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Additive covalent radii fitted for near-sixfold metal bonds

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A modern chemistry laboratory workspace with multiple glass beakers and flasks containing colored liquids in shades of red, pink, and black, laboratory glassware, scientific instruments including adjustable stands and clamps, and a gray storage organizer on a reflective white surface with bright overhead lighting.
Research area:Inorganic chemistryInorganic ChemistryChemical bond

What the study found

The study found a set of additive covalent radii for metal dimers involving group 4–8 transition metals and the actinides Th–Np. The authors describe these as relevant to systems with 12 valence electrons in approximately molecular orbitals, and note that the values are typically 10–20 pm shorter than previous triple-bond radii.

Why the authors say this matters

The authors present these fitted radii as a way to describe metal-metal bonding in cases approaching sixfold chemical bonding. They also suggest extrapolated values for suitable cases in Group 3, including rare earths, and Group 9 plus Pu.

What the researchers tested

The researchers fitted additive covalent radii to a combination of experimental data, accurate ab initio computations, and more approximate DFT (density functional theory) metal-metal bond lengths. They focused on MM' bond lengths for elements Ti–Fe, Zr–Ru, Hf–Os, and Th–Np.

What worked and what didn't

The fitted radii were obtained for the listed element ranges and were reported to be shorter than the previous triple-bond radii by about 10–20 pm. The abstract does not describe any failed cases or negative results.

What to keep in mind

The available summary does not give details on the fitting procedure, the quality of the fit, or how well the extrapolated values perform. It also does not describe limitations beyond the specific element groups named in the abstract.

Key points

  • Additive covalent radii were fitted for metal dimers involving group 4–8 transition metals and Th–Np.
  • The fit used experimental data, accurate ab initio computations, and approximate DFT bond lengths.
  • The radii are described as typically 10–20 pm shorter than previous triple-bond radii.
  • The abstract says the bonding cases involve 12 valence electrons in approximately molecular orbitals.
  • Extrapolated values were also proposed for suitable cases in Group 3, Group 9, and Pu.

Disclosure

Research title:
Additive covalent radii fitted for near-sixfold metal bonds
Authors:
Pekka Pyykkö, Michiko Atsumi
Institutions:
University of Helsinki, University of Oslo
Publication date:
2026-02-25
DOI:
10.1002/chem.70818
OpenAlex record:
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AI provenance: This post was generated by gpt-5.4-mini (OpenAI). The original authors did not write or review this post.