Structures And Magnetic Properties Of Azido-Bridged Coordination Polymers

Structural design and magnetic properties of coordination polymers are currently of considerable interest. The azido ion as a bridge has been an intriguing synthetic approach to molecular-based magnets due to their remarkable diversities in structural and magnetic behaviors. In this thesis, ten azido-ridged ID and 2D novel coordination polymers with different organic co-ligands have been synthesized and characterized by means of analyses, IR, X-ray analyses; variable-temperature and variable-field magnetic measurements. The main points are as follows.(1) Three ID Mn(II)-azido coordination polymers (1-3) and a 2D molecular-based magnet (8). In the ID complexes, Mn(II) ions are alternately bridged by two end-to-end (EE) and two end-on (EO) azido ligands. Magnetic analyses have revealed the existence of alternating ferromagnetic and antiferromagnetic interactions through the EO and EE azido bridges, respectively. The magnetostructural correlations have been investigated. Compound 8 is a sheet of dimmers, in which two Mn(II) ions are bridged by two EO azides into a dimer and the dimers are linked by the single EE bridges into a sheet. The complex behaves as a weak ferromagnet with the critical temperature is 20 K.(2) Four ID Cu(II)-azido coordination polymers with interesting topologies (4-7). Compound 4 is the first complex with only single EO azido bridges, exhibiting antiferromagnetic interactions between neighboring metal ions. Compound 5 is the second complex that contains alternating single EO and single EE azido bridges but the first one that exhibits alternating ferromagnetic interactions. Compound 6 exhibits an unprecedented "chain of rings" topology built via three kinds of EO bridges: four coppers are bridged into a tetranuclear ring by alternating single anddouble EO azides and the rings are linked by double EO bridges into a chain. Ferromagnetic interactions are dominant within the chain. Compound 5 is a chain of dimers, in which two coppers are bridged by two EO azido ions into a dimer and the dimers are linked by the co-ligand into a chain.(4) Chiral and racemic molecular-based magnets (9-10). By incorporating an achiral diazine ligand, 2-pyridylmethylketazine, which can be locked in a chiral conformation upon coordination, into the manganese(II)-azido system, a homochiral 2D network is induced, in which neighboring Mn(II) ions are bridged via two end-on azido and a diazine ligands into chiral dimeric units, and neighboring units are interlinked via single end-to-end azido bridges. The interdimer chirality preservation is achieved via the homochiral ID helical linkage formed by Mn(II) and end-to-end azido ions. The 2D layers are stacked in hetero- and homochiral fashion to yield simultaneously racemic and chiral crystals, indicating a partial spontaneous resolution. Both compounds behave as spin-canted weak ferromagnets but the critical temperatures are different.