| Abstract |
Four sterically congested and highly electronically unsaturated bis(5-aryl-2-iminopyrrolyl) ML2 complexes of Fe(II) and Co(II), [M\kappa N-2,N-5-(2,6-R-2-C6H3)-NC4H2-2-C(H)=N(2,6-Pr-i(2)-C6H3))(2)] (M = Fe, R = H (1a); M = Fe, R = Me (1b); M = Co, R = H (2a); M = Co, R = Me (2b)), were synthesized by metathetic reaction of the in situ prepared sodium salts of the new 5-aryl-2-(N-2,6-diisopropylformimino)pyrrole HL type ligand precursors (R = H (1a), Me (1b)) with FeCl2 or CoCl2, in moderate to good yields. The four coordinate complexes were characterized by elemental analysis, X-ray diffraction, magnetic susceptibility measurements in solution and in solid state, and Fe-57 Mossbauer spectroscopy. All complexes have a high-spin electronic configuration, as measured both in solution, through the Evans method, and in solid state, through SQUID magnetic measurements, and Mossbauer spectroscopy for the case of Fe(II) complexes, displaying a tetracoordinated distorted tetrahedral coordination geometry about the respective metal center, as elucidated by X-ray diffraction. The inclusion of ortho-methyl groups in the 5-phenyl substituent of the 2-iminopyrrolyl ring in complexes 1b and 2b has an important influence in the structure of the complexes, giving rise to pronounced geometry distortions in particular for 1b. This complex exhibits a see-saw-like geometry whereas a pyramidalization of the pyrrolyl nitrogen is observed for 2b. Overall, the magnetic properties of the complexes can be rationalized by taking into account the effect of the magnetic anisotropy arising from the second-order spin-orbit coupling and the geometrical distortion. The simulation of the magnetic data using a zero-field splitting (ZFS) Hamiltonian led to values of the axial anisotropy, D, that are coherent for Co(II) and Fe(II) tetrahedral complexes, D approximate to -50 cm(-1) (2a, 2b) and 4 cm(-1) (1a). In the case of 1b the simulation evidenced a strong magnetic anisotropy with both axial and rhombic contributions (D approximate to -50 cm(-1), E approximate to 10 cm(-1)) which are in line with the strongly distorted coordination sphere of the complex. (C) 2018 Published by Elsevier Ltd. |
