Structure and luminescence of extraframework TiCl62− in Cs+-containing zeolite LTA

Octahedral TiCl62− 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 \(Pm\bar {3}m\) (a = 12.228(1) A) and refined to the error index R1 = 0.046. Its composition was confirmed by energy-dispersive X-ray analysis. Octahedral TiCl62− ions center 8% of the large cavities. The TiCl62− ion is stabilized by eight surrounding Cs+ ions to form a Cs8TiCl66+ cluster. Each of these Cl− ions bonds further to an 8-ring Cs+ ion. These 8-ring Cs+ ions bridge between TiCl62− ions of adjacent unit cells to form a Cs11TiCl69+ 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.