Metal–Organic Frameworks Assembled From Erbium Tetramers and 2,5-Pyridinedicarboxylic Acid

Two novel three-dimensional lanthanide-organic
frameworks, [Er6(OH)8(pydc)5(H2O)3]­·2.5H2O (1) and [Er3(OH)6(pydc)­Cl] (2) (pydc2– is the deprotonated residue of 2,5-pyridinedicarboxylic
acid - 2,5-H2pydc), were prepared by hydrothermal synthesis.
Compound 1 consists of an unique one-dimensional (1D)
cationic [Er6(OH)8(H2O)3]n10n+ inorganic
chain
embedded into an organic matrix formed by the linker. Individual chains
are disposed in the ab plane of the unit cell in
a brick-wall fashion and result from the coalescence of cubane-type
clusters of Er3+. Compound 2 comprises densely
packed cationic [Er3(OH)6Cl]n2n+ inorganic layers, constructed
by the lateral coalescence of 1D chains identical to those found in 1. These layers are pillared by the organic linkers along
the [001] direction of the unit cell yielding the crystal structure
of 2. Considering the metallic tetramers and the ligands
as framework nodes, compounds 1 and 2 are
7- and 2-nodal networks, respectively. While the former is unprecedented
among metal–organic framework (MOF) structures, the latter
is reminiscent of the known tcj/hc topological type.
The crystal structures and properties of the two compounds have been
investigated by (single-crystal and powder) X-ray diffraction, electron
microscopy (SEM and EDX), vibrational spectroscopy, CHN elemental
analyses, and thermogravimetry. The magnetic properties of 1 also have been investigated.