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Heterometallic Oxo-Alkoxides of Europium, Titanium and Potassium

by Berger, Erik

Abstract (Summary)
Coordination compounds of europium and titanium with oxide, ethoxide (OCH2CH3), iso-propoxide (OCH(CH3)2) and tert-butoxide (OC(CH3)3) ligands have been studied. These belong to the general class of oxo-alkoxides, MxOy(OR)z, with alkoxide ligands (OR) containing an organic, aliphatic part R. The R group can be systematically varied, permitting the investigation of the influence of electronic and steric effects on the coordination of metal and oxygen atoms. Their tendency towards hydrolysis and formation of metal-oxygen-metal bridges also makes (oxo)alkoxides interesting as precursors in liquid solution-based or gas phase-based synthesis of many technologically important materials.The structure of a termetallic oxo-alkoxide of formula Eu3K3TiO2(OH/OCH3)(OR)11(HOR) (R = C(CH3)3) was revealed by a combination of single-crystal X-ray diffraction and IR spectroscopy. Its unusual structure features a facial oxygen-centered Eu3K3O octahedron sharing one face with an oxygen-centered K3TiO tetrahedron. Six-coordination of oxygen by a combination of alkali metal and lanthanoid atoms is not uncommon for alkoxides, but the attachment of a tetrahedron to one of its faces provides a new dimension to the library of oxo-alkoxide structures. The structure was the result of incomplete metathesis in the synthesis attempt of europium-titanium oxo-tert-butoxides.Eu4TiO(OR)14 and (Eu0.5La0.5)4TiO(OR)14 (R = CH(CH3)2) were found to be isostructural with previously published Ln4TiO(OR)14 structures (Ln=Sm, Tb0.9Er0.1). X-ray diffraction and UV-Vis absorption results show no site preference for La in either the solid state or hexane solution. The Ln4TiO(OR)14 structure forms part of an interesting group of Ln4MO(OR)10+z­(HOR)q structures where M is another lanthanoid (Ln) or a di-, tri- or tetravalent heteroatom, giving either a square pyramidal or a trigonal bipyramid-like coordination of the central oxygen atom, depending on the chemistry and size of M.Eu2Ti4O2(OR)18(HOR)2 (R = CH2CH3) was deduced from IR data to have the same molecular structure as Er2Ti4O2(OR)18(HOR)2. UV-Vis measurements are also in agreement with the presence of one symmetry-unique europium site in the molecular structure. Structure determination by single-crystal X-ray diffraction has yet to be performed. Coordination compounds of europium and titanium with oxide, ethoxide (OCH2CH3), isopropoxide(OCH(CH3)2) and tert-butoxide (OC(CH3)3) ligands have been studied. Thesebelong to the general class of oxo-alkoxides, MxOy(OR)z, with alkoxide ligands (OR)containing an organic, aliphatic part R. The R group can be systematically varied, permittingthe investigation of the influence of electronic and steric effects on the coordination of metaland oxygen atoms. Their tendency towards hydrolysis and formation of metal-oxygen-metalbridges also makes (oxo)alkoxides interesting as precursors in liquid solution-based or gasphase-based synthesis of many technologically important materials.The structure of a termetallic oxo-alkoxide of formula Eu3K3TiO2(OH/OCH3)(OR)11(HOR)(R = C(CH3)3) was revealed by a combination of single-crystal X-ray diffraction and IRspectroscopy. Its unusual structure features a facial oxygen-centered Eu3K3O octahedronsharing one face with an oxygen-centered K3TiO tetrahedron. Six-coordination of oxygen bya combination of alkali metal and lanthanoid atoms is not uncommon for alkoxides, but theattachment of a tetrahedron to one of its faces provides a new dimension to the library of oxoalkoxidestructures. The structure was the result of incomplete metathesis in the synthesisattempt of europium-titanium oxo-tert-butoxides.Eu4TiO(OR)14 and (Eu0.5La0.5)4TiO(OR)14 (R = CH(CH3)2) were found to be isostructuralwith previously published Ln4TiO(OR)14 structures (Ln=Sm, Tb0.9Er0.1). X-ray diffraction andUV-Vis absorption results show no site preference for La in either the solid state or hexanesolution. The Ln4TiO(OR)14 structure forms part of an interesting group of Ln4MO(OR)10+z-(HOR)q structures where M is another lanthanoid (Ln) or a di-, tri- or tetravalent heteroatom,giving either a square pyramidal or a trigonal bipyramid-like coordination of the centraloxygen atom, depending on the chemistry and size of M.Eu2Ti4O2(OR)18(HOR)2 (R = CH2CH3) was deduced from IR data to have the samemolecular structure as Er2Ti4O2(OR)18(HOR)2. UV-Vis measurements are also in agreementwith the presence of one symmetry-unique europium site in the molecular structure. Structuredetermination by single-crystal X-ray diffraction has yet to be performed.
Bibliographical Information:

Advisor:

School:Uppsala universitet

School Location:Sweden

Source Type:Master's Thesis

Keywords:NATURAL SCIENCES; Chemistry; Inorganic chemistry; Coordination chemistry; Alkoxides; Europium; Lanthanoids; Electronic absorption spectroscopy; f-f spectroscopy; Oorganisk kemi; Inorganic Chemistry

ISBN:

Date of Publication:01/01/2010

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