Curie-Weiss relation

These paramagnetic compounds obey the Curie-Weiss relation down to about 100 K. But the effective magnetic moment of the uranium complex varies from about 3.37 /xb at room temperature to about 2.76 p.B at 87 K. It is always less than the 3.62 /xb expected for simple Russell-Saunders coupling without crystal field effects. 

A new measurement of the magnetic susceptibility of UF3 (166) confirms that it obeys the Curie-Weiss relation over the temperature range 100-300 K and gives a Weiss constant of -12 K compared with earlier values of -98 K (142), -32.2 K (167), and -110 K (168). A lower effective magnetic moment is reported, 3.30 ib, compared with 3.66 (142), 3.50 (167) and 3.62 (168). These differences very probably reflect differences in the purity of the UF3 used (142, 167). 

The magnetic susceptibility of the THF adduct obeys the Curie-Weiss relation in the temperature range 2.5-22 K, with ju-eff = 1.69 /xq, 6 = 2.9, and also in the range 22-55 K with / eff = 1.08 /xb, 6 = 10. It was suggested that a crystal field splitting of the f ground state by about 15 cm" might account for these data (372). 

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