Quantitative Descriptions of Dewar-Chatt-Duncanson Bonding Model: A Case Study of Zeise and Its Family Ions

Historically, Dewar-Chatt-Duncanson (DCD) model is a heuristic device to advance the development of organometallic chemistry and deepen our understanding of the metal-ligand bonding nature. Zeise's ion, the first man-made organometallic compound and a quintessential transition metal-olefin complex, was qualitatively explained using the DCD bonding scheme in 1950s. In this work, we quantified the explicit contributions of the σ donation and π back-donation to the metal-ligand bonding in Zeise and its family ions, [PtX₃ L]^- (X=F, Cl, Br, I, and At; L=C₂ H₄ , CO, and N₂ ), using state-of-the-art quantum chemical calculations and energy decomposition analysis. The relative importance of the σ donation and π back-donation depends on both X and L, with [PtCl₃ (C₂ H₄ )]^- being a critical case in which the σ donation is marginally weaker than the π back-donation. The changes along this series are controlled by the energy levels of the correlated molecular orbitals of PtX₃ ^- and ligand L. This study deepens our understanding of the bonding properties for transition metal complexes beyond the qualitative description of the DCD model.

Unsupported Mg-Alkene Bonding

The first intermolecular early main group metal-alkene complexes were isolated. This was enabled by using highly Lewis acidic Mg centers in the Lewis base-free cations (Me BDI)Mg+ and (tBu BDI)Mg+ with B(C6 F5 )4 - counterions (Me BDI=CH[C(CH3 )N(DIPP)]2 , tBu BDI=CH[C(tBu)N(DIPP)]2 , DIPP=2,6-diisopropylphenyl). Coordination complexes with various mono- and bis-alkene ligands, typically used in transition metal chemistry, were structurally characterized for 1,3-divinyltetramethyldisiloxane, 1,5-cyclooctadiene, cyclooctene, 1,3,5-cycloheptatriene, 2,3-dimethylbuta-1,3-diene, and 2-ethyl-1-butene. In all cases, asymmetric Mg-alkene bonding with a short and a long Mg-C bond is observed. This asymmetry is most extreme for Mg-(H2 C=CEt2 ) bonding. In bromobenzene solution, the Mg-alkene complexes are either dissociated or in a dissociation equilibrium. A DFT study and AIM analysis showed that the C=C bonds hardly change on coordination and there is very little alkene→Mg electron transfer. The Mg-alkene bonds are mainly electrostatic and should be described as Mg2+ ion-induced dipole interactions.

Bunsen the Geochemist: Icelandic Volcanism, Geyser Theory, and Gas, Rock and Mineral Analyses

Following the eruption of Hekla in 1845-1846 Bunsen was invited by King Christian VIII of Denmark and Iceland to participate in a geochemical expedition to Iceland together with the geologist Sartorius von Waltershausen and the physiologist Carl Bergmann from Göttingen. The French mineralogist Des Cloizeaux went to Iceland separately and joined the expedition. The eudiometer invented by Bunsen was crucial for his accurate characterization of volcanic gases and determination of the composition of mixtures. His analyses of the chemical compositions of numerous rocks and minerals led him to the classification of two fundamental rock types, the more silica rich (nowadays called felsic) and the less silica rich, more basic (mafic) in agreement with Des Cloizeaux and the Danish scientist J. C. Schythe. Bunsen also formulated the correct mechanism of geyser action and helped disband the theory of connections between geysers, volcanoes and the sea. He disagreed vehemently with Waltershausen over the mechanisms of formation of sal ammoniac and of volcanic rocks and their chemical compositions. He revealed himself as an ardent experimentalist vigorously opposed to hypotheses of any kind, which also made him dismiss the new chemical theories, for example, those of Dumas and Kekulé.

Ørsted and Bunsen: Voltaic Batteries, Electric Arcs, Electromagnetism, and Electrolysis

200 years ago Ørsted laid the foundation of electromagnetism in his famous experiment in which a magnetic needle is deflected in the electrical field of a platinum wire. For this he used his own Cu-Zn trough battery, which was among the best then available, but 21 years later it was surpassed by the coal-zinc battery invented by Bunsen, which became highly successful and acclaimed. That year, 1841, Bunsen made his first direct contact with Scandinavia when he visited Berzelius in Stockholm, Palmstedt in Gothenburg, and Ørsted, Scharling, and Zeise in Copenhagen. Like almost everybody in continental Europe, they adopted Bunsen's battery, and Ørsted used it for his experiments with a very large electromagnet. The paths of Ørsted's and Bunsen's research crossed again much later through the synthesis of elemental aluminum, which was first achieved by Ørsted in 1825 (although it was probably not obtained as the pure metal) and performed quite differently by Bunsen, by electrolysis using his coal-zinc battery, in 1854.

Trichloro(Dinitrogen)Platinate(II)

Zeise's salt, [PtCl₃ (H₂ C=CH₂ )]^- _, is the oldest known organometallic complex, featuring ethylene strongly bound to a platinum salt. Many derivatives are known, but none involving dinitrogen, and indeed dinitrogen complexes are unknown for both platinum and palladium. Electrospray ionization mass spectrometry of K₂ [PtCl₄ ] solutions generate strong ions corresponding to [PtCl₃ (N₂ )]^- , the identity of which was confirmed through ion-mobility spectrometry and MS/MS experiments that proved it to be distinct from its isobaric counterparts [PtCl₃ (C₂ H₄ )]^- and [PtCl₃ (CO)]^- . Computational analysis established a gas-phase platinum-dinitrogen bond strength of 116 kJ mol^-1 , substantially weaker than the ethylene and carbon monoxide analogues but stronger than for polar solvents such as water, methanol and dimethylformamide, and strong enough that the calculated N-N bond length of 1.119 Å represents weakening to a degree typical of isolated dinitrogen complexes.

Before Radicals Were Free – the Radical Particulier of de Morveau

Today, we universally understand radicals to be chemical species with an unpaired electron. It was not always so, and this article traces the evolution of the term radical and in this journey, monitors the development of some of the great theories of organic chemistry.