Study of Beryllium, Magnesium, and Spodium Bonds to Carbenes and Carbodiphosphoranes

The aim of this article is to present results of theoretical study on the properties of C⋯M bonds, where C is either a carbene or carbodiphosphorane carbon atom and M is an acidic center of MX2 (M = Be, Mg, Zn). Due to the rarity of theoretical data regarding the C⋯Zn bond (i.e., the zinc bond), the main focus is placed on comparing the characteristics of this interaction with C⋯Be (beryllium bond) and C⋯Mg (magnesium bond). For this purpose, theoretical studies (ωB97X-D/6-311++G(2df,2p)) have been performed for a large group of dimers formed by MX2 (X = H, F, Cl, Br, Me) and either a carbene ((NH2)2C, imidazol-2-ylidene, imidazolidin-2-ylidene, tetrahydropyrymid-2-ylidene, cyclopropenylidene) or carbodiphosphorane ((PH3)2C, (NH3)2C) molecule. The investigated dimers are characterized by a very strong charge transfer effect from either the carbene or carbodiphosphorane molecule to the MX2 one. This may even be over six times as strong as in the water dimer. According to the QTAIM and NCI method, the zinc bond is not very different than the beryllium bond, with both featuring a significant covalent contribution. However, the zinc bond should be definitely stronger if delocalization index is considered.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

In this review, we provide a consistent description of noncovalent interactions, covering most groups of the Periodic Table. Different types of bonds are discussed using their trivial names. Moreover, the new name “Spodium bonds” is proposed for group 12 since noncovalent interactions involving this group of elements as electron acceptors have not yet been named. Excluding hydrogen bonds, the following noncovalent interactions will be discussed: alkali, alkaline earth, regium, spodium, triel, tetrel, pnictogen, chalcogen, halogen, and aerogen, which almost covers the Periodic Table entirely. Other interactions, such as orthogonal interactions and π-π stacking, will also be considered. Research and applications of σ-hole and π-hole interactions involving the p-block element is growing exponentially. The important applications include supramolecular chemistry, crystal engineering, catalysis, enzymatic chemistry molecular machines, membrane ion transport, etc. Despite the fact that this review is not intended to be comprehensive, a number of representative works for each type of interaction is provided. The possibility of modeling the dissociation energies of the complexes using different models (HSAB, ECW, Alkorta-Legon) was analyzed. Finally, the extension of Cahn-Ingold-Prelog priority rules to noncovalent is proposed.

Cooperative interaction between hydrogen bond and N···Y interactions (Y = H, Li, F, Cl, and Br): a comparative study

A comparative ab initio study is performed to investigate the cooperativity between the N···H hydrogen bond and the N···Y interactions in XCN···HCN···YCN complexes, where X = H, F, and Y = H, Li, F, Cl, and Br. To understand the properties of the systems better, the corresponding dimers are also studied. It is found that the lithium bond has a larger influence on the hydrogen bond than vice versa. The shortening of the N···H distances in the trimers is dependent on the strength of the H···Y interactions and they become larger in the order lithium bond > hydrogen bond > halogen bond. The estimated values of cooperative energy Ecoop are all negative with much larger Ecoop in absolute value for the systems including lithium.

Cooperative effects in hydrogen bond and pnicogen bond: a comparative study

A comparative study of the cooperative effects of hydrogen and pnicogen bonding on open-chain clusters of (PH2CN)n=2–7 and (HCN)n=2–7 is performed at the MP2/6-311++G(d,p) level of theory. These effects are studied in terms of geometric and energetic properties, electron density analysis, and 15N chemical shielding parameters of the clusters at the MP2/6-311++G** level. The intermolecular distances observed in the (HCN)n clusters exhibit quite larger bond contractions than those found in the (PH2CN)n clusters. Our results strongly suggest that cooperative effects induced by pnicogen and hydrogen bonds are significant in both linear PH2CN and HCN clusters, respectively. They also provide some evidence that these effects seem to reach a limit for a relatively small number of monomers. The n-dependent variation in the 15N chemical shielding tensor should serve as a useful signature of cooperativity effects in the PH2CN and HCN clusters.