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

Abstract

The six isotypic alkali ortho chalcogenido manganates A6[MnIIQ4] (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 P63mc, 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 C3 symmetric, but very close to ideal tetrahedral, ortho manganate(II) anions [MnIIQ4]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 d5 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.

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

“…They are shorter than the sum of Shannons radii (287 pm,[39]), but similar to the values found in other tellurido manganates(II), like e.g. in the ortho salts A 6 MnTe 4 (275-282 pm,[13,15]). The sodium cations occupy two special positions 4e [site symmetry 2; Na(1) and Na(2)] and one general position [Na(3)].…”

“…For the lighter alkali elements sodium and potassium, all ortho manganates A 6 MnQ 4 have long been known [13,14]. Only recently, the structural chemistry was extended by the successful preparation and characterization of the whole series of the respective rubidium and cesium salts, which are isotypic to the Na/K compounds (Na 6 ZnO 4 -type, [15]). The heavier alkali cations K, Rb and Cs form the whole series of sulfido, selenido and tellurido manganates(II) A 2 MnQ 2 [8], which crystallize without exception in the orthorhombic K 2 ZnO 2 -type structure containing linear chains of tetrahedra [MnQ 4/2 ].…”

“…All compounds of this composition form the Na 6 ZnO 4 -type structure. While lithium salts of this type are missing, the structure family has recently been extended to the respective manganates(II) of rubidium and cesium, which are indeed isotypic to the Na/K salts [15]. Attempts to prepare other Rb/Cs metallate(II) salts of this type (i.e.…”

“…structure (cf. discussion and Bärnighausen symmetry tree in [15]). In contrast to the less A-richer 'ino' and 'phyllo' manganates discussed below, also the larger Rb + and Cs + cations occupy (distorted) octahedral and even tetrahedral voids in the chalcogenide close packing.…”

K5[InSe4] and K12[InS4]2(S): New Alkali Chalcogenido Indates with [InQ4]5–ortho Anions

“…Many of these as yet unknown compounds appeared as by-products during the synthetic work in the quaternary systems A-Mn-In-Q (see below). Therefore, we already performed a systematic investigation of the chalcogen series of the new Rb/Cs ortho manganates(II) A 6 [MnQ 4 ] [20] and the potassium diindates K 6 [In 2 Q 6 ] containing anions of two edgesharing tetrahedra. [21] The unexpected observation of the existence of these very A-rich manganates(II) A 6 [MnQ 4 ] -even for the largest alkali cations -suggests, that the less A-rich ortho indates A 5 [InQ 4 ] may also exist for all A and all Q elements.…”