The coordination chemistry of macrocyclic diamides. Transition metal complexes of 5,7-dioxo-1,4,8,11-tetraazacyclotetradecane |
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Authors: | Robert W. Hay Paul R. Norman |
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Affiliation: | (1) Chemistry Department, University of Stirling, FK9 4LA Stirling, Scotland |
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Abstract: | Summary A convenient preparation of the 14-membered macrocyclic diamide 5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (LH2) is described. The pKNH+ values of the ligand are pK1 = 5.76 and pK2 = 9.63 at 25° and I = 0.1 mol dm–3 (KNO3). With metal ions able to ionise amide hydrogens, the ligand acts as a planar quadridentate, L2–. Thus copper(II) and nickel(II) give the neutral complexes ML, and conductivity measurements confirm that they are nonelectrolytes in aqueous solution. Both the nickel(II) and copper(II) complexes are acid labile unlike the analogues of 1,4,8,11-tetraazacyclotetradecane (cyclam).The cobalt(III) complex [CoL(NH3)2]Cl has been characterised and1H n.m.r. measurements established the N-meso stereochemistry at the chiral nitrogen centres. |
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