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Abstract: The tetra-capped Keggin anion-supported Cobalt–Phenanthroline complex [Co2(phen)2(OH)2(H2O)4]0.5[{Co(phen)2(H2O)}2AsMo6 VIMo2 VV8 IVO44]·2H2O (1) and the bicapped Keggin anion-based Nickel–phenanthroline compound [Ni(phen)2H2O]2[AsMo11 VIMoVO40(VIVO2)0.5].2H2O(2), have been hydrothermally synthesized and structurally characterized by elemental analyses, single crystal X-ray diffraction, IR and X-ray photoelectron spectrum. The interesting structural feature of 1 is that there are two types of free complex cation [Co2(phen)2(OH)2(H2O)4]2+ in different orientations in the crystal structure of 1, and these free complex cations coexist in the space between polyoxometalate clusters. The structure of compound 2 is very like compound 1 except that the Keggin unit is bi-capped instead of tetra-capped. Compounds 1 and 2 are examples that Arsenicum-centered vanadomolybdate anion acts as an active building block in the fabrication of polyoxometalates-supported hybrid solids. Then, the magnetic characteristic of 1 is typical of a dominant ferromagnetic interactions in the 6–300K temperature range and a succedent antiferromagnetic interactions in the very low temperature range (2–6K), while the magnetic behavior for 2 is characteristic of a dominant ferromagnetic interactions in the 6–300K temperature range and succedent antiferromagnetic interactions in the very low temperature range (2–6K). [Copyright &y& Elsevier]