Spin density and cobalt electronic structure in phthalocyaninatocobalt(II): a polarised neutron diffraction study

Abstract

The collection of polarised neutron diffraction data for β-phthalocyaninatocobalt(II), [Co(pc)](CoII, S=½), is described. Flipping ratios for 145 and 337 Bragg reflections were observed at 4.2 K and at magnetic field strengths of 1.49 and 4.6 T respectively. By use of the 4.2 K neutron diffraction nuclear structural data, these were converted into magnetic structure factors FM(hkl). A model of the spin distribution in [Co(pc)] was considered, employing the 3d and diffuse 4s-type orbitals of cobalt, and orbitals of the inner-ring nitrogen and carbon atoms of the ligand macrocycle. The spin populations of these orbitals were refined by a least-squares procedure which fitted calculated to observed magnetic structure factors. The spin populations 3dxz0.40(10), dxz,yz0.17(10), dz20.79(12), dx2–y2–0.21(10), ‘4s’–0.14(6) were found, together with a total populations of –0.17(5) spin on the macrocycle N and C atoms. The cobalt orbital electronic populations deduced are thus 3dxy1.60, dxz1.83, dz21.21, dx2–y20.21 together with either ‘4s’0.14 or ‘4s’1.86. The above orbital populations, except for the dxy case, are in reasonable concordance with knowledge of the electronic structure of the Co2+ ion, particularly when spin–orbit coupling is considered. However, the negative ligand spin densities which must arise through spin polarisation effects are in some conflict with the 1H n.m.r. contact shift deductions. The magnetic moment per cobalt atom, along the b axis, 〈µb〉, at 4.6 T, is determined to be 0.55 B.M. (1 B.M. = 9.274 × 10–24 A m2).