Chemical Manipulation Over Coordination Polymers And Chiral Symmetry Breaking

Since Richard Robson synthesized and described the first coordination polymer[Cu^â… (C(C₆H₄CN)₄)]ⁿ⁺ in 1989,the research of coordination polymers have attracted numerous attention in the field of coordination chemistry,physical chemistry, solid state chemistry,chemical topology,etc.Coordination polymers were mainly assembled with coordination bonds,and some molecular interactions or host-guest interactions as well.The corresponding bond energies are relatively low,compared to the covalent bonds,which makes coordination polymers have incredible large amount of architectures and flexible framework.In that case,various structures might easily exist under subtle change of synthesis condition.Herein,the subject of this dissertation is to fully understand the intrinsic assemble of coordination polymers, so as to construct chiral coordination polymers and realized the chiral symmetry breaking.First of all,the role of pH in binary ligands system has been studied.In the Cu^â…¡/benzoate/4,4'-bipyridine system,five compounds 1-5 ranged from 0D to 2D structures were obtained by merely increasing the pH value from 5.5 to 8.0.By analyzing the details of the structure,the coordination ability of 4,4'-bipyridine which is controlled by pH value is the key of assemble mechanism.Secondly,the role of solvent in similar binary ligands system was taken into consideration.Instead of 4,4'-bipyridine,the o-phthalic acid was chosen to increase the freedom of connectivity.In the Cu^â…¡/ o-phthalate/imidazole system,the 1D substructure[Cu(Him)₂(o-pht)]_n was obtained by constraining the reaction pH value. Based on the substructure,1D coordination polymers 6,7 were generated in binary solvents EtOH/H₂O,while 2D coordination polymer 8·2H₂O was obtained in pure water.Furthermore,adjusting the proportion of the binary solvent could generate centrosymmetric 6 and acentric 7,showing the solvent-dependent symmetric assemble. Thirdly,new tetracarboxylate ligands with dihydroxyl(L₁) and crown ether (L₂) functionalities have been synthesized and treated with Cu^â…¡,Zn^â…¡ions and diaminocyclohexane to generate 3D coordination polymers 9-12 and supramolecular 13,14.Considering the potential axial chirality of 2,2'-biphenol unit, coordination-bonded assemble as well as chiral induction were both tried to realize the structural symmetry breaking.However,the 2,2'-biphenol unit are easily disorded,which always result in centrosymmetric structure.Based on the three steps illustrated above,Cu^â…¡/succinate/4,4'-bipyridine system was chosen to construct 3D chiral coordination polymers.By adjusting the reaction pH value,two phases were obtained in binary solvent system:enantiomeric helix-based structure 15,and racemic pillared structure 16.Further investigation of the chiral resolution over 15 revealed a relationship:ammonia concentration∝pH value∝(reaction speed)^-1∝(crystallization speed)^-1.Thus,excess ammonia was added into the system to compete with the binary ligands,in order to slow down the reaction speed and crystallization speed.In that case,the primary nucleation was greatly limited.On the other hand,the statistical fluctuation of coin flipping shows that flipping a coin many times naturally resulted in 50-50 ratio of heads and tails, while flipping a coin once resulted in a single outcome,either a head of a tail.So, would It be nice if isolating a single-enantiomer form of 15 were as simple as flipping a coin? When the primary nucleation was greatly limited by simply adding excess ammonia,it is easy to make it happen! For more details,please read the whole story in the dissertation.