand behaves as a pentadentate ligand. Cyclic voltammetric studies of nickel(II) complexes indicate a quasi-reversible redox wave in the negative potential range.
Synthesis of 2,4-dideoxy-.beta.-D-erythro-hexopyranosyl nucleosides
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine (12) 1 was accomplished using two different synthetic routes. It was obtained starting either from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose or from tri-O-acetyl-D-glucal. The other modified nucleosides, with either a cytosine, guanine, or adenine moiety, were synthesized using the second reaction scheme. Deoxygenation reactions were accomplished with the (2,4-dichlorophenoxy)thiocarbonyl derivatives generated in situ