Andrej Kržan,Peter Kamaras, Michael H. Dickman, DeLanson R. Crist, Vaclav Horák

National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
Georgetown University, Department of Chemistry, Washington D.C. 20057, USA
 

ABSTRACT

Unlike previously reported X-ray structures of ortho quinone monooximes, which exhibit either intramolecular hydrogen bonding or chain-like structures in the solid state, the sterically demanding 4,6-di-tert-butyl-1,2-benzoquinone-2-monooxime (DT) crystallizes as dimers. In crystals from toluene DT forms dimers held together by two hydrogen bonds in a six-membered ring commonly found for simple oximes, but not for ortho quinone monooximes. Crystals from methanol contain DT dimers held together by two bridging methanol molecules, each of which participate in three hydrogen bonds. Although phenolic and quinonoid tautomeric forms of DT coexist in solution, with nonpolar solvents favoring the aromatic phenolic tautomer, both crystals exist in the quinonoid form, independent of the solvent from which they were crystallized. These quinonoid forms are stabilized by intermolecular multi center hydrogen bonds and dipole-dipole interactions countering the effect of the loss of aromatic stabilization. With copper (II) perchlorate, DT yielded crystals of Cu(II)(HL)(L).ClO4, where HL = DT. HL and L ligands are coordinated to Cu(II) in a cis relationship.