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

The term spodium bond (SpB) has been recently proposed to describe the noncoordinative interaction that can be established between a polarized group 12 metal and a mild Lewis base (LB). Most of the systems showing short metal-donor distances compatible with SpB are characterized by the coexistence of multiple weak interactions, including hydrogen and halogen bonding, making the assessment of real importance of SpB difficult. Here, we show that the relative importance of each contribution can be probed by dissecting the orbital component of the interaction through the extended transition state-natural orbital for chemical valence-charge displacement analysis (ETS-NOCV-CD). The latter gives useful information about relative energies and electrons involved, for model systems ([(thiourea)(2)MX2]center dot center dot center dot LB; M = Zn, Cd, and Hg; X = Cl and I; and LB = CH2S, CH2O, CH3CN, and CO) and a variety of structures extracted from experimentally characterized adducts, allowing us to demonstrate the lack of a direct correlation between a favorable metal-base distance and the presence of an orbital contribution for the SpB.

Automated summary

The concept of spodium bond (SpB) is proposed to describe noncoordinative interactions between group 12 metals and mild Lewis bases. Assessing the real importance of SpB is challenging due to the presence of multiple weak interactions. By using ETS-NOCV-CD analysis, the orbital contribution to the interaction can be dissected, showing that a direct correlation between metal-base distance and orbital contribution for SpB may be lacking.