Tetravalent metal complexation by Keggin and lacunary phosphomolybdate anions

Roy Copping, Leif Jonasson, Andrew J. Gaunt, Dennis Drennan, David Collison, Madeleine Helliwell, Ross J. Pirttijarvi, Chris J. Jones, Anne Huguet, David C. Apperley, Nikolas Kaltsoyannis, Iain May, Anne Huguett

Research output: Contribution to journalArticlepeer-review


We report the synthesis, spectroscopic and structural characterization, and computational analysis of a series of phosphomolybdate complexes with tetravalent metal cations. The reaction between CeIV and Th IV with phosphomolybdate at the optimum pH for the stabilization of the lacunary heteropolyoxometalate anion, [PMo11O39] 7-, results in the formation of compounds containing the anions [Ce(PMo11O39)2]10- and [Th(PMo 11O39)2]10-, respectively. Single crystal X-ray diffraction analysis was performed on salts of both species, Cs10[Ce(PMo11O39)2]·20H 2O and (NH4)10[Th(PMo11O 39)2]·22H2O. In both anionic complexes the f-block metal cation is coordinated to the four unsaturated terminal lacunary site oxygens of each [PMo11O39]7- anion, yielding 8 coordinate sandwich complexes, analogous to previously prepared related complexes. Spectroscopic characterization points to the stability of these complexes in solution over a reasonably wide pH range. Density functional analysis suggests that the Ce-O bond strength in [Ce(PMo 11O39)2]10- is greater than the Th-O bond strength in [Th(PMo11O39)2] 10-, with the dominant bonding interaction being ionic in both cases. In contrast, under similar reaction conditions, the dominant solid state ZrIV and HfIV complexes formed contain the anions [Zr(PMo12O40)(PMo11O39)] 6- and [Hf(PMo12O40)(PMo11O 39)]6-, respectively. In these complexes the central Group 4 d-block metal cations are coordinated to the four unsaturated terminal lacunary site oxygens of the [PMo11O39]7- ligand and to four bridging oxygens of a plenary Keggin anion, [PMo 12O40]3-. In addition, (NH4) 5{Hf[PMo12O40][(NH4)PMo 11O39]}·23.5H2O can be crystallized as a minor product. The structure of the anion, {Hf[PMo12O 40][(NH4)PMo11O39]}5-, reveals coordination of the central HfIV cation via four bridging oxygens on both the coordinated [PMo11O39]7- and [PMo12O40]3- anions. Unusually, the highly charged lacunary site remains uncoordinated to the Hf metal center but instead interacts with an ammonium cation. 31P NMR indicates that complexation of the Keggin anion, [PMo12O40]3-, to HfIV and ZrIV will stabilize the Keggin anion to a much higher pH than usually observed. © 2008 American Chemical Society.
Original languageEnglish
Pages (from-to)5787-5798
Number of pages11
JournalInorganic Chemistry: including bioinorganic chemistry
Issue number13
Publication statusPublished - 7 Jul 2008


  • ZR-IV
  • BOND


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