[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.