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Keywords:

  • Supramolecular chemistry;
  • Mass spectrometry;
  • Noncovalent interactions;
  • Metallogrids;
  • Analytical methods

Abstract

Matrix assisted laser desorption/ionisation mass spectrometry (MALDI-MS) methods have been developed for the characterisation of neutral [2×2] metallogrids derived fromdiimine, dihydrazone and diacylhydrazone ligands. Such grids may be protonated in solution to give cationic species but in most cases these are labile, so that rather delicate conditions are required for observation of the intact metallogrids as monoprotonated derivatives in the gas phase. As a MALDI matrix, 2,4,6-trihydroxyacetophenone (THAP) is sufficiently acidic to enable monoprotonation of the grids unaccompanied by dissociation, and if the grid sample is initially deposited by a layering technique to avoid any preliminary dissociation in solution the mass spectrum of the intact monoprotonated grid is readily obtainable. The stoichiometry of 24 grids obtained from several different ligands and metals was confirmed with this optimized protocol. The deposition technique used means that the best signal-to-noise ratio in the spectra is obtained with only a small number of laser shots (ca. 5) to volatilise the sample. This MALDI-MS protocol can be applied to the study of grid dissociation in solution and in the case of CuII grids, in particular, has revealed the formation of various unusual clusters. The crystal structure is reported of one such cluster that was isolated and contains a nonionisable ligand that is related to that incorporated within the grids analysed by the MALDI-MS protocol.