(NH4)(2)Ge7O15 is the first microporous material containing nine-rings constituted by tetrahedral and octahedral germanium species. Its channel structure is characterized by a nine-ring channel running along the [001] direction. These channels are lined forming cages which are capped by six-rings giving rise to smaller tunnels in [110] [010] directions. Two, related by inversion center, NH4+ cations are housed in each cage bonded to several oxygen atoms of the framework through hydrogen bonds. The paper reports the full structural data as well as thermal stability conditions and the first catalytic essays. (C) 1999 Elsevier Science Ltd. All rights reserved.