Functional Coordination Clusters Based On Linear Conjugated Pyrazole-pyridine Ligand

Molecular materials,organic,inorganic and coordination compounds,can be grouped by their dimensionalities,viz:zero-dimensional clusters,one-dimensional chains,and two-dimensional layers and three-dimensional networks.The latter two types of structures can also be called coordination polymers or metal-organic frameworks.With the extensive synthesis and in-depth study of various coordination polymers and MOFs,they have become a research hot spot,and consequently,the related theoretical research of coordination polymers has been greatly developed.However,zero-dimensional complexes,especially coordination clusters,are still in the development stage.It is developing into another hot spot research area of coordination chemistry,due to their novel structures and potential applications in optics,electricity,magnetism,catalysis,medicine,engineering and fuel transportation,etc.Based on the background and research ideas,this dissertation aims to design and synthesize the transition metal functional materials with special structures and properties,and study their structures and properties in order to develop structure property relationships as well understanding them using theoiretical tools such as DFT and band structure calculations in order to have a deeper understanding.The main achievements are developed in the following chapters of the thesis.1.Hexanuclear copper complexes based on 5 5'-pyridyl-3,3'-bis-1H-pyrazoleIn chapter one,a new design concept has been realized for the construction of molecular conductors,whereby the building unit contains a core reservoir of carriers made up of metal-ions with controllable valence states and shelled by flat organic ligands having an extended ?-system to promote supramolecular electronic communication.Therefore,reacting the conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1H-pyrazole with different copper salts solvothermally led to three interesting hexameric salts having different ground-state valences,[Cu?6(L)4(NO3)(CH3OH)2](NO3)3.4CH3OH(1),[(CH3)2NH2][Cu?Cu?5(L)4](SO4)2·4H2O(2)and[Cu?2Cu?4(L)4](NO3)2·2CH3OH(3).The monovalent Cu?6 salt is an insulator,but the mixed-valent Cu?-Cu?5 and Cu?2-Cu?4 salts are semiconductors.Magnetic exchange interactions up to JNN =-158 cm-1 dominate the susceptibilities and led to ground state spin ST = 1(Cu?6),1/2(Cu?5-Cu?)and 0(Cu?4-Cu?2)at 40 K.Cyclic voltammetry shows the stepwise one-electron oxidation-reduction through all the possible valence states.The theoretical calculations of the electronic and band structures of the three compounds substantiate the experimentally observed physical properties.2.Nonanuclear copper complexes based on 5,5'-pyridyl-3,3'-bis-1H-pyrazoleIn chapter two,we report the syntheses,structures and optical,magnetic and electrical properties of a series of electrically conducting solids formed of planar[3×3]nonanuclear copper complexes held together by 5,5'-pyridyl-3,3'-bi-1H-pyrazole.Starting with different copper salts resulted in three different valence states,viz:[Cu?9(L)6(CF3SO3)4](CF3SO3)2·3CH3CN(4),[Cu?2Cu?7(L)6(NO3)(CH3OH)](NO3)3·6CH3OH(5),[Cu?4Cu?s(L)6](SO4)·2CHsOH(6),[Cu?4Cu?S(L)6](ClO4)2·2CH3OH(7),[Cu?4Cu?S(L)6](SbF6)2·2CH3OH(8).While the cluster structures are closely related,the presence of coordinated solvent in the former two complexes prevents close contact between molecules and the mixed-valent state in the latter four complexes renders them more conducting.Band structure calculations reveal semiconducting behavior as observed experimentally and DFT calculations of the spin and charge densities are consistent with the valence states of the copper atoms based on X-Ray diffraction data.Stepwise electron oxidation-reduction through a range of valence states were observed in the cyclic voltametry.Given the low exchange between molecules in the solids,the observed magnetic properties were successfully modeled to each molecule,according to the valence distributions found by crystallography.The present results add momentum to the idea put forward in chapter one,that solids built from units having mixed-valent clusters wrapped by organic ligand with delocalized ?-electrons is a way forward to acheive molecular conductors.3.Hexadecanuclear copper(I)complexes based on 5,5'-pyridyl-3,3'-bis-1H-pyrazoleIn chapter three,we use the ? conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1H-pyrazole reaction with cupric sulfate solvothermally to obtain an interesting hexadecameric copper(?)complex[Cu?,16(L)8](9).There were rich Cu..Cu interactions(2.6-2.8 A)in the single crystal structure,resulting in orange-red emission around 610 nm.Three solvent-containing complexes were obtained by soaking in water,methanol and ethanol through single-crystals to single-crystals transformations,viz:[Cu?16(L)8]·4H2O(10),[Cu?16(L)8]·2CH3OH(11)and[Cu?16(L)8]·2CH3CH2OH(12),respectively.After removal of the solvent molecules,the fluorescence emission of the complex gradually weakens until it disappears.Interestingly,this dynamic fluorescence emission and quenching can be reversibly controlled by soaking the solvent and removing the solvent by heating.4.A Heptacosanuclear mixed valence copper complex based on 5,5'-pyridyl-3,3'-bis-1H-pyrazoleIn chapter four,the ? conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1H-pyrazole solvothermal reaction with cupric sulfate in acetonitrile led to a highest-nuclearity mixed-valence heptacosameric complex[Cu?6Cu?21(L)18(CN)6(SO4)](SO4)2·8CH3CN(13).The 3×[3×3]grid has a highly delocalized electronic system that renders the mixed-valence complex very stable.Obviously,compound Cu27 was generated by three Cu9 units,one central core sulfate sitting on a pseudo-C3 axis and six in-situ generated bridging cyanide from the CH3CN linking their edges.The formation process was also monitored by mass spectrometry.The overall magnetic susceptibility and the interactions involved can be explained by considering the effective magnetic orbitals based on the electronic configurations of Jahn-Teller distorted Cu? centers.The 3×[3×3]grid-type copper complex can be considered to be electrochemically and structurally changeable molecular units,a desirable characteristic for the development of molecular devices.