No abstract

Five homologues of the new complex series [LnL(µ-OTf)] 2 with Ln ) Pr (1), Nd (2), Sm (3), Y (4), Yb (5) have been prepared from [Ln(OTf) 3 ] and Na 2 L, where L designates two cyclopentadienyl rings tethered by a 2,6-bis(methylene)pyridyl unit and -OTf the triflate (trifluoromethanesulfonate) anion. According to crystal structure analyses of 2, 4, and 5, each triflate ligand bridges two Ln ions (Ln-O-S(O)-O′-Ln′), while, owing to substantial Ln-N(pyridyl) bonding, the LnL fragments turn out to be notably rigid entities. Nevertheless, the variable-temperature (VT) 1 H NMR spectra of all complexes reveal notable fluxionality. According to a detailed VT 19 F NMR study of 4, two dinuclear isomers, differing in the trans and cis orientations, respectively, of their two L fragments, interconvert with a negligibly small entropy of activation ∆S q . A motion reminiscent of the Berry turnstile would most plausibly explain the experimental findings.