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The synthesis and characterization of copper(II) phosphinate coordination polymers

University of British Columbia

A number of disubstituted and monosubstituted copper(II) phosphi-nate coordination polymers, {Cu[R₂PO₂]₂}x and {Cu[R(H)PO₂]₂}[sub x], respectively, where R is an alkyl or a phenyl group, has been prepared and characterized. The physical, electronic and magnetic properties of these systems were investigated using physical methods such as thermal analysis, vibrational and electronic spectroscopy, and magnetic susceptibility measurements. The effect that the different substituents on phosphorus had on the structures and the properties was examined. The possibility of magnetic exchange propagated through the three-atom O-P-O bridge made the investigation of magneto-structural correlations of particular interest. The series of compounds containing straight chain alkyl groups, of one to twelve carbon atoms, were found to exist in two forms, labelled α and β; in some cases, derivatives were isolated in both forms. X-ray crystallography showed that the structures of both forms consisted of infinite linear chains of eight—membered rings, formed by two copper atoms in flattened tetrahedral environments, joined by two bridging phosphinate ligands. The structural differences between the two isomers were associated with different degrees of distortion of the CuO₄ chromophore from regular tetrahedral geometry, and with different orientations of the alkyl groups on phosphorus. These structural differences were manifested in the thermal, spectral and magnetic properties, making the two isomer groups distinguishable on this basis. Magnetic exchange was found in both forms; the α-isomers exhibited antiferromagnetic exchange with values of the exchange parameter, J, ranging from ca. -1 to -30 cm⁻¹, while the β-isomers showed weak ferro-magnetism with J approximately +2 cm⁻¹. This behavior was discussed in relation to the known structural differences between the two forms. The copper(II) phosphinate polymers containing branched chain alkyl groups were proposed to be linear polymers, while the diphenyl derivative was postulated to be crosslinked, on the basis of their properties. Similarly, the monosubstituted compounds were proposed to be crosslinked. All -these derivatives probably contain four-coordinate copper(II) atoms, from a consideration of the vibrational and electronic spectra, with degrees of distortion from regular tetrahedral geometry similar to that found in the di-n-alkylphosphinates. The exception to this was the diphenyl compound, which was postulated to have a more flattened CuO₄ chromophore than the latter derivatives. This unique structure was suggested to arise as a result of the steric requirements of the bulky phenyl substituents and the effect of this on the crosslinked structure. No evidence for or against magnetic exchange was found in these compounds over the temperature range studied.

Text

2010-06-13

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http://hdl.handle.net/2429/25660

Chemistry

University of British Columbia

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