Aspects of the Stereochemistry of Eight-Coordination

Isolation of a Square-Planar Th(III) Complex: Synthesis and Structure of [Th(OC6H2tBu2-2,6-Me-4)4]1

Reduction of Th(OC₆H₂^tBu₂-2,6-Me-4)₄ using either KC₈ or Li in THF forms a new example of a crystallographically characterizable Th(III) complex in the salts [K(THF)₅(Et₂O)][Th(OC₆H₂^tBu₂-2,6-Me-4)₄] and [Li(THF)₄][Th(OC₆H₂^tBu₂-2,6-Me-4)₄]. Surprisingly, in each structure the four aryloxide ligands are arranged in a square-planar geometry, the first example of this coordination mode for an f element complex. The Th(III) ion and four oxygen donor atoms are coplanar to within 0.05 Å with O-Th-O angles of 89.27(8) to 92.02(8)° between cis ligands. The ligands have Th-O-C(ipso) angles of 173.9(2) to 178.6(4)°, and the aryl rings make angles of 58.5 to 65.1° with the ThO₄ plane. The effect of the eight tert-butyl substituents in generating the unusual structure through packing and/or dispersion forces is discussed. EPR spectroscopy reveals an axial signal consistent with a metal-based radical in a planar complex. DFT calculations yield a C₄-symmetric structure that accommodates a low-lying SOMO of 6d_z² character with 7s Rydberg admixture.

Structural changes within the alkaline earth uranyl phosphites

Three new alkaline earth (AE) uranyl phosphites and one barium uranium(IV) phosphate were synthesized under hydrothermal conditions. The carbonate salts of the AE's were employed both as cation sources and as pH regulators. Despite having very similar formulas and uranyl building units, the Ca(2+), Sr(2+) and Ba(2+) uranyl phosphites have three different extended networks. The calcium compound also contains a Ca(2+)/UO2(2+) mixed cation position. The four structure types will be presented herein with the AE cations generating distinct structural transformations.

Coordination-perturbed single-molecule magnet behaviour of mononuclear dysprosium complexes

By changing the ratio of reactants, two mononuclear Dy complexes, [Dy(phen)(acac)(3)] (1) and [Dy(phen)(2)(NO(3))(2)(acac)]·H(2)O (2) have been synthesized and structurally characterized. In 1, a Dy atom bearing square-antiprism coordination geometry exhibits SMM behaviour, while compound 2 with a bicapped-square-antiprism geometry does not show such SMM properties. The different magnetic behaviours seen in 1 and 2 are probably due to a different coordination environment and ligand field around the Dy(III) ions. The results proved the important influence of the structural environment of a SMM on its magnetic behaviour.

Crystal structure of potassium pentafluorozirconate monohydrate, KZrF5 · H2O

The crystal structure of KZrF5 · H2O has been determined by single crystal X-ray analysis. The crystals are monoclinic, a = 7.628(1), b = 12.081(1), c = 11.100(1) Å, β = 99.62(2)°, space group P21/c, Z = 8. The structure was refined by full-matrix least-squares methods to an R value of 0.0236 for 1674 independent observed reflections. The structure can be described as built up by K+ cations and [Zr2F10(H2O)2]2− double-polyhedron units which are linked into infinite chains parallel [100] by single F bridges. The double-polyhedron unit [Zr2F10(H2O)2]2− results from the association of two independent nonregular [ZrF7(H2O)] polyhedra sharing a triangular face. The chains are additionally strengthened by hydrogen bonds and are connected to layers parallel (010) by further hydrogen bonds. These hydrogen-bonded layers are held together by potassium cations located between the layers in irregular coordinations.