These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Polyphosphate ions encapsulated in oxothiomolybdate rings: synthesis, structure, and behavior in solution.
    Author: Cadot E, Pouet MJ, Robert-Labarre C, du Peloux C, Marrot J, Sécheresse F.
    Journal: J Am Chem Soc; 2004 Jul 28; 126(29):9127-34. PubMed ID: 15264848.
    Abstract:
    Cyclic oxothiomolybdates containing polyphosphate ions were prepared by simple reactions in aqueous medium of the corresponding polyphosphate ions and the cyclic precursor K(2)I(2)Mo(10)S(10)O(10)(OH)(10)(OH(2))(5).15H(2)O. K(5)[Cl(P(2)O(7)]Mo(12)S(12)O(12)(OH)(12)(H(2)O)(4)].22H(2)O (1) was isolated from concentrated chloride solution (2.5 mol.L(-1)). 1 reveals a remarkable complex containing two different substrates encapsulated in a dodecanuclear ring, a H-bonded Cl(-) ion, and a covalently bonded [P(2)O(7)] group. The chloride ion in 1 can be selectively removed for a monohydrogenophosphate group yielding K(6)[(HPO(4))(P(2)O(7))Mo(12)S(12)O(12)(OH)(12)(H(2)O)(2)].19H(2)O (2), a mixed species containing a [P(2)O(7)] and a [HPO(4)] group. The substitution is accompanied by a significant change of the ring, which adopts a "pear-shape" conformation. In the presence of triphosphate ion, the "heart-shaped" decanuclear ring Rb(3)[(H(2)P(3)O(10))Mo(10)S(10)O(10)(OH)(10)].17.5H(2)O (3) is formed containing a linear [P(3)O(10)] group intimately embedded in the inorganic cyclic host. The three compounds were structurally characterized by single-crystal X-ray diffraction. The behaviors of 1, 2, and 3 in solution were studied by (31)P NMR. Variable temperature experiments, supported by a two-dimensional COSY (31)P experiment, revealed that the supramolecular interaction existing between the chloride ion and the ring in solid 1 is maintained in solution. Nevertheless, 1 remains labile, and successive equilibria were evidenced and interpreted as an ion-pair association involving a halide ion (Cl, Br, or I), responsible for the conformational change of the [P(2)O(7)] group within the cavity. The influence of the nature of the halide guest (Cl(-), Br(-), and I(-)) on the successive equilibria was studied, and the thermodynamic constant related to the postulated equilibrium was determined. The stability of the supramolecular association decreases in the order Cl > Br > I. In solution, a phosphate exchange is observed for 2 while for 3 the absence of temperature dependence of the (31)P NMR spectrum confirms the conformation of the host-guest system is blocked. Elemental analysis and infrared characterizations are also supplied.
    [Abstract] [Full Text] [Related] [New Search]