Crystal structure and spectroscopic study of 3,3-dimethyl-3,4-dihydroisoquinolyl-1-carbaldehyde oxime

The crystal structure of 3,3-dimethyl-3,4-dihydroisoquinolyl-1-carbaldehyde oxime (I) was determined by X-ray diffraction analysis (Enraf-Nonius CAD-4, MoKα radiation, graphite monochromator, θ/2θ scan mode, 2θmax = 56°, 2927 unique nonzero reflections with 1 ≥ 2σ(I), R = 0.041). Crystals I are monoclinic; a = 9.684(3), b = 12.072(8), and c = 19.166(8) Å; β= 100.08(3)°; sp. gr. P21/c; Z = 8, V = 2201(1) Å3; and ρcalc = 1.334 g/cm3. Compound I crystallizes in the oxime form as an (E)-s-trans isomer in which the exocyclic and cyclic C=N bonds are trans to each other. Two intermolecular hydrogen bonds are formed in the crystal between the oxime groups and the cyclic nitrogen atoms of adjacent molecules. One of the hydrogen bonds links independent molecules into pairs, whereas the other bond interlinks these pairs into slightly pucked ribbons running along the X-axis. Compound I was characterized spectroscopically. It was shown that, in isopropanol solutions, the conformation of I becomes intermediate between (E)-s-cis and (E)-s-trans conformations. The shifts of the long-wavelength bands in the electronic absorption spectra of I upon its reaction with CuCl2 or Co(ClO4)2 (Δλmax ≈ 39-52 nm) indicate the formation of chelate complexes, and the shifts observed upon reaction with Co(II), Fe(III), or Cr(III) chlorides or Ag(I) nitrate (Δλmax ≈ 15-28 nm) suggest the monodentate coordination of I through the cyclic N atom.