Total spontaneous resolution of nine-coordinate complexes

Abstract

Because Na₅[Dy(oda)₃](H₂O)₆(BF₄)₂ (oda = oxodiacetate) (1a), Na₅[Er(oda)₃](H₂O)₆(BF₄)₂ (1b) and Na₅[Pr(oda)₃](H₂O)₆(BF₄)₂ (1c) all crystallise in a Sohncke space group (R32), absolute asymmetric synthesis has been possible; we have obtained an optically active crystal batch of eg1b without using chiral starting materials. Nine-coordinate enantiomers have thus been resolved (without the use of chiral ligands). The crystal structures have been analysed in order to identify factors favouring spontaneous resolution, and two racemic phases of Na₃[Gd(oda)₃](H₂O)₆ (2) and Na₃NH₄[Pr(oda)₃](SCN)(H₂O)₄ (3) were prepared for comparison. The Na⁺, BF₄⁻, and H₂O building blocks in 1a–c result in a chiral network that can transfer stereochemical information between the chiral nine-coordinate [Ln(oda)₃]³⁻ anions, ultimately leading to the formation of enantiopure crystals. In the absence of NaBF₄ (as in 2), or by the replacement of NaBF₄ with NH₄SCN (as in 3), neither stereochemical transfer nor spontaneous resolution occurred.