Competitive transport, extraction and coordination chemistry of a number of ligands with selected transition and post-transition metal ions

Sheng, Xia (Stellenbosch : Stellenbosch University, 2008-12)

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008.


The competitive transport, extraction, and coordination chemistry for a series of N- (thio)phosphorylated (thio)amide and N-(thio)phosphorylated (thio)urea ligands were investigated with the seven transition and post-transition metal ions Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II) and Pb(II). Three N-benzylated derivatives of 1,4,7,10- tetraazacyclododecane (cyclen) were synthesized and a similar study carried out with the same metal ions and the deprotonated precursors. The ligands were all potential specific carriers (ionophores) in the organic phase. The seven metal ions had equal concentrations in the source phase. The experimental arrangement for the transport studies employed a set-up involving three phases: a source phase and a receiving phase (both aqueous), separated by a chloroform membrane (organic phase). Competitive metal ion solvent extraction involved two phases: an aqueous phase and an organic phase. Similar conditions were used in transport and extraction studies. The metal ion concentrations in the aqueous phases were analyzed by atomic absorption spectroscopy (AAS). The transport results of deprotonated N-(thio)phosphorylated (thio)amides and N- (thio)phosphoryated (thio)ureas showed that PhC(S)NPO(OPri)2 (L1), BrPhC(S)NPO-(OPri)2 (L11) and PriNHC(S)NPO(OPri)2 (L16) transported Ag(I) into the receiving phase. Under these experimental conditions, L1 had the highest Ag(I) transport efficiency, at 36.3%, while L11 only transported one metal ion, viz. Ag(I). With NH2C(S)NP(S)(OPri)2 (L4), 94.6% of Ag(I) remained in the membrane phase. Thus L4 appeared to have the highest formation constant with Ag(I). A small amount of Cu(II) was also transported by L1, NH2C(S)NP(O)(OPri)2 (L9), L16 and ButNHC(S)-NPO(OPri)2 (L20). L20 had the highest selectivity for Cu(II). Results of competitive metal ion extraction studies revealed that most ligands extracted up to 100% Ag(I), except L1 and morpholine substituted ligands (L7, L17) . The formation constant of L1 effects a subtle balance between metal uptake and metal loss into and out of the respective membrane phase. HL7 and HL17 had low solubility in chloroform. L4 extracted the highest percentage of Cu(II) (49%). Two neutral ligands, PhCONHPO(OPri)2 (1) and BrPhCONHPO(OPri)2 (2) were isolated and their molecular structure determined. They had monoclinic unit cells in the space groups C2/c and P21/n, respectively. An unprecedented octanuclear [Ag(I)(L4-S,N)]8 (3) complex was also crystallized. The extended structure showed three different cavities alternating with two unique 16-membered rings, creating a novel AgS2N2 cage. Two polynuclear Cu(I) chelates with deprotonated L4 and L6 (tBuNHC(S)NP(S)(OPri)2) were isolated by the same crystallization method. The complex [Cu(I)(L4–S,S)]9 (4) consisted of a hexagonal-prismatic hexamer, which exhibited an unusual and unprecedented supramolecular “honeycomb” packing. The trinuclear [Cu(I)(L6–S,S)]3 (5) consisted of a 6-membered Cu3S3 ring attached to a hydroxy tetrahydrofuran molecule. Di-, tri- and tetra-benzyl-1,4,7,10-tetraazacyclododecane (cyclen) was synthesized, and characterized. None of these compounds was effective in metal transport under these experimental conditions. Nevertheless, Tetra-benzyl cyclen showed the highest extraction efficiency for Ag(I), at 100%, and the highest selectivity for Ag(I) extraction, compared to Cu(II). An intermediate of dibenzyl cyclen compound dibenzylated dioxocyclen (6) was crystallized and found a host THF molecule in the lattice. The crystal and molecular structure confirmed the cis-configuration. The X-ray structure of the Cu(II) complex with dibenzylated cyclen (7) was determined for the first time. It was found to have an ideal square pyramidal coordination geometry around the central metal ion. A serendipitous organic compound of isopropylammonium(isopropylamino)- oxoacetate mono-hydrate (8) was crystallized. The crystal was held together by inter-molecular hydrogen bonds, which lead to two-dimensional layers with hydrophobic interactions.

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