Novel Three-Dimensional Organic–Inorganic Heterometallic Hybrid Built by Sandwich-Type Tetra-Mn-Substituted Germanotungstates through Mixed 3d and 4f Metal Linkers

The
reaction of trivacant Keegin germanotungstate [A-α-GeW9O34]10– with Mn2+ and
Ce4+ cations in the presence of oxalate ligand under hydrothermal
conditions led to the isolation of a novel organic–inorganic
hybrid 3d–4f heterometallic germanotungstate K4Na4[Ce2(ox)3(H2O)2]2{[Mn(H2O)3]2[Mn4(GeW9O34)2(H2O)2]·14H2O (1) (ox = oxalate),
which has been characterized
by elemental analysis, IR spectroscopy, thermogravimetric (TG) analysis,
and single-crystal X-ray crystallography. Interestingly, each tetra-MnII-substituted sandwich-type unit acts as 14-dentate ligands
to link eight Ce3+ centers and six Mn2+ centers
further into a three-dimensional (3D) architecture. The 3D structure
can be considered as two parts: one is the two-dimensional layer formed
by sandwich-type [Mn4(H2O)2(GeW9O34)2]12– fragments
and Mn2+ linkers; the other layer is constructed from Ce3+ cations and oxalate bridges, and the two layers are combined
together alternately through W–O–Ce–O–W
linkers, resulting in the 3D framework. Notably, 1 exhibits
the first 3d–4f 3D organic–inorganic hybrid framework
constructed by sandwich-type TM-substituted polyoxoanions and mixed
3d and 4f metal linkers in POM chemistry.