Spin density and manganese electronic structure in phthalocyaninatomanganese(II)

Abstract

The collection of polarised neutron diffraction data for ferromagnetic (Tc= 8.6 K)β-phthalocyaninatomanganese(II), [Mn(pc)](MnII, S=), is described. Flipping ratios for 552 unique Bragg reflections were observed at 4.2 K and at a magnetic field strength of 1.49 T applied along the b crystal axis direction. These were used, together with the 5.8 K neutron diffraction nuclear structural data, to refine by a least-squares procedure a model of the spin-density distribution in the [Mn(pc)] crystal. The magnetic moments on the two [Mn(pc)] molecules in the monoclinic cell lie approximately perpendicular to the planes of the molecules. The molecules pack in a ‘herringbone’ fashion, with each molecular plane inclined at ca. 45° to the monoclinic b axis. The orientation of the magnetic moments has been described in terms of two refineable angles ρ and ψ. The angle that the magnetic moment makes with the b axis, ρ, is 37.3(7)° and ψ, the angle the projection of the moment onto the ac plane makes with the a axis, is –40.3(11)° measured in a clockwise sense towards the c axis. The model of the spin-density distribution also employed the 3d and diffuse 4s-type orbitals of manganese, and orbitals of the inner-ring nitrogen and carbon atoms of the macrocyclic ligand. The manganese spin populations 3dxy0.74(6), 3dxz, yz1.17(6), 3dz20.83(6), 3dx2–y2–0.15(6), ‘4s’–0.44(6) were found, together with a total population of –0.31 (3) spin on the macrocycle N and C atoms. The manganese orbital electronic populations deduced are thus 3dxy1.26, 3dxy1.0, 3dyz1.0, 3dz20.83,3dx2–y20.15, ‘4s’1.56. These orbital populations are shwon to be in reasonable agreement with the predictions of an angular overlap ligand-field model treatment, and with those populations determined from an X-ray diffraction analysis of [Mn(pc)] at 116 K. The observed negative ligand spin densities, which must arise through spin polarisation effects, are in concordance with the results of a polarised neutron diffraction analysis of [Co(pc)].