RESONANCE INTERACTIONS IN METAL-CHELATES OF O-HYDROXYAZO COMPOUNDS - CRYSTAL-GROWTH, STRUCTURE, AND SPECTRA OF 1-(2-PYRIDYLAZO)-2-NAPHTHOLATOCHLOROCOPPER(II)

Single crystals of the title compound have been grown by a modified gel diffusion technique. The compound crystallizes in the monoclinic system, space group P21/a, with a=15.817 (3) Å, b=8.255 (1)Å, c=10.404 (3) Å, β=103.46 (2)°, V=1321.1 (5) Å3, Z=4, dcalcd=1.746 g cm-3-dmeas=1.71 g cm-3. Intensities were collected by counter methods on a cardcontrolled diffractometer operating in the θ-2θ mode and employing Mo Kα radiation. The structure, including hydrogen atoms, was solved by the heavy-atom method and refined by full-matrix least squares to R1=0.031 and R2=0.040. The pyridylazonaphthol ligand (PAN) coordinates to copper as a planar tridentate chelate with strong covalent bonds through the pyridyl nitrogen (1.991 (2) Å), the azo nitrogen adjacent to the naphthol group (1.964 (2) Å), and the naphthol oxygen (1.984 (2) Å). In the fourth position of an approximately square planar array about copper is found a strongly bound chloride ion (2.263 (1) Å). Pairs of these Cu(PAN)Cl units combine to form a centrosymmetric dimer through weak bridging Cu-Cl bonds (2.647 (1) Å) in the axial or fifth coordination site. The net coordination around copper is approximately square pyramidal, with the copper displaced 0.145 Å from the equatorial plane toward the axial chlorine atom. The possibility for delocalization of electron density in anions of o-hydroxyazo compounds is discussed. The bond lengths observed in the ligand in Cu(PAN)Cl agree well with those predicted for a resonance hybrid involving roughly equal contributions from 12 canonical structures. Qualitative single-crystal polarized reflectance measurements indicate possible directions for the molecular transition moments. © 1978, American Chemical Society. All rights reserved.