ELECTRONIC-SPECTRA AND STRUCTURES OF CU2+ AND NI2+ COMPLEXES WITH DIOXOTETRAAZACYCLOALKANEDIACETATES AND THEIR DIESTER DERIVATIVES

Functionalized macrocyclic ligands, dioxotetraazacycloalkanediacetic a cid with different ring sizes and their diester derivatives were synth esized, and their Cu2+ and Ni2+ chelates were characterized by electro nic absorption spectra in solution. A single-crystal X-ray analysis of nickel(II) 2,9-dioxo-1,4,7, 10-tetraaza-4,7-cyclotetradecanediacete p entahydrate showed that the central metal ion had an octahedral coordi nation with two amine nitrogen atoms, two carboxylate oxygen atoms and an amide oxygen atom from a ligand molecule and an oxygen atom from a water molecule: the metal complex crystallized in the monoclinic spac e group P2(1)/n with a = 9.040(1), b = 13.539(1), c = 18.168(2) Angstr om, beta = 101.895(2)degrees and Z = 4. Electronic spectra showed that all the complexes studied had similar structures in acidic solutions, in alkaline solutions, some metal chelates had a distorted planar str ucture in which two deprotonated amide nitrogen atoms and two amine ni trogen atoms were coordinated to the central metal ion. The tendency o f deprotonation of amide groups is dependent on the ring size of the l igand, the nature of the central metal inn and the ability of the pend ant arm to coordinate with the central metal ion. (C) 1998 Elsevier Sc ience S.A.