SEARCH

SEARCH BY CITATION

Keywords:

  • chemical adaptability;
  • inclusion compounds;
  • NMR spectroscopy;
  • polyoxometalates;
  • solution chemistry

Abstract

Unique properties of the two giant wheel-shaped molybdenum-oxides of the type {Mo154}≡[{Mo2}{Mo8}{Mo1}]14 (1) and {Mo176}≡[{Mo2}{Mo8}{Mo1}]16 (2) that have the same building blocks either 14 or 16 times, respectively, are considered and show a “chemical adaptability” as a new phenomenon regarding the integration of a large number of appropriate cations and anions, for example, in form of the large “salt-like” {M(SO4)}16 rings (M=K+, NH4+), while the two resulting {Mo146 (K(SO4))16} (3) and {Mo146 (NH4(SO4))16} (4) type hybrid compounds have the same shape as the parent ring structures. The chemical adaptability, which also allows the integration of anions and cations even at the same positions in the {Mo4O6}-type units of 1 and 2, is caused by easy changes in constitution by reorganisation and simultaneous release of (some) building blocks (one example: two opposite orientations of the same functional groups, that is, of H2O{Mo[DOUBLE BOND]O} (I) and O[DOUBLE BOND]{Mo(H2O)} (II) are possible). Whereas Cu2+ in [(H4CuII5)MoV28MoVI114O432(H2O)58]26− (5 a) is simply coordinated to two parent O2− ions of {Mo4O6} and to two fragments of type II, the SO42− integration in 3 and 4 occurs through the substitution of two oxo ligands of {Mo4O6} as well as two H2O ligands of fragment I. Complexes 3 and now 4 were characterised by different physical methods, for example, solutions of 4 in DMSO with sophisticated NMR spectroscopy (EXSY, DOSY and HSQC). The NH4+ ions integrated in the cluster anion of 4 “communicate” with those in solution in the sense that the related H+ ion exchange is in equilibrium. The important message: the reported “chemical adaptability” has its formal counterpart in solutions of “molybdates”, which can form unique dynamic libraries containing constituents/building blocks that may form and break reversibly and can lead to the isolation of a variety of giant clusters with unusual properties.