Eric Burkholder

Hydrothermal synthesis of polyoxotungstate clusters, surface-modified with M(II)-organonitrogen subunits

Abstract The hydrothermal reactions of Na2WO4·2H2O with secondary metal cation sources in the presence of an appropriate organonitrogen donor yield a series of molecular clusters. The compounds [Ni(bpy)3]1.5[Ni(bpy)2(H2O){H3W12O40}]·0.5H2O (1·0.5H2O), [{Ni(phen)2(H2O)}2{H4W12O40}]·4H2O (2·4H2O) and [{Cu(phen)2}4{H2W12O40}] [{Cu(phen)2}2{H2W12O40}]·3H2O (4·3H2O) are constructed from the α-metatungstate cluster [H2W12O40]6− core, covalently linked through oxo-bridges to secondary metal-organonitrogen ligand subunits. In the case of 1, the tungstate cluster is decorated by a single {Ni(bpy)2(H2O)}2+ subunit yielding an anionic bimetallic cluster, while in 2, two {Ni(phen)2(H2O)}2+ moieties are linked to the tungstate core to form a neutral bimetallic cluster. It is noteworthy that 4 is constructed of a cationic cluster, exhibiting a central tungstate core linked to four {Cu(phen)2}2+ units, and an anionic bimetallic polyoxoanion, featuring a tungstate core bonded to two {Cu(phen)2}2+ moieties. Compound 3, [{Cu(bpy)2}2W10O32]·2H2O (3·2H2O) consists of two {Cu(bpy)2}2+ subunits linked to the opposite sides of a decatungstate cluster, while compound 5 contains {Co(bpy)3}3+ cations and the common Keggin anion, [CoW12O40]6−.

A building block approach to the synthesis of organic–inorganic oxide materials: the hydrothermal synthesis and network structure of [{Ni4(tpypyz)3}{Mo5O15(O3PCH2CH2PO3)}2]·23H2O (tpypyz = tetra-2-pyridylpyrazine)

The hydrothermal reaction of MoO3, [Ni(CH3CO2)2] x 4H2O, tpypyz, ethylenediphosphonic acid and water yields the 2D material [[Ni4(tpypyz)3][Mo5O15(O3PCH2CH2PO3)]2] x 23H2O (1 x 23H2O), constructed from [Mo5O15(O3PCH2CH2PO3)]4- clusters linked in one-dimension through the ethylene tethers of the diphosphonate component; these molybdodiphosphonate chains are in turn linked into a 2D network through the tetranuclear secondary metal-ligand subunit [Ni4(tpypyz)3]8+.

Novel molybdenum(V) squarato complexes based on the dinuclear metal–metal bonded unit: syntheses and structural characterization of dinuclear [Mo2O4(C4O4)(R-Py)4] and tetranuclear [Mo4O8(C4O4)4]4−

Reactions of mononuclear oxohalomolybdates(V) with squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione) afforded two types of {Mo2O4}2+ containing species with the squarato ligand engaged in a μ2-1,2-bis(monodentate) binding mode. In the presence of pyridine (Py) or 3,5-lutidine (3,5-Lut) neutral, dinuclear complexes [Mo2O4(C4O4)(Py)4]·2MeOH·0.5Py 1a, [Mo2O4(C4O4)(Py)4]·2Py 1b and [Mo2O4(C4O4)(3,5-Lut)4]·2(3,5-Lut) 1c were obtained. A pair of nitrogen donor ligands and a squarate oxygen occupy the three coordination sites of each metal in the {Mo2O4}2+ unit in 1a, 1b and 1c. The squarate functions as a third, auxiliary bridge between a pair of molybdenum atoms at an average distance of 2.55 A. Using 2,4,6-collidine (Col) afforded (ColMe)4[Mo4O8(C4O4)4]·2MeOH·2Col 2a (ColMe+ = N-methylcollidinium cation, NC9H14+) and (ColH)4(PyEt)[Mo4O8(C4O4)4]Br 2b (ColH+ = protonated 2,4,6-collidine, NC8H12+; PyEt+ = N-ethylpyridinium cation, NC7H10+). The tetranuclear anions of 2a and 2b consist of a rare, cube-like {Mo4O4(μ3-O)4}4+ core with four squarato ligands attached to its periphery. The squarato ligands in the [Mo4O8(C4O4)4]4− anions bridge pairs of molybdenum atoms from neighbouring {Mo2O4}2+ units, spanning an average distance of 3.43 A. The compounds were fully characterized by infrared vibrational spectroscopy, NMR spectroscopy, elemental analyses and X-ray diffraction studies.

Solid state coordination chemistry: structural consequences of variations in tether length in the oxovanadium–copper–bisterpy–{O3P(CH2)nPO3}4− system, n= 1–6 (bisterpy = 2,2′:4′,4″:2″,2‴-quarterpyridyl-6′,6″-di-2-pyridine)

Hydrothermal reactions of Na3VO4, an appropriate Cu(II) source, bisterpy and an organodiphosphonate, H2O3P(CH2)nPO3H2 (n = 1-6) yielded a family of materials of the type [Cu2(bisterpy)]4+/VxOy(n-)/[O3P(CH2)nPO3]4-. This family of bimetallic oxides is characterized by an unusual structural diversity. The oxides [[Cu2(bisterpy)]V2O4[O3PCH2PO3H]2] (1), [[Cu2(bisterpy)(H2O)]VO2[O3P(CH2)3PO3][HO3P(CH2)3PO3H2]] (4) and [[Cu2(bisterpy)]V2O4[O3P(CH2)6PO3H]2].2H2O (7.2H2O) are one-dimensional, while [[Cu2(bisterpy)(H2O)2]V2O4[O3P(CH2)2PO3][HO3P(CH2)2PO3H]2] (2), [[Cu2(bisterpy)]V4O8[O3P(CH23PO3]2].4H2O (3.4H2O) and [[Cu2(bisterpy)]V2O4(OH)2[O3P(CH2)4PO3]].4H2O (5.4H2O) are two-dimensional. The V(IV) oxide [[Cu2(bisterpy)]V4O4[O3P(CH2)5PO3H]4].7.3H2O (6.7.3H2O) provides a relatively unusual example of a three-dimensional bimetallic oxide phosphonate. The structures reveal a variety of V/P/O substructures as building blocks.

Solid state coordination chemistry: construction of 2D networks and 3D frameworks from phosphomolybdate clusters and binuclear Cu(II) complexes. The syntheses and structures of [{Cu2(tpypyz)(H2O)2}(Mo5O15)(HOPO3)2]·nH2O [n = 2, 3; tpypyz = tetra(2-pyridyl)pyrazine]

The hydrothermal reaction of MoO3, Cu(C2H3O2)2.H2O, tpypyz, H3PO4 and H2O yields a 2D material, [(Cu2(tpypyz)(H2O)2)(Mo5O15)(HOPO3)2].2H2O (1.2H2O), constructed from (Mo5O15(HOPO3)2)4- clusters linked through (Cu2(tpypyz)(H2O)2)2+ components; in contrast, use of Cu2O in the synthesis in place of Cu(C2H3O2)2.H2O yields a 3D material [(Cu2(tpypyz)(H2O)2)(Mo5O15)(HOPO3)2].3H2O (2.3H2O), constructed from the same building blocks as 1.2H2O.

The hydrothermal syntheses and characterization of one- and two-dimensional structures constructed from metal–organic derivatives of polyoxometalates: [{Cu(bpy)2}{Cu(bpy)(H2O)}(Mo5O15){O3P(CH2)4PO3}]·H2O and [{Cu2(tpypyz)(H2O)2}(Mo5O15)(O3PCH2CH2PO3)]·5.5H2O [bpy = 2,2′-bipyridine, tpypyz = tetra(2-pyridyl)pyrazine]

The hydrothermal reaction of CuSO4·5H2O, Na2MoO4·2H2O and 2,2′-bipyridine with the bridging diphosphonate ligand H2O3P(CH2)4PO3H 2 yields the one-dimensional chain [{Cu(bpy)2}{Cu(bpy)(H2O)2 }(Mo5O15){O3P(CH2) 4PO3}]·H2O; the introduction of a second bridging component in the reaction of Cu(MeCO2)2·H2O, MoO3, H2O3PCH2CH2PO3H 2 and tetra(2-pyridyl)pyrazine yields the network solid [{Cu2(tpypyz)(H2O)2}(Mo5 O15)(O3PCH2CH2PO3 )]·5.5H2O.