Abstract
The series of new mixed chalcogenido metallates A3I(MnIn)Q4 containing MnII and InIII 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 (Tmax = 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 (I41/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) [Mn2In2S6S4/2]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 A3Fe2II/IIIQ4 and the alkaline-earth trielates A3II(Al/Ga/In)2(N/P/As)4.
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