Synthesis and Structural Studies of Two New Base Adducts of Bis(2,4‐pentanedionato)cobalt( II )

The syntheses, spectroscopic properties and crystal structures of two new base adducts of bis(2,4‐pentanedionato)cobalt( II ) with 3,5‐dimethylpyrazole (Hdmpz) ( 1 ) and dimethylethanolamine (Hdmea) ( 2 ) are described. The crystal structures of both compounds contain monomeric Co II complexes with cis ‐distorted octahedral environments, even for the monodentate Hdmpz ligand which is quite unique. These mononuclear complexes are linked by hydrogen bonds between the anionic 2,4‐pentanedionato groups and the neutral Hdmpz or Hdmea ligands. The low‐temperature polycrystalline‐powder EPR spectra display unresolved metal hyperfine coupling. The g values are anisotropic in both cases; the anisotropy is larger for the Hdmea adduct. Interesting insights into the coordination effects were gained with the help of electron‐density descriptors (Laplacian of density and Natural Bond Orbitals). This revealed a slight deviation of the coordinating lone pairs of the pentanedionato ligands from the Co−O axis, as well as a nonstandard hybrid composition. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)