RESUMEN

The hexadecanuclear, mixed-valence cluster [Mo(16)O(42)(OH)(2)(3-iPrC(3)H(3)N(2))(12)].H(2)O (1), has been synthesized and characterized by X-ray crystallography, IR spectroscopy and mass spectrometry. The C(2)-symmetric complex consists of a cubane Mo(VI) (4)O(4) "jewel" held in a 10-point "setting" comprised of five dinuclear Mo(V) units tethered together by two tetrahedral Mo(VI) centers. The dinuclear units are ligated by twelve 3-isopropylpyrazole units that interact with the Mo--O framework through a network of hydrogen bonds. Structural parameters, charge requirements, and bond valence sum analyses support the assignment of +5 and +6 oxidation states to the dinuclear and cubane/tetrahedral Mo centers, respectively. Space filling models reveal that the pyrazole groups coat much of the surface of the molecule, apart from a number of oxo-rich seams that trace a chiral pattern across the surface. Complex 1 exhibits a unique structure that combines moieties generally atypical of polyoxometalates, viz., a Mo cubane containing only two terminal oxo ligands, and three distinct Mo(V) (2) units (including a 5-coordinate Mo center) tethered into a 10-point "setting" by tetrahedral Mo(VI) centers.

RESUMEN

Two different one pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO(2) (-))(3)O(-), which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M(8){C(CO(2))(3)O}(4)](H(2)O)(12) (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M(4)O(4) cubane core, each oxygen component of which is provided by the alkoxo centre of a C(CO(2) (-))(3)O(-) ligand. Reaction of 2,2'-pyridil, (2-C(5)H(4)N)COCO(2-C(5)H(4)N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca(4)L(4)(NO(3))(4)] in which L=(2-C(5)H(4)N)(2)C(COOR)O(-) (R=Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2'-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C(5)H(4)N)(2)SO(3)C(OH)}(2)M] (M=Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M(4){(C(5)H(4)N)(2)SO(3)C(O)}(4)] (M=Zn, Mn) can be obtained directly from 2,2'-dipyridyl ketone in one-pot reaction systems (sealed tube, 120 degrees C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C(5)H(4)N)(2)SO(3)C(OH)](-) bisulfite addition compound; the [(C(5)H(4)N)(2)SO(3)C(O)](2-) ligand in this case plays the same cubane-forming role as the ligands C(COO(-))(3)O(-) and (2-C(5)H(4)N)(2)C(COOR)O(-) above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the monoanionic complexes, [M(3)Na{(C(5)H(4)N)(2)SO(3)C(O)}(4)](-) (M=Zn, Mn, Co) with an M(3)NaO(4) cubane core, are formed directly from 2,2'-dipyridyl ketone.

Asunto(s)

Metales Pesados/química , Metanol/análogos & derivados , Ligandos , Metanol/síntesis química , Modelos Moleculares , Estructura Molecular , Compuestos Organometálicos/química

RESUMEN

Aqueous reaction mixtures containing dihydroxyfumaric acid, M2+ (M = Zn, Co, Fe, and Mg) and acetate ion at room temperature give crystals, suitable for single-crystal X-ray diffraction studies, of composition [(MII)8(C4O7)4(H2O)12].24H2O, in which the C4O74- component is the alkoxide-tricarboxylate tetra-anionic species -OC(CO2-)3, a new oxyanion of carbon. All four compounds crystallize in the body-centered space group I3m with cell dimensions a approximately 15.0 A. Discrete electrically neutral [(MII)8(C4O7)4(H2O)12] molecules are present, with a cubane-like core consisting of four trigonal prismatic metal centers and four mu3-alkoxo bridges from separate -OC(CO2-)3 ligands. The octametallic molecule is highly symmetrical, with four fac tri-aqua octahedral metal centers tetrahedrally appended to the central cubane-based [(MII)8(C4O7)4 ]8- unit. The molecules assemble in the crystal in a body-centered cubic fashion, each being attached to its eight neighbors by 24 equivalent hydrogen bonds-an extreme example of self-complementarity.

RESUMEN

A supramolecular cube has been formed by linking WS3Cu3 clusters with bidentate ligands. Eight WS3Cu3 clusters, which have an incomplete cubane-like structure, serve as the three connecting nodes of the cube, while 12 bridging cyanide anions coordinated to copper centers lie along the edges of the cube. Eight chloride anions and four lithium cations are located inside the cube.