Studies On Supramolecular Lanthanide Helicates With Flexible Acylhydrazone Ligands

Helices are the central structural motif in biological molecules.Helical metal-coordination compounds(also known as helicates),have been extensively investigated.Controlling the structure of helicates assemblies is one of the leading challenges for supramolecular chemists.While this challenging task is quite successfully accomplished with transition metals,the polynuclear helicates with lanthanides were not developed to such an extent because of the fact that trivalent lanthanide ions display high kinetic lability and lack of stereochemical preferences.As well known,lanthanide ions have strong tendency to combine Schiff base ligands,and linear amide-containing ligand,is of enormous capability for the extraordinary construction of supramolecular lanthanide complexes.Therefore,the design and synthesis of new lanthanide helicates with flexible open-chain Schiff base ligands became the main purpose of this work.To confirm how different terminal groups,different anions,cations influence supramolecular self-assembly of lanthanide complexes,four Schiff base ligands and their lanthanide complexes were designed and synthesized.The dissertation covers following five sections:1.The concepts,methods,histories and new developments of helicates are briefly introduced.2.To explore the effect of terminal groups of ligands on the structure of the complexes,we have designed and synthesized two amide type ligands H2L? and H2L?,and their lanthanide complexes.Compareing with the bi-metallic double-helicate and quadruple-stranded helicate,we discussed how different terminal groups influence supramolecular self-assembly of lanthanide complexes.3.To confirm how different anions influence supramolecular self-assembly of lanthanide complexes,two flexible amide type ligands,H2L ? and H2L? and their lanthanide chloride,perchlorate and nitrate complexes have been designed and assembled.The self-assembly process depends strongly on anion templates,tetrahedral ClO4-anion and trigonal-planar NO3-anion induce to form the novel hexanuclear lanthanum circular helicate and tetranuclear quadruple-stranded helicate complexes,respectively.Both types of the lanthanide supramolecular clusters are reported firstly.The size,shape,and binding modes of the anions are the key factors that determine the stereochemistry of the product.4.We studied how to distinguish between CO32-and NO3-in lanthanide complexes.The lanthanum complexes dynamically converted a circular helicate structure to a quadruple-stranded helicate one upon addition of NO3-anion stimulus,mimicking configurations of biomacromolecules and fulfilling the goal of selective recognition of NO3-anion.5.Trying to do a tentative exploration in self-assembly of 3s-4f and 3d-4f heterometallic helicates.The heterotetrametallic triple-stranded helicate[La2K2L?3(H2O)2]2+was synthesized.The inability to form analogous helicate structures with other alkali and alkali earth metal ions demonstrating that K+ ions plays an important role during the self-assembly process.In other words,ihis complex presents high affinity for K+and good selectivity over Li+,Na+,Rb+,Cs+,Mg2+,Ca2+,Ba2+.