Preparation, structure, and characterization of a novel diphosphoheptadecatungstate complex, [(P2O7)W17O51]4-

A novel diphosphoheptadecatungstate complex, [(P 2 O 7 )W 17 O 51 ] 4- was prepared from a 200 mM (M = mol dm -3 ) W(VI)-10 mM P 2 O 7 4- -0.6M HCl-40% (v/v) CH 3 CN system, and characterized by IR, UV-vis, 31 P NMR, and 183 W NMR spectroscopy, and voltammetry. Single-crystal X-ray analysis was made on [(C 2 H 5 ) 4 N] 4 [(P 2 O 7 )W 17 O 51 ]. CH 3 CN, which crystallized in the monoclinic space group P2 1 /n, with cell parameters a = 16.1877(8), b = 22.103(1), c = 22.670(1) A, β = 90.847(1)°, V = 8110.3(7) A 3 , and Z = 4. The anion consists of a PW 8 O 31 fragment derived from a β-Keggin-type [PW 12 O 40 ] 3- structure, and two PW 8 O 31 units are linked by five oxygen atoms and a WO 5 square pyramid. The [(P 2 O 7 )W 17 O 51 ] 4- anion exhibited a four-step reversible one-electron redox wave in CH 3 CN, and a three-step two-electron redox wave resulted in the presence of acid. This is the first example of an electrochemically-active diphosphotungstate complex.