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Alkali chalkogenido metalates(II/III)

Subject Area Solid State and Surface Chemistry, Material Synthesis
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 313431712
 
Final Report Year 2025

Final Report Abstract

Within the framework of the project, new mixed-valence alkali metal (A) chalcogenido (Q ) ferrates (II) and (III) were synthesized (mainly from the elements) and characterized crystallographically (single-crystal structure analyses), by bond theory (band structures and molecular DFT) and, in some cases, magnetically and by UV/vis spectroscopy. The substitution of FeII for MnII and of FeIII for (Al/In)III allowed both the preparative control of the mixed-valence state and the investigation of the influence of d-orbital interactions on crystal chemistry and magnetism. The pure metallates(II) and (III) of Fe, Mn, Al, and In were also included in the investigations. The simple A-rich salts with isolated metallate building blocks (A5-6 MQ4 ), dimetallate ions (A6-7 M2 Q6 ), and chain or cluster metallate ions (A1-2 MQ2 ) serve as simple model systems for complex compounds, from the biologically relevant Fe/S clusters to the magnetically complex Fe-based superconductors. The series of A-rich salts with ortho- (isolated [MQ4 ] tetrahedra) and bimetallic ions ([M2 Q6 ] double tetrahedra) were extensively expanded, and crystal-chemical criteria for the partly diverse structural chemistry were developed. The new mixed-valent Na salt Na7 [Fe2 S6 ] not only displays an interesting complex triclinic structure, but also a – for mixed-valent ferrates(II/III) – very unusual FM state with practically pure ’spin-only’ values. The Na salt Na12 [MnInQ6 ][InQ4 ] contains the corresponding heterobimetallic tetrahedral dimer with Mn2+ and In3+ cations. The pure metallates A2 MII Q2 and AFeIII Q2 exhibit linear chains of trans-edge-sharing [MQ4/2 ] tetrahedra (K2 ZnO2 - and KFeS2 -type structure, respectively) as metallate building blocks, while the p-block metallates(III) AAlIII Q2 are dominated by layered structures of T 2 supertetrahedra (KInS2 - type, i.e., pure corner connections). The corresponding salt series were also extensively completed within the scope of the project. The mixed-valence salts A3 M2 Q4 (or generally A1-2 MQ2 ), on the other hand, exhibit a remarkably diverse crystal chemistry: In compounds with chain metallate ions, strong and complex corrugations of the chains occur, with correspondingly large translation periods, up to modulated structures, e.g. in K7.15 [FeS2 ]4. With the complete series A3 [MnAlQ4 ] und A3 [MnInQ4 ] (A=K–Cs, Q =S–Te), and especially with the complex chain in Cs13 [Mn4 Al5 S18 ], the synthesis of heterobimetallic MnII –(Al/In)III model systems was also successful, showing that only the ’odd’ number of A counterions and by no means magnetic effects are responsible for the corrugation of the chains. Only in the case of mixed-valence ferrates with FeII contents between 50 and 75 % (i.e. A6-7 [Fe4 Q8 ]) the present [Fe4 Q8 ](6 – 7) – ’tetrahedra stars’ serve as model systems for the biologically relevant 4Fe4S clusters.

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