Synthesis and properties of a new series of bis(macrocyclic) dicopper(II,II), dinickel(II,II) and dinickel(III,III) complexes based on the 14-membered pentaaza unit

Abstract

Template condensation of [M(danda)]²⁺(M = Ni or Cu; danda = 3,7-diazanonane-1,9-diamine) with formaldehyde and aliphatic diamines H₂N(CH₂)_nNH₂(n= 2–5) results in new types of dinickel and dicopper bis(macrocyclic) complexes [M₂L^x]⁴⁺(x=n) in which two 1,4,6,8,11-pentaazacyclotetradecane subunits ([ML¹]²⁺) are linked by polymethylene chains of various lengths through the uncoordinated N⁶ bridgehead atoms. The complexes synthesized were characterized by means of spectral (UV/VIS, IR and ESR) and electrochemical (cyclic voltammetry) techniques. The close similarity in properties of the bis(macrocyclic) dinickel(II), dicopper(II) and dinickel(III) complexes [M₂L^x]^m+(m= 4 or 6) in comparison to their monocyclic analogues [ML¹]^m+(m= 2 or 3) indicates the lack of interaction between the metal centres in the ditopic molecules. The only exceptionis [Cu₂L²]⁴⁺ having the shortest dimethylene connecting chain, for which effects caused by the electrostatic influence of the neighbouring metal ion were observed in the ESR spectrum and cyclic voltammograms. A study of equilibria between the low-spin square-planar and high-spin six-co-ordinated forms of the dinickel(II) complexes in neutral aqueous and acidic sulfate solutions revealed some peculiarities which may be related to the conformational properties of the ditopic compounds.