The Synergy Between The Halogen Bond And The Covalent Effect In The Three Series Of Systems

1： The interplay between covalent and non-covalent interactions has been investigated inH3N-MCN-XF (X=H, Li, Cl, Br; M=Ag, Cu, Au) complexes using ab initio calculations at theMP2leveloftheory.Thecoinagemetalasasubstituenthasanirregularenhancingeffect(Au<Cu<Ag) on the strength of non-covalent interaction in MCN-XF, while the covalent interaction inH3N-MCN becomes stronger with the reverse order. Interesting cooperativity effects were observedwhen covalent and non-covalent interactions coexist in the same complex, and they become moreprominentforthestrongercovalentandnon-covalentinteractions.2：Quantum chemical calculations have been performed to study the interplay between the Lewisacid-baseinteractionandhalogenbondinteractioninF3B-NCX-NCMcomplexes,whereX=Cl、Br、I and M=Cl、Br、I、Li、Na. It was found that cooperativity exists between the Lewis acid-baseinteraction and halogen bond interaction. The interactions energies of Lewis acid-base interactionand halogen bond interaction in the triads are larger than those in the dyads, indicating bothinteractions are enhanced. Energy decomposition analysis indicates that the enhancement of theformer is due to induction energy, while the latter is originated from electrostatic energy andinductionenergy.3：N-heterocycliccarbenes(NHCs)areimportantligandsinorganometalliccatalyticreactions.Thisstudy focuses on thehalogenbonds with NHCs as theelectrondonors. Theresults show that NHCsare better electron donors in halogen bonds. Our interest is how to make a halogen bond have apartially covalent property, which depends on the strength of halogen bonding. The covalentpropertyofhalogenbondingisrelatedtothenatureofthehalogendonor.Iodineisfavorabletoformahalogenbond withcovalentpropertythanchlorineandbromine. Thecovalentpropertyofhalogenbond is greatly affected by substituents. Strong electron-donating groups in NHCs could reinforcethe covalent attribute of bromine bonding, whereas strong electron-withdrawing groups in NHCsmake iodine bonding lose the covalent nature. The covalent property of halogen bond is furtherheightenedthroughthecooperativeeffectbetweenthecarbene-halogenbondandanotherinteraction.Thiscovalentpropertyresultsinamuchshortbindingdistanceandaprominentbondelongation.