Spontaneous assembly of double-stranded helicates from oligobipyridine ligands and copper(I) cations: structure of an inorganic double helix.

TLDR

Spontaneous assembly of oligobipyridine ligands with metal ions creates organized structures that enable design of self‑assembling systems with cooperativity and regulatory features, suggesting further organic, inorganic, and biochemical applications. The dinuclear and trinuclear complexes adopt double‑helical structures, with two ligand strands wrapped around two or three Cu(I) ions held together by pseudotetrahedral Cu(I)–bis(bipyridine) coordination and confirmed chiral NMR signatures. Synthesis of oligobipyridine ligands yields dinuclear and trinuclear copper(I) complexes that form double‑stranded helicates, and X‑ray crystallography confirms the trinuclear species as an inorganic double helix with DNA‑like helical parameters.

Abstract

Two oligobipyridine ligands containing two and three 2,2'-bipyridine subunits separated by 2-oxapropylene bridges have been synthesized and some of their complexation properties with metal ions have been investigated. In particular, with copper(I) they form, respectively, a dinuclear and a trinuclear complex containing two ligand molecules and two or three Cu(I) ions. In view of the pseudotetrahedral coordination geometry of Cu(I) X bis(bipyridine) sites and of NMR data indicating that the present complexes are chiral, one may assign to these dinuclear and trinuclear species a double-helical structure in which two molecular strands are wrapped around two or three Cu(I) ions, which hold them together. These complexes may thus be termed "double-stranded helicates." Determination of the crystal structure of the trinuclear species has confirmed that it is indeed an inorganic double helix, possessing characteristic features (helical parameters, stacking of bipyridine bases) reminiscent of the DNA double helix. This spontaneous formation of an organized structure by oligobipyridine ligands and suitable metal ions opens ways to the design and study of self-assembling systems presenting cooperativity and regulation features. Various further developments may be envisaged along organic, inorganic, and biochemical lines.