An organic-inorganic polymer with Dawson-type polyoxometalates as building blocks: synthesis, characterization and crystal structure of [{Pr(DMF)6} {Pr(DMF)7}(P2W18O62)]n

An organic-inorganic polymer of [Pr(DMF)6Pr(DMF)7(P2W18O62)]n has been synthesized in acetonitrile-water (5 : 2, volume ratio) mixed solvent. Single-crystal X-ray structural analysis indicates that the title compound crystallizes in a monoclinic lattice, P21/C, with a = 1.8574(4), b=2.3907(5), c=2.4222(5) nm, β=99.48(3)°, Z = 4, ∨=10.609(4) nm3, Dc=3.501 Mg/m3, F(000)=9972, R1=0.0654 and wR2= 0.1098. The result of crystal structure analysis reveals that Pr3+(1) complex ion is eight-coordinated with a distorted bicapped trigonal prismatic environment, which is combined with the heteropolyanion by terminal oxygen atom, whereas Pr3+(2) complex ion is also eight-coordinated with a distorted square antiprismatic environment, which is linked to the heteropolyanion by terminal oxygen atom. Adjacent structure units of [Pr(DMF)6Pr(DMF)7(P2W18O62)] are bridged through W-O-Pr1-O-W links to form an unprecedented one-dimensional zigzag linear chain by alternate polyanions and cationic units in the polymer. Thermal analysis reveals that the framework of the title polyanion decomposes at 613.8°C.