Analysis of Electronic Structures and Chemical Bonding of Metal‐rich Compounds. 2. Presence of Dimer ( T – T ) 4– and Isolated T 2– Anions in the Polar Intermetallic Cr 5 B 3 ‐Type Compounds AE 5 T 3 ( AE = Ca, Sr; T = Au, Ag, Hg, Cd, Zn)

First principles density functional calculations were carried out to probe the oxidation states of the transition‐metal and alkaline‐earth elements in the Cr 5 B 3 ‐type compounds AE 5 T 3 consisting of T 2 dimers and isolated T atoms (i.e., Ca 5 Au 3 , Ca 5 Ag 3 , Ca 5 Hg 3 , Sr 5 Cd 3 , and Ca 5 Zn 3 ). The electronic structures of all these AE 5 T 3 compounds are best described as [( AE 2+ ) 5 ( T – T ) 4– ( T 2– )]+4e – . In the covalent bonding of the AE 2+ ions with the transition metal anions T 2– , the ( n –1)d orbitals of AE 2+ contribute more than the n s and n p orbitals of AE 2+ .