[Co@Sn₆Sb₆]³⁻: An Off‐Center Endohedral 12‐Vertex Cluster

Abstract

We report on the asymmetric occupation of a 12‐vertex cluster centered by a single metal atom. Three salts of related intermetalloid cluster anions, [Co@Sn6Sb6]3− (1), [Co2@Sn5Sb7]3− (2), and [Ni2@Sn7Sb5]3− (3) were synthesized, which have pseudo‐C4v‐symmetric or pseudo‐D4h‐symmetric 12‐vertex Sn/Sb shells and interstitial Co− ions or Ni atoms. Anion 1 is a very unusual single‐metal‐“centered” 12‐atom cluster, with the inner atom being clearly offset from the cluster center for energetic reasons. Quantum chemistry served to assign atom types to the atomic positions and relative stabilities of this cluster type. The studies indicate that the structures are strictly controlled by the total valence electron count—which is particularly variable in ternary intermetalloid cluster anions. Preliminary 119Sn NMR studies in solution, supported by quantum‐chemical calculations of the shifts, illustrate the complexity regarding Sn:Sb distributions of such ternary systems.

Structure and Bonding in [Sb@In8Sb12]3− and [Sb@In8Sb12]5−

“…The outer Sb 12 In 8 shell can be considered topologically related to the Sb 20 unit of [Sb@M 12 @Sb 20 ] q − , but the presence of a single Sb atom inside the cluster rather than an icosahedral Sb@M 12 unit pulls the eight In vertexes inwards, so that only they bond directly with the central Sb atom. The cubic coordination of Sb is also broadly consistent with the known structural chemistry of centered main‐group (semi‐)metal cages . The gas‐phase potential energy surface for the [Sb@In 8 Sb 12 ] 5− cluster is complex, featuring eight equivalent minima with a single displaced In + center, linked by low‐lying transition states where the additional electron pair is delocalized over two adjacent In centers (similar to the situation found in the trans ‐bent double bonds, R 2 E=ER 2 , of the heavier group‐IV elements).…”

The Arachno‐Zintl Ion (Sn5Sb3)3− and the Effects of Element Composition on the Structures of Isoelectronic Clusters: Another Facet of the Pseudo‐Element Concept

“… a) The structure of the anion (Sn 5 Sb 3 ) 3− ( 1 ); the two‐color ellipsoids (50 % probability) indicate mixed occupation with the outer color representing the occupation in the global minimum isomer that was obtained upon geometry optimization by quantum chemical calculations with DFT methods (see text). b),c) 8‐atom fragments (highlighted in color) within the reported anions [Co@Sn 6 Sb 6 ] 3− (b), and [{CuSn 5 Sb 3 } 2 ] 4− (c) . Sn orange, Sb blue.…”

“…No 8‐vertex main group‐element clusters of the type ST2 or ST3 have been isolated; however, there are known coordination compounds and intermetalloid clusters with (formally) isoelectronic and structurally related moieties. Square anti‐prism motifs (ST3) are found in a number of related compounds, such as {Tl 2 Bi 6 } 2− in [Tl 2 Bi 6 {Ru(cod)}] 2− , and {Bi 8 } 2+ in (CuBi 8 )[AlCl 4 ] 3 , {Sn 8 } 6− in Rb 4 Li 2 Sn 8 , and {Sn 4 Sb 4 } 2− in [Co@Sn 6 Sb 6 ] 3− (Figure b) . The structural motif of ST2 is less common.…”

The Arachno‐Zintl Ion (Sn5Sb3)3− and the Effects of Element Composition on the Structures of Isoelectronic Clusters: Another Facet of the Pseudo‐Element Concept

“…a) The structure of the anion (Sn 5 Sb 3 ) 3À (1); [17] the two-color ellipsoids (50 % probability) indicate mixed occupation with the outer color representing the occupation in the global minimum isomer that was obtained upon geometry optimization by quantum chemical calculations with DFT methods (see text). b),c) 8-atom fragments (highlighted in color) within the reported anions [Co@Sn 6 Sb 6 ] 3À (b), [11] and [{CuSn 5 Sb 3 } 2 ] 4À (c). [12] Sn orange, Sb blue.…”

“…Square anti-prism motifs (ST3) are found in a number of related compounds, such as {Tl 2 Bi 6 } 2À in [Tl 2 Bi 6 {Ru-(cod)}] 2À , [14] and {Bi 8 } 2+ in (CuBi 8 )[AlCl 4 ] 3 , [15] {Sn 8 } 6À in Rb 4 Li 2 Sn 8 , [7] and {Sn 4 Sb 4 } 2À in [Co@Sn 6 Sb 6 ] 3À (Figure 2 b). [11] The structural motif of ST2 is less common. The heterometallic cluster [Sb 6 (RuCp*) 2 ] 2À has a remarkably similar 8vertex core.…”