Stabilization of Near Identical Hydrogen Bonded Octameric Water Clusters in Crystal Structures of Three Distinct Non-Charged Polyamide Macrocyclic Host Molecules.

In this paper, we present a comparative analysis of the solid state structures of three well-resolved hydrates of macrocyclic host molecules , , and containing an intrannular amide-aryl substituent (lariat arm) connected to a fixed 26-membered ring in a normal (-NHCOAr, hosts and ) or reverse manner (-CONHAr, host ). Despite different chemical structures, these hosts crystallize as isostructural tetrahydrates in the same -1 space group. Moreover, their crystals exhibit identical hydrogen bond motifs resulting in a stabilization of an almost identical unusual octameric water cluster built from the cyclic tetramer core and four water molecules, attached sequentially in an "up-and-down" manner. Further analysis reveals that, among the series, the structure of host provides the most suitable environment for the accommodation of this type of water cluster.