Structural Chemistry of Halide including Thallides A8Tl11X1−n (A = K, Rb, Cs; X = Cl, Br; n = 0.1–0.9)

Abstract

A8Tl11 (A = alkali metal) compounds have been known since the investigations of Corbett et al. in 1995 and are still a matter of current discussions as the compound includes one extra electron referred to the charge of the Tl117− cluster. Attempts to substitute this additional electron by incorporation of a halide atom succeeded in the preparation of single crystals for the lightest triel homologue of the group, Cs8Ga11Cl, and powder diffraction experiments for the heavier homologues also suggested the formation of analogous compounds. However, X-Ray single crystal studies on A8Tl11X to prove this substitution and to provide a deeper insight into the influence on the thallide substructure have not yet been performed, probably due to severe absorption combined with air and moisture sensitivity for this class of compounds. Here, we present single crystal X-Ray structure analyses of the new compounds Cs8Tl11Cl0.8, Cs8Tl11Br0.9, Cs5Rb3Tl11Cl0.5, Cs5.7K2.3Tl11Cl0.6 and K4Rb4Tl11Cl0.1. It is shown that a (partial) incorporation of halide can also be indirectly determined by examination of the Tl-Tl distances, thereby the newly introduced cdd/cdav ratio allows to evaluate the degree of distortion of Tl117− clusters.

Spotlight on Alkali Metals: The Structural Chemistry of Alkali Metal Thallides

“…For example, K 49 Tl 108 is only known for potassium, whereas at a similar VEC A 15 Tl 27 (A = Rb, Cs) is reported. The question arises, if the compounds K 15 Tl 27 or Rb 49 Tl 108 exist or if the formed structure type is unique for potassium respectively rubidium/cesium. An approach could be the employment of mixed alkali metals in order to prove, if there are site preferences and if yes, which alkali metal on which site is essential for structure formation.…”

“…The anionic moiety is represented by a Tl11 cluster, but in contrast to their highest possible symmetry (D3h in A15Tl27; see Section 3.2), here only D3 symmetry for the Tl11 unit is realized, according to their site symmetry. The substitution of the extra electron in A8Tl11 by halide results in A8Tl11X, in which a less degree of distortion of the Tl11 7− cluster is observed, electronic effects of the extra electron therefore cannot be excluded [49]. Due to the high symmetry of the crystal structure, only two The possibility of an ordered substitution of Rb4 by the largest alkali metal cesium was shown for the compound Rb 14 CsTl 27 [35].…”

“…This makes the position of Rb1 conspicuous and indeed, having a closer look at the crystal structure, this position is involved in the formation of a distorted octahedral arrangement around a void. This void can be filled by halide yielding an enlarged number of surrounding atoms of Rb1 of 13 [49]. In general, for binary A 8 Tl 11 no site occupancy preferences for different alkali metals have been reported.…”

The Role of Different Alkali Metals in the A15Tl27 Type Structure and the Synthesis and X-ray Structure Analysis of a New Substitutional Variant Cs14.53Tl28.4

“…This extra electron can be replaced by halide in A 8 Tr 11 X, and for Cs 8 Ga 11 Cl diamagnetic behavior is observed [16][17][18][19]. Detailed investigations on A 8 Tl 11 X showed that this replacement is accompanied by a less pronounced distortion of the Tl 11 clusters from ideal D 3h symmetry [17,18]. In general, Tl 11 7clusters represent a favored geometry as they also can be perceived as doubletetrahedral star units, which represent a very common structural motif in intermetallic compounds [20].…”

“…In these compounds, an extra electron is present A 8 [Tr 11 7-][e -] being responsible for pauli paramagnetism and metallic behavior. This extra electron can be replaced by halide in A 8 Tr 11 X, and for Cs 8 Ga 11 Cl diamagnetic behavior is observed [16][17][18][19]. Detailed investigations on A 8 Tl 11 X showed that this replacement is accompanied by a less pronounced distortion of the Tl 11 clusters from ideal D 3h symmetry [17,18].…”