The borderless world of chemical bonding across the van der Waals crust and the valence region

Inducing Platinophilic Interactions in [Pt(SCN)4]2- Salts by Cation Tuning

A series of simple [Pt(SCN)4]2- salts with a variety of cations was synthesized and characterized using X-ray crystallography to determine factors that could induce platinophilic interactions between [Pt(SCN)4]2- anions, including cation size and shape, charge, and ability to participate in hydrogen bonding. The salts [N(PPh3)2]2[Pt(SCN)4], [AsPh4]2[Pt(SCN)4], and [Co(1,10-phenanthroline)3][Pt(SCN)4] feature bulky, noncoordinating cations where the [Pt(SCN)4]2- anions are completely separated from each other, with no Pt-Pt interactions present. Salts containing the hydrogen-bonding cations [Co(NH3)6]2[Pt(SCN)4]3 and [Co(en)3]2[Pt(SCN)4]3 (en = 1,2-ethylenediamine) display close Pt-Pt distances, with both compounds exhibiting platinophilic interactions with distances of 3.373(2) and 3.539(8) Å, respectively, the first reported platinophilic interactions with the [Pt(SCN)4]2- unit. [Co(en)3]2[Pt(SCN)4]3 also presents intermolecular chalcogen S···S and Pt···S interactions, resulting in increased dimensionality while also assisting in assembling the platinophilic interaction. The compounds are emissive at 77 K in the solid state, exhibiting a d-d metal-centered transition regardless of whether or not any platinophilic interactions are present. Overall, hydrogen-bonding cations are most likely to promote close proximity of the Pt(II) metal centers and induce the formation of platinophilic interactions in [Pt(SCN)4]2-.

Pendulum-like hemilability in a Ti-based frustrated Lewis Trio

We describe the first experimental example of a theoretically predicted Frustrated Lewis Trio (FLT). A tetradentate PNNP ligand is used to stabilise a highly electrophilic [TiCl3]+ fragment in a way that results in two equally long and frustrated Ti-P bonds. A combined experimental and computational approach revealed a distinct role of each Lewis basic phosphine in the heterolytic activation of chemical bonds. This dual functionality is characterised by a pendulum-like hemilability, where one of the phosphines acts as a nucleophile while the other serves as a hemilabile ligand that dynamically tunes the Ti-P distance as a function of the required electron density at the Ti centre.

The Fluoride Method: Access to Silver(III) NHC Complexes

We have synthesized the first silver(III) carbene complexes, (CF3 )3 Ag(NHC), by direct reaction of the silver(III) fluoride precursor complex [PPh4 ][(CF3 )3 AgF] with different imidazolium salts. This novel methodology circumvents the use of free NHC molecules. The silver(III) carbene complexes thus prepared are unprecedented and show remarkable thermal stabilities. They display square-planar or square-pyramidal geometry. Following our calculations, the electronic structure of a model representative complex exhibits Inverse Ligand Field (ILF). The compounds reported herein are synthetic analogues of the elusive difluorocarbene and carbonyl species proposed as intermediates in the acidic decomposition of [Ag(CF3 )4 ]- . The synthetic procedure reported is envisaged to enable access to carbene complexes of other late transition-metals in high oxidation states.

Azido-mediated intermolecular interactions of transition metal complexes

The coordinated azido ligand has a variety of ways to establish intermolecular contacts whose nature is computationally analysed in this work on dimers of the [N3-Hg(CF3)] complex with different interactions involving only N⋯N contacts, or with an additional Hg⋯N contact. The applied tools include the molecular electrostatic map of the monomer, an energy decomposition analysis (EDA), a topological AIM analysis of the electron density and the study of NCI (non-covalent interactions) isosurfaces. The interactions between two azido ligands are found to be weakly stabilizing (by 0.2 to 2.7 kcal mol-1), topology-dependent and require dispersion forces to complement orbital and electrostatic stabilization. Those interactions are supplemented by the formation of simultaneous Hg⋯N secondary interactions by about -1 kcal mol-1, and by the ability of the monomer to simultaneously interact with several neighbours in the crystal structure.

A focus on penetration index - a new descriptor of chemical bonding

Electron clouds surrounding atoms interpenetrate in a molecule, due to weak van der Waals interactions or formation of a genuine chemical bond. Now, Alvarez and Echeverría (S. Alvarez, J. Echeverría, Chem. Sci., 2023, https://doi.org/10.1039/D3SC02238B) suggest a simple descriptor of how deep this interpenetration is, calling it a penetration index, i [Å]. This property may easily be related to a combined thickness of the van der Waals regions of two bond-forming atoms, thus giving rise to a dimensionless penetration index, pAB [%]. How far this new index may take us will be discussed in this article.