Issue 24, 2023

Polarity-extended 8 − Neff rule for semiconducting main-group compounds with the TiNiSi-type of crystal structure

Abstract

Application of chemical bonding analysis in position-space techniques based on combined topological analysis of the electron density and electron-localizability indicator distributions has recently led to the formulation of a polarity-extended 8 − Neff rule for consistent inclusion of quantum chemically obtained polar-covalent bonding data into the classical 8 − N scheme for main-group compounds. Previous application of this scheme to semiconducting main-group compounds of the cubic MgAgAs type of structure with 8 valence electrons per formula unit (8 ve per f.u.) has shown a covalent bonding tendency preferring one zinc blende type partial structure over the other one, which seems to corroborate the classical Lewis picture of maximally four covalent bonds per main-group element. In contrast to the MgAgAs type, the orthorhombic TiNiSi type of structure displays a much higher geometrical flexibility to incorporate different kinds of metal atoms. The analysis of polar-covalent bonding in semiconducting 8 ve per f.u. containing main-group compounds AAE of this structure type reveals a transition to non-Lewis type bonding scenarios of species E with up to ten polar-covalently bonded metal atoms. This kind of situation is consistently included into the extended 8 − Neff type bonding scheme. A systematic increase of partially covalent bonding from chalcogenides E16 to the tetrelides E14 is found, summing up to as much as 2 covalent bonds E14–A and E14A′, and correspondingly remaining 4 lone pair type electrons on species E14. The familiar notion of this structure type consisting of a ‘[NiSi]’-type framework with ‘Ti’-type atoms filling the voids cannot be supported for the compounds investigated.

Graphical abstract: Polarity-extended 8 − Neff rule for semiconducting main-group compounds with the TiNiSi-type of crystal structure

Supplementary files

Article information

Article type
Paper
Submitted
28 Feb 2023
Accepted
10 May 2023
First published
18 May 2023
This article is Open Access
Creative Commons BY license

Dalton Trans., 2023,52, 8222-8236

Polarity-extended 8 − Neff rule for semiconducting main-group compounds with the TiNiSi-type of crystal structure

R. Freccero, Y. Grin and F. R. Wagner, Dalton Trans., 2023, 52, 8222 DOI: 10.1039/D3DT00621B

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