New deintercalation reaction of calcium from calcium disilicide. Synthesis of layered polysilane

Deintercalation of calcium from the interlayer of CaSi2 was performed by using concentrated HCl solutions at low temperatures, 0 and −30 °C. In the reaction at 0 °C, the deintercalation took place in two steps with evolution of 12 mole of hydrogen per mole of CaSi2 in each step. In the reaction at −30 °C, little evolution of hydrogen was observed. The quantitative chemical analysis, infrared and X-ray photoelectron spectroscopies, and X-ray powder diffraction measurements revealed that the solid obtained by the reaction at −30 °C was a non-oxidized layered polysilane (Si6H6)n with incorporation of chlorine in a molar ratio of ClSi = 16. The optical band gap of the layered polysilane was measured to be 2.4 eV. The deintercalation was topotactic, and the layered polysilane reverted to Si platelet crystals on heating at 900 °C in vacuum.