Theoretical Studies On The Nature Of Some Secondary Bond Systems

Secondary bond is a general term for all kinds of chemical bond except covalent bond,ionic bond and metal bond.Secondary bond involves the interaction between molecules and intramolecular groups,the structure and properties of supramolecules and various molecular aggregates,and the internal interaction of living substances.But up to now,the understanding of secondary bond is still very limited.In the 21st century,secondary bond is still the main subject of chemical bond research.When the distance between atoms in different molecules is the sum of van der Waals radii,it can be considered that there is van der Waals force between molecules.When the distance between atoms is between the range of chemical bond and van der Waals force,it can be considered that secondary bond is formed between atoms.We often say that hydrogen bond and halogen bond belong to secondary bond,very strong hydrogen bond and halogen bond are like covalent bond,very weak hydrogen bond and halogen bond are close to van der Waals effect.Most of the hydrogen bond and halogen bond are in the middle of these two extreme states.In this paper,we use density functional theory(DFT)to analyze the structure frequency,hybrid mode,electrostatic mode,energy decomposition,weak interaction analysis and Ad NDP bonding of spodium bond in Hg Cl₂???L(L=Cl R,SR₂,PR₃)dimer,I₃^-and related electron-rich(22 shell electrons)systems and polyhalide anion system at a certain theoretical level.The main research contents are as follows:1.Theoretical analysis of interaction essence of spodium bondRecently,Bauzá,A.et al.proposed a new noncovalent interaction,spodium bond,to refer to a net attractive interaction between any element of group 12 and electron rich atoms.In Sp X₂L₂(Sp=Zn,Cd,Hg)compounds,the coordination bond(classical ligand–Metal bond)and noncovalent interactions were differentiated by the term spodium bond.However,only the four-coordinated Sp atoms were concerned in that work.Due to strong relativistic effect,Hg is much different from the other group 12 elements,which prefers more linear coordination in sp hybridization,e.g.,cinnabar(hexagonal,red Hg S)and(Hg S)_nclusters.There should also be similar spodium bond between linear coordinated Hg atom and the electron rich atoms.The S???Hg secondary bonding networks in(Hg S)_nclusters suggested in our previous work should be taken as spodium bond in definition.To give a systematic study on spodium bond of linear coordinated Hg atom,this work theoretically investigated the Hg Cl₂???L(L=Cl R,SR₂,PR₃families)dimers.Hg Cl₂is a well-known linear molecule in chemistry books at the high schools,which is soluble in water but is difficult to be ionized.In this molecule,a large positive electrostatic potential is generated on the waist of Hg atom.Thus,there should be strong attraction between Hg and an electron donor species(Hg???L),and Hg???O spodium bond may result in high solubility of Hg Cl₂in water.On the other hand,with an electron donor species,the linearity of Hg Cl₂molecule is broken a tittle.Hybridization of Hg atom should have certain sp²character,and the Hg???L interaction should have some character of coordination bond.Therefore,both coulombic(spodium bond)and covalent(coordination bond)components are important in Hg Cl₂???L dimer.In this study,taking Hg Cl₂???L(L=Cl R,SR₂,PR₃families)dimers as test cases,we theoretically studied the trend of contributions of coulombic and covalent interactions,uncovering the nature of these kinds of weak intermolecular interactions.2.Theoretical study of halogen bond and Multiple Centre bond in linear three body systemTriiodonium is the most basic existence of polyiodonium anions,and its status can not be ignored.Its existence provides a very important basis for the later study of other polyiodonium anions.According to the structural data of CSD,there are two explanations for describing chemical bond in linear three body systems,such as I₃^-and related electron rich(22 shell electron)systems.The first is to use the idea of multi center bonding,and regard the whole as a 3-center 4-electron(3c-4e)model.The second is to understand it as a donor/acceptor charge transfer model,because the iodide trianion can be obtained by the reaction of I₂+I^-?I₃^-,in which the iodide ion is considered to be a Lewis base,and the iodide is considered to be a Lewis acid,so the iodide trianion is considered to be composed of halogen bond.The total bond order of the two models in these systems is 1.The former is more suitable for symmetric systems,while the latter is more suitable for strong asymmetric systems.However,no one has ever linked these two models.We use Ad NDP bonding analysis and noncovalent interaction(NCI)index,ELF(electronic localization function)analysis and LOL(localized orbital)analysis.It is found that these two models can well explain the linear three body system,so we think that halogen bond can be classified into multi center bonding system.They are interrelated and should not be understood as two independent systems.3.Theoretical study on Multiple Centre bonding of polyhalide anionsIn addition to being used in important halogenated compounds,halogens can also form polyhalogens,polyhalogens anions and polyhalogens cations.Compared with polyhalide cations,which are not well studied at present,polyhalide anions have much more diversity,which also shows its important role and prospects.The polyhalides with negative charge described in this paper are called polyhalide anions.Polyhalide anions can be anions containing only one halogen,or anions containing fluorine,chlorine,bromine and iodine.Therefore,according to the difference of the elements in the polyhalogen anion,it can be further divided into the anions between the polyhalogen and the polyinterhalogen.At present,polyhalide anions are known to form monoions and diions,and there are many kinds of polyhalide anions.Among them,polyiodide anions are the most involved.The polyiodide anions found at present mainly include I₃^-,I₄^2-,I₅^-,I₆^2-,I₇^-,I₈^2-,I₉^-,I₁₀^2-,I^-₁₁,I₁₂^2-,I^-₁₃,I₁₄^2-,I^-₁₅,I₁₆^2-,I₁₈^2-,I₂₀^2-.The second is polybrominated anions,mainly including Br₃^-,Br₄^2-,Br₅^-,Br₆^2-,Br₇^-,Br₈^2-,Br₉^-,Br₁₀^2-,Br^-₁₁,Br₁₄^2-,Br₁₆^2-,Br₂₀^2-,Br₂₄^2-.The anions of chlorine and fluorine are much less,mainly involving Cl₃^-,Cl₅^-,Cl₈^2-,Cl₉^-,Cl^-₁₁,Cl₁₂^2-,Cl₁₃^-and F₃^-,F₅^-.This paper mainly studies the system of polyiodide anions and some classical polyhalide anions,such as I₂Cl₃^-?ICl₄^-and Cl I₈^-.We want to prove theoretically that polyhalides and anionic systems between polyhalides can be regarded as Multiple Centre bonding.This work can also be seen as a follow-up development of our previous work.