d10Cations within triple-helical cryptand hosts; a structural and modelling study

Abstract

Dicopper(I) analogues of disilver(I) iminocryptates show intercationic separations substantially larger, by as much as 1.5 Å, than do their disilver(I) analogues. This has been confirmed via X-ray crystallography of the tris(ethylene)-capped cryptate [Cu₂L³][BPh₄]₂, 1, and the tris(trimethylene)-capped cryptate [Cu₂L²][ClO₄]₂, 2, for comparison with structurally characterised disilver analogues. A heterobinuclear Ag^I–Cu^I cryptate [CuAgL²][ClO₄]₂, 3, with an intermediate M⋯M′ internuclear distance has also been synthesized. These cryptates have been studied by solution ¹H NMR and solid state MAS CP ¹³C and ¹⁵N spectroscopy, and compared with the disilver analogues of these and related cryptand hosts. Although both copper(I) and silver(I) cations are formally closed shell systems, density functional calculations show non-zero bond order between the silver cations. The ¹H NMR solution spectra reveal the presence of only one conformer for all dicopper cryptates studied, as well as for the tris(ethylene)-capped disilver analogues, while in the tris(trimethylene)-capped disilver systems several conformers coexist in solution.