Structure and luminescence of extraframework TiCl₆ ²⁻ in Cs⁺-containing zeolite LTA

Octahedral TiCl₆ ²⁻ ions were introduced into zeolite LTA at extraframework positions by allowing TiCl₄(g) to react with dehydrated Cs,Na-A. The structure of the product, Ti,Cl,Cs,Na-A, was determined by single-crystal crystallographic technique in the space group Pm3 ¯ m (a = 12.228(1) Å) and refined to the error index R₁ = 0.046. Its composition was confirmed by energy-dispersive X-ray analysis. Octahedral TiCl₆ ²⁻ ions center 8% of the large cavities. The TiCl₆ ²⁻ ion is stabilized by eight surrounding Cs⁺ ions to form a Cs₈TiCl₆ ⁶⁺ cluster. Each of these Cl⁻ ions bonds further to an 8-ring Cs⁺ ion. These 8-ring Cs⁺ ions bridge between TiCl₆ ²⁻ ions of adjacent unit cells to form a Cs₁₁TiCl₆ ⁹⁺ continuum in the surface volume of the crystal. The X-ray induced luminescence spectrum of the product is a broad band from 360 to 700 nm, peaking at 475 nm. The emission is red-shifted and less intense than those of M,Cl,Cs,Na-A, M = Zr and Hf, but appears to occur by the same self-trapped exciton (STE) mechanism.