Inducing Ferrimagnetic Exchange in 1D-FeSe2 Chains Using Heteroleptic Amine Complexes: [Fe(en)(tren)][FeSe2]2

[Fe(en)(tren)][FeSe2]2 (en = ethylenediamine, C2H8N2, tren = tris(2-aminoethyl)amine, C6H18N4) has been synthesized by a mixed-ligand solvothermal method. Its crystal structure contains heteroleptic [Fe(en)(tren)]2+ complexes with distorted octahedral coordination, incorporated between 1D-FeSe2 chains composed of edge-sharing FeSe4 tetrahedra. The twisted octahedral coordination environment of the Fe-amine complex leads to partial dimerization of Fe-Fe distances in the FeSe2 chains so that the FeSe4 polyhedra deviate strongly from the regular tetrahedral geometry. 57Fe Mössbauer spectroscopy reveals oxidation states of +3 for the Fechain atoms and +2 for the Fecomplex atoms. The close proximity of Fe atoms in the chains promotes ferromagnetic nearest neighbor interactions, as indicated by a positive Weiss constant, θ = +53.8(6) K, derived from the Curie-Weiss fitting. Magnetometry and heat capacity reveal two consecutive magnetic transitions below 10 K. DFT calculations suggest that the ordering observed at 4 K is due to antiferromagnetic intrachain interactions in the 1D-FeSe2 chains. The combination of two different ligands creates an asymmetric coordination environment that induces changes in the structure of the Fe-Se fragments. This synthetic strategy opens new ways to explore the effects of ligand field strength on the structure of both Fe-amine complexes and surrounding Fe-Se chains.

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.

The new sodium tellurido manganates(II) Na2Mn2Te3, Na2Mn3Te4, Na2 AMnTe3 (A=K, Rb), and NaCsMnTe2

A series of new sodium and mixed Na/A (A = K, Rb, Cs) tellurido manganates have been synthesized from melts of the pure elements (or MnTe) at maximum temperatures of 600–1000°C. The monoclinic crystal structures of the two pure sodium salts Na2Mn2Te3 (space group C2/c, a = 1653.68(2), b = 1482.57(2), c = 773.620(10) pm, β = 117.52°, Z = 8, R1 = 0.0225) and Na2Mn3Te4 (space group C2/m, a = 1701.99(3), b = 438.741(8), c = 691.226(12) pm, β = 90.3171(8)°, Z = 2, R1 = 0.0270) are both based on a hexagonal close packed Te2− arrangement. Na2Mn2Te3 is isotypic with Na2Mn2S3 and Na2Mn2Se3 and contains layers of [MnTe4] tetrahedra, which are connected via common edges to form tetramers [Mn4Te6]. These tetramers are further connected via μ 3-Te atoms. Na2Mn3Te4 crystallizes in a new structure type, recently also reported for the selenido salt Na2Mn3Se4. Mn(2) forms ribbons of vertex-sharing dinuclear units ∞ 1 [ Te 2 / 2 MnTe 2 MnTe 2 / 2 ] $_\infty ^1[{\rm{T}}{{\rm{e}}_{2/2}}{\rm{MnT}}{{\rm{e}}_2}{\rm{MnT}}{{\rm{e}}_{2/2}}]$ running along the short b axis of the monoclinic cell. The Te atoms of these ribbons are also the ligands of edge-sharing [Mn(1)Te6] chains of octahedra. Similar to Na2Mn2Te3, the Na+ cations are octahedrally coordinated and the cations occupy tetrahedral (Mn2+) and octahedral (Na+, Mn2+) voids in the close Te2− packing. The isotypic K/Rb salts Na2 AMnTe3 crystallize in a new structure type (orthorhombic, space group Pmc21, a = 1069.70(4)/1064.34(2), b = 1350.24(5)/1350.47(3), c = 1238.82(4)/1236.94(3) pm, Z = 4, R1 = 0.0445/0.0210). In contrast to the simple formula indicating a Mn(III) compound, the complex structure contains one layer consisting of undulated chains of edge-sharing tetrahedra ∞ 1 [ Mn II Te 4 / 2 ] $_\infty ^1[{\rm{M}}{{\rm{n}}^{{\rm{II}}}}{\rm{T}}{{\rm{e}}_{4/2}}]$ separated by free ditelluride dumbbells [Te2]2− and a second layer containing a complex chain of edge- and vertex-sharing [MnIITe4] tetrahedra, in which Mn(II) is coordinated to μ 1- and μ 2-Te2− ligands and an η 1-ditellurido ligand. The cesium salt NaCsMnTe2 (orthorhombic, space group Cccm, a = 694.21(2), b = 1536.57(4), c = 664.47(2) pm, Z = 4, R1 = 0.0131) likewise forms a new structure type, which is an ordered superstructure of ThCr2Si2. Linear chains ∞ 1 [ MnTe 4 / 2 ] $_\infty ^1[{\rm{MnT}}{{\rm{e}}_{4/2}}]$ of edge-sharing tetrahedra are connected with similar chains ∞ 1 [ NaTe 4 / 2 ] $_\infty ^1[{\rm{NaT}}{{\rm{e}}_{4/2}}]$ to form [NaMnTe2] layers. The larger alkali cations Cs+ between the layers exhibit a cubic (CN = 8) coordination.

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.

Crystal and Magnetic Structures of the Chain Antiferromagnet CaFe4Al8

The crystal structure of CaFe₄Al₈ was studied by X-ray single crystal and powder diffraction as well as high-resolution neutron powder diffraction. CaFe₄Al₈ crystallizes with a tetragonal CeMn₄Al₈-type structure, an ordered variant of the ThMn₁₂-type (Pearson symbol tI26, space group I4/ mmm, a = 8.777(1), c = 5.077(1) Å). Similarly to the well-known A15-type superconductors, the structure of CaFe₄Al₈ contains one-dimensional chains of d-metal atoms, which are parallel to the crystallographic fourfold axis. CaFe₄Al₈ is paramagnetic at room temperature and exhibits long-range antiferromagnetic ordering at about 180 K, combined with a short-range ordered spin arrangement. The magnetic structure, determined by powder neutron diffraction at 4 K, shows that the magnetic moments on the Fe atoms form mirror-inverted chains along the c-direction and are slightly canted from the axis.