Structure, magnetism, and electrochemistry of the multinickel polyoxoanions [Ni6As3W24O94(H2O)2]17-, [Ni3Na(H2O)2(AsW9O34)2]11-, and [Ni4Mn2P3W24O94(H2O)17-

The three novel, multi-nickel-substituted heteropolytungstates [Ni6As3W24O94(H2O)(2)](17-) (1), [Ni3Na(H2O)(2)(AsW9O34)(2)](11-) (2), and [Ni4Mn2P3W24O94(H2O)(2)](17-) (3) have been synthesized and characterized by IR, elemental analysis, electrochemistry, and magnetic studies. Single-crystal X-ray analysis was carried out on Na16.5Ni0.25[Ni6As3W24O94-(H2O)(2)](.)54H(2)O, which crystallizes in the triclinic system, space group P (1) over bar, with a = 17.450(4) Angstrom, b = 17.476(4) Angstrom, c = 22.232(4) Angstrom, a = 85.73(3)degrees, beta = 89.74(3)degrees, gamma = 84.33(3)degrees, and Z = 2, Na-11[Ni3Na(H2O)(2)(AsW9O34)(2)].30.5H(2)O, which crystallizes in the triclinic system, space group P (1) over bar, with a = 12.228(2) Angstrom, b = 16,743(3) Angstrom, c = 23,342(5) Angstrom, alpha = 78.50(3)degrees, beta = 80.69(3)degrees, gamma = 78.66(3)degrees, and Z=2, and Na-17[Ni4Mn2P3W24O94(H2O)(2)].50.5H(2)O, which crystallizes in the monoclinic system, space group P2(1)/c, with a = 17.540(4) Angstrom, b = 22.303(5) Angstrom, c = 35.067(7) Angstrom, beta = 95.87(3) Angstrom, and Z = 4. Polyanion 1 consists of two B-alpha-(Ni3AsW9O40) Keggin moieties linked via a unique AsW6O16 fragment, leading to a banana-shaped structure with C-2v, symmetry. The mixed-metal tungstophosphate 3 is isostructural with 1. Polyanion 2 consists of two lacunary B-alpha-[AsW9O34](9-) Keggin moieties linked via three nickel(II) centers and a sodium ion. Electrochemical studies show that 1-3 exhibit a unique and reproducible voltammetric pattern and that all three compounds are stable in a large pH range, An investigation of the magnetic properties of 1-3 indicates that the exchange interactions within the trimetal clusters are ferromagnetic. However, for 1 and 3 intra- and intermolecular interactions between different trinuclear clusters are also present.