Kaliophilite structure determination highlighted in Science!
Pisa, 19/01/2021 The paper by Mugnaioli et al. published on IUCrJ on the crystal structure determination of Kaliophilite mineral, unknown since 180 years, has been highlighted in the “Editor Choice” of Science as a remarkable achievement of mineralogy. The existence of kaliophilite was attested in 1839, at the dawn of modern mineralogy. Despite the seemingly simple formula KAlSiO4 and a well-defined diffraction signal, the structure of this porous mineral could not be determined in more than one century of x-ray crystallography. The difficulty derives from the huge asymmetric unit of kaliophilite, which ranks among the twenty most complex minerals known so far, and from a complex tangle of pseudo-symmetries and twinning. The long-lasting riddle was finally solved by Mugnaioli et al., which applied cutting-edge 3D electron diffraction protocols developed by the Electron Crystallography research line at CNI@NEST and succeeded in the acquisition of structural data from coherent kaliophilite domains of few hundreds of nanometers. Once the correct crystalline class and an ab-initio model were attained, kaliophilite structure could be refined using high-quality single-crystal x-ray data. The topology of kaliophilite revealed particularly complex, because comprises three different types of 6-tetrahedra rings, a feature never observed in either natural or synthetic frameworks. Thus, the existence of kaliophilite structure poses unforeseen challenges and perspectives in the design of material for catalysis, photonics and green chemistry.