Synthesis, Structure, and Bonding of Hypoelectronic SrIn₄:  Direct Example of a Dominant Size Effect in Structure Selection

Abstract

The structure of the new title compound, the same type as EuIn4, was refined in the monoclinic space group C2/m, with Z = 4. The compound exhibits a complex three-dimensional network built of four- and five-bonded indium atoms in fused and interbonded pentagons that sandwich the strontium atoms. Both electronic band-structure calculations and property measurements show that the compound is metallic. A detailed band-structure analysis indicates that the compound is hypoelectronic with a one-electron deficiency, but the In−In bonding is effectively optimized in the structure. The important role of cation size in the structure choice is noted in a comparative study of BaIn4, which has the closely related BaAl4-type structure in which barium atoms are sandwiched by six-membered rings.

Synthesis, structure and bonding of the hypoelectronic cluster compound Sr3Tl5

“…This appears to be clear for comparing with the structures for Sr 3 In 5 [12] vs. Sr 3 Tl 5 and Sr 3 In 5 vs. La 3 In 5 [16] in which the larger Tl in the former pair and the smaller La in the latter lead to Sr 3 Tl 5 or La 3 In 5 crystallizing in Pu 3 Pd 5 type [15] rather than Ca 3 Ga 5 type [18] network version. In the former pair, although both isoelectronic, the natural increase in the atomic radii from In to Tl, difference of ~0.02 Å, results in a different strontium cationic matrix, in which the shortest strontium separation is 4.08 Å for the In vs. 4.26 Å for the Tl phase, increasing ~0.2 Å overall.…”

“…The Nb container that was then jacketed in evacuated fused silica tubing, sealed, and heated in a resistance furnace, which have been described elsewhere [19]. During explorations of new binary thallide intermetallic phases similar to orthorhombic Sr 3 In 5 [12], single crystals of title compound were first obtained in about 20% yield from the stoichiometric loaded composition Sr 3 Tl 5 . The weighed Sr-Tl components were first homogenized at 1050 °C for one day, quenched, and then annealed at 1000 °C for one week, after which the system was slowly cooled at 3 °C h 1 to room temperature.…”

“…As examples of the former are isolated polyanionic clusters such as Tl 5 7 and Tl 9 9 in Na 2 K 21 Tl 19 [6], In 11 7 in K 8 In 11 [7], Tl 13 10 and Tl 13 11 , respectively, in Na 4 A 6 Tl 13 (A = K, Rb, Cs) and Na 3 K 8 Tl 13 [8], and Tl 5 7 , Tl 4 8 , Tl 3 7 and Tl 5 in Na 23 K 9 Tl 15.3 [9]. For the latter, a rich collection of more complex three-dimensional anionic networks, BaIn 4 [10], SrIn 4 [11], Sr 3 In 5 [12], BaTl 4 [13], BaIn 2 [14], etc. have been characterized.…”

“…As a part of our continuing effort of the factors governing structure selection and phase stability, our recent exploration of alkaline-earthmetal examples has led to synthesis of the intermetallic phase Sr 3 Tl 5 . This curious phase, different from the other network-like alkaline-earthmetal-triel phases, crystallizes in the Pu 3 Pd 5 structure type [15] with distinctive square pyramidal clusters, isostructural with La 3 In 5 [16] or Sr 3 Sn 5 [17] rather than the nominally isoelectronic Sr 3 In 5 [12] (Ca 3 Ga 5 type [18]) network structure type.…”

Exploratory synthesis of reduced rare-earth-metal halides, chalcogenides, intermetallics

“…Since most are metallic, there are no closed-shell or other simple and transferable bonding rules to aid these selections, rather an aggregate of complex factors [108,109]. To delocalized metal-metal bonding in the major R host lattice one must add the less well-known R-Z heterometal and R-Te interactions, and the Madelung energies of such assemblies of polar components are likely to be of major importance as well.…”