Zintl-Klemm ions

Zintl ions are polyanions formed by anion clustering in ionic alloys. Two categories were considered those that fit the so-called Zintl-Klemm concept and those that are electron-deficient. 

Abstract This chapter reviews the methods that are useful for understanding the structure and bonding in Zintl ions and related bare post-transition element clusters in approximate historical order. After briefly discussing the Zintl-Klemm model the Wade-Mingos rules and related ideas are discussed. The chapter concludes with a discussion of the jellium model and special methods pertaining to bare metal clusters with interstitial atoms. 

Early Efforts to Rationalize the Structures of the Zintl Ions The Zintl-Klemm Concept... 

Early efforts to rationalize the observed formulas and chemical bonding of Zintl ions and related species used initially the Zintl-Klemm concept [10, 11] and subsequently the Mooser-Pearson [12] extended (8 — AO rule. In this rule, refers... 

This simple Zintl-Klemm concept has some obvious limitations as illustrated by differences in the two MTl intermetallics (M = Na [27] and Cs [28]). Thus complete electron transfer from M to T1 leads to M TF, where the TF anion with four valence electrons is isoelectronic with a neutral group 14 atom and four bonds are needed to attain the octet configuration. Hence, the TF anion should form structures similar to allotropes of carbon or heavier group 14 elements. Indeed, NaTl has a stuffed diamond structure [27] with internal Na ions and an anionic (TF)oo lattice similar to diamond. However, the TF anions in [CsTl] form tetrago-nally compressed octahedra [28] unlike any structures of the allotropes of carbon or its heavier congeners. 

The efforts to rationalize the formulas and structures of Zintl ions and related species predated extensive definitive structural information on anionic post-transition metal clusters obtained by Corbett and his group in the 1970s [8, 9]. After enough such structural information on the bare post-transition metal clusters became available, the resemblance of their polyhedra to the known polyhedral boranes became apparent. For this reason, the simple Zintl-Klemm concept has been largely superseded by newer, more advanced descriptions of chemical bonding in such clusters, initially those applied to the polyhedral boranes. 

Answer. Assuming an ionic Zintl-Klemm model and the common oxidation state of these metals, we have C23- ions locally in the octahedral cavities formed from the... 

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