Five new isostructural d 0 transition metal oxide fluoride compounds Rb 3 Na(NbOF 5 ) 2 · H 2 O and A 3 Na(MO 2 F 4 ) 2 · H 2 O (A ϭ K, Rb and M ϭ Mo, W) have been synthesized by hydrothermal methods and their original structures determined by single-crystal X-ray diffraction. In these compounds, the sodium ions preferentially engage in strong electrostatic interactions with the least polarizable fluoride ions and concurrently the Nb 5ϩ , M 6ϩ (M ϭ Mo, W) metal centers displace toward the oxide ion(s) located trans to the fluorides in order to maintain atomic valences. Consequently, the oxide and fluoride sites retain unequal charge and the most oxide and fluoride ions disordered, preventing bondvalence analysis. A recent examination of the cationϪanion interactions in KNaNbOF 5 and CsNaNbOF 5 , the first reported examples of an ordered [NbOF 5 ] 2Ϫ anion in an inorganic phase, revealed topological connectivities determined by electronic potentials and chemical hardness [7].Examination of the cation-anion interactions in the isostructural mixed-cation phases Rb O indicates that electronic potentials and chemical hardness also determine the connectivities of the anionic units. In particular, the [WO 2 F 4 ] 2Ϫ anions in A 3 Na(WO 2 F 4 ) 2 · H 2 O (A ϭ K, Rb) coordinate more strongly to the surrounding cations through the two fluorides trans to the oxides and is a cis-director for the first time. The adaptive coordination behavior of these anions renders them attractive building units and suggests that their long-range assembly may be controlled by careful selection of counter-cations. Experimental SectionSynthesis Caution: Hydrofluoric acid is toxic and corrosive, and must be handled with extreme caution and the appropriate protective gear! If contact with the liquid or vapor occurs, proper treatment procedures should immediately be followed [8].Materials: Nb 2 O 5 (99.9 %, Aldrich), Na 2 WO 4 · 2H 2 O (99.9 %, Aldrich), Na 2 MoO 4 · 2H 2 O (99.9 %, Aldrich), NaF (99.9 %, Aldrich), KF (99.9 %, Aldrich), RbF (99.9 %, Aldrich) and aqueous hydrofluoric acid (HF) (48 % HF by weight, Aldrich) were used as received. Owing to their hygroscopic nature, the alkali fluorides were manipulated under nitrogen in a dry box.General Procedure: All reactants were sealed in Teflon [fluoro-(ethylenepropylene)] "pouches" [9]. Single or multiple pouches were placed in a Parr pressure vessel filled 33 % with deionized H 2 O as backfill [10]. The pressure vessel was heated for 24 h at 150°C and cooled to room temperature over an additional 24 h. The pouches were opened in air, and the products were recovered by vacuum filtration. In all reactions, excess solvent water or 48 % HF (aq.) was added and the A

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The valence matching principle is used to explain the loss of inversion symmetry in the noncentrosymmetric (NCS) polymorph of KNaNbOF5 in comparison to its centrosymmetric (CS) polymorph. The [NbOF5](2-) anion has five contacts to both potassium and sodium in the NCS polymorph, whereas in the CS polymorph there are only four contacts to potassium and six contacts to sodium. The lower average Lewis acidity of the cationic framework in the NCS polymorph relative to the CS polymorph reflects the loss of inversion symmetry. This lower average Lewis acidity is achieved during hydrothermal synthesis with a potassium-rich solution when the K:Na ratio in the reaction is greater than 1:1, as the Lewis acidity of potassium is lower than that of sodium. The contrasting coordination environments are manifested in secondary distortions that weaken the primary Nb═O interaction and lengthen the Nb═O bond in the NCS polymorph. An unusual heat-induced phase transition from the CS to the NCS polymorph was studied with in situ powder X-ray diffraction. The transition to the NCS polymorph upon cooling occurs through an intermediate phase(s).

Hemin (chloro(protoporhyrinato)iron(III)) was found to bind to mesoporous nanocrystalline (anatase) TiO2 thin films from dimethyl sulfoxide solution, Keq=10(5) M-1 at 298 K. Band gap illumination in methanol reduced hemin to heme and led to the appearance of TiO2 electrons, heme/TiO2(e-). Reactions of heme/TiO2(e-) with CCl4 or 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT) led to the formation of stable carbene products in greater than 60% yield. The spectroscopic data are fully consistent with a dissociative two-electron organohalide reduction mechanism of CCl4 and DDT to yield (protoporhyrinato)FeIICCl2 and (protoporhyrinato)FeIIC=C(p-Cl-phenyl)2 respectively.

The rational design of crystal structures, in particular noncentrosymmetric materials, and how to differentiate polar, polar-chiral, and chiral structures, is an ongoing theme in crystal engineering. In KNaNbOF 5 , the combination of a second-order Jahn Teller active d 0 transition metal oxyfluoride anionic unit and mixed K/Na cation coordination environments are shown to result in a polar structure (space group Pna2 1 ). The crystal structure analysis of the Na/K-O/F interactions reveals that the potassium cations form one of the two contacts to the under-bonded oxide ions. These interactions satisfy the expected bond valence sums and Pauling's second crystal rule (PSCR), leading to O/F ordering and acentric packing of the [NbOF 5 ] 2anionic unit.