Novel associations of ortho quinone monooximes: Hydrogen bonded dimers of 4,6-di-tert-butyl-1,2-benzoquinone-2-monooxime

Unlike previously reported X-ray structures of ortho quinone monooximes, wh ich exhibit either intramolecular hydrogen bonding or chain-like structures in the solid state, the sterically demanding 4,6-di-tert-butyl-1,2-benzoqu inone-2-monooxime (DT) crystallizes as dimers. In crystals from toluene DT forms dimers held together by two hydrogen bonds in a six-membered ring com monly found for simple oximes, but not for orhto quinone monooximes. Crysta ls from methanol contain DT dimers held together by two bridging mehtanol m olecules, each of which participate in three hydrogen bonds. Although pheno lic and quinonoid tautomeric forms of DT coexist in solution, with nonpolar solvents favoring the aromatic phenolic tautomer, both crystals exist in t he quinonoid form, independent of the solvent from which they were crystall ized. These quinonoid forms are stabilized by intermolecular multi center h ydrogen bonds and dipole-dipole interactions countering the effect of the l oss of aromatic stabilization. With copper (II) perchlorate, DT yielded cry stals of Cu(II)(HL)(L)CLO4, where HL=DT. HL and L ligands are coordinated t o Cu(II) in a cis relationship.