Crystallization of the Fundamental Tetracyanamidometallates Li4[Si(CN2)4] and Li4[Ge(CN2)4] from Polymeric Li-T-(NCN)-I Precursors (T=Si, Ge)

The tetracyanamidometallates Li-4[T(CN2)(4)] with T=Si, Ge were prepared by solid-state metathesis (SSM) reactions between TI4 and Li-2(CN2). The new compounds Li-4[T(CN2)(4)] are obtained as crystalline phases in high yields and represent the most basic examples of the family of tetracyanamidometallates. The formation of these compounds, via SiI4 and Li-2(CN2), is analyzed by means of differential scanning calorimetry (DSC). The [Si(CN2)(4)](4-) ion in the structure of Li-4[Si(CN2)(4)] can be considered an analogue to the [SiO4](4-) ion in Li4SiO4. The crystal structures of Li-4[T(CN2)(4)] were solved and refined isotypically on the basis of single-crystal X-ray diffraction data in the space group C2/c, and further characterized by infrared and solid-state NMR techniques.