Mixed Mn/In chalcogenides A 3 ( Mn II In III ) 3 I Q 4 (A = Na, K, Rb, Cs; Q = S, Se, Te)

Highlights: • Eleven new alkali mixed Mn/In chalcogenido metallates A^I₃(Mn^IIIn^III)Q₄ were prepared from melts of the elements/metal chalcogenides. • According to their role as model systems for the mixed-valent ferrate(II,III) analogs, the salts of the heavier alkalis K to Cs crystallize in the Na₃Fe₂S₄-type with undulated chains of edge-sharing [MQ_4/2] tetrahedra. • Na₃InMnSe₄ shows a reduced edge-conntection and exhibits ribbons of vertexsharing dimers (Na₂Mn₃Te₄-type). • The Na sulfido metallate Na₃InMnS₄ finally exhibits only vertex-sharing tetrahedra, specifically two interpenetrating 3D networks of supertetrahedra (β-Ca₃Ga₂N₄-type). • The structure chemistry of the title compounds compares to that of mixed-valent ferrates and the alkaline-earth pentelido trielates A^II₃M₂Pn₄. The series of new mixed chalcogenido metallates A₃^I(MnIn)Q₄ containing Mn^II and In^III in a 1:1 ratio were systematically studied as model systems for the respective structurally diverse mixed-valent ferrate(II,III) analogs. The title compounds were synthesized from stoichiometric melts (T_max=700–1000°C) consisting of elemental chalcogen and indium, the manganese monochalcogenides MnQ, and either the alkali metals themselves or the alkali sulfides Na₂S, Na₂S or Cs₂S₂ (for the sulfides) as starting materials. The K, Rb and Cs salts of all chalcogens form the orthorhombic Na₃Fe₂S₄-type structure uniformly (Pnma, e.g. a=725.50(2), b=1189.63(3), c=1148.76(3) pm, Z=4, R1=0.0194 for A/Q=K/S), which contains buckled chains of edge-sharing tetrahedra. They are thus isotypic to the mixed-valent Na, K and Rb sulfido and selenido ferrates. The coordination numbers (CN) of the two crystallographically different A cations are 6 and 6+1. In contrast, the sodium sulfido metallate Na₃(MnIn)S₄, which is isostructural to Na₃(MnGa)S₄ and crystallizes in the tetragonal β-Ca₃Ga₂N₄-type structure ($I{4}_1/acd$, a=1324.55(4), c=1906.94(7) pm, Z=4, R1=0.0394), has no analog among the ferrates(II/III). The metallate anion consists of supertetrahedra (tetrahedra of corner-sharing tetrahedra) [Mn₂In₂S₆S_4/2]⁶⁻, which are connected via four vertices to form two interpenetrating diamond-like networks. The coordination numbers of the two Na⁺ cations are increased to 4+1 and 6. The sodium selenido salt Na₃(MnIn)Se₄ is isotypic with Na₂Mn₃Te₄ (=Na₂Mn^[6](Mn₂^[4])Te₄; monoclinic, $C2/m$, a=1605.5(2), b=415.64(4), c=671.02(7) pm, β=90.831(7)^∘, Z=2, R1=0.0316) and exhibits dimers of two edge-sharing tetrahedra [M₂Se₆], which are further connected via four vertices to form ribbons running along the short b axis. The Na⁺ CN is further reduced to 4(+2) Q. In accordance with the very similar ionic radii of Mn²⁺ and In³⁺, no superstructures based on Mn/In (which are distinguishable by X-ray diffraction methods) ordering are found. The structure chemistry of the overall eleven new compounds is compared with those of the corresponding mixed-valent ferrates A₃Fe₂^II/IIIQ₄ and the alkaline-earth trielates A₃^II(Al/Ga/In)₂(N/P/As)₄.