Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A hexagonal planar transition-metal complex


Transition-metal complexes are widely used in the physical and biological sciences. They have essential roles in catalysis, synthesis, materials science, photophysics and bioinorganic chemistry. Our understanding of transition-metal complexes originates from Alfred Werner’s realization that their three-dimensional shape influences their properties and reactivity1, and the intrinsic link between shape and electronic structure is now firmly underpinned by molecular-orbital theory2,3,4,5. Despite more than a century of advances in this field, the geometries of transition-metal complexes remain limited to a few well-understood examples. The archetypal geometries of six-coordinate transition metals are octahedral and trigonal prismatic, and although deviations from ideal bond angles and bond lengths are frequent6, alternative parent geometries are extremely rare7. The hexagonal planar coordination environment is known, but it is restricted to condensed metallic phases8, the hexagonal pores of coordination polymers9, or clusters that contain more than one transition metal in close proximity10,11. Such a geometry had been considered12,13 for [Ni(PtBu)6]; however, an analysis of the molecular orbitals suggested that this complex is best described as a 16-electron species with a trigonal planar geometry14. Here we report the isolation and structural characterization of a simple coordination complex in which six ligands form bonds with a central transition metal in a hexagonal planar arrangement. The structure contains a central palladium atom surrounded by three hydride and three magnesium-based ligands. This finding has the potential to introduce additional design principles for transition-metal complexes, with implications for several scientific fields.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Get just this article for as long as you need it


Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Preparation of hexagonal planar complexes.
Fig. 2: Preparation of group-10 hydride complexes with magnesium ligands.
Fig. 3: Analysis of the chemical bonding in the hexagonal planar geometry.

Data availability

Crystallographic models are available as .cif files from the Cambridge Crystallographic Data Centre (CCDC,; CCDC numbers 1589323–1589324, 1909687–1909690 and 1946045). Neutron diffraction images can be obtained from A.J.E. The derived structure factors have been deposited with the CCDC, with CCDC number 1946045. Data associated with DFT calculations (.xyz coordinate file) along with NMR spectroscopic data (.mnova files) are available from a public repository at Full details of the syntheses are provided in the Supplementary Information.


  1. Werner, A. On the constitution and configuration of higher-order compounds. Nobel Lecture, 11 December 1913. The Nobel Prize (1913).

    Article  CAS  Google Scholar 

  2. Hoffmann, R., Beier, B. F., Muetterties, E. L. & Rossi, A. R. Seven-coordination. A molecular orbital exploration of structure, stereochemistry, and reaction dynamics. Inorg. Chem. 16, 511–522 (1977).

    Article  CAS  Google Scholar 

  3. Rossi, A. R. & Hoffmann, R. Transition metal pentacoordination. Inorg. Chem. 14, 365–374 (1975).

    Article  CAS  Google Scholar 

  4. Gray, H. B. & Ballhausen, C. J. A molecular orbital theory for square planar metal complexes. J. Am. Chem. Soc. 85, 260–265 (1963).

    Article  CAS  Google Scholar 

  5. Gray, H. B. Molecular orbital theory for transition metal complexes. J. Chem. Educ. 41, 2–12 (1964).

    Article  CAS  Google Scholar 

  6. Alvarez, S. Distortion pathways of transition metal coordination polyhedra induced by chelating topology. Chem. Rev. 115, 13447–13483 (2015).

    Article  CAS  Google Scholar 

  7. García-Monforte, M. A., Baya, M., Falvello, L. R., Martín, A. & Menjón, B. An organotransition-metal complex with pentagonal-pyramidal structure. Angew. Chem. 51, 8046–8049 (2012).

    Article  Google Scholar 

  8. Yang, L.-M. et al. Two-dimensional Cu2Si monolayer with planar hexacoordinate copper and silicon bonding. J. Am. Chem. Soc. 137, 2757–2762 (2015).

    Article  CAS  Google Scholar 

  9. Niu, Z., Ma, J.-G., Shi, W. & Cheng, P. Water molecule-driven reversible single-crystal to single-crystal transformation of a multi-metallic coordination polymer with controllable metal ion movement. Chem. Commun. 50, 1839–1841 (2014).

    Article  CAS  Google Scholar 

  10. Tanabe, M. et al. Tetrapalladium complex with bridging germylene ligands. Structural change of the planar Pd4Ge3 core. J. Am. Chem. Soc. 133, 18598–18601 (2011).

    Article  CAS  Google Scholar 

  11. Yamada, T., Mawatari, A., Tanabe, M., Osakada, K. & Tanase, T. Planar tetranuclear and dumbbell-shaped octanuclear palladium complexes with bridging silylene ligands. Angew. Chem. 48, 568–571 (2009).

    Article  CAS  Google Scholar 

  12. Ahlrichs, R., Fenske, D., Oesen, H. & Schneider, U. Synthesis and structure of [Ni(PtBu)6] and [Ni5(PtBu)6(CO)5] and calculations on the electronic structure of [Ni(PtBu)6] and (PR)6, R = tBu,Me. Angew. Chem. 31, 323–326 (1992).

    Article  Google Scholar 

  13. Hey-Hawkins, E., Pink, M., Oesen, H. & Fenske, D. Synthesen und charakterisierung von [Ni(tBuAs)6] und [Pd(tBuAs)6]. Z. Anorg. Allg. Chem. 622, 689–691 (1996).

    Article  CAS  Google Scholar 

  14. Tang, H., Hoffman, D. M., Albright, T. A., Deng, H. & Hoffmann, R. [Ni(PtBu)6] and [Ni(SiH2)6] are isolobal, related to [In{Mn(CO)4}5]2−, and have 16-electron counts. Angew. Chem. 32, 1616–1618 (1993).

    Article  Google Scholar 

  15. Kubas, G. J. Dihydrogen complexes as prototypes for the coordination chemistry of saturated molecules. Proc. Natl Acad. Sci. USA 104, 6901–6907 (2007).

    Article  ADS  CAS  Google Scholar 

  16. Crabtree, R. H. A new oxidation state for Pd? Science 295, 288–289 (2002).

    Article  CAS  Google Scholar 

  17. Chen, W., Shimada, S. & Tanaka, M. Synthesis and structure of formally hexavalent palladium complexes. Science 295, 308–310 (2002).

    Article  ADS  CAS  Google Scholar 

  18. Aullón, G., Lledós, A. & Alvarez, S. Hexakis(silyl)palladium(vi) or palladium(ii) with η2-disilane ligands? Angew. Chem. 41, 1956–1959 (2002).

    Article  Google Scholar 

  19. Butler, M. J. & Crimmin, M. R. Magnesium, zinc, aluminium and gallium hydride complexes of the transition metals. Chem. Commun. 53, 1348–1365 (2017).

    Article  CAS  Google Scholar 

  20. Abdalla, J. A. B. et al. Coordination and activation of Al–H and Ga–H bonds. Chem. Eur. J. 20, 17624–17634 (2014).

    Article  CAS  Google Scholar 

  21. Abdalla, J. A. B. et al. Structural snapshots of concerted double E–H bond activation at a transition metal centre. Nat. Chem. 9, 1256–1262 (2017).

    Article  CAS  Google Scholar 

  22. Riddlestone, I. M. et al. Activation of H2 over the Ru–Zn bond in the transition metal–Lewis acid heterobimetallic species [Ru(IPr)2(CO)ZnEt]+. J. Am. Chem. Soc. 138, 11081–11084 (2016).

    Article  CAS  Google Scholar 

  23. Sharninghausen, L. S. et al. The neutron diffraction structure of [Ir4(IMe)8H10]2+ polyhydride cluster: testing the computational hydride positional assignments. J. Organomet. Chem. 849–850, 17–21 (2017).

    Article  Google Scholar 

  24. Pauling, L. Atomic radii and interatomic distances in metals. J. Am. Chem. Soc. 69, 542–553 (1947).

    Article  CAS  Google Scholar 

  25. Pyykkö, P. & Atsumi, M. Molecular single-bond covalent radii for elements 1–118. Chem. Eur. J. 15, 186–197 (2009).

    Article  Google Scholar 

  26. Mukherjee, D. & Okuda, J. Molecular magnesium hydrides. Angew. Chem. 57, 1458–1473 (2018).

    Article  CAS  Google Scholar 

  27. Brookhart, M., Green, M. L. H. & Parkin, G. Agostic interactions in transition metal compounds. Proc. Natl Acad. Sci. USA 104, 6908–6914 (2007).

    Article  ADS  CAS  Google Scholar 

  28. Shoshani, M. M., Liu, J. & Johnson, S. A. Mechanistic insight into H/D exchange by a pentanuclear Ni–H cluster and synthesis and characterization of structural analogues of potential intermediates. Organometallics 37, 116–126 (2018).

    Article  CAS  Google Scholar 

  29. Kudo, K., Hidai, M. & Uchida, Y. Dihydride complexes of platinum(ii) and palladium(ii). J. Organomet. Chem. 56, 413–418 (1973).

    Article  CAS  Google Scholar 

  30. Leviston, P. G. & Wallbridge, M. G. H. The preparation of some bulky dihalo-, halohydrido- and dihydro- phosphineplatinum(ii) compounds. J. Organomet. Chem. 110, 271–279 (1976).

    Article  CAS  Google Scholar 

Download references


We thank the Royal Society and the European Research Council (FluoroFix: 677367) for funding, Johnson Matthey for the gift of PdCl2, and ANSTO for allocation of neutron beam time on KOALA to proposal P6932. We thank Oxford Cryosystems Ltd and ANSTO for funding a Russell Studentship with the University of Oxford (GAS).

Author information

Authors and Affiliations



M.G. and C.B. carried out the synthetic studies. M.G. conducted DFT, QTAIM and related calculations. A.J.P.W. collected, processed and refined single-crystal X-ray diffraction data. A.J.E., R.I.C. and G.A.S. undertook the single-crystal Laue neutron diffraction experiment, data reduction and refined the neutron diffraction structural model. M.R.C. managed the project. All authors contributed to the writing and editing of the manuscript.

Corresponding author

Correspondence to Mark R. Crimmin.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Peer review information Nature thanks Jean-François Halet and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Fig. 1 Synthesis of group-10 hydride complexes with magnesium ligands.

a–e, Synthetic schemes for the preparation of complexes 1a (a), 2a (b), 2b (c), 2c (d) and 3 (e); for 3, the hydride ligands are derived from the C–H bonds of the benzene solvent.

Supplementary information

Supplementary Information

This file contains Supplementary Figures S1–S28 and Supplementary Tables S1–S12.

Supplementary Data

This cif file contains Neutron Diffraction Data.

Supplementary Data

This cif file contains X-ray Diffraction Data.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Garçon, M., Bakewell, C., Sackman, G.A. et al. A hexagonal planar transition-metal complex. Nature 574, 390–393 (2019).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing