1. Contribution from Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Acad. Lavrentiev Prosp., 630090 Novosibirsk, Russia, and Institut für Radiopharmazie and Institut für Radiochemie, Forschungszentrum Dresden-Rossendorf, PF 510119, 01314 Dresden, Germany