| Summary: | Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. Chemistry Bibliography: leaves 103-113. This thesis describes synthesis, structural and magnetic properties of high nuclearity cluster complexes self assembled from polydentate alkoxo-diazine ligands. In Chapter 1. clusters and self-assembly have been briefly reviewed. In Chapter 2. synthesis, characterization. X-ray structures and the magnetic properties of three trinuclear copperf II) complexes are described. These compounds exhibit moderate to strong antiferromagnetic coupling as a result of superexchange via the N-N linkages. The magnetic properties are explained on the basis of large rotational angles of the copper magnetic planes about the diazine bridges. In Chapter 3. four predominantly square grid M4(ji-0)4 (M = Cu(II). Ni(II) and Co(II)) complexes and a rectangular Mru(N-N):0: grid complex are synthesized and structurally characterized by X-ray techniques. The square [2*2] copper(II) cluster exhibits intramolecular ferromagnetic spin exchange, associated with the orthogonal alkoxide bridging arrangement and the close proximity of the copper centers. Both the Ni4(|i-0)4 and Co4(ja-0)4 clusters are antiferromagnetically coupled due to the large M-O-M angles and for the rectangular Mru complex the exchange is dominated by antiferromagnetic coupling via the N-N bridge. Chapter 4 describes the ligand paoh. which has two widely separated tridentate (N:0) terminal coordination pockets, and uncoupled square [2*2] Fe(II)4 grid complex. Replacement of the NH: groups with 2-pyridyl residues gives the ligand dpkoh with the additional coordination capacity of an exo-N4 coordination pocket, leading to an octanuclear metallacyclic cluster complex [Ni8(dpkoh-2H)4(H20)8](Cl04)8-4H20, in which eight nickel(II) centers are bridged just by the diazine N-N single bond. Substantial antiferromagnetic coupling exists between the nickel(II) ions throughout the metallacycle. In Chapter 5. The synthesis, structural characterization and magnetism studies of [3*3] Mn(ll) and CutII) nanonuclear square grid complexes are described. The Mn(II)o systems exhibit intramolecular antiferromagnetic coupling, while for the Cu(II)q complexes ferromagnetic exchange is observed with an S = 7/2 ground state. The aggregation of nine octahedral Mn(II) and Cu(II) centers (fifty four coordination positions) into an alkoxo-bridged. portcullis-like [3*3] grid by six heptadentate 2poap ligands (fifty four donor positions) is a unique example of a self assembly process.
|
|---|