Single-Crystal X-ray Structure and Magnetic Properties of the Polyoxotungstate Complexes Na16[M4(H2O)2(P2W15O56)2].cntdot.nH2O (M = MnII, n = 53; M = NiII, n = 52): An Antiferromagnetic MnII Tetramer and a Ferromagnetic NiII Tetramer | doi.page