Nickel oxides have been widely used for electrochromic anodes for the last decades. They give relatively neutral and thus favorable coloration but have some practical problems: dark residual coloration after deposition either by EB deposition or sputtering, dissolution in the organic electrolytes, and lower charge capacity. As optical and electrochemical properties of crystalline NiO were well approximated by the cluster ([Ni6O19](26-)), the model clusters, [Ni5Mz+O19]((28-z)-) (M = 3 d, 4d, and 5d transition metals), were constructed and examined using molecular orbital (MO) calculations. The main objective of this paper is to analyze the molecular properties of partially substituted nickel oxide clusters [Ni5Mz+O19]((28-z)-) and to elucidate their optical characteristics. (C) 2003 Elsevier B.V. All tights reserved.