Open-Framework Cadmium Oxalates with Channels Stabilized by Alkali Metal Ions

Two new cadmium oxalates, M4Cd2(C2O4)4·4H2O, M=Na(I) and K (II) with open architectures have been synthesized hydrothermally. The Cd atoms have the unusual eight-coordination with respect to the oxalate oxygens. The connectivity between the Cd and oxalate units forms layers with 12-membered apertures (six Cd and six oxalate units), with the layers interpenetrating to give rise to three-dimensional structures possessing 8-membered channels (four Cd and four oxalate units), wherein the Na+ and K+ ions are nestled. The Na+ ion conductivity in I is rather low, but the activation energy for conduction is comparable to those in glasses. Crystal data for I: monoclinic, space group P21/n (No. 14), a=12.8779(8), b=11.444(7), c=14.1301(8) Å, β=113.01(10)°, V=1916.7(2) Å3, Z=4, M=732.84, R 1=0.032; for II, orthorhombic, space group Fdd2 (No. 43), a=14.686(2), b=18.080(2), c= 7.8162(8) Å, V=2075.4(4) Å3, Z=8, M=398.64, R 1=0.021.