Lanthanide Complexes of Macrocyclic Polyoxovanadates by VO₄ Units: Synthesis, Characterization, and Structure Elucidation by X-ray Crystallography and EXAFS Spectroscopy

Reactions of a tetravanadate anion, [V₄O₁₂]^4–, with a series of lanthanide­(III) salts yield three types of lanthanide complexes of macrocyclic polyoxovanadates: (Et₄N)₆[Ln^IIIV₉O₂₇] [Ln = Nd (<b>1</b>), Sm (<b>2</b>), Eu (<b>3</b>), Gd (<b>4</b>), Tb (<b>5</b>), Dy (<b>6</b>)], (Et₄N)₅[(H₂O)­Ho^III(V₄O₁₂)₂] (<b>7</b>), and (Et₄N)₇[Ln^IIIV₁₀O₃₀] [Ln = Er (<b>8</b>), Tm (<b>9</b>), Yb (<b>10</b>), Lu (<b>11</b>)]. Lanthanide complexes <b>1</b>–<b>11</b> are isolated and characterized by IR, elemental analysis, single-crystal X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS). Lanthanide complexes <b>1</b>–<b>6</b> are composed of a square-antiprism eight-coordinated Ln^III center with a macrocyclic polyoxovanadate that is constructed from nine VO₄ tetrahedra through vertex sharing. The structure of <b>7</b> is composed of a seven-coordinated Ho^III center, which exhibits a capped trigonal-prism coordination environment by the sandwiching of two cyclic tetravanadates with a capping H₂O ligand. Lanthanide complexes <b>8</b>–<b>11</b> have a six-coordinated Ln^III center with a 10-membered vanadate ligand. The structural trend to adopt a larger coordination number for a larger lanthanide ion among the three types of structures is accompanied by a change in the vanadate ring sizes. These lanthanide complexes are examined by EXAFS spectroscopies on lanthanide L_III absorption edges, and the EXAFS oscillations of each of the samples in the solid state and in acetonitrile are identical. The Ln–O and Ln···V bond lengths obtained from fits of the EXAFS data are consistent with the data from the single-crystal X-ray studies, reflecting retention of the structures in acetonitrile

Lanthanide Complexes of Macrocyclic Polyoxovanadates by VO₄ Units: Synthesis, Characterization, and Structure Elucidation by X-ray Crystallography and EXAFS Spectroscopy

Reactions of a tetravanadate anion, [V₄O₁₂]^4–, with a series of lanthanide­(III) salts yield three types of lanthanide complexes of macrocyclic polyoxovanadates: (Et₄N)₆[Ln^IIIV₉O₂₇] [Ln = Nd (<b>1</b>), Sm (<b>2</b>), Eu (<b>3</b>), Gd (<b>4</b>), Tb (<b>5</b>), Dy (<b>6</b>)], (Et₄N)₅[(H₂O)­Ho^III(V₄O₁₂)₂] (<b>7</b>), and (Et₄N)₇[Ln^IIIV₁₀O₃₀] [Ln = Er (<b>8</b>), Tm (<b>9</b>), Yb (<b>10</b>), Lu (<b>11</b>)]. Lanthanide complexes <b>1</b>–<b>11</b> are isolated and characterized by IR, elemental analysis, single-crystal X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS). Lanthanide complexes <b>1</b>–<b>6</b> are composed of a square-antiprism eight-coordinated Ln^III center with a macrocyclic polyoxovanadate that is constructed from nine VO₄ tetrahedra through vertex sharing. The structure of <b>7</b> is composed of a seven-coordinated Ho^III center, which exhibits a capped trigonal-prism coordination environment by the sandwiching of two cyclic tetravanadates with a capping H₂O ligand. Lanthanide complexes <b>8</b>–<b>11</b> have a six-coordinated Ln^III center with a 10-membered vanadate ligand. The structural trend to adopt a larger coordination number for a larger lanthanide ion among the three types of structures is accompanied by a change in the vanadate ring sizes. These lanthanide complexes are examined by EXAFS spectroscopies on lanthanide L_III absorption edges, and the EXAFS oscillations of each of the samples in the solid state and in acetonitrile are identical. The Ln–O and Ln···V bond lengths obtained from fits of the EXAFS data are consistent with the data from the single-crystal X-ray studies, reflecting retention of the structures in acetonitrile