Structure of phthalocyaninatocobalt(II) at 4.3 K: a neutron-diffraction study

Abstract

The crystal and molecular structure of the β-polymorphic form of phthalocyaninatocobaIt(II), [Co(pc)], has been determined by single-crystal neutron-diffraction methods at 4.3 K. Crystals are monoclinic, space group P2₁/c, with a= 14.495(5), b= 4.742(4), c= 19.107(5)Å, β= 120.76(2)°, and Z= 2. Automatic diffractometry has provided Bragg intensities for 1 261 independent reflections. Data are of limited resolution along the b axis direction (hkl with k⩽ 2). The structure has been refined by full-matrix least-squares methods to R 0.031. Bond lengths at 4.3 K show systematic deviations from those determined at 295 K by X-ray diffraction data of moderate resolution. This is explained primarily in terms of errors in the X-ray determined atomic positions due to the effects of asphericity of the valence electrons, with thermal motion at 295 K having only a small effect. Within the central cavity of the macrocyclic phthalocyaninate ligand, the cobalt atom co-ordinates to a precisely planar array of nitrogen atoms, with Co–N bond lengths 1.908(2) and 1.915(2)Å at 4.3 K which differ significantly from the values obtained at 295 K by X-ray diffraction. The neutron-scattering length of cobalt has been found by least-squares refinement to be 0.252(7)× 10^–l2 cm.