Structure and Magnetic Properties of Pyridine Coordinated Sandwich‐type Heteropolyanion {[Na(H 2 O) 2 ] 3 [Ni(C 5 H 5 N)] 3 (AsW 9 O 33 ) 2 } 9−

The pyridine coordinated sandwich‐type heteropolytungstate Na 7 [Ni(H 2 O) 6 ]{[Na(H 2 O) 2 ] 3 [Ni(C 5 H 5 N)] 3 ‐ (AsW 9 O 33 ) 2 }·28H 2 O was obtained by the reaction of Na 2 WO 4 ·2H 2 O, NaAsO 2 and pyridine with NiCl 2 ·6H 2 O at pH=7.0 and characterized by elemental analysis, IR, UV‐Vis, 1 H NMR spectra and magnetic measurement. The structure of this heteropolytungstate was determined by X‐ray diffraction analysis, which crystallized in triclinic system, space group $ P {\bar 1} $ with a =1.3153(9) nm, b =1.7228(12) nm, c =2.6866(19) nm, α =74.130(11)°, β =78.032(12)°, γ =73.179(12)° and Z =2, R 1 =0.0604, wR 2 =0.0915 [ I >2 δ ( I )]. Polyanion {[Na(H 2 O) 2 ] 3 [Ni(C 5 H 5 N)] 3 ‐(AsW 9 O 33 ) 2 } 9− has approximately C 3 symmetry, and three pyridine coordinated Ni(C 5 H 5 N) 2+ and three Na(H 2 O) 2 + are encapsulated between two AsW 9 O 33 9− . Magnetic measurements show that central Ni 3 unit in the polyanion exhibits ferromagnetic NiNi exchange interactions ( J =6.17 cm −1 ).