Ligand sphere-enhanced magnetic anisotropy in cobalt(II) and manganese(II) 2,6-bis-(benzimidazol-2′-yl)-pyridine dichloride

Temperature variation of the effective magnetic moment for a pentacoordinate [Co(bzimpy)Cl-2] complex shows a pronounced deviation from linearity below 120 K. Quantitative analysis based on the diagonalisation of the spin Hamiltonian matrices gave the set of magnetic parameters: g(x) = 2.501, g(y) = 2.622, g(z) = 1.476, D/hc = 71.7 cm(-1), E/hc = 1.4 cm(-1), alpha(TIP) = 0.98 x 10(-9) m(3) mol(-1) and zJ/hc = -0.184 cm(-1) (SQUID data). The extreme Value of the axial zero-field splitting parameter D shows that the magnetic anisotropy determined by the non-spherical distribution of the spin density is enhanced by the low symmetry of the pentacoordinate chromophore. For the [Mn(bzimpy)Cl-2] . 1/2 MeOH analogue, only a moderate ZFS is found (D/hc = -2.7 cm(-1)). (C) 1999 Elsevier Science B.V. All rights reserved.