[(η2-(Si/Ge)4)Zn(η2-(Si/Ge)4)]6– – mixed silicon and germanium tetrahedra bridged by a zinc atom

Thomas Fässler and colleagues at Technische Universität München have recently reported the synthesis and structural characterisation of a novel Zn-bridged dimer of tetrahedral Zintl clusters.

 
The reaction of the ternary Zintl phase K₁₂Si₁₂Ge₅ with Zn(C₆H₅)₂ in liquid ammonia and in the presence of the sequestering agent 2,2,2-crypt yielded crystals of composition K₆ZnSi_4.7Ge_3.3(NH₃)₁₁, which were found to contain [(η²-E₄)Zn(η²-E₄)]^6– ions (E = Si/Ge). These cluster anions consist of two [E₄]^4– tetrahedra bridged by a Zn²⁺ ion.

[(η²-E₄)Zn(η²-E₄)]^6–.

The two Zn-coordinated edges are twisted by approximately 90 ° relative to each other. The Si atoms were found to preferentially occupy the positions coordinated to Zn; the Si occupancies of these positions were found to vary between 68 and 82%, while those of the non-coordinated positions were in the range 36-53%.

Zn-bridged dimers of tetrahedral Zintl clusters have been previously observed in Cs₆Ge₈Zn, which was synthesised in the solid state by Slavi Sevov and co-workers, however [(η²-E₄)Zn(η²-E₄)]^6– is the first metal-bridged dimer to be obtained from solution. Fässler and colleagues hope that this research could potentially open up variable routes to mixed semiconducting nanomaterials.