Structure and magnetic properties of two bis(nitronyl nitroxide) adducts of bis(hexafluoroacetylacetonato) manganese(II). Molecular orbital interpretation of the coupling in manganese-nitroxide complexes

Two new bis adducts were obtained by reaction of manganese hexafluoroacetylacetonate, Mn(hfac),, with the nitronyl nitroxide ligands 2,4,4,5,5-pentamethyl-4,5-dihydr1oH-- imidazolyl- 1-oxy 3-oxide, NITMe, and 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro- 1H-imidazolyl-1-oxy 3-oxide, NITPh. The X-ray crystal structure showed that Mn(hfac),(NITPh), (11) is monoclinic, space group P2,/c, with a = 12.343 (6) A, b = 15.474 (7) A, c = 22.47 (1) A, p = 100.03 (2)O, and 2 = 4, and Mn(hfac),(NITMe), (I) is monoclinic, space group P2,jn, with a = 17.235 (8) A, b = 17.679 (7) A, c = 11.446 (5) A, (J’ = 90.73 (2)O, nd Z = 4. The magnetic properties of both complexes have been studied by static susceptibility and EPR techniques. The ma. ganese(I1) ions and the radicals are antiferromagnetically coupled, with a ground quartet state. An extended Huckel formalism has been used to establish structural-magnetic correlations in manganese-nitroxide complexes.