Syntheses and Characterizations of Palladium-Based Molecular Triangle/Square Compounds and Hybrid Composites with Polyoxometalates

Syntheses and characterizations of a Pd-based molecular triangle and square and hybrid composites with
polyoxometalates are examined. The equilibrium between the Pd-based molecular triangle [(en*)Pd(4,4‘-bpy)]3(NO3)6 and square [(en*)Pd(4,4‘-bpy)]4(NO3)8 largely depends on the solvents, and both compounds have successfully
been isolated:  [(en*)Pd(4,4‘-bpy)]3(NO3)6·3.5DMSO, monoclinic Cc (No. 9), a = 19.8210(2) Å, b = 34.3667(5) Å,
c = 27.5484(4) Å, β = 89.9420(10)°, V = 18765.5(4) Å3; [(en*)Pd(4,4‘-bpy)]4(NO3)8, monoclinic C2/c (No. 15), a
= 45.6921(16) Å, b = 8.7721(8) Å, c = 36.719(3) Å, β = 126.509(2)°, V = 11829.4(14) Å3. The reactions of the
Pd-based molecular triangle/square with [W6O19]2-, [W10O32]4-, and [α-SiW12O40]4- form {[(en*)Pd(4,4‘-bpy)]4[⊃W6O19]}[W6O19]3, {[(en*)Pd(4,4‘-bpy)]4[⊃W6O19]}(NO3)6, {[(en*)Pd(4,4‘-bpy)]4[⊃W10O32]}[W10O32], [(en*)Pd(4,4‘-bpy)]4[W10O32]2, and [(en*)Pd(4,4‘-bpy)]4[α-SiW12O40]2. The molecular square does not encapsulate the largest
[α-SiW12O40]4-, but it does encapsulate [W6O19]2- and [W10O32]4-. The isolation of [W6O19]2- and [α-SiW12O40]4-
from the mixture by use of the molecular square is possible by utilizing the quite different solubility of {[(en*)Pd(4,4‘-bpy)]4[⊃W6O19]}(NO3)6 and [(en*)Pd(4,4‘-bpy)]4[α-SiW12O40]2 formed in DMSO. The size-selective encapsulation
property of supramolecules may open the new way to rationalize isolation methods of the useful polyoxometalates.