Reactions between K 4Ge 9, Ni(CO) 2(PPh 3) 2, and 2,2,2-crypt in ethylenediamine solutions give two different products depending on reaction conditions. The [Ni 6Ge 13(CO) 5] 4− ion ( 1) is formed at low temperatures (∼40 °C) and short reaction times whereas the [Ge 9Ni 2(PPh 3)] 2− ion ( 2) forms at higher temperatures (∼118 °C). Both complexes were isolated as [K(2,2,2-crypt)] + salts and characterized by single-crystal X-ray diffraction, electrospray mass spectrometry (ESI-MS) and NMR studies ( 13C and 31P). 1 has a hypo- closo cluster electron count (Wades Rules) and adopts an interpenetrating biicosahedral structure with 17 vertices and 2 interstitials, which is unique in transition metal Zintl ion clusters. 2 also has a hypo- closo cluster electron count but displays an open, nido-like 10-vertex structure with a Ni interstitial. The composition of 2 was established through ESI-MS studies and corrects an earlier report that characterized the cluster as [Ge 10Ni(PPh 3)] 2− with an interstitial Ge.