COORDINATION ABILITY OF NOVEL TETRADENTATE AMIDE-AND-OXIME LIGANDS - DIFFERENTIAL BINDING TO CU-II AND NI-II

Four cationic and anionic complexes of Ni-II and Cu-II with new open c hain oxime-and-amide ligands, ,N'-bis(2-hydroxyiminopropionyl)-1,2-dia minoethane (H(2)pen) and 1,4-diaminobutane (H(2)pab) were isolated and characterised by X-ray crystallography and a variety of spectroscopic techniques. The ligands were found to exhibit two types of co-ordinat ion modes depending on pH: N(oxime),O(amide) bis-bidentate and N-2(oxi me),N-2(amide) tetradentate. The first bonding mode leads to bridging of the two ligands thus forming binuclear cationic complexes [{Cu(Hpab )(ClO4). 2H(2)O}(2)] Ib and Li[Ni(H(-1)pen)]. 4H(2)O 2a which have bee n determined by single-crystal X-ray analysis. In Ib the bis-bidentate co-ordination mode leads to the formation of a dimeric complex cation containing a loose 22-membered macrocyclic cavity incorporating two C u-II ions as a part of the ring skeleton. The central atoms in fb are distorted square-pyramidal with the water molecule in the apical posit ion. N-4-tetradentate co-ordination observed in 2a leads to the format ion of a square-planar complex anion with a closed pseudo-macrocyclic environment stabilised by a short intramolecular H-bond between the ox ime oxygen atoms.