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The synthesis, magnetic and mossbauer spectral properties of poly-[mu]-bis (di-n-octylphosphinato) iron(II) and its zinc(II)-doped analogues

University of British Columbia

The inorganic coordination polymer, poly-μ-bis(di-n-octylphosphinato)iron(II), (Fe[(n-C₈H₁₇)₂PO₂])[sub n] , was prepared and characterized. The physical properties of this compound were analyzed using differential scanning calorimetry, vibrational, electronic and Mossbauer spectroscopy and temperature dependent magnetic susceptibility studies. Evidence for polymorphism in this compound was found, leading to the postulation of the existence of two forms of this material, labelled I and II. Evidence was seen suggesting that a Form I to Form II transition occurs upon the application of pressure. Differential scanning calorimetry results suggested that this transition was not thermally induced over the temperature range 35 to 300°C. Both forms were suggested to be four-coordinate and to possess a highly compressed tetrahedral metal-oxygen chromophore. Mossbauer spectral studies suggested that the iron(II) centres in this material were in the rare triplet ground state, giving an intermediate spin S=1 system. Mossbauer spectroscopy also showed a substantial positive contribution to the splitting of the S=1 quadrupole doublet, possibly as a result of σ-donation properties of the ligands. The magnetic susceptibility vs. temperature data, collected in the range of 2-80 K and analyzed according to a linear chain Heisenberg S=1 model, showed the iron centres to be antiferromagnetically coupled and also to have unexpectedly large Lande splitting factor, g. The high g value was presumed to be the result of large orbital angular momentum contributions. Based on these results, electronic structure schemes were proposed for Forms I and II. In addition, zinc(II)-doped samples of this compound, {Fe[sub 1-x] Zn [ (n-C₈H₁₇)₂ PO₂ ]₂}[sub n] , were prepared with x=0.05, 0.1 and 0.2. These compounds were analyzed by differential scanning calorimetry, vibrational and Mossbauer spectroscopy and temperature dependent magnetic susceptibility studies and also appeared to occur in the polymorphic forms I and II. Mossbauer spectroscopy again suggested the presence of iron (II) S=1 centres, but also showed the presence of S=2 iron (II). This led to the proposal that the effect of doping zinc(II) into this system is to distort the geometries of the iron centres adjacent to the zinc centres to a more tetrahedral configuration. A large quadrupole splitting was observed for the S=2 lines, again perhaps a result of substantial σ-donation from the ligands. Magnetic susceptibility vs. temperature data were also collected over the range 2-80 K for these samples; the details of these results are discussed in a qualitative manner.

Text

2010-08-22

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http://hdl.handle.net/2429/27615

Chemistry

University of British Columbia

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