Structures And Magnetic Properties Of Azido-Bridged Coordination Polymers

In the field of coordination chemistry, the design and magnetic properties of polynuclear molecules and especially clusters of high nuclearility and coordination polymers currently attract considerable interest. In order to design supermolecular architectures and reveal the fundamental mechanism of magnetic interaction and the megneto-structural correlation, we selected transition metal ions and organic co-ligands containing special coordination information as the object of our study. Meanwhile we chose sodium azide as the bridging ligand, which is an intriguing synthetic approach to molecular-based magnets due to the remarkable diversities of sodium azide in structural and magnetic behaviors. In this thesis, 14 compounds have been synthesized and characterized by elemental analyses, IR, X-ray analyses, variable-temperature and variable-field magnetic measurements.This thesis contains two main parts: (1) the structures and magnetic properties of azido -bridged complexes with bidentate Shiff-base ligands, and (2) the structures and magnetic properties of azido-bridged complexes with bi(bidentate) diazine ligands.1. The structures and magnetic properties of azido-bridged complexes with bidentate Shiff-base ligands(i) Three 1D Mn (II) -azido coordination polymers (1-3). In the three Mn(II) 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. In order to deduce some information about magnetostructural correlation, the structural and magnetic data have been investigated.(ii) Two 1D Cu(II)-azido coordination polymers (4, 5). Two complexes with onlysingle EO azido bridges, exhibiting antiferromagnetic and ferromagnetic interactions between neighboring metal ions, respectively.(iii)One 2D Mn(II)-azido coordination polymers (6). Compound 6 is a sheet of dimmers, in which two Mn(II) ions are bridged by two EO azides and the dimers are linked by the single EE bridges into a sheet. Magnetic studies on the complex reveal that ferromagnetic and antiferromagnetic interactions are mediated through the EO and EE azido bridges, respectively. The complex exhibits spin canting related to the lack of inversion centers between the EE azido bridged Mn(II) ions, but long-range ordering of the residual spins is not achieved.2. The structures and magnetic properties of azido-bridged complexes with bi(bidentate) diazine ligands(i) Two 1D Chiral Mn(II) and one 2D Mn(II)-azido coordination polymers (7-9). By incorporating an achiral diazine ligand, which can be locked in a chiral conformation upon coordination, into the Mn(II)- azido system, two ID chiral chain is induced. The process is called spontaneous resolution. The 2D layers are consisted of Mn(II) tetranuclear units, which are centrosymmetric. Compound 7 represents a new example of the rare phenomenon of homometallic ferrimagnetism, and behaves as a metamagnet built of ferrimagnetic chains, the critical temperature of antiferromagnetic ordering and the critical field of the antiferro-to-ferromagnetic transition being TN = 2.9 K and Hc = 1.1 kG, respectively. The noncompensation in spin moment is achieved by a specific alternation of ferro- and antiferromagnetic interactions within the unusual "fused triangles" chain. Compound 8 is a ID antiferromagnet with antiferromagnetic interactions mediated by the double diazine and the single EE azido bridges. Compound 9 exhibits weak ferromagnetism due to spin canting, while it undergoes two magnetic transitions at about 10.1 and 14.6 K, respectively.(ii) Five Cd(II)-azido coordination polymers (10-14). The various arrangements of azido ions give two 2D polymeric sheets of complexes 10, 11 and three 3D networks of 3, 4, and 5. Meanwhile the interesting structures of the five azido-bridged complexes containing a series of bi(bidentate) diazine ligands indicate the varieties of azido ions in designing polymeric archi...