Cyclic Water Hexamers and Decamers in a Porous Lanthanide−Organic Framework: Correlation between Some Physical Properties and Crystal Structure

Erbium fumarate [Er2(fum)3(H2O)4]·8H2O, 1, (fum = fumarate dianion) crystallizes at room temperature in a silica gel column. The structure is three-dimensional and consists of layers of erbium fumarate pillared
by fumarate dianions acting in the bis-chelating mode. The layers contain arrays of erbium cations bridged by
fumarate dianions acting in the bis-bidentate bridging mode. The relatively large channels formed in the direction
of the a and c axes are filled by water molecules that form a hydrogen bonded layer, comprising cyclic hexamers
with both boat and chair conformations and cyclic decamers with boat−chair−boat conformation. The water molecules
are reversibly removed at 90 °C. The evacuated metal−organic framework, 2, is stable up to 400 °C. Both compounds
1 and 2 exhibit weak antiferromagnetic interactions.