Hydrothermal reactions of molybdenum-oxide precursors with polyalcohols in the presence of base yielded two series of mixed-valence oxomolybdenum clusters, the hexadecanuclear species [XH(12)((MoO3)-O-VI)(4)(Mo12O40)-O-V](m-) (X = Na+, m = 7; X = 2H(+), m = 6) and the superclusters [XH(12)Mo(6)(VI)Mo(36)(V)O(109){(OCH2)(3)CR}(7)](m-) (X = Na(H2O)(3)(+), m = 9, n = 13; X = Na(H2O)(3)(+), m = 7, n = 15; X = MoO3, m = 9, n = 14; X = MoO3, m = 10, n = 13). In a representative synthesis for the hexadecanuclear class of materials, the hydrothermal reaction of a mixture of Na2MoO4 . 2H(2)O, MoO3, Mo metal, and NH4Cl produced (NH4)(7)[NaMo16(OH)(12)O-40]. 4H(2)O(1 . 4H(2)O) as red-orange crystals.The compound (Me(3)NH)(4)K-2[H2Mo16(OH)(12)O-40]. 8H(2)O(2 . 8H(2)O) was prepared in a similar fashion. The structure of the anion of 1 consists of an epsilon-Keggin core {H12Mo12O40}, capped on four hexagonal faces by {MoO3} units and encapsulating a Na+ cation. The structure of the oxomolybdenum framework of 2 is essentially identical to that of 1; however, the central cavity is now occupied by 2H(+). The synthesis of the "superclusters" exploits similar hydrothermal conditions, resulting in the isolation of (Me(3)NH)(2)(Et(4)N)Na-4[Na(H2O)(3)H-15-Mo42O109{(OCH2)(3)CCH2OH}(7)]. 15H(2)O (3 . 15H(2)O), (Me(3)NH)(2)(H3O)Na-6[Na(H2O)(3)H13Mo42O109{(OCH2)(3)CCH2-OH}(7)]. 7H(2)O (4 . 7H(2)O), Na-9[(MoO3)H14Mo42O109{(OCH2)(3)CCH2OH}(7)]. 0.5C(CH2OH)(4) . 25H(2)O (5 . 0.5C(CH2OH)(4) . 25H(2)O), and (Me(4)N)(Et(2)NH(2))(H3O)(2)Na-6 [(MoO3)H13Mo42O109{(OCH2)(3)CCH3}(7)]. 10H(2)O (6 . 10H(2)O). The structures of these superclusters resemble a bowl consisting of an oxomolybdenum framework, constructed from eighteen pairs Mo(V)-Mo(V) dimers and linked through edge-sharing of {MoO6} octahedra, with six cis-dioxomolybdate(VI) sites protruding outward to provide the surface of a channel to the molecular cavity of the complex anion. The cavity is populated by a Na(H2O)3(+) group in 3 and 4 and by a {MoO3} unit in 5 and 6. Crystal data are as follows. 1 . 4H(2)O: cubic (No. 216), a = 26.978(3) Angstrom, Z = 8. 2 . 8H(2)O: orthorhombic Cmcm (No. 63), a = 18.493(4) Angstrom, b = 19.685(4) Angstrom, c = 19.518(4) Angstrom, Z = 4. 3 . 15H(2)O: triclinic (No. 2), a = 22.159(4) Angstrom, b = 27.049(5) Angstrom, c = 17.726(3) Angstrom, a = 98.34(1)degrees, beta = 112.56(2)degrees, gamma = 82.81(1)degrees, Z = 2. 4 . 7H(2)O: monoclinic C2/c (No. 15), a = 54.901(11) Angstrom, b = 17. 616(4) Angstrom, c = 36.571(7) Angstrom, beta = 94.04(2)degrees, Z = 8. 5 . 0.5C(CH2OH)(4) . 25H(2)O: triclinic (No. 2), a = 17.302(3) Angstrom, b = 20.865(4) Angstrom, c = 26.734(5) Angstrom, a = 103.90(3)degrees, beta = 99.26(3)degrees, gamma = 108.95(3)degrees, Z = 2. 6 . 10H(2)O: orthorhombic Pbcm (No. 57), a 17.916(4)Angstrom, b = 44.614(9) Angstrom, c = 23.372(5) Angstrom, Z = 4.f?