The Mechanochemistry And Solid-State Reaction Of Metal-Organic Salts And Their Corresponding Complexes Based On N-Containing Multidentate Ligands

Metal-organic salts(MOSs)refer to a hybrid material consists of metal complex anions and organic cations,which are connected by the second-sphere coordination interactions.Due to their diversity of topological structure,it has been deeply studied and widely applied in many fields,such as metal recognitions and separations,nonlinear optical materials(NLO),fluorescent probes,magnetic switches and other fields.Coordination complex,as an important content of inorganic chemistry,has been applied into all aspects of modern chemistry and received extensive attention and in-depth research.However,the reactivity of metal organic salts and their corresponding complexes in the solid-state did not attract much attention,and the corresponding researches were still rarely seen.Therefore,we had carried out the following work aimed to design and synthesize four different N-containing organic ligands L1—L4 in this thesis,and used these ligands with metal chlorides to prepare metal-organic salts(second sphere coordination adducts)and corresponding complexes as the research objects of solid-state reactions.(1)The ligand 1,3-bis(2-pyridylmethyl)imidazolium chloride(L1)was synthesized by mechanical ball-milling,and used to prepare the metal-organic salts 1—3 and coordination complexes 4—6 in the solid-state,and their crystal structures were characterized.The reversible conversion conditions between salts and complexes were studied by mechanical grinding,solid-gas adsorption and PXRD.The HCl moleculars can be removed by grinding the metal-organic salts 1—3 with potassium tert-butoxide(KTB)at a molar ratio of 1:2 to give the complexes 4—6 in solid-state respectively.Oppositely,the HCl molecules were inserted into the coordination bonds and the corresponding metal-organic salts were obtained by exposing the powder of the complexes in the atmosphere of the concentrated HCl,realizing the reversible transformations between the metal-organic salts and the complexes.This work revealed the interconversions between hydrogen bond network and coordination bond in the solid-state and provided a unique method for the synthesis of complexes.(2)Nonporous complexes 7 and 8 were prepared by solution-based methods using chiral ligand(1R,2R)-N,N?-dibenzyl-1,2-cyclohexanediamine(L2).The"bimolecular"solid-gas adsorption reaction mechanism of nonporous complexes 7,8 was studied by BET specific surface area analysis,PXRD,¹H NMR,TGA,etc.Two kinds of gas molecules would be adsorbed in a cooperative manner by exposing the complexes to a sealed HCl/methanol atmosphere.On the one hand,the complex adsorbed HCl gas for a chemical reaction,causing the cleavage of Cu-N coordination bond,on the other hand,methanol molecules were inserted into the crystal lattice through physical adsorption,generating the same metal-organic salt 9,which was dominated by non-covalent N–H···Cl hydrogen bondings.The ¹H NMR had shown that ethanol molecules could replace methanol into the crystal structure to obtain the ethanol-containing metal-organic salts 10.Furthermore,the HCl molecules can be released by grinding the metal-organic salts 9 with the strong base KOH at a molar ratio of 1:2 to form the binuclear Cu(II)complex 8,which has fully proved the selectivity of mechanochemistry.The energy and relative stability of complexes 7,8 and metal-organic salt 9 were discussed by density functional theory(DFT)calculations.(3)The metal-organic salts 11,12 and coordination complex 13 were obtained by using tetradentate ligand(1R,2R)-N,N?-bis(pyridine-3-ylmethyl)cyclohexane-1,2-diamine(L3),and their crystal structures were characterized.The solid-state reactivity of Cu(II)compounds among first and second coordination spheres were studied by BET specific surface area analysis,PXRD,TGA,DSC,etc.In air,11 transformed into a new hydrated outer sphere structure 12 differing in the chemistry and geometry of the Cu(II)metal center.Upon heating,12 reversibly transformed into 11 in the solid-state.The 12?11reaction occured via ligand exchange with the transfer of a Cl^-from the outer sphere to the Cu(II)first sphere replacing the coordinated H₂O.Using mechanochemistry,compound 12 reacted with KOH at a molar ratio of 1:4 to form the complex(first sphere coordination)13,which was consists of a five-membered chelating ring,and the reversible process(second-to-first coordination sphere)13?12 can be carried out upon chemisorption of HCl and H₂O.Insights into the relative stabilities of key crystalline phases had been obtained by means of quantum-mechanical(QM)calculations,and a simple rationalization of the reaction[CuCl₄]^2-+H₂O?[CuCl₃(H₂O)]^-+Cl^-had been provided.(4)Herein,we had designed and synthesized the tetradentate ligand(1R,2R)-N,N?-bis(pyridin-4-ylmethyl)cyclohexane-1,2-diamine(L4)and its protonated ligand L4'.Using mechanochemistry,two copper salts 14 and 15 were prepared via 1:1and 1:2 stoichiometric controlled synthesis.The reversible transformations of the two salts were dynamically monitored by fluorescence spectroscopy,PXRD and Raman spectroscopy.Quantum-mechanical(QM)calculations provided some insights into the relative stabilities of the two salts,indicating driving forces for the reversible transformations.We also had synthesized salts 16 and 17,and used as the precursors to carry out the corresponding solid-gas and solid-state reactions.The solid-gas reaction process of 16 was dynamically monitored by PXRD,and its reaction mechanism was revealed at the molecular level.The HCl and water molecules were adsorbed to yield a mixture of salts 14 and 15 by exposing the salts 16 to a sealed HCl atmosphere.The stoichiometric controlled solid-state reaction of salt 17 was studied,that was,grinding 17with an equimolar CuCl₂·2H₂O can accurately obtain salt 15.The solid-state synthesis method for salt 18 and its potential application in adsorption were briefly explored.In summary,we had prepared the metal-organic salts 1—3,9—12,14—17 and the corresponding complexes 4—6,7,8,13,18 as the research objects,and the synthesis methods,structures analysises,properties and solid-state reversible conversions between the salts and their corresponding complexes had been studied.The solid-state reactivity of compounds containing different ligands was investigated,the changing factors of energy of the solid-state reactions were revealed,and the synthesis of coordination complexes in a green way was explored.We deeply believe that as people gradually pay attention to solid-state reactions,the aim of green chemistry will be achieved.