Open-framework cadmium oxalates with channels stabilized by alkali metal ions

Abstract

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) ų, Z=4, M=732.84, R₁=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) ų, Z=8, M=398.64, R₁=0.021.