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Abstract The interaction between two square palladium (II) dianions PdX42−(X=Cl, Br) is evaluated by crystal study and analyzed by quantum chemical means. The arrangement within the crystal between each pair of PdX42−neighbors is suggestive of a Pd⋅⋅⋅X noncovalent bond, which is verified by a battery of computational protocols. While the potential between these two bare dianions is computed to be highly repulsive, the introduction of even just two counterions makes this interaction attractive, as does the presence of a constellation of point charges. It is concluded that there is indeed a stabilizing Pd⋅⋅⋅X bond, but it is incapable of overcoming the strong coulombic repulsive force between two dianions. While the QTAIM, NBO, and NCI tools can indicate the presence of a noncovalent bond, they are unable to distinguish an attractive from a repulsive interaction.
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Experimental and theoretical evidence of attractive interactions between dianions: [PdCl 4 ] 2− ⋯[PdCl 4 ] 2−
Inspection of the arrangement of tetrachloridopalladate( ii ) centers in a crystalline solid places the Cl of one [PdCl 4 ] 2− directly above the Pd center of its neighbor. A survey of the CSD provides 22 more examples of such MX 4 2− ⋯MX 4 2− complexes, with M being a Group 10 metal and X = Cl, Br, or I. Quantum calculations attribute this arrangement to a π-hole bond wherein Cl lone pairs of one unit transfer charge to vacant orbitals above the Pd center of its neighbor. The stabilizing effect of this bond must overcome the strong Coulombic repulsion between the two dianions, which is facilitated by a polarizable environment as would be present in a crystal, but much more so when the effects of the neighboring counterions are factored in. These conclusions are extended to other [MX 4 ] 2− homodimers, where M represents other members of Group 10, namely Ni and Pt.
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- Award ID(s):
- 1954310
- PAR ID:
- 10326175
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 57
- Issue:
- 98
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 13305 to 13308
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1CC05640A
