Two Dawson-Templated Three-Dimensional Metal−Organic Frameworks Based on Oxalate-Bridged Binuclear Cobalt(II)/Nickel(II) SBUs and Bpy Linkers

The Dawson anion P2W18O626− has been used as a noncoordinating polyoxoanion template for the construction of two metal−organic frameworks, namely, [M2(bpy)3(H2O)2(ox)][P2W18O62]2(H2-bpy)·nH2O (M = Co(II), n = 3 (1); M = Ni(II), n = 2 (2)) (bpy = 4,4′-bipyridine; ox = C2O42−). Single-crystal X-ray analysis reveals that both of the structures exhibit 3D host frameworks constructed from the oxalate-bridged binuclear superoctahedron secondary building units (SBUs) and bpy linkers and the voids of which are occupied by Dawson anions, guest bpy, and water molecules. Magnetic studies reveal that there are antiferromagnetic exchange interactions among the transition-metal centers in compounds 1 and 2. Furthermore, a compound 1-modified carbon paste electrode (1-CPE) displays good electrocatalytic activity toward the reduction of nitrite.