MAGNETISM AND ELECTRONIC-STRUCTURE OF A SERIES OF ENCAPSULATED 1ST-ROW TRANSITION-METALS

The temperature dependence of the magnetic susceptibility (4.2-300 K) is reported for a series of crystalline salts of first-row transition-metal ions encapsulated by hexaamine ligands of the sar type, namely, [M(sar)]n+, where sar = 3,6,10,13,16,19-hex-aazabicyclo[6.6.6]icosane, or [M((X,Y)sar)],n+, where X = Y = 1,8-NH21,8-NH3.+or X = 1-CH3, Y = 8-H. The cage complexes of Fe111, Co111, and Ni111all exhibit low-spin ground states [of2T2gand1A1g(Oh) and2A1g(D4h) origin] whereas that of Mnm is high-spin [5A,1gor5B1g(D4h)]. The complexes of Mn11, Co11, and Ni11are high-spin [of6A1g,4T1g, and3A2g(0*) origin], but surprisingly, those of Fe11 exhibit either a low-spin (1A1g) or a high-spin (5T2g) ground state depending on the nature of the apical substituent and the lattice. Clearly, the magnitude of the ligand field parameters (10Dq and B)+generated by these saturated macrobicycles for the 3d6Fe11is that required for the high-spin/low-spin crossover for six saturated amine ligands. The ground states for Viv(2T2g), V111(3T1g), Cr111(4A2g), Cu11(2B1gin D4h), and Zn11(1A1g) appear to be unambiguous. The magnitude of the zero-field-splitting parameter has been estimated from the low-temperature x(T) data for the Cr111and high-spin Mn111, Mn11, Fe11, Co11, and Ni11cage complexes. The low-spin (2Egorigin) state for Co11is stabilized by the (aza)capten ligand because of the larger nephelauxetic effect of sulfur combined with appreciable Jahn-Teller splitting of the2E3ground state. The magnetic properties in general reflect the reduction in symmetry observed crystallographically for the individual metal ions. © 1990, American Chemical Society. All rights reserved.