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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.

We have investigated the stereoselectivity and reactivity of the sodium borohydride reduction of 2-X-cyclohexanones (X=H, Cl, Br) using a combined approach of competitive experiments and density functional theory calculations. Our results show that the hydride addition proceeds via a late transition state in which the C–H bond is nearly formed, consistent with the mild reducing power of NaBH4. The reaction barrier decreases from the 2-halocyclohexanones to the unsubstituted cyclohexanone, in line with relative reactivities observed in the competitive experiments. Furthermore, we provide a protocol to solve the longstanding issue of properly modelling the axial–equatorial facial selectivity of hydride addition to the carbonyl group substituted with a vicinal polar group. The inclusion of implicit solvation in combination with an explicit solvent molecule is crucial to reproduce the stereoselective formation of the cis product observed experimentally.

The formation of Co(iii)-thiolate complexes from Co(ii)-disulfide complexes using the anionic ligand 8-quinolinolate (quin−) has been studied experimentally and quantum chemically. Two Co(ii)-disulfide complexes [Co2(LxSSLx)(Cl)4] (x = 1 or 2; L1SSL1 = 2,2′-disulfanediylbis(N,N-bis(pyridin-2-ylmethyl)ethan-1-amine; L2SSL2 = 2,2′-disulfanedylbis (N-((6-methylpyridin-2-yl)methyl)-N-(pyridin-2-ylmethyl) ethan-1-amine) have been successfully converted with high yield to their corresponding Co(iii)-thiolate complexes upon addition of the ligand 8-quinolinolate. Using density functional theory (DFT) computations the d-orbital splitting energies of the cobalt-thiolate compounds [Co(L1S)(quin)]+ and [Co(L2S)(quin)]+ were estimated to be 3.10 eV and 3.07 eV, indicating a slightly smaller ligand-field strength of ligand L2SSL2 than of L1SSL1. Furthermore, the orientation of the quin− ligand in the thiolate compounds determines the stability of the thiolate complex. DFT computations show that the thiolate structure benefits from more electrostatic attraction when the oxygen atom of the quin− ligand is positioned trans to the sulfur atom of the [Co(L1S)]2+ fragment. Quin− is the first auxiliary ligand with which it appeared possible to induce the redox-conversion reaction in cobalt(ii) compounds of the relatively weak-field ligand L2SSL2

We discuss the fundamental aspects of the EDA-NOCV method and address some critical comments that have been made recently. The EDA-NOCV method unlike most other methods focuses on the process of bond formation between the interacting species and not just only on the analysis of the finally formed bond. This is demonstrated using LiF as an example. There is a difference between the interactions between the initial species which form the bond and are also the final product of bond cleavage, and the interactions between the fragments in the eventually formed molecule. The flexibility of the method allows the choice of the interacting fragments which helps to identify the charge and electron configuration of the fragments which describe the bond. This is very helpful in cases where the bond may be described with several Lewis structures. We reject the idea that it would be a disadvantage to have “bond path functions” as the energy components in the EDA, which actually indicate the variability of the method. The bonding analysis in a different sequence of the bond formation gives important results for the various questions that can be asked. This is demonstrated by using CH2, CO2 and the formation of a guanine quartet as examples. The fact that a bond is always defined by the bound molecule, the fragments, and their states is universal and deeply physical, as we show here again for various examples. The results of the EDA-NOCV method are in full accordance with the physical mechanism of the chemical bond as revealed by Ruedenberg.

The gauche conformer in 1-X,2-Y-disubstituted ethanes, that is, the staggered orientation in which X and Y are in closer contact, is only favored for relatively small substituents that do not give rise to large X···Y steric repulsion. For more diffuse substituents, weakly attractive orbital interactions between antiperiplanar bonds (i.e., hyperconjugation) cannot overrule the repulsive forces between X and Y. Our quantum chemical analyses of the rotational isomerism of XCH2CH2Y (X = F, OH; Y = I) at ZORA-BP86-D3(BJ)/QZ4P reveal that indeed the anti conformer is generally favored due to a less destabilizing I···F and I···O-H steric repulsion. The only case when the gauche conformer is preferred is when the hydroxyl hydrogen is oriented toward the iodine atom in the 2-iodoethanol. This is because of the significantly stabilizing covalent component of the I···H-O intramolecular hydrogen bond. Therefore, we show that strong intramolecular interactions can overcome the steric repulsion between bulky substituents in 1,2-disubstituted ethanes and cause the gauche effect. Our quantum chemical computations have guided nuclear magnetic resonance experiments that confirm the increase in the gauche population as X goes from F to OH.

The redox-conversion reaction of cobalt(II)-disulfide to cobalt(III)-thiolate complexes triggered by addition of the bidentate ligand 2,2'-bipyridine has been investigated. Reaction of the cobalt(II)-disulfide complex [Co2(L1SSL1)(X)4] (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyldisulfide; X = Cl or Br) [1X] with 2,2'-bipyridine (bpy) resulted in the formation of two different products, namely the cobalt(III)-thiolate complex [Co(L1S)(bpy)]X2 and the unexpected side product [Co2(L1SSL1)(bpy)2(X)2]X2. Crystals of [Co2(L1SSL1)(bpy)2(Cl)2](BPh4)2 [2Cl](BPh4)2 obtained after anion exchange showed the cobalt(II) ions to be in octahedral geometries with the nitrogen donors of the disulfide ligand arranged in a facial conformation and the chloride ion trans to the tertiary amine nitrogen. Remarkably, this side product cannot be converted to the cobalt(III)-thiolate compound [Co(L1S)(bpy)](SbF6)2 [3](SbF6)2 by removal of the chloride ion with use of a silver salt, as this causes scrambling of the ligands, resulting in the formation of [Co(bpy)3]n+. [Co(L1S)(bpy)](SbF6)2 was obtained in a pure form by addition of bpy to a solution in acetonitrile of the compound [Co(L1S)(MeCN)2]2+ [4]2+. Addition of NEt4Cl to [3](SbF6)2 regenerates the cobalt(II)-disulfide complex [1Cl] as confirmed spectroscopically. DFT studies revealed that the conversion from [1Cl] to [3]2+ most likely occurs via the hypothetical intermediate species [2Cl]2+mer, in which the nitrogen atoms of the disulfide ligand are arranged in a meridional conformation. Interestingly, the estimated d-orbital splitting energy of [3]2+ is lower than that of [4]2+, indicating that the ligand-field strength of bpy is lower than anticipated, which hampers clean conversion in the redox-conversion reaction. This study shows that the redox-conversion reaction between cobalt(II)-disulfide and cobalt(III)-thiolate complexes is intricate rather than straightforward.