Metal phosphonate

Metal phosphonates are coordination compounds in which metal ions or metal clusters are coordinated by phosphonates. They are characterized by a highly flexible and complex structural chemistry. Porous metal phosphonates represent a subgroup of metal-organic framework compounds.

History

Research on metal phosphonates was pioneered in 1978 by Alberti and Costantino et al., who prepared three zirconium phosphonates: zirconium phenylphosphonate, Zr(C6H5PO3)2; zirconium hydroxymethylphosphonate, Zr(HOCH2PO3)2; and zirconium ethylphosphate, Zr(C2H5OPO3)2.

Section of the crystal structure of Al2[O3PC2H4PO3](H2O)2F2·H2O along the a axis. It consists of chains of AlO4F2 octahedra linked by ethylene diphosphonate units, forming a structure with pores parallel to the a axis.

While early work focused primarily on using simple phosphonic acids to synthesize new solid-state materials, research later expanded to diphosphonic acids of the general formula [(HO)2OP−R−PO(OH)2], where R represents an organic group of varying length and type. This enabled the synthesis of extended framework structures with one-, two-, and three-dimensional cross-linking. A primary objective was to specifically increase the porosity of these materials. Although many early metal diphosphonates featured channels whose size was determined by the length of the linker molecule, the distances between molecules were often very small (less than 5 Å), restricting access to the internal pore space for potential applications. Various strategies were subsequently developed to enlarge these pore spaces.

The first method, reported by Dines et al. in 1983, utilized a phosphate ester alongside the diphosphonic acid; porosity was introduced into the resulting material by hydrolyzing the phosphate ester to create voids. The second method involves the controlled topotactic substitution of a diphosphonate within a layered host. The third common method relies on forming the porous material through the co-precipitation of a metal species with the diphosphonic acid and a minor substituent, R-PO(OH)2—such as phosphoric acid (R = OH), phosphorous acid (R = H), or methylphosphonic acid (R = CH3). This methodology was employed by Alberti and Clearfield to prepare several microporous diphosphonates containing tetravalent or divalent metal ions, respectively.

A major advance was the extension of this synthetic chemistry to trivalent metal ions, particularly aluminum, by Maeda et al. in 1994 and Attfield et al. in 2000. Interest in open-framework aluminum phosphonates was stimulated by the discovery of two microporous aluminum methylphosphonates, AlMePO-α and AlMePO-β, described by Maeda et al. beginning in 1994. These two structures, which share the stoichiometry Al2(MePO3), are polymorphs and feature one-dimensional hexagonal channels with a diameter of 6 Å. In these structures, aluminum exhibits both tetrahedral and octahedral coordination.

Although early syntheses predominantly yielded dense metal phosphonates, the use of bulky, rigid, and sterically demanding linker molecules starting in the early 2000s enabled the generation of increasingly ordered microporosity.

Properties

Porous metal phosphonates

Compared to many carboxylate- or imidazolate-based MOFs, metal phosphonates typically exhibit high thermal, chemical, and mechanical stability. This stability is primarily attributed to strong metal–phosphonate bonds, as well as the high charge density and basicity of the deprotonated phosphonate groups. Exceptionally stable framework compounds can be formed, particularly with hard metal ions such as Ti(IV), Zr(IV), or Hf(IV).

The coordination modes of the phosphonate group are significantly more versatile than those of carboxylate groups. A single phosphonate group can coordinate up to eight metal centers via its three oxygen atoms. The specific binding mode depends on factors such as the degree of deprotonation, reaction temperature, the choice of metal ion, and any additional functional groups on the linker molecule. While this coordination flexibility drives the high structural diversity of metal phosphonates, it also complicates the targeted synthesis of crystalline and porous materials.

Structural chemistry

Due to the thermodynamic stability of the M–O–P bond, metal phosphonates tend to form dense structures. Historically, initial syntheses utilizing mono- and diphosphonates predominantly yielded dense, layered structures.

Harris notation is frequently employed to describe the coordination modes of phosphonate groups. A descriptor of the form [M.O1O2O3] indicates the total number of metal centers (M) coordinated by the oxygen atoms (O1, O2, and O3) of a phosphonate group, as well as the number of metal ions bound to each individual oxygen atom.

Examples of Harris notation for phosphonate coordination modes, where R = alkyl or aliphatic radical.
Examples of Harris notation for phosphonate coordination modes, where R = alkyl or aliphatic radical.

Porous metal phosphonates

Porosity can be introduced via interlayer gaps, structural defects, mixed-linker systems, or the utilization of sterically demanding, rigid linkers. In particular, rigid, non-linear aromatic phosphonic acids can impede dense layer packing, thereby favoring more open framework structures.

Synthesis

Metal phosphonates are typically synthesized in solution via hydrothermal or solvothermal synthesis. In this process, metal sources react with organic phosphonic acids or their precursors (phosphonates) at elevated temperatures, frequently within autoclaves or other sealed reaction vessels, and less commonly under reflux conditions. Crystallization is heavily dependent on kinetic and thermodynamic factors, particularly the strength of the metal–oxygen bond and the rate of ligand exchange. The synthesis of crystalline, porous metal phosphonates remains challenging because strong P–O–M interactions often result in rapid nucleation, poor crystallinity, or the formation of dense phases.

Phosphonic acids

Alkylphosphonic acids are prepared via the Arbuzov reaction. Alkyl phosphonates and α-halogenated phosphonates can be synthesized using the Michaelis-Becker reaction.For aromatic phosphonic acid linkers, the Hirao reaction, the Tavs reaction, and coupling strategies involving pre-phosphonated aromatics, such as the Suzuki coupling, are widely utilized. Typically, phosphonate esters are synthesized first and subsequently hydrolyzed to the corresponding phosphonic acids. Alternatively, phosphinic acids can be prepared and subsequently oxidized using hydrogen peroxide.

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Literature

References

  1. ↑ Abraham Clearfield (2007), "Metal Phosphonate Chemistry", Progress in Inorganic Chemistry, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 371–510, ISBN 978-0-470-16648-2
  2. 1 2 3 4 Phosphonate Chemistry, Technology, and Applications, Elsevier, 2026, doi:10.1016/c2024-0-00017-3, ISBN 978-0-443-33374-3
  3. ↑ Stephen J.I. Shearan, Norbert Stock, Franziska Emmerling, Jan Demel, Paul A. Wright, Konstantinos D. Demadis, Maria Vassaki, Ferdinando Costantino, Riccardo Vivani, Sébastien Sallard, Inés Ruiz Salcedo, Aurelio Cabeza, Marco Taddei (2019-05-24), "New Directions in Metal Phosphonate and Phosphinate Chemistry", Crystals, vol. 9, no. 5, p. 270, Bibcode:2019Cryst...9..270S, doi:10.3390/cryst9050270, hdl:11568/1024477{{citation}}: CS1 maint: multiple names: authors list (link)
  4. 1 2 Howard G. Harvey, Simon J. Teat, Martin P. Attfield (2000), "Al2[O3PC2H4PO3](H2O)2F2·H2O: a novel aluminium diphosphonate", Journal of Materials Chemistry, vol. 10, no. 12, pp. 2632–2633, doi:10.1039/b006851i{{citation}}: CS1 maint: multiple names: authors list (link)
  5. ↑ Margaret L. Blohm, Douglas E. Fjare, Wayne L. Gladfelter (March 1983), "Formation of a new nitrido cluster from a cluster coordinated isocyanate", Inorganic Chemistry, vol. 22, no. 6, pp. 1004–1006, doi:10.1021/ic00148a037{{citation}}: CS1 maint: multiple names: authors list (link)
  6. ↑ Giulio Alberti, Umberto Costantino, Fabio Marmottini, Riccardo Vivani, Piergiorgio Zappelli (September 1993), "Zirconium Phosphite (3,3′,5,5′-Tetramethylbiphenyl)diphosphonate, a Microporous, Layered, Inorganic–Organic Polymer", Angewandte Chemie International Edition in English, vol. 32, no. 9, pp. 1357–1359, doi:10.1002/anie.199313571{{citation}}: CS1 maint: multiple names: authors list (link)
  7. ↑ G. Alberti, U. Costantino, F. Marmottini, R. Vivani, P. Zappelli (May 1998), "Preparation of a covalently pillared α-zirconium phosphite-diphosphonate with a high degree of interlayer porosity", Microporous and Mesoporous Materials, vol. 21, no. 4–6, pp. 297–304, Bibcode:1998MicMM..21..297A, doi:10.1016/S1387-1811(98)00032-8{{citation}}: CS1 maint: multiple names: authors list (link)
  8. ↑ Baolong Zhang, Damodara M. Poojary, Abraham Clearfield (1998-04-20), "Synthesis and Characterization of Layered Zinc Biphenylylenebis(phosphonate) and Three Mixed-Component Arylenebis(phosphonate)/Phosphates", Inorganic Chemistry, vol. 37, no. 8, pp. 1844–1852, doi:10.1021/ic9712380{{citation}}: CS1 maint: multiple names: authors list (link)
  9. ↑ Kazuyuki Maeda, Junji Akimoto, Yoshimichi Kiyozumi, Fujio Mizukami (1995-06-16), "AlMepO-α: A Novel Open-Framework Aluminum Methylphosphonate with Organo-Lined Unidimensional Channels", Angewandte Chemie International Edition in English, vol. 34, no. 11, pp. 1199–1201, doi:10.1002/anie.199511991{{citation}}: CS1 maint: multiple names: authors list (link)
  10. ↑ Kazuyuki Maeda; Junji Akimoto; Yoshimichi Kiyozumi; Fujio Mizukami (1995), "Structure of aluminium methylphosphonate, AIMepO-β, with unidimensional channels formed from ladder-like organic–inorganic polymer chains", J. Chem. Soc., Chem. Commun., no. 10, pp. 1033–1034, doi:10.1039/C39950001033
  11. ↑ Howard G. Harvey; Simon J. Teat; Martin P. Attfield (2000), "Al2[O3PC2H4PO3](H2O)2F2·H2O: a novel aluminium diphosphonate", Journal of Materials Chemistry, vol. 10, no. 12, pp. 2632–2633, doi:10.1039/b006851i
  12. ↑ Kazuyuki Maeda; Junji Akimoto; Yoshimichi Kiyozumi; Fujio Mizukami (1995-06-16), "AlMepO-α: A Novel Open-Framework Aluminum Methylphosphonate with Organo-Lined Unidimensional Channels", Angewandte Chemie International Edition in English, vol. 34, no. 11, pp. 1199–1201, doi:10.1002/anie.199511991
  13. ↑ Kazuyuki Maeda; Yoshimichi Kiyozumi; Fujio Mizukami (1994-12-05), "Synthesis of the First Microporous Aluminum Phosphonate with Organic Groups Covalently Bonded to the Skeleton", Angewandte Chemie International Edition in English, vol. 33, no. 22, pp. 2335–2337, doi:10.1002/anie.199423351
  14. ↑ Kazuyuki Maeda; Junji Akimoto; Yoshimichi Kiyozumi; Fujio Mizukami (1995), "Structure of aluminium methylphosphonate, AIMepO-β, with unidimensional channels formed from ladder-like organic–inorganic polymer chains", J. Chem. Soc., Chem. Commun., no. 10, pp. 1033–1034, doi:10.1039/C39950001033
  15. ↑ Marco Taddei; Francesca Nardelli; Songzhu Qi; Matouš Kloda; Jan Demel; Lucia Calucci (September 2026), "Unravelling the structure and adsorption properties of a highly stable porous hafnium phosphonate framework", Journal of Solid State Chemistry, vol. 361, doi:10.1016/j.jssc.2026.126096
  16. ↑ Stephen J.I. Shearan, Norbert Stock, Franziska Emmerling, Jan Demel, Paul A. Wright, Konstantinos D. Demadis, Maria Vassaki, Ferdinando Costantino, Riccardo Vivani, Sébastien Sallard, Inés Ruiz Salcedo, Aurelio Cabeza, Marco Taddei (2019-05-24), "New Directions in Metal Phosphonate and Phosphinate Chemistry", Crystals, vol. 9, no. 5, p. 270, Bibcode:2019Cryst...9..270S, doi:10.3390/cryst9050270, hdl:11568/1024477{{citation}}: CS1 maint: multiple names: authors list (link)
  17. ↑ Abraham Clearfield (2007), "Metal Phosphonate Chemistry", Progress in Inorganic Chemistry, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 371–510, ISBN 978-0-470-16648-2
  18. ↑ Guang Cao, Haiwon Lee, Vincent M. Lynch, Thomas E. Mallouk (August 1988), "Synthesis and structural characterization of a homologous series of divalent-metal phosphonates, MII(O3PR).cntdot.H2O and MII(HO3PR)2", Inorganic Chemistry, vol. 27, no. 16, pp. 2781–2785, doi:10.1021/ic00289a008{{citation}}: CS1 maint: multiple names: authors list (link)
  19. ↑ Robert A. Coxall, Steven G. Harris, David K. Henderson, Simon Parsons, Peter A. Tasker, Richard E. P. Winpenny (2000), "Inter-ligand reactions: in situ formation of new polydentate ligands", Journal of the Chemical Society, Dalton Transactions, vol. 14, no. 14, pp. 2349–2356, Bibcode:2000DTr....14.2349C, doi:10.1039/b001404o{{citation}}: CS1 maint: multiple names: authors list (link)
  20. ↑ Phosphonate Chemistry, Technology, and Applications, Elsevier, 2026, doi:10.1016/c2024-0-00017-3, ISBN 978-0-443-33374-3
  21. ↑ Toshikazu Hirao, Toshio Masunaga, Yoshiki Ohshiro, Toshio Agawa (January 1980), "Stereoselective synthesis of vinylphosphonate", Tetrahedron Letters, vol. 21, no. 37, pp. 3595–3598, doi:10.1016/0040-4039(80)80245-0{{citation}}: CS1 maint: multiple names: authors list (link)
  22. ↑ Peter Tavs (August 1970), "Reaktion von Arylhalogeniden mit Trialkylphosphiten und Benzolphosphonigsäure-dialkylestern zu aromatischen Phosphonsäureestern und Phosphinsäureestern unter Nickelsalzkatalyse", Chemische Berichte, vol. 103, no. 8, pp. 2428–2436, doi:10.1002/cber.19701030815
  23. ↑ Alexandra Schütrumpf, Andrew Duthie, Enno Lork, Gündoğ Yücesan, Jens Beckmann (2018-10-17), "Synthesis of Some Di- and Tetraphosphonic Acids by Suzuki Cross-Coupling", Zeitschrift für anorganische und allgemeine Chemie, vol. 644, no. 19, pp. 1134–1142, doi:10.1002/zaac.201800197{{citation}}: CS1 maint: multiple names: authors list (link)