Transition metal phosphate complex

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Some bonding modes in phosphate complexes.

Transition metal phosphate complexes are

bidentate coordination mode is common. The second and third pKa's of phosphoric acid
, pKa2 and pKa3, are 7.2 and 12.37, respectively. It follows that HPO2−4 and PO3−4 are sufficiently basic to serve as ligands. The examples below confirm this expectation. Molecular metal phosphate complexes have no or few applications.

Examples

  • Co(H2NCH2CH2NH2)2PO4
    Co(H2NCH2CH2NH2)2PO4
  • [Pt2(HPO4)4(SC4H8)2]2−
    [Pt2(HPO4)4(SC4H8)2]2−
  • [Re3Cl9(PO4)]3−
    [Re3Cl9(PO4)]3−
  • Phosphotungstic acid H3PW12O40
    Phosphotungstic acid H3PW12O40
  • Bidentate, chelating: One example is [Co(ethylenediamine)2(PO4)].[1]
  • Bidentate, bridging: Phosphate, like carboxylate and sulfate, is well suited to span
    metal-metal bonds. This bonding mode is illustrated by [Mo2(HPO4)4]4−, which features a Mo-Mo triple bond.[2] Related [Pt(III)]2 complexes have been reported.[3]
  • Tridentate, bridging. Several triangulo clusters feature a capping phosphate ligand, e.g. [Re3Cl9(PO4)]3−.[4]
  • Encapsulated: In phosphotungstic acid, all four oxygen atoms of phosphate are bonded to metals.[5]

Other transition metal phosphates

Aside from molecular metal phosphate complexes, the topic of this article, many or most transition metal phosphates are nonmolecular, being

Vanadyl phosphate
(VOPO4(H2O)) is a commercial catalyst for oxidation reactions. Many metal phosphates occur as minerals.

Di- and polyphosphates

Phosphates exist in many condensed oligomeric forms. Many of these derivatives function as ligands for metal ions. Pyrophosphate (P2O4−7)[6] and trimetaphosphate ([P3O9]3−) have been particularly studied. They typically function as bi- and tridentate ligands.

Structure of [(C6H6)Ru(P3O9)]−. Color code: red = O, violet = P, blue = Ru, gray = C.[7]

References

  1. PMID 850030
    .
  2. doi:10.1021/ic50202a053
    .
  3. doi:10.1021/ic00228a019
    .
  4. doi:10.1002/zaac.19905870121
    .
  5. ISBN 978-0-08-037941-8
    .
  6. PMID 21578209
    .
  7. ^ S.Kamimura, T.Iida, K.Kanao, C.Nogawa, Y.Tanabe, K.Oh-ishi, S.Fukuzawa, Y.Ishii (2005). Journal of the Institute of Science and Engineering,Chuo University. 11: 1. {{cite journal}}: Missing or empty |title= (help)CS1 maint: multiple names: authors list (link)
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