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Synergistic Geometrical and Electronic Features in the Intermetallic Phases Ca 2 Ag M 2 , Ca 2 Mg M 2 , and Ca 2 Ga M 2 ( M = Pd, Pt)
Author(s) -
Ponou Siméon,
Miller Gordon J.
Publication year - 2015
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201500090
Subject(s) - orthorhombic crystal system , crystallography , monoclinic crystal system , crystal structure , electronegativity , chemistry , intermetallic , valence (chemistry) , valence electron , electronic structure , computational chemistry , electron , physics , organic chemistry , alloy , quantum mechanics
Six new analogous phases, Ca 2 Ag M 2 , Ca 2 Mg M 2 , and Ca 2 M 2 Ga ( M = Pd, Pt), were rationally prepared by direct combination of the respective elements at high temperature, allowing us to clarify the factors controlling the structural selection between the orthorhombic W 2 CoB 2 ‐type structure ( Immm ) and its distorted monoclinic Gd 2 AlGe 2 ‐type derivative ( C 2/ c ), as well as to investigate the mechanism and the extent of the electronic flexibility of the W 2 CoB 2 ‐type structure. All crystal structures were refined from single‐crystal X‐ray diffraction data. Two pairs of compounds Ca 2 Ag M 2 (5 ve/f.u) and Ca 2 Mg M 2 (6 ve/f.u) adopt the orthorhombic W 2 CoB 2 type, whereas the pair of Ga analogues Ca 2 M 2 Ga (7 ve/fu) crystallize in the monoclinic Gd 2 AlGe 2 ‐ or Ca 2 Ir 2 Si‐type structure, confirming the valence electron count (vec) as the dominant factor controlling the structural selection in this series. The stability factors and chemical bonding features behind the similarities and differences of these closely related structures were theoretically investigated using first‐principles density functional calculations. They provide additional evidences of the decisive influence of the vec as well as the electronegativity differences between constituent elements, on the structural trends. In addition, the cooperative roles of the geometrical and electronic flexibility associated with the inherent anisotropy of the orthorhombic symmetry of the W 2 CoB 2 type are emphasized.