Structure and Solution Speciation of U^IV Linked Phosphomolybdate (Mo^V) Clusters

Crystals of [NaU­(Mo₆P₄O₃₁H₇)₂]·5Na·(H₂O)_<i>n</i> (<b>NaUMo</b>_<b>6</b>) have been synthesized by slow evaporation of an aqueous mixture containing uranyl nitrate, sodium molybdate, phosphoric acid, and sodium dithionate. Single crystal diffraction of <b>NaUMo</b>_<b>6</b> reveals the assembly of {Mo₆P₄} clusters linked into one-dimensional chains with alternating Na⁺ and U⁴⁺ cations. To our knowledge, <b>NaUMo</b>_<b>6</b> is a unique example of Mo⁵⁺ based polyoxometalate associated with actinides. With the use of similar synthesis conditions but without uranium in the aqueous solution, [Na­(Mo₆P₄O₃₁H₁₀)₂]·5Na·(H₂PO₄)·(H₂O)_<i>n</i> (<b>NaMo</b>_<b>6</b>) is obtained. <b>NaMo</b>_<b>6</b> is a sandwich type cluster which is built on the assemblage of two {Mo₆P₄} units linked by one sodium cation. Using small-angle X-ray scattering techniques and aqueous electrolyte based dissolution strategies, we can accurately observe chains of [UNa­(Mo₆P₄O₃₁H₇)₂]_<i>n</i>^5<i>n</i>, where <i>n</i> = 7 is the dominant soluble specie. Likewise, the dimeric form of [Na­(Mo₆P₄O₃₁H₁₀)₂]^5– dominates the aqueous solution, revealing the structural units observed in the crystal structure are also stable in solution, under appropriate dissolution conditions

[Sc₂(μ-OH)₂(H₂O)₆(NO₃)₂](NO₃)₂: Aqueous Synthesis and Characterization

[Sc₂(μ-OH)₂(H₂O)₆(NO₃)₂]­(NO₃)₂ has been synthesized from an aqueous scandium nitrate solution by using zinc powder as a reducing agent for nitric acid, which drives an increase in pH and forces the condensation of aqua scandium cations. This preparative route readily produces gram-scale samples with yields near 65%. A single-crystal X-ray diffraction study reveals a structure characterized by a hydroxo-bridged Sc dimer. The FTIR spectrum of the compound has been modeled via ab initio computations, allowing the identification of signature IR peaks. Some initial observations on the thermal transformation of the compound to Sc₂O₃ are also reported

Pseudocryptand Hosts for Paraquats and Diquats

H-bonding interaction of acidic moieties (CH₂OH, COOH) at the 5- and 5′-positions of bis­(1,3-phenylene)-32-crown-10 (<b>1</b>) with di- or tritopic anions leads to enhanced formation of inclusion complexes with <i>N</i>,<i>N</i>′-dialkyl-4,4′-bipyridinium salts (“paraquats”, <b>2</b>); the enforced folding of the crown ethers into pseudocryptands thus leads to pseudo-pseudorotaxanes. Strikingly, in the presence of the most effective anion (trifluoroacetate, TFA), the apparent bimolecular association constants for crown–paraquat complexation increase by more than an order of magnitude and approach those for covalent cryptands derived from the crown ether. Even though they may form pseudocryptands, the picolinate, nicotinate, and isonicotinate diesters <b>6</b> of <i>cis</i>-(4,4’)-bis­(hydroxymethyl)­dibenzo-30-crown-10 do not exhibit enhanced binding of either diquat or paraquat relative to the starting diol in contrast to the picolinate ester of isomeric 5,5′-bis­(hydroxymethyl)­bis­(<i>m</i>-phenylene)-32-crown-10, which displayed a higher binding constant than the starting diol. The results for the analogous reverse esters <b>7</b> derived from <i>cis</i>-(4,4’)-dicarboxydibenzo-30-crown-10 and pyridylmethanols reveal weaker complexes with diquat than the normal esters <b>6</b>; however, surprisingly, two reverse esters <b>7</b> complex paraquat more strongly than isomers <b>6</b>