(2,2'-Bipyrid-yl-κ(2) N,N')bis-(η(5)-penta-methyl-cyclo-penta-dien-yl)barium.

In the title compound, [Ba(C10H15)2(C10H8N2)], the Ba-N distances are 2.798 (3) and 2.886 (3) Å, and the Cp ring centroid distances to Ba(2+) are 2.7291 (7) and 2.7192 (9) Å. The angle between the N atoms in the bypyridine ligand and the metal ion is 56.80 (8)° and the N-C-C-N torsion angle in the bi-pyridine ligand is 1.7 (4)°. The bi-pyridine ligand is almost planar, the dihedral angle formed by the intersection of the planes defined by the pyridyl rings being 3.04 (19)°, and the angle between the plane defined by the Ba(2+) ion and the two bipyridyl N atoms and the plane defined by the 12 atoms of the bi-pyridine ligand is 10.2 (3)°. The average Ba-N and Ba-centroid distances are 0.16 and 0.14 Šlonger, respectively, than the equivalent distances in the isotypic strontium compound [Kazhdan et al. (2008 ▶). Acta Cryst. E64, m1134]. This difference is in accord with the difference between the ionic radii of 0.16 Šsuggested by Shannon [Acta Cryst. (1976 ▶), A32, 751-767].

Intermediate-valence tautomerism in decamethylytterbocene complexes of methyl-substituted bipyridines.

Multiconfigurational, intermediate valent ground states are established in several methyl-substituted bipyridine complexes of bis(pentamethylcyclopentadienyl)ytterbium, Cp2*Yb (Me(x)-bipy). In contrast to Cp2*Yb(bipy) and other substituted-bipy complexes, the nature of both the ground state and the first excited state are altered by changing the position of the methyl or dimethyl substitutions on the bipyridine rings. In particular, certain substitutions result in multiconfigurational, intermediate valent open-shell singlet states in both the ground state and the first excited state. These conclusions are reached after consideration of single-crystal X-ray diffraction (XRD), the temperature dependence of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine-structure (EXAFS), and magnetic susceptibility data, and are supported by CASSCF-MP2 calculations. These results place the various Cp2*Yb(bipy) complexes in a new tautomeric class, that is, intermediate-valence tautomers.

Decamethylytterbocene complexes of bipyridines and diazabutadienes: multiconfigurational ground states and open-shell singlet formation.

Partial ytterbium f-orbital occupancy (i.e., intermediate valence) and open-shell singlet formation are established for a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, (C(5)Me(5))(2)Yb, abbreviated as Cp*(2)Yb. Data used to support this claim include ytterbium valence measurements using Yb L(III)-edge X-ray absorption near-edge structure spectroscopy, magnetic susceptibility, and complete active space self-consistent field (CASSCF) multiconfigurational calculations, as well as structural measurements compared to density functional theory calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground-state wave function that has both an open-shell singlet f(13)(pi*)(1), where pi* is the lowest unoccupied molecular orbital of the bipyridine or diazabutadiene ligands, and a closed-shell singlet f(14) component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the lack of temperature dependence of the measured intermediate valence. These results have implications for understanding chemical bonding not only in organolanthanide complexes but also for f-element chemistry in general, as well as understanding magnetic interactions in nanoparticles and devices.

Di-µ-hydroxido-κO:O-µ-trifluoro-methane-sulfonato-κO:O'-bis-[(5,5'-dimethyl-2,2-bipyridine-κN,N')(η-penta-methyl-cyclo-penta-dien-yl)ytterbium(III)] tetra-phenyl-borate 5,5'-dimethyl-2,2-bipyridine.

The title compound, [Yb(2)(CF(3)O(3)S)(C(10)H(15))(2)(OH)(2)(C(12)H(12)N(2))(2)](C(24)H(20)B)·C(12)H(12)N(2), crystallizes as a half-sandwich complex with a bridging trifluoro-methane-sulfonate as well as two bridging hydroxide groups. The bound bipyridine ligands have N-C-C-N torsion angles of 13.1 (9) and -12.1 (8)°. The structure also contains an uncoordinated 5,5'-dimethyl-2,2'-bipyridine molecule with an N-C-C-N torsion angle of 169.5 (7)°. The triply bridged Yb centers are 3.5990 (4) Šapart. The Yb-N bond lengths are in the range 2.389 (6)-2.424 (5) Å.

(2,2-Bipyrid-yl)bis-(η-penta-methyl-cyclo-penta-dien-yl)strontium(II).

In the title compound, [Sr(C(10)H(15))(2)(C(10)H(8)N(2))], the Sr-N distances are 2.624 (3) and 2.676 (3) Å, the Sr⋯Cp ring centroid distances are 2.571 and 2.561 Šand the N-C-C-N torsion angle in the bipyridine ligand is -2.2 (4)°. Inter-estingly, the bipyridine ligand is tilted. The angle between the plane defined by the Sr atom and the two bipyridyl N atoms and the plane defined by the 12 atoms of the bipyridine ligand is 10.7 (1)°.