Hydrolysis of ammonium oxofluorotungstates: A 19F, 17O and 183W NMR study

Self-Assembly through Noncovalent Preorganization of Reactants: Explaining the Formation of a Polyfluoroxometalate

High-order elementary reactions in homogeneous solutions involving more than two molecules are statistically improbable and very slow to proceed. They are not generally considered in classical transition-state or collision theories. Yet, rather selective, high-yield product formation is common in self-assembly processes that require many reaction steps. On the basis of recent observations of crystallization as well as reactions in dense phases, it is shown that self-assembly can occur by preorganization of reactants in a noncovalent supramolecular assembly, whereby directing forces can lead to an apparent one-step transformation of multiple reactants. A simple and general kinetic model for multiple reactant transformation in a dense phase that can account for many-bodied transformations was developed. Furthermore, the self-assembly of polyfluoroxometalate anion [H₂ F₆ NaW₁₈ O₅₆ ]^7- from simple tungstate Na₂ WO₂ F₄ was demonstrated by using 2D ¹⁹ F-¹⁹ F NOESY, 2D ¹⁹ F-¹⁹ F COSY NMR spectroscopy, a new 2D ¹⁹ F{¹⁸³ W} NMR technique, as well as ESI-MS and diffusion NMR spectroscopy, and the crucial involvement of a supramolecular assembly was found. The deterministic kinetic reaction model explains the reaction in a dense phase and supports the suggested self-assembly mechanism. Reactions in dense phases may be of general importance in understanding other self-assembly reactions.

Dinuclear oxofluorometallates as a new structural type of d(0) transition metal oxofluoride compound

Five isomorphous d(0) transition metal oxofluoride compounds A(3)[M(2)O(x)F(11-x)]·(AF)(0.333) (A = K, Rb, NH(4); M = Nb, Mo, W; x = 2, 4) have been synthesized from acid fluoride solutions, and their crystal structures have been determined by single-crystal X-ray diffraction. The basic structural building units are dinuclear M(2)X(11) (dimers) formed from NbOF(5) or Mo(W)O(2)F(4) octahedra connected by the fluorine bridging atom. In the Nb(2)O(2)F(9) dimer, the O atoms occupy apical corners. In the M(2)O(4)F(7) (M = Mo, W) dimers two O atoms are also apically placed, whereas the other two O atoms are statistically disordered in equatorial planes. The arrangement of dimers is so that the hexagonal tunnels containing `free' fluoride ions are formed. During the irradiation process the orthorhombic structure of K(3)Nb(2)O(2)F(9)·(KF)(0.333) transforms into a pseudo-trigonal one with a = 23.15 Å, which is the [101] diagonal of the orthorhombic unit cell. The other four trigonal crystals are merohedral twins.