J. Augustinus Viljoen

University of the Free State, Bloemfontein, Free State, South Africa

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Publications (9)2.08 Total impact

  • Source
    Article: Di-μ-hydroxido-bis-[tris-(4,4,4-trifluoro-1-phenyl-acetyl-acetonato-κO,O')hafnium(IV)] dimethyl-formamide disolvate.
    J Augustinus Viljoen, Hendrik G Visser, Andreas Roodt
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    ABSTRACT: The binuclear molecule of the title compound, [Hf(2)(C(10)H(6)F(3)O(2))(6)(OH)(2)]·2C(3)H(7)NO, lies across an inversion centre and contains a Hf(IV) atom which is eight-coordinated and surrounded by three chelating β-diketonato tris-(4,4,4-trifluoro-1-phenyl-acetyl-acetonate (tfba(-)) ligands and two bridging OH(-) groups in a distorted square-anti-prismatic geometry. The Hf-O bond lengths vary from 2.073 (2) to 2.244 (2) Å and the O-Hf-O bite angles vary from 73.49 (9) to 75.60 (9)°. Weak O-H⋯O hydrogen-bonding inter-actions are observed between the bridging hy-droxy groups and the dimethylformamide solvent mol-ecules. The unit cell contains solvent-accessible voids of 131 Å(3), but the residual electron density in the difference Fourier map suggests no solvent mol-ecule occupies this void.
    Acta Crystallographica Section E Structure Reports Online 12/2011; 67(Pt 12):m1822-3. · 0.35 Impact Factor
  • Source
    Article: Tetra-kis(5,7-dimethyl-quinolin-8-olato-κN,O)hafnium(IV) dimethyl-formamide disolvate.
    J Augustinus Viljoen, Hendrik G Visser, Andreas Roodt
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    ABSTRACT: In the title compound, [Hf(C(11)H(10)NO)(4)]·2C(3)H(7)NO, the Hf(IV) atom is coordinated by four N,O-donating bidentate 5,7-dimethyl-8-quinolino-late (Ox(-)) ligands arranged to give a distorted square-anti-prismatic coordination polyhedron. The average Hf-O and Hf-N distances are 2.098 and 2.298 Å, respectively, and the average O-Hf-N bite angle is 70.2°. The crystal packing is controlled by π-π inter-actions between Ox(-) ligands of neighbouring mol-ecules, giving rise to a three-dimensional supra-molecular grid network. The inter-planar distances vary from 3.441 (1) to 3.509 (1) Å, while the centroid-centroid distances vary from 3.688 (2) to 3.759 (12) Å. A non-classical C-H⋯O hydrogen bond is observed between the complex and one of the solvate mol-ecules.
    Acta Crystallographica Section E Structure Reports Online 10/2011; 67(Pt 10):m1428-9. · 0.35 Impact Factor
  • Article: Tetrakis(1,3-diphenylpropane-1,3-dionato)hafnium(IV)
    J. Augustinus Viljoen, Hendrik G. Visser, Roodt Andreas
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    ABSTRACT: In the title compound, [Hf(C15H11O2)4], the HfIV atom is coordinated by four 1,3-diphenylpropane-1,3-dionato ligands with an average Hf—O distance of 2.17 (3) Å and O—Hf—O bite angles varying from 74.5 (1) to 75.02 (9)°. The coordination polyhedron shows a slightly distorted Archimedean square-antiprismatic geometry. The crystal packing is stabilized by weak C—H...O interactions.
    Acta Crystallographica Section E. 01/2010;
  • Source
    Article: Tetra-kis(1,3-diphenyl-propane-1,3-dionato)hafnium(IV).
    J Augustinus Viljoen, Hendrik G Visser, Andreas Roodt
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    ABSTRACT: In the title compound, [Hf(C(15)H(11)O(2))(4)], the Hf(IV) atom is coordinated by four 1,3-diphenyl-propane-1,3-dionato ligands with an average Hf-O distance of 2.17 (3) Å and O-Hf-O bite angles varying from 74.5 (1) to 75.02 (9)°. The coordination polyhedron shows a slightly distorted Archimedean square-anti-prismatic geometry. The crystal packing is stabilized by weak C-H⋯O inter-actions.
    Acta Crystallographica Section E Structure Reports Online 01/2010; 66(Pt 9):m1053-4. · 0.35 Impact Factor
  • Article: Tetrakis(quinolin-8-olato-κ2N,O)hafnium(IV) toluene disolvate
    J. Augustinus Viljoen, Hendrik G. Visser, Roodt Andreas, Steyn Maryke
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    ABSTRACT: In the title compound, [Hf(C9H6NO)4]·2C7H8, the hafnium metal centre is coordinated by four N,O-donating bidentate quinolin-8-olate ligands arranged to give a square-antiprismatic coordination polyhedron with a slightly distorted dodecahedral geometry. The average Hf—O and Hf—N distances are 2.096 (3) and 2.398 (3) Å, respectively, and the average O—Hf—N bite angle is 70.99 (11)°. The crystal packing is controlled by π–π interactions between quinoline ligands of neighbouring molecules and hydrogen-bonding interactions. The interplanar distances vary between 3.138 (1) and 3.208 (2) Å, while the centroid–centroid distances range from 3.576 (1) to 4.074 (1) Å.
    Acta Crystallographica Section E. 01/2009;
  • Source
    Article: Di-μ-hydroxido-bis[tris(1,1,1,5,5,5-hexa-fluoro-acetyl-acetonato-κO,O')hafnium(IV)] acetone solvate.
    J Augustinus Viljoen, Hendrik G Visser, Andreas Roodt, Maryke Steyn
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    ABSTRACT: The binuclear title compound, [Hf(2)(C(5)HF(6)O(2))(6)(OH)(2)]·C(3)H(6)O, contains an Hf(IV) atom which is eight coordinated and surrounded by three chelating β-diketonato 1,1,1,5,5,5-hexa-fluoro-acetyl-acetonate (hfaa) ligands and two bridging OH groups situated on a twofold rotation axis. The HfO(8) coordination polyhedron shows a slightly distorted Archimedean square anti-prismatic coordination with average Hf-O, C-O, C-C(Me) distances of 2.19 (2), 1.26 (2) and 1.49 (2) Å, respectively, and an O-Hf-O bite angle of 75.3 (5)°. Weak O-H⋯O hydrogen bonding inter-actions are observed between one of the bridging hydr-oxy groups and the disordered solvent mol-ecule.
    Acta Crystallographica Section E Structure Reports Online 01/2009; 65(Pt 11):m1367-8. · 0.35 Impact Factor
  • Source
    Article: Tetra-kis(quinolin-8-olato-κN,O)hafnium(IV) toluene disolvate.
    J Augustinus Viljoen, Hendrik G Visser, Andreas Roodt, Maryke Steyn
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    ABSTRACT: In the title compound, [Hf(C(9)H(6)NO)(4)]·2C(7)H(8), the hafnium metal centre is coordinated by four N,O-donating bidentate quinolin-8-olate ligands arranged to give a square-anti-prismatic coordination polyhedron with a slightly distorted dodeca-hedral geometry. The average Hf-O and Hf-N distances are 2.096 (3) and 2.398 (3) Å, respectively, and the average O-Hf-N bite angle is 70.99 (11)°. The crystal packing is controlled by π-π inter-actions between quinoline ligands of neighbouring mol-ecules and hydrogen-bonding inter-actions. The inter-planar distances vary between 3.138 (1) and 3.208 (2) Å, while the centroid-centroid distances range from 3.576 (1) to 4.074 (1) Å.
    Acta Crystallographica Section E Structure Reports Online 01/2009; 65(Pt 12):m1514-5. · 0.35 Impact Factor
  • Article: Di-μ-hydroxido-bis[tris(1,1,1,5,5,5-hexafluoroacetylacetonato-κ2O,O′)hafnium(IV)] acetone solvate
    J. Augustinus Viljoen, Hendrik G. Visser, Roodt Andreas, Steyn Maryke
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    ABSTRACT: The binuclear title compound, [Hf2(C5HF6O2)6(OH)2]·C3H6O, contains an HfIV atom which is eight coordinated and surrounded by three chelating β-diketonato 1,1,1,5,5,5-hexafluoroacetylacetonate (hfaa) ligands and two bridging OH groups situated on a twofold rotation axis. The HfO8 coordination polyhedron shows a slightly distorted Archimedean square anti-prismatic coordination with average Hf—O, C—O, C—CMe distances of 2.19 (2), 1.26 (2) and 1.49 (2) Å, respectively, and an O—Hf—O bite angle of 75.3 (5)°. Weak O—H...O hydrogen bonding interactions are observed between one of the bridging hydroxy groups and the disordered solvent molecule.
    Acta Crystallographica Section E. 01/2009;
  • Source
    Article: Tetra-kis(1,1,1-trifluoro-acetyl-acetonato-κO,O')hafnium(IV) toluene disolvate.
    J Augustinus Viljoen, Alfred Muller, Andreas Roodt
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    ABSTRACT: In the title compound, [Hf(C(5)H(4)F(3)O(2))(4)]·2C(7)H(8), the Hf(IV) atom, lying on a twofold rotation axis, is coordinated by eight O atoms from four 1,1,1-trifluoro-acetyl-acetonate ligands with an average Hf-O distance of 2.173 (1) Å and O-Hf-O bite angles of 75.69 (5) and 75.54 (5)°. The coordination polyhedron shows a slightly distorted Archimedean square antiprismatic geometry. The asymmetric unit contains a toluene solvent mol-ecule. The crystal structure involves C-H⋯.F hydrogen bonds.
    Acta Crystallographica Section E Structure Reports Online 01/2008; 64(Pt 6):m838-9. · 0.35 Impact Factor