Differing modes of crown binding to potassium: K, 18-crown-6 salt of the cyclic phosphate (OCH₂CMe₂CH₂O)P(O)(OH) as a hydrate

Abstract

The molecular structure of [K,18-crown-6]⁺[(OCH₂CMe₂CH₂O)P(O₂)]^-.H₂O (<b>3</b>) has been determined. Potassium is eight coordinate and is connected to an oxygen of the phosphate (that is not part of the six-membered ring), the water oxygen and six oxygen atoms of the crown. The two non-crown oxygens coordinated to potassium are on the same side with respect to the mean plane of the crown oxygen atoms; this mode of coordination is different from that observed in [K,18-crown-6]⁺[<i>myo</i>-C₆H₆-2-{OC(O)Ph}-1,3,5-(O₃CH)-{4,6-O₂P(O)O}]^-.3H₂O (2) in which the coordination of the non-crown oxygens (an oxygen from the inositol residue and an oxygen from the phosphate) occurs from the opposite sides of the mean plane of the crown oxygen atoms. The water oxygen is hydrogen bonded to two oxygen atoms (that are not part of the six-membered ring) of the phosphate leading to a chain. The six-membered phosphorinane ring has a chair conformation.