"A new phenomenon which can, under certain circumstances, account for anomalous magnetic and spectral behavior of planar nickel(II) complexes has been discovered. This is a molecular association of the solute molecules in solvents of low coordinating power. It is shown that the magnetic moment and spectrum of bis(2.6-dimethyl1-3,5-heptanediono)nickel(II), Ni(DIBM)z, dissolved in toluene, are dependent upon both temperature and concentration.