Covalence and Ionicity in MgAgAs‐Type Compounds

Abstract

MgAgAs-type "half-Heusler" compounds are known to realize two out of three possible atomic arrangements of this structure type. The number of transition metal components typically determines which of the alternatives is favored. On the basis of DFT calculations for all three variants of 20 eight- and eighteen-valence-electron compounds, the experimentally observed structural variant was found to be determined by basically two different bonding patterns. They are quantified by employing two complementary position-space bonding measures. The Madelung energy E((M)(QTAIM)) calculated with the QTAIM effective charges reflects contributions of the ionic interactions to the total energy. The sum of nearest-neighbor delocalization indices ςnn characterizes the covalent interactions through electron sharing. With the aid of these quantities, the energetic sequence of the three atomic arrangements for each compound is rationalized. The resulting systematic is used to predict a scenario in which an untypical atomic arrangement becomes most favorable.

Soft Chemistry, Coloring and Polytypism in Filled Tetrahedral Semiconductors: Toward Enhanced Thermoelectric and Battery Materials

“…While a thorough analysis would require an immense amount of computational time, identifying common trends in site preferences can expedite the scanning of possible crystal structures. Here again, the half‐Heusler (MgAgAs‐type) serves as a good prototype because it is the most comprehensively studied among dozens of commonly adopted structure types …”

“…Here again,t he half-Heusler (MgAgAs-type) serves as a good prototype because it is the mostc omprehensively studied among dozens of commonly adopted structure types. [64] Within the MgAgAs crystal structure, there are multiple common structural motifs consistent with conflicting types of bonding. Using the XYZ notation discussede arlier,ahighly ionic rock salt packing pattern is observed between Xa nd Y atoms.…”

8 –NRule and Chemical Bonding in Main-Group MgAgAs-Type Compounds

“…On the contrary, in AT HC E and T′T HC E compounds, ionic interactions do not play the decisive role because the arrangement of the charges is unfavorable. 16 The model of the polyanionic network describes chemical bonding in MgAgAs-type semiconductors as a combination of ionic and covalent interactions. 17 The least electronegative component X transfers its n valence electrons to the polyanion [YZ] n− .…”

Chemical Bonding Analysis as a Guide for the Preparation of New Compounds: The Case of VIrGe and HfPtGe

“…[26] Then earestneighbor sharing & nn is related to the overall extent of covalent bonding and sums up the delocalization indices between all nearest neighbors per formula unit. [26] Then earestneighbor sharing & nn is related to the overall extent of covalent bonding and sums up the delocalization indices between all nearest neighbors per formula unit.…”

“…[26] Three new trends are analyzed in the following.When the two transition metals of the same period approach each other in the periodic table of elements (T '$T), the nearest neighbor sharing increases significantly.T he extent of the QTAIM Madelung energy does not show as trict trend but decreases in most cases (Figure 3a;s ee the Supporting Information for numerical data). [26] Three new trends are analyzed in the following.When the two transition metals of the same period approach each other in the periodic table of elements (T '$T), the nearest neighbor sharing increases significantly.T he extent of the QTAIM Madelung energy does not show as trict trend but decreases in most cases (Figure 3a;s ee the Supporting Information for numerical data).…”