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

Abstract

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 μ3-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 $_\infty ^1[{\rm{T}}{{\rm{e}}_{2/2}}{\rm{MnT}}{{\rm{e}}_2}{\rm{MnT}}{{\rm{e}}_{2/2}}]$ 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 Na2AMnTe3 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 $_\infty ^1[{\rm{M}}{{\rm{n}}^{{\rm{II}}}}{\rm{T}}{{\rm{e}}_{4/2}}]$ 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 μ1- and μ2-Te2− ligands and an η1-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 $_\infty ^1[{\rm{MnT}}{{\rm{e}}_{4/2}}]$ of edge-sharing tetrahedra are connected with similar chains $_\infty ^1[{\rm{NaT}}{{\rm{e}}_{4/2}}]$ to form [NaMnTe2] layers. The larger alkali cations Cs+ between the layers exhibit a cubic (CN = 8) coordination.