High tetraalkylaluminate fluxionality in half-sandwich complexes of the trivalent rare-earth metals.

Steric factors govern the formation of half-sandwich complexes (C5Me4R)Ln[N(SiHMe2)2]2 according to acid-base reactions utilising Ln[N(SiHMe2)2)3(thf)2 and substituted cyclopentadienes. Subsequent trimethylaluminium-promoted silylamide elimination produces the first half-sandwich bis(tetramethylaluminate) complexes (C5Me4R)Ln(AlMe4)2.

Molecular structures of two metal tetrakis(tetrahydroborates), Zr(BH4)(4) and U(BH4)(4): equilibrium conformations and barriers to internal rotation of the triply bridging BH4 groups.

The molecular structures of Zr[(mu-H)(3)BH](4) and U[(mu-H)(3)BH](4) have been investigated by density functional theory (DFT) calculations and gas electron diffraction (GED). The triply bridged bonding mode of the tetrahydroborate groups in the former is confirmed, but both DFT calculations and GED structure refinements indicate that the BH(4) groups are rotated some 12 degrees away from the orientation in which the three bridging B-H bonds are staggered with respect to the opposing ZrB(3) fragment. As a result the symmetry of the equilibrium conformation is reduced from T(d) to T.

Molecular Structure of a Monomeric, Base-Free Metal(I) Amide, TlN[Si(CH(3))(3)](2), by Gas Electron Diffraction and by Density Functional Theory and ab Initio MP2 Calculations.

Thallium bis(trimethylsilyl)amide is a monomer in the gas phase. The molecular symmetry is C(2), the Tl-N bond length is 214.8(12) pm by gas electron diffraction as compared to about 258 pm in the crystalline dimer (Klinkhammer, K.