Two interesting organic–inorganic hybrid solids [{Cu(2,2′-bipy)₂}₂(β-Mo₈O₂₆)] (1), [{Cu(py)₃}₂{Cu(py)₂}₂(α-Mo₈O₂₆)] (2), and a new two-electron-reduced Keggin-core compound [Cu(py)₂]₄[Mo₁₂O₃₆(SO₄)] (3), were synthesized by hydrothermal methods and structurally characterized by X-ray diffraction. The structure of 1 consists of discrete [{Cu(2,2′-bipy)₂}₂(β-Mo₈O₂₆)] clusters, constructed from β-[Mo₈O₂₆]⁴⁻ subunits covalently bonded to two [Cu(2,2′-bipy)₂]²⁺ coordination cations via bridging oxo groups that connect two adjacent molybdenum sites. The structure of 2 consists of heterometallic dodecanuclear clusters, [{Cu(py)₃}₂{Cu(py)₂}₂(α-Mo₈O₂₆)], connected via π–π stacking contacts into an extended 1-D chain. Each [α-Mo₈O₂₆]⁴⁻ anion forms weak covalent interactions to two [Cu(py)₃]⁺ and two [Cu(py)₂]⁺ units through terminal oxo groups of the octamolybdate cluster. A new compound [Cu(py)₂]₄[Mo^V₂Mo₁₀O₃₆(SO₄)] (3), with two-electron-reduced Keggin anions, was unexpectedly obtained from the similar hydrothermal treatment of 2. Compounds 1–3 are of interest due to their unusual Cu-coordination geometries; trigonal bipyramidal Cu(II), distorted tetrahedral, T-shaped trigonal, and linear Cu(I) are observed, and in 2, two distinct Cu(I)-coordination geometries are observed in the same structure!