A singly stranded, helical di-ruthenium(II) complex of a novel 6,6-ethynyl-linked bis(terpyridine) ligand. Distortion of the ethyne linkage and inversion of helicity

The new, ethynyl-bridged ditopic ligand, 1,2-bis[4'-(4-methylphenyl)-2,2':6 '2 "-terpyridin-6-yl]ethyne (L) was prepared and used in the formation of t he helical dinclear complex [L{Ru(ttpy)}(2)][PF6](4) (ttpy = 4'-(4-methylph enyl)-2,2':6',2 "-terpyridine), whose crystal structure exhibits pronounced bending of the central ethynyl bridge and whose solution NMR spectra indic ate a rapid inversion of helicity at 335 K.