Structure, Magnetism, and Electrochemistry of the Multinickel Polyoxoanions [Ni\\r sub/6sub\\r As\\r sub/3sub\\r W\\r sub/24sub\\r O\\r sub/94sub\\r (H\\r sub/2sub\\r O)\\r sub/2sub\\r ]\\r 17-\\r , [Ni\\r sub/3sub\\r Na(H\\r sub/2sub\\r O)\\r sub/2sub\\r (AsW\\r sub/9sub\\r O\\r sub/34sub\\r )\\r sub/2sub\\r ]\\r 11-\\r , and [Ni\\r sub/4sub\\r Mn\\r sub/2sub\\r P\\r sub/3sub\\r W\\r sub/24sub\\r O\\r sub/94sub\\r (H\\r sub/2sub\\r O)\\r sub/2sub\\r ]\\r 17-