Sr2Pd4Al5: Synthesis, Crystal and Electronic Structures, and Chemical Bonding of a Polar Intermetallic Compound.

The new intermetallic compound Sr₂Pd₄Al₅ was prepared from the elements by reaction in niobium ampoules. The structure was refined from single-crystal data, which indicate the formation of a new structure type in the orthorhombic crystal system [ a = 1814.49(10), b = 431.64(4), c = 1102.47(4) pm] with space group Pnma ( wR2 = 0.0251, 1666 F² values, 68 parameters). Full ordering of the transition-metal and aluminum sites was observed. The compound can be described as a polar intermetallic phase with a polyanionic [Pd₄Al₅] ^δ- network; however, a quite unique bonding situation was found within this framework. In addition to the usual Pd-Al bonding, significant contributions to the stability of the framework caused by homoatomic Pd-Pd and Al-Al interactions can also be found. Structural relaxation confirmed the electronic stability and predicted the compound to be a metallic conductor. [ABSTRACT FROM AUTHOR]