Crowned Tetrameric Spirocyclic Water Chain: An Unusual Building Block of a Supramolecular Metal−Organic Host

A 3D supramolecular metal−organic host could be realized in solid in which the water assembly as a whole acted as a
building block of the 3D framework with rectangular channels where guest molecules reside, adding a new dimension to water cluster
research where the role of water has been shifted from its usual behavior of guest to that of a host. The crystal structure of the compound,
{[Cu(mal)2](picH)2·5H2O}n, 1 [mal = malonate dianion, picH = protonated 2-amino-4-picoline], synthesized from purely aqueous media,
shows that the Cu(II)−malonate 2D coordination polymeric sheets are locked together by the water assembly that lines up perpendicular
to the Cu(II)−malonate sheets constituting a 3D infinite supramolecular host where within the channels protonated 2-amino-4-picoline
auxiliary ligands are accommodated. A spirocyclic tetrameric water chain having a dimeric crown on it describes the composition of the
water assembly that runs down the c-axis.