A new unsymmetric imidazole based tripodal ligand with different arm lengths (N,N′-bis(imidazole-4-ylmethyl-5-methyl)histamine, bimhm), its tridentate constituent (N-(imidazole-4-ylmethyl-5-methyl)histamine, imhm) and a related ligand (N-methyl-N′-(2-ylmethylpyridine)ethylenediamine, pyrdiam) not containing an imidazole unit have been synthesized. Equilibrium and solution structure of their copper(II) and zinc(II) complexes have been investigated by pH-metry, UV/VIS, EPR and 1H NMR spectroscopy as structural models of metal-binding multi-imidazole motifs of metalloproteins. Several mono- and bis-complexes having different protonation states are formed, except for the zinc(II)-bimhm system, where only mono-complexes have been detected. Most of these species possess (distorted) octahedral geometry, but a pentaco-ordinated structure is preferred in the [ML]2+ complexes of bimhm. The spectroscopic data indicate a square pyramidal geometry for [Cu(bimhm)]2+, while a trigonal bipyramidal structure is proposed for [Zn(bimhm)]2+. The deprotonation of the complex [Cu(imhm)]2+ results in an imidazolate-bridged [Cu(imhmH-1)nn+ oligomer, while in the absence of such a bridging unit, the hydroxo-mixed [CuL(OH)]+ complex is formed with pyrdiam.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - Jul 18 2002|
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