emperature independent paramagnetism
Compounds which are expected to be diamagnetic may exhibit this kind of weak paramagnetism. It arises from a second-order Zeeman effect in which additional splitting, proportional to the square of the field strength, occurs. It is difficult to observe as the compound inevitably also interacts with the magnetic field in the diamagnetic sense. Nevertheless, data are available for the permanganate ion. It is easier to observe in compounds of the heavier elements, such as uranyl compounds.
The temperature-independent paramagnetism of permanganate is discussed in terms of molecular orbital theory. It is shown that the major contribution to the paramagnetism arises from electrons in metal d orbitals, and that the amount of charge-transfer from the ligands to the metal ion can be estimated. The theory is applicable to any complex in which the metal ion possesses vacant low-lying d orbitals.