Syntheses, structures and electrochemical properties of single and double helical inorganic complexes containing new polypyridine ligands

Abstract

New polypyridines [1,3-bis(2,2′:6′,2″-terpyridin-6-yl)benzene L¹ and 1,3-bis[4-(4-tert-butylphenyl)-2,2′:6′,2″-terpyridin-6-yl)benzene] L² were prepared. Their reactions with copper(II) acetate and silver(I) acetate gave [Cu₂L¹₂]⁴⁺, [Cu₂L²₂]⁴⁺, [Ag₂L¹₂]²⁺ and [Ag₂L²₂]²⁺ while [Ru₂L²(terpy)₂]⁴⁺ was obtained from [Ru(terpy)Cl₃](terpy = 2,2′:6′,2″-terpyridine) with L². The complexes [Cu₂L²₂][PF₆]₄·6MeCN and [Ag₂L²₂][PF₆]·Me₂CO have been established by X-ray crystal analyses to have double helical structures. Electrospray mass spectrometry showed that the double helical [Cu₂L²₂]⁴⁺ and [Ag₂L¹₂]²⁺ complexes and the single helical [Ru₂L²(terpy)₂]⁴⁺ complex are the only species present in solutions. All five complexes undergo reversible oxidations or reductions. Interestingly, the electrochemical data indicate substantial electronic coupling within the bimetallic double helical [M₂L₂]³⁺(M = Cu or Ag, L = L¹ and L²) but not the single helical [Ru₂L²(terpy)₂]⁴⁺ systems.