Abstract
Each of the following ions with spin S = 3/2, octahedral chromium(III), five-coordinate iron(III), and tetrahedral cobalt(II), possesses a 4 A 2 ground state. The theory describing their paramagnetic properties is therefore the same, though some of the parameters change appreciably from ion to ion. This theory is described along with examples of experimental data. The implications of the paramagnetic properties for the magnetic ordering phenomena exhibited by complexes of these ions are also described.