1. Institute for Inorganic Chemistry, University of Bonn, Gerhard‐Domagk‐Str. 1, 53121 Bonn, Germany, Fax: +49‐228‐73‐5660
2. Universidade Federal de Santa Maria, Departamento de Química, Caixa Postal 5031, 97.105‐970 Santa Maria, RS, Brazil, Fax: +55‐3220‐8031