Description:
<jats:title>Abstract</jats:title><jats:p>A multi-methodological study of the (K,Ca)-variety of the zeolite merlinoite from Fosso Attici, Sacrofano, Italy was carried out on the basis of electron microprobe analysis in wavelength dispersive mode, singlecrystal X-ray diffraction (at 100 K), Raman and infrared spectroscopy. Thechemical formula of the merlinoite from Fosso Attici is (Na<jats:sub>0.37</jats:sub>K<jats:sub>5.69</jats:sub>)<jats:sub>Σ=6.06</jats:sub>(Mg<jats:sub>0.01</jats:sub>Ca<jats:sub>1.93</jats:sub>Ba<jats:sub>0.40</jats:sub>)<jats:sub>Σ=2.34</jats:sub>(Fe<jats:sub>0.02</jats:sub><jats:sup>3+</jats:sup>Al<jats:sub>10.55</jats:sub>Si<jats:sub>21.38</jats:sub>)<jats:sub>Σ=31.9</jats:sub>O<jats:sub>64</jats:sub>·19.6H<jats:sub>2</jats:sub>O,compatible with the ideal chemical formula K<jats:sub>6</jats:sub>Ca<jats:sub>2</jats:sub>[Al<jats:sub>10</jats:sub>Si<jats:sub>22</jats:sub>O<jats:sub>64</jats:sub>]·20H<jats:sub>2</jats:sub>O.</jats:p><jats:p>Anisotropic structure refinements confirmed the symmetry and the framework model previously reported (space group <jats:italic>Immm</jats:italic>, <jats:italic>a</jats:italic> = 14.066(5),<jats:italic>b</jats:italic> = 14.111(5), <jats:italic>c</jats:italic> = 9.943(3) Å at 100 K). Refinement converged with four cationic sites and six H<jats:sub>2</jats:sub>O sites; refined bond distances of the framework tetrahedra suggest a highly disordered Si/Al-distribution. The Raman spectrum of merlinoite (collected between 100and 4000 cm<jats:sup>–1</jats:sup>) is dominated by a doublet of bands between 496–422 cm<jats:sup>–1</jats:sup>, assigned to tetrahedral T–O–T symmetric bending modes. T–O–T antisymmetric stretching is also observed; stretching and bending modes of the H<jats:sub>2</jats:sub>Omolecules are only clearly visible when using a blue laser. The single-crystal near-infrared spectrum shows a very weak band at 6823 cm<jats:sup>–1</jats:sup>, assigned to the first overtone of the O–H stretching mode, and a band at 5209 cm<jats:sup>–1</jats:sup>, due to the combination of H<jats:sub>2</jats:sub>Ostretching and bending modes. Avery broad and convoluted absorption, extending from 3700 to 3000 cm<jats:sup>–1</jats:sup> occurs in the H<jats:sub>2</jats:sub>O stretching region, while the ν2 bending mode of H<jats:sub>2</jats:sub>O is found at 1649 cm<jats:sup>–1</jats:sup>. The powder mid-infraredspectrum of merlinoite between 400–1300 cm<jats:sup>–1</jats:sup> is dominated by tetrahedral T–O–T symmetric and antisymmetric stretches. Raman and Fourier-transform infrared spectroscopy spectra of merlinoite and phillipsite provide a quick identification tool for these zeolites,which are often confused due to their close similarity.</jats:p>