Structural features and near infra-red (NIR) luminescence of isomeric Yb(iii) bipyridyl-N,N′-dioxide coordination polymers

Abstract

The synthesis and structural characterization of a series of lanthanide complexes formed from YbX₃ salts (X = NO₃⁻ or CF₃SO₃⁻) and the isomeric 4,4′-bipyridine-N,N′-dioxide (4,4′-bpdo) or 3,3′-bipyridine-N,N′-dioxide (3,3′-bpdo) ligands has been undertaken by X-ray crystallography. Depending on the choice of anion, the complexes isolated with L = 4,4′-bpdo yield either an extended 1D linear chain {[Yb(L)(NO₃)₃(CH₃OH)]}_∞ or a coordination polymer network {[Yb(L)₄](CF₃SO₃)₃}_∞ which are isostructural with previously reported compounds using other Ln(III) metals. The isomeric 3,3′-bpdo ligand yields a similar extended 1D linear chain {[Yb(L)(NO₃)₃(CH₃OH)]}_∞ when NO₃⁻ is used as the anion. However, when substituted by the typically non-coordinating CF₃SO₃⁻ anion, inner sphere coordination yields a coordination polymer {[Yb(L)₃(CF₃SO₃)](CF₃SO₃)₂}_∞ with a (2²·4⁸·6⁵) network topology. In an effort to rationalize the observed difference in coordinating behavior, DFT calculations of the isomeric bipyridyl-N,N′-dioxide ligands have been undertaken, but revealed no significant differences in the charge distribution of the coordinating N-oxide groups. Lastly, sensitized Yb(III) emission in the Near Infra-Red (NIR) region operating via the well-known antennae effect has been observed and compared for two of the coordination polymers.