Tetrahedral [Sb(AuMe)₄]³⁻Occurring in Multimetallic Cluster Syntheses: About the Structure‐Directing Role of Methyl Groups

Abstract

The anion of [K(crypt-222)] 3 [Sb(AuMe) 4 ]•py ( 1; crypt-222 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane;py= pyridine) represents arare example of ah omoleptic heavy p-block metal atom being surrounded by four free-standing transition metal complex fragments,and the thirdexample for acorresponding Sb compound. In contrast to all reported complexes of this type,t he transition metal atoms possess twofold coordination only,h ence the complex as aw hole does not exhibit significant steric shielding or further linkage of the metal atoms.This is reflected in ahigh flexibility, as confirmed by slight deviations from atetrahedral coordination of the Sb atom in the crystal and soft vibrational modes. An alternative pyramidal conformer,o bserved for ar elated arsenic compound with terminal phosphine ligands,i sa pparently disfavored owing to electron correlation effects.T he compound is formed in areaction that in another solvent or at other reactant concentrations yields salts of ternary cluster anions.B yacombined experimental and theoretical study of different reaction conditions and previously unidentified sideproducts,weprovideinsight into multimetallic cluster synthesis reactions.

Capture the missing: formation of (PbBi3)− and {[AuPb5Bi3]2}4− via atom exchange or reorganization of the pseudo‐tetrahedral Zintl anion (Pb2Bi2)2−

“…In contrast, the products that are reproducibly obtained from these reactions are independent from the ratio of the reactants, as the three compounds were isolated as the only crystal types from the corresponding Schlenk tubes (with the reactant ratios ranging from 1:3 to 3:1), respectively. This is in contrast to the recently reported Au/Sn/Sb systems, where not only the solvent, but also the reactant ratios significantly influenced the composition of the isolated compounds 27 …”

“…The salt comprises three types of anions: [AuMe 2 ] − and two (Pb x Bi 4− x ) x − pseudo ‐tetrahedral units (see Figure 1). The [AuMe 2 ] − complex was previously reported and additionally suggested as one of the side products on the way toward the formation of {[AuSn 5 Sb 3 ] 2 } 4− 27,28 . Although the Pb and Bi atoms are not distinguishable by common X‐ray diffraction experiments (which also allows for the trigonal symmetry with the threefold axis running through the pseudo‐ tetrahedral anions), we can still assign the atom positions based on the following considerations and experimental evidence: the overall −4 charge of the three anions, which is derived from the presence of four [K(crypt‐222)] + cations, leave three negative charges for the two pseudo‐ tetrahedral units in the sum.…”

“…This is in contrast to the recently reported Au/Sn/Sb systems, where not only the solvent, but also the reactant ratios significantly influenced the composition of the isolated compounds. 27 For further comparison, we additionally investigated the Au/Pb/Sb system and performed the reactions between…”

“…[22][23][24][25] On the other hand, reactions with softer Lewis acids like the Au(I) cation, (Tt 2 Pn 2 ) 2− anions can also stay intact in the resulting complexes [Au{η 2 -(Tt 2 Pn 2 )} 2 ] 3− (Tt/Pn = Sn/Sb, Sn/Bi, and Pb/Bi). 1,26,27 To understand the limits of such decisions pro-or contradeconstruction of the tetrahedral units, it is essential to further explore these heavy atom anions in the context of atom exchange, fragmentation, and reorganization reactions. According to recent reports, the (relative) stabilities of binary pseudo-tetrahedral anions are related to the ratio of the corresponding atomic radii-the exchange reactions become more favorable for smaller differences in the covalent radii of the involved atoms.…”

“…Consequently, a series of intermetalloid or heterometallic clusters were reported, such as [U@Pb 7 Bi 7 ] 3− , [Th@Bi 12 ] 4− , [Bi@Ga 8 (Bi 2 ) 6 ] q − ( q = 3, 5), and [(Bi 6 )Zn 3 (TlBi 5 )] 4− 22–25 . On the other hand, reactions with softer Lewis acids like the Au(I) cation, (Tt 2 Pn 2 ) 2− anions can also stay intact in the resulting complexes [Au{η 2 ‐(Tt 2 Pn 2 )} 2 ] 3− (Tt/Pn = Sn/Sb, Sn/Bi, and Pb/Bi) 1,26,27 …”