Conversions between dimeric and polymeric ketopiperazinediacetato complexes constructed by water-layers

Abstract

Degradations of the layered polymeric products [M₂(kpda)₂(H₂O)₄]_n·6nH₂O (M = Co, 1; Ni, 2; Zn, 3; H₂kpda = ketopiperazinediacetic acid, C₈H₁₂N₂O₅) result in the formation of dimeric units [M₂(kpda)₂(H₂O)₆]·H₂O (M = Co, 4; Ni, 5; Zn, 6) in an ethanol solution, where the layered structures shrink from 11.23 Å to 6.22 Å. This is attributed to the dehydration of interesting 2D water layers based on X-ray structural analysis. The quasi-interconversion was monitored by IR, NMR measurements and product isolations, which involved complicated hydrated–dehydrated reactions.