Syntheses, Structures And Magnetic Properties Of Coordination Polymers With Pseudohalides And Different Organic Coligands

The design and preparation of polynuclear and multidimensional complexes containing paramagnetic centers connected through small bridges have attracted much attention in recent years because of their importance in understanding the mechanism of superexchange magnetic interactions,discovering new magnetic phenomena,and generating new magnetic materials.The pseudohalides ions such as azide and thiocyanate are among the most extensively studied bridges,and their abilities in bridging metal ions in various modes,propagating magnetic exchange of a different nature,building extended networks with diverse topologies,and generating new magnetic phenomena have been demonstrated by a plethora of studies.In this thesis, different bis(tetrazole)ligands[1,2-bis(tetrazol-1-yl)ethane(btze),1,2-bis(tetrazol-1-yl) propane(btzp),1,4-bis(tetrazol-1-yl)butane(btzb),1,6-bis(tetrazol-1-yl)hexane (btzh)]and a betaine-type ligand[1-carboxymethylpyridinium-4-carboxylate(HL¹)] were used as co-ligands to synthesize a series of metal-azide and metal-thiocyanate coordination compounds.The compounds have been characterized by means of elemental analyses,IR spectra and single-crystal X-ray analyses.The magnetic studies on relevant compounds have also been performed.The main points are as follows:1.Azido-bridged coordination polymers with flexible bis(tetrazole)ligands as co-ligands.(a)Two novel type of 3D hybrid frameworks have been obtained,in which the 2D Cu(â…¡)-azido inorganic layers constructed via bothμ₂-1,1 andμ₃-1,1,3 azide bridges are pillared by organic spacers.The 2D azido-bridged lattice is unprecedented,and the compounds represent the first examples of 3D molecular metamagnets built of ferromagnetic Cu(â…¡)-azido layers.The antiferromagnetic transition temperature of these tow compounds is 4 K,their critical field are 700 Oe and 300 Oe respectively.These features clearly indicate that ferromagnetic interactions between Cu ions are predominate throughout the layer,and the presence of interlayer antiferromagnetic interactions lead to the antiferromagnetic ordering and metamagnetic behavior.The different of their critical.field are caused by the interlayer Cu…Cu separations,which indicate that varying the pillar length can effectively tune. the interlayer antiferromagnetic interactions and hence the bulk magnetic behaviors. (b)A series of three-dimensional Co(â…¡)and Mn(â…¡)coordination polymers in which metal-azido layers are pillared by flexible bis(tetrazole)ligands have been synthesized. The quasilinear azido ions adopt the single EE bridging mode and join the metal ions into a two-dimensional(4,4)square-grid-like layer.(c)Two 2D azido-bridged Co(â…¡) and Cd(â…¡)complexes have been obtained,in which the metal ions are connected through double EE azide bridges to form 1D chains.The neighbor chains are constructed to 2D layers through the flexible bis(tetrazole)ligands.(d)A 1D azido-bridged Cu(â…¡)coordination polymer has been synthesized,in which the azide ions adopt double EO bridging mode and join the metal ions into a one-dimensional chain.The ligand btzc is connected to Cu(â…¡)ions as terminal ligand.2.Metal-thiocyanate coordination polymers with flexible bis(tetrazole)as co-ligands.(a)For Co(â…¡)compounds,the structures are dependent upon the length of the organic ligands and synthetic conditions.The short btze ligand gives singly bridged 2D square grid layers with 2-fold parallel interpenetration or 1D linear chains with deep interdigitation,dependent upon the metal-to-ligand ratio used for the synthesis.The btzb ligand links the metal ions into doubly bridged chains composed of bimetallacycles.Most interestingly,the long btzh ligand leads to 2D layers with both single and double bridges between Co(â…¡)ions,and the inclined interpenetration of layers generates a 3D polycatenated structure with a high degree of catenation.(b) A 2D thiocyanato-bridged Cu(â…¡)complex has been obtained,in which the metal ions are connected through double EE thiocyanate bridges to form 1D chains.The neighbor chains are constructed to 2D plane through the flexible ligands btze.The EE thiocyanate bridges propagate antiferromagnetic interaction between copper ions.(c) A 3D Cd(â…¡)coordination polymer has been synthesized.The quasilinear thiocyanato ions adopt the single EE bridging mode and join the metal ions into two-dimensional (4,4)square-grid-like layers,which are pillared by flexible bis(tetrazole)ligands3.Azido-bridged coordination polymers with betaine-type ligands as co-ligands.(a) A 3D material has been obtained,in which Co(â…¡)chains with coexistent azide and carboxylate bridges are cross-linked by long organic spacers containing aliphatic CH₂ linkers.Although the ferromagnetic and anisotropic chains are covalently interlinked in the structural sense,they are well isolated in the magnetic sense.The combined static and dynamic magnetic investigations suggest that the material behaves as a Single-Chain Magnets.(b)A 2D Cu(â…¡)complexes has been obtained,in which the azido ions adopt double EO bridging mode and join two Cu(â…¡)ions to form a dinuclear unit,The betaine ligands join the dinuclear units into a 2D layer.