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NAtrium SuperIonic CONductor (NASICON) structured phosphate framework compounds are attracting a great deal of interest as suitable electrode materials for "rocking chair" type batteries. Manganese-based electrode materials are among the most favored due to their superior stability, resource non-criticality, and high electrode potentials. Although a large share of research was devoted to Mn-based oxides for Li- and Na-ion batteries, the understanding of thermodynamics and phase formation in Mn-rich polyanions is still generally lacking. In this study, we investigate a bifunctional Na-ion battery electrode system based on NASICON-structured Na 1+2 x Mn x Ti 2- x (PO 4 ) 3 (0.0 ≤ x ≤ 1.5). In order to analyze the thermodynamic and phase formation properties, we construct a composition-temperature phase diagram using a computational sampling by density functional theory, cluster expansion, and semi-grand canonical Monte Carlo methods. The results indicate finite thermodynamic limits of possible Mn concentrations in this system, which are primarily determined by the phase separation into stoichiometric Na 3 MnTi(PO 4 ) 3 ( x = 1.0) and NaTi 2 (PO 4 ) 3 for x < 1.0 or NaMnPO 4 for x > 1.0. The theoretical predictions are corroborated by experiments obtained using X-ray diffraction and Raman spectroscopy on solid-state and sol-gel prepared samples. The results confirm that this system does not show a solid solution type behavior but phase-separates into thermodynamically more stable sodium ordered monoclinic α-Na 3 MnTi(PO 4 ) 3 (space group C 2) and other phases. In addition to sodium ordering, the anti-bonding character of the Mn-O bond as compared to Ti-O is suggested as another important factor governing the stability of Mn-based NASICONs. We believe that these results will not only clarify some important questions regarding the thermodynamic properties of NASICON frameworks but will also be helpful for a more general understanding of polyanionic systems., Competing Interests: The authors declare no competing financial interest., (© 2021 American Chemical Society.)

We report on the synthesis and self-assembly study of novel supramolecular monomers encompassing quadruple hydrogen-bonding motifs and metal-coordinating 2,2'-bipyridine units. When mixed with metal ions such as Fe 2+ or Zn 2+ , the tetrahedron cage complexes are formed in quantitative yields and full diastereoselectivity, even in highly polar acetonitrile or methanol solvents. The symmetry of the complexes obtained has been shown to depend critically on the flexibility of the ligand. Restriction of the rotation of the hydrogen-bonding unit with respect to the metal-coordinating site results in a T -symmetric cage, whereas introducing flexibility either through a methylene linker or rotating benzene ring allows the formation of S 4 -symmetric cages with self-filled interior. In addition, the possibility to select between tetrahedral cages or helicates and to control the dimensions of the aggregate has been demonstrated with a three-component assembly using external hydrogen-bonding molecular inserts or by varying the radius of the metal ion (Hg 2+ vs Fe 2+ ). Self-sorting studies of individual Fe 2+ complexes with ligands of different sizes revealed their inertness toward ligand scrambling.