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

New polypyridines [1,3-bis(2,2′:6′,2″-terpyridin-6-yl)benzene L1and 1,3-bis[4-(4-tert-butylphenyl)-2,2′:6′,2″-terpyridin-6-yl) benzene] L2were 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 = L1and L2) but not the single helical [Ru2L2(terpy)2]4+systems.