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

Robert J Wilson,Florian Weigend,Stefanie Dehnen

doi:10.1002/ange.202002863

Abstract

AbstractThe pseudo‐element concept, in its most general formulation, states that isoelectronic atoms form equal numbers of bonds. Hence, clusters such as Zintl ions usually retain their structure upon isoelectronic replacement of some or all atoms. Here, a deviation from this common observation is presented, namely the formation of (Sn5Sb3)3− (1), a rare example of an eight‐vertex Zintl ion, and an unprecedented example of a Zintl ion synthesized by solution means that has an arachno‐type structure according to the Wade–Mingos rules. Three structure‐types of interest for (Sn5Sb3)3− were identified by DFT calculations: one that matched the X‐ray diffraction data, and two that that were reminiscent of fragments of known clusters. A study on the isoelectronic series of clusters, (SnxSb8−x)2−x (x=0–8), showed that the relative energies of these three isomers vary significantly with composition (independent of electron count) and that each is the global minimum at least once within the series.

Highlights

The pseudo-element concept, in its most general formulation, states that isoelectronic atoms form equal numbers of bonds
Classical Zintl ion chemistry has long borrowed the Wade–Mingos rules to relate structures to the number of bonding or valence electrons.[3]. These rules were developed to explain the observed structures of borane clusters,[4] and are applicable to Zintl ions owing to the isoelectronic relationship between fragments {B-H} and E atoms (E = Si–Pb), which both contribute two electrons to cluster bonding orbitals
The clusters are classified according to the number of “missing” vertices relative to a parent deltahedron; the labels of closo, nido, arachno, and hypho are given to clusters with 0, 1, 2, and 3 missing vertices and cluster skeletal electron (SE) counts of 2n + 2, 2n + 4, 2n + 6, and 2n + 8, where n is the number of actual cluster vertices

Summary

Introduction

The pseudo-element concept, in its most general formulation, states that isoelectronic atoms form equal numbers of bonds. Deltahedral Zintl ions with 4–7, 9, 10, and 12 vertices have been crystallized and structurally characterized as their respective salts from ethylenediamine (en) or liquid ammonia solutions (Figure 1 a).

Results

Conclusion