Vol. 77 der we would predict since it represents the order of decreasing diamagnetism. In other words, apparently the diamagnetism of the ligands is significantly retained in the complex and is not quenched.However, as Proctor and Yu suggest, the mere diamagnetic effect is not large enough to explain these large shifts in resonance frequency. Instead, these authors are led to assume "the existence of electronic energy levels very close to that of the ground state" an assumption which is justified by a temperature dependence16 of the resonant frequency. These low lying electronic energy levels correspond, as Ramsey points out,17 to those encountered in Van Vleck's second order paramagnetism.In the case of the pentammine complexes meas-( 17) N. F. Ramsey, Phys. Rev., 86, 245 (1952).ured in this work, we can therefore account for the high "residual paramagnetism" by assuming low lying excited states. In going from the nitro complex to the formato complex, it will not be surprising to find an appreciable change in magnetic moment since the magnetic susceptibility depends not only on the nature of the excited state but also on its symmetry. The symmetry may be particularly important since the orbital quenching of the moment in the excited state is very sensitive to the electrical symmetry in the complex. Measurements on the nuclear magnetic resonance of cobalt in these complexes would be of great interest as also would be a study of the temperature dependence of both the magnetic susceptibility and the nuclear resonance shift.
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