A New Polyborate: The Heptaborate Ion in a Silver Icosadiborate.-The crystal structure of Ag2O·11 B2O3·5 en·20 H2O ( III) is determined by single crystal XRD (triclinic, P1, Z = 1). The unit cell contains two heptaborate anions, (B7O9(OH)5)2-, two tetraborate anions, two ethylenediammonium cations, and one ((Hen)+Ag+( en)Ag+(enH)+) cation.-(TIMPER, U.; HELLER, G.