1. Laboratory of Inorganic Chemistry, Department of Chemistry, P.O. Box 55, and Accelerator Laboratory, P.O. Box 43, FIN-00014, University of Helsinki, Helsinki, Finland, Department of Chemistry, University of Liverpool, Liverpool L69 3ZD, U.K., and Epichem Oxides and Nitrides, Power Road, Bromborough, Wirral, Merseyside CH62 3QF, U.K.