[Cd(Sn9)2]6− and [Cd(Ni@Sn9)2]6−: Reactivity and coordination chemistry of empty and Ni-centered [Sn9]4− Zintl ions

To investigate the reactivity of homoatomic clusters [E9]4− (E = Si-Pb) and intermetalloid clusters [M@E9]q−, the reactions of the Zintl anions [Sn9]4− and [Ni@Sn9]4− with the CdMes2 (Mes = Mesitylene) in the presence of 2.2.2-crypt were carried out. Two new compounds [K(2.2.2-crypt)]6[(Sn9)Cd(Sn9)]·en (1) and [K(2.2.2-crypt)]6[(Ni@Sn9)Cd(Ni@Sn9)]·en (2) were afforded. Both 1 and 2 were characterized by single-crystal X-ray diffraction, energy dispersive X-ray (EDX), and electrospray ionization mass spectrometry (ESI-MS), and can be viewed as two [Sn9]4− or [Ni@Sn9]4− subunits bridged by Cd ion in an η3:η3 coordination mode. Quantum chemical calculations reveal the relationships between the geometries and electronic structures of clusters 2a, [Ni3Ge18]4− and [Cu4@Sn18]4−. Further electron localization technique (AdNDP method) was performed to explain chemical bonding patterns of 1a.