[Ni5Sb17]4- transition-metal zintl ion complex:: Crossing the zintl border in molecular intermetalloid clusters

K3Sb7 and Ni(COD)(2) react in the presence of 2,2,2-cryptand in ethylenediamine solutions (similar to 1:8 Ni/Sb molar ratio) to give dark-brown crystals of the paramagnetic cluster anion [Ni5Sb17](4-) as the [K(2,2,2-crypt)](+) salt. The cluster has a Ni(cyclo-Ni4Sb4) ring unit that sits inside a Sb-13 bowl. The structure is similar to that of the previously reported [Pd7As16](4-) ion containing a Pd(cyclo-Pd4As4) ring unit that sits inside a Pd2As12 bowl. Density functional theory and bond valence analyses suggest delocalized charge distributions and intermetallic-like properties.