Construction Of Inorganic-organic Molecular Salts And Its Synthesis And Transformation Of Chelating Complexes In The Solid State

Nowadays, the organic solvent is commonly used in a general organic synthesisprocess, which can react with the dispersed phase to promote the reaction. However,its toxicity and difficult recovery of the agents can take an effect on the environment.In recent years, an effective green synthesis method in the solid state has graduallyattracted much interest and attention.Coordination complex is a kind of chemical compound formed by joiningindependent molecules or ions with a central metallic atom by coordinate bonds.Chelate complexes as a kind of classic coordination have been studied extensively.The main feature of these complexes is that the bidentate or polydentate ligands arecoordinated with a central ion through two or more coordinated atoms simultaneously.They usually have stable cyclic structures. Currently the synthesis of coordination isprimarily achieved by the solution synthesis, although it has many deficiencies.Recently, the synthesis of complexes in the solid state has been developed which canmakes up the defects and shortcomings of solution synthesis. The reaction is simpleand effective. Thus, the green solid-phase synthetic method has good prospects fordevelopment.In order to explore the new green synthetic methods of inorganic-organicsynthesis reactions, herein, we successfully achieved the solid state structuraltransformation of hydrogen bonded complex salts into a metal complexes to formN-containing chelating coordination complexes via dehydrochlorination usingmechanochemistry for the first time. The procedure is as follows:First, we prepare four flexible bidentate ligands: N, N, N’, N’-tetrabenzylethane-1,2-diamine(L1), N, N, N’,N’-tetrakis(4-methoxybenzyl)ethane-1,2-diamine(L2), N, N, N’, N’-tetrabenzylpropane-1,3-diamine(L3) and N, N, N’,N’-tetrabenzylbutanediamine-1,4-diamine(L4).The structural features of the ligandsare that they all contain two N atoms, and the methylene groups (CH2)nare insertedbetween N atoms. Second, hydrogen salts of protonated L1, L2, L3, L4and metal chloride areformed.Third, we prepare chelate complexes from hydrogen salts via adehydrochlorination reaction in the solid state.The results showed that,(1) When the number of intermediate methylene istwo(n=2), i.e., ligand L1and L2, we can get the solid state structural transformation ofhydrogen salts into chelate complexes via dehydrochlorination usingmechanochemistry. The quantity of KOH was added to promote thedehydrochlorination reaction in the solid state by liquid assisted grinding in themechanical grinding process. With increasing number of methylene groups(n=3,4),i.e., ligand L3and L4, we can not get the chelate complexes but achieve thetransformation of hydrogen bonding salts into ligands.(2) From the point of view of crystal engineering we investigated the process oftransformation of chelate hydrogen bond into Cu-N coordination bond. We found thatthe formation of chelate hydrogen bond Cu-Cl···H-N in the hydrogen salts isimportant when they are transformed into chelate complexes.(3) Density functional theory (DFT) calculations were used to discuss that thenumber of methylene has impact on the transformation process from the hydrogensalts to chelate complexes, and the stability of the chelate structures is determined.