Synthesis and Properties of Ba6Fe2Te3S7, with an Fe Dimer in a Magnetic Singlet State

A new quaternary sulfide telluride, Ba6Fe2Te3S7, was synthesized by a solid-state reaction, and its crystal structure is novel. X-ray diffraction data on powder and single crystals reveal an orthorhombic lattice with a = 9.7543(3) Å, b = 18.2766(6) Å, and c = 12.0549(4) Å, and the noncentrosymmetric space group Cmc21 (No. 36). The properties of the compound were studied by magnetic susceptibility investigations, specific heat measurements, Mössbauer spectroscopy, and density functional theory calculations. Assuming Ba2+ and, as verified by the Mössbauer spectra, Fe3+, the charge balance requires the presence of a polytelluride, suggested to be a straight-chain [Te34-] polyanion. Further, the crystal structure contains [Fe2S7]8- dimers of two vertex-sharing tetrahedra, with a nearly linear Fe-S-Fe atom arrangement. The dimer exhibits antiferromagnetic coupling, with a coupling constant J = -10.5 meV (H = -2JS1S2) and S = 5/2, resulting in a spin singlet ground state. The interdimer magnetic interaction is so weak that the magnetic dimers can be treated as individuals.

New sodium-rich mixed Mn/In chalcogenido metallates Na 12 MnIn 2 Q 10 (Q = S, Se)

The sodium-rich sulfido and selenido metallates Na12MnIn2 Q 10 (Q = S/Se) were synthesized in pure phase from melts composed of stoichiometric quantities of the manganese monochalcogenides MnQ, elemental indium and the chalcogens together with either Na2S (Q = S) or elemental sodium (Q = Se) as starting material. The samples were heated up to maximum temperatures of 1000/900 °C under an argon atmosphere; crystallization was achieved by slow cooling rates of 10 K h−1. The two isotypic compounds (monoclinic, space group P21/m, a = 678.26(2)/698.85(10), b = 2202.77(7)/2298.7(3), c = 766.39(3)/800.59(13) pm, β = 90.232(2)/90.147(5)°, Z = 2, R1 = 0.0516/0.0575) crystallize in a new structure type. According to the division of the formula as Na12[InQ 4][MnInQ 6] the salts contain ortho indate anions [InIII Q 4]5− besides hetero-bimetallic dimers [MnIIInIII Q 6]7−, which consist of two edge-sharing [MQ 4] tetrahedra. The seven crystallographically different sodium cations exhibit an either tetrahedral or octahedral coordination by the chalcogen atoms. Thus, the overall structure of the salt is best described by a hexagonal close packing of the sulfide/selenide anions, in which the octahedral voids of every second interlayer section are fully occupied by the (overall 5/f.u.) Na + positions with CN = 6. In the other half of the interlayer sheets, all tetrahedral voids (overall 10/f.u.) are occupied by the seven CN = 4 Na + cations, one In3+ of the ortho anion and the two Mn2+/In3+ cations (which statistically occupy one crystallographic site). This structure relation is also verified by a Bärnighausen group-subgroup tree connecting the h.c.p. (Mg type) aristotype (with its tetrahedral and octahedral voids) by an overall index of 60 with the structure of the two title compounds.

New mixed-valent alkali chain sulfido ferrates A 1+x [FeS2] (A = K, Rb, Cs; x = 0.333–0.787)

Four new mixed-valent chain alkali metal (A) sulfido ferrates of the general structure family A 1 + x Fe x II Fe 1 − x III S 2 ${A}_{1+x}\left[{\text{Fe}}_{x}^{\text{II}}{\text{Fe}}_{1-x}^{\text{III}}{\text{S}}_{2}\right]$ were synthesized in the form of tiny green-metallic needles from nearly stoichiometric melts reacting elemental potassium with natural pyrite (A = K) or previously prepared Rb2S/Cs2S2 with elemental iron and sulfur (A = Rb/Cs). The crystal structures of the compounds were determined by means of single crystal X-ray diffraction: In the (3+1)D modulated structure of K7.15[FeS2]4 (space group Ccce(00σ 3)0s0, a = 1363.87(5), b = 2487.23(13), c = 583.47(3) pm, q = 0,0,0.444, R1 = 0.055/0.148, x = 0.787), a position modulation of the two crystallographically different undulated [ FeS 4 / 2 ] ∞ 1 ${}_{\infty }{}^{1}\left[{\text{FeS}}_{4/2}\right]$ tetrahedra chains and the surrounding K cations is associated with an occupation modulation of one of the three potassium sites. In the case of the new monoclinic rubidium ferrate Rb4[FeS2]3 (x =  1 3 $\frac{1}{3}$ ; space group P21/c, a = 1640.49(12), b = 1191.94(9), c = 743.33(6) pm, β = 94.759(4)°, Z = 4, R1 = 0.1184) the undulation of the tetrahedra chain is commensurate, the repetition unit consists of six tetrahedra. In the second new Rb ferrate, Rb7[FeS2]5 (x = 0.4; monoclinic, space group C2/c, K7[FeS2]5-type; a = 2833.9(2), b = 1197.36(9), c = 744.63(6) pm, β = 103.233(4)°, Z = 4, R1 = 0.1474) and its isotypic mixed Rb/Cs-analog Rb3.6Cs3.4[FeS2]5 (a = 2843.57(5), b = 1226.47(2), c = 759.890(10) pm, β = 103.7170(9)°, R1 = 0.0376) the chain buckling leads to a further increased repetition unit of 10 tetrahedra. For all mixed-valent ferrates, the Fe–S bond lengths continuously increase with the amount (x) of Fe(II). The buckling of the chains is controlled through the local coordination of the S atoms by the variable number of A cations of different sizes.

Alkali chalcogenido ortho manganates(II) A 6MnQ 4 (A=Rb, Cs; Q=S, Se, Te)

The six isotypic alkali ortho chalcogenido manganates A 6[MnII Q 4] (A=Rb, Cs; Q=S, Se, Te) were synthesized – in most cases in pure phase – from stoichiometric mixtures of the manganese monochalcogenides MnQ, the elemental chalcogens and Rb2S/Cs2S2 (sulfido salts) or the pure alkali elements (selenido and tellurido salts) as alkali sources at maximum temperatures between 650 and 800°C. Their hexagonal crystal structures were refined by means of X-ray single crystal data (space group P63 mc, Na6ZnO4-type structure, Z=2; A/Q: Rb/S: a=1019.34(2), c=792.560(10) pm, R1=0.0166; Rb/Se: a=1055.74(2), c=821.14(2) pm, R1=0.0275; Rb/Te: a=1126.68(2), c=860.54(2) pm, R1=0.0152; Cs/S: a=1056.68(2), c=831.22(2) pm, R1=0.0168; Cs/Se: a=1096.04(3), c=858.13(2) pm, R1=0.0194; and Cs/Te: a=1167.72(3), c=896.95(2) pm, R1=0.0140). The chiral structures contain isolated C 3 symmetric, but very close to ideal tetrahedral, ortho manganate(II) anions [MnII Q 4]6− with Mn–Q distances of 248.7–250.7 (Q=S), 260.7–263.0 (Q=Se) and 280.0–282.4 pm (Q=Te). The chalcogenide ions form a hexagonal closed packing with slightly puckered 36 nets, in which the A(2) cations occupy 3/4 of the octahedral interstices, whereas Mn takes 1/8 and A(1) 3/8 of the tetrahedral voids. Magnetic measurements on the three Cs compounds showed Curie-Weiss behavior down to a temperature of 1.9 K, with magnetic moments significantly reduced with respect to the expected spin-only value of a d 5 ion. The electronic band structures of the four salts (Na/Rb)6Mn(S/Te)4, which were calculated within the GGA+U approach, allow a comparison of the chemical bonding characteristics and the magnetic properties within the alkali cation and the chalcogenido ligand series.