Disentanglement of orthogonal hydrogen and halogen bonds via natural orbital for chemical valence: A charge displacement analysis

Abstract

As known, the electron density of covalently bound halogen atoms is anisotropically distributed, making them potentially able to establish many weak interactions, acting at the same time as halogen bond donors and hydrogen bond acceptors. Indeed, there are many examples in which the halogen and hydrogen bond coexist in the same structure and, if a correct bond analysis is required, their separation is mandatory. Here, the advantages and limitations of coupling the charge displacement analysis with natural orbital for chemical valence method (NOCV‐CD) to separately analyze orthogonal weak interactions are shown, for both symmetric and asymmetric adducts. The methodology gives optimal results with intermolecular adducts but, in the presence of an organometallic complex, also intramolecular interactions can be correctly analyzed. Beyond the methodological aspects, it is shown that correctly separate and quantify the interactions can give interesting chemical insights about the systems.

Quantifying the Orbital Contribution in the “Spodium Bond” via Natural Orbital for Chemical Valence-Charge Displacement Analysis

“…Each interaction has been integrated along its axis (Cd-S for Δρ0, the bisector of the SSS angle for Δρ1 and Cl-H for Δρ2) to give 3 separate CD functions. 15 CD0 is found to be positive at any position, suggesting that the Cd←S charge transfer overcomes any polarization effect. The value of Δq at the isoboundary, CT0 (CTSpB) is 125 me.…”

“…Obviously, the two things are not mutually independent, as the presence of an interaction can make the others stronger. 15 The other donors investigated in combination with 1 fall in between these two extremes, in the order ESpB CH2S > CH2O > CH3CN > CO, with a clear correlation between Eint, Eorb and ESpB.…”

Assessing the Orbital Contribution in the “Spodium Bond” by Natural Orbital for Chemical Valence-Charge Displacement Analysis

“…This is mostly a consequence of the coexistence of multiple interactions, which all contribute to the final geometry. 32 This is true even for simple biatomic molecules, 40 Starting with zinc systems, two different adducts can be isolated from the ASEZIJ lattice (-a and -b in Table 4), the former of which has an Eint much smaller than the latter. In both cases, the bromine atom, although it is spatially close to the zinc and laying approximately on the prolongation of the Br-Zn bond (Br-Zn ... Br angles = 163.9 and 143.9°, respectively), does not show any SpB orbital contribution.…”

Assessing the Orbital Contribution in the “Spodium Bond” by Natural Orbital for Chemical Valence-Charge Displacement Analysis

“…Also, while generally larger SpB contributions lead to shorter M … LB distances, there is no obvious correlation between donor-acceptor distance and interaction energy in none of the compound series. This is mostly a consequence of the coexistence of multiple interactions, which all contribute to the final geometry 32. This is true even for simple biatomic molecules,40 but becomes crucial for adducts held together by multiple weak interactions.By analyzing the database of structures with reduced M ... LB distances compatible with SpB,22 we have selected exemplificative adducts for each metal containing different ligands, charges and donor types (Scheme 2).…”