Structural characterisation was performed by Rietveld refinements using the GSAS suite of programs. A multiphase refinement was performed to address the 2.5% merlinoite impurity from the hydrothermal synthesis of K-L. The background curve was fitted using a shifted Chebyschev polynomial with 15 coefficients. To reduce the number of refinement parameters, isotropic displacement factors were constrained to be equal for T-atoms (silicon and aluminium), framework oxygens, extra-framework water oxygens and K cations. The refinement of the parent K-L zeolite was modelled on the structure of K + /Na + -L with space group P6/mmm first reported by Barrer (ICSD 18099). The refined structure of K-L was then used as a starting model for refinements of the partially exchanged Li-L and Cs-L zeolites. K + was replaced by Cs + or Li + at each site and their fractional occupancies and crystallographic coordinates were refined. Fourier maps were used to help refine partial occupancies of sites populated with both K + and either Li + or Cs + ions. Extra Li + or Cs + ions were added to the phase structure and tested at these sites by refining their fractional occupancies. This process was repeated until the fit to the data was optimised. Atoms at each of the sites for Cs-L were tested in light of Cs-gallosilicate L reported by Gigli and Lee and Li + positions in light of DFT calculations reported by Meeprasert et al. .