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Synthesis and characterization of some transition metal phosphinates and their complexes

University of British Columbia

A number of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) monophenyl- and diphenylphosphinates have been synthesized and characterized using physical methods such as thermal analysis, X-ray crystallography, vibrational and electronic spectroscopy and magnetic susceptibility measurements. Complexes of some of these metal phosphinates with neutral donor molecules such as formamide, acetamide, methylformamide, monophenylphosphinic acid, pyridine, pyrazine and the aquo ligand have also been prepared and characterized. Studies on the magnetic properties of some manganese(II)-cadmium(II) mixed metal systems are also reported in this thesis. Co[H(C₆H₅)PO₂J₂ was prepared in three structural forms and indirect evidence supports polymeric chain structures with phosphinate ligands bridging tetrahedral metal centers in all three forms. Two of the forms exhibit antiferromagnetism; the third form exhibits ferromagnetic, field dependent behaviour. The related compounds, M[H(C₆H₅)PO₂]₂, where M is Mn(II), Cd(II), Ni(II) and Cu(II) are concluded to have polymeric structures with double phosphinate bridged chains of octahedrally coordinated metal centers cross-linked to form sheet structures. While the manganese and copper compounds are weakly antiferromagnetic the nickel compound exhibits ferromagnetic, field dependent behavior. The binary metal diphenylphosphinates, M[(C₆H₅)₂PO₂]₂ (where M is Mn(II) and Co(II)), were found to exist in two forms, labelled β and γ. Single crystal X-ray crystallography showed that the structures of the γ -forms consist of infinite linear chains, formed by metal ions in nearly regular tetrahedral environments, joined by bridging phosphinate ligands. The structural differences (between the (β - and γ -forms) are manifested in their thermal, spectral and magnetic properties, making the two forms distinguishable on this basis. The (J- and y-forms of both compounds are antiferromagnetic. Single crystal X-ray diffraction studies on M(HCONH₂)₂[H(C₆H₅)PO₂]₂ (where M is Mn(II), Cd(II) and Co(II)) and MnL₂ [H(C₆H₅)PO₂]₂ (where L is CH₃CONH₂ and H(C₆H₅)PO₂H) revealed polymeric structures with metal atoms linked by double phosphinate bridges and neutral ligands coordinating in the axial sites, completing a distorted octahedral coordination around each metal. The cobalt and manganese complexes are antiferromagnetic and in the case of the manganese complexes, the magnitude of the exchange coupling has been correlated with structural parameters. Similar phosphinate bridged polymeric structures have been proposed, primarily on the basis of spectroscopic evidence, for the following complexes: M(H₂O)₂[H(C₆H₅)PO₂]₂ (where M is Mn, Co and Ni), M(pyz)[H(C₆H₅)PO₂]₂ (where M is Co and Ni), M(py)₂[H(C₆H₅)PO₂]₂ (where M is Mn, Co and Ni) and Ni(HCONH₂)₂[H(C₆H₅)PO₂]₂- Magnetic studies indicate that regardless of the metal involved, the strength of antiferromagnetic coupling in these complexes increases in the order L = py < pyz < H₂O < HCONH₂. In the course of this work the following mononuclear phosphinate complexes were prepared and structurally characterized by single crystal X-ray diffraction: Co(H₂O)₄[H(C₆H₅)PO₂]₂, Ni[HCON(CH₃)₂]₂[(C₆H₅)₂PO₂H]₂[(C₆H₅)₂PO₂]₂ and [Ni[HCON(CH₃)₂]₂(H₂O)₄}(H₂O)₂[(C₆H₅)₂PO₂]₂. Magnetic studies indicate no significant magnetic exchange in any of these complexes. The compound Cd(H₂O)Cl[H(C₆H₅)PO₂] was also prepared and characterized by single crystal X-ray diffraction. The compound has a sheet structure involving both bridging phosphinate and bridging chloride ligands. To investigate the effects of cadmium doping on magnetic exchange in phosphinate bridged manganese(II) complexes the following mixed metal systems were prepared and studied: Mn₁₋x Cdx[H(C₆H₅)PO₂]₂, Mn₁₋x Cdx(HCONH₂)₂[H(C₆H₅)PO₂]₂ and Mn₁₋x Cdx [(n-C₆H₁₃)₂PO₂]₂ (where x varies from ~ 0.01 to ~ 0.54). In all three studies the results showed that the effect of Cd doping is to break the polymer chain into finite segments and to generate monomeric impurities in odd numbered segments. As the extent of doping increases the average chain length decreases and the fraction of monomer increases. In addition the exchange coupling constant was found to decrease as the average chain length decreases.

Text

2011-01-24

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http://hdl.handle.net/2429/30800

Chemistry

University of British Columbia

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