Eu2P7X and Ba2As7X (X = Br, I): Chiral double-Zintl salts containing heptapnictotricyclane clusters

Chiral double Zintl salts present tunable crystal structures with enhanced structural flexibilities and potential for applications requiring chiral control and enantioselectivity. To accompany the chiral Sr₂P₇I and Sr₂P₇Br double Zintl salts reported by us previously, six new chiral Zintl salts of the form Ba_2-ySr_yAs₇I (y = 0, 0.23, 2), Eu₂P₇I, Eu₂P₇Br, and Eu_1.3Ba_0.7P₇Br have been synthesized and characterized by single crystal X-ray diffraction and SEM-EDS analyses. All new compounds crystallize in the Sohncke space group P2₁3 (No. 198) with variations of P₇^3- (heptaphosphanortricyclane) or As₇^3- (heptaarsanortricyclane) clusters surrounded by alkaline-earth or Eu cations and halogen anions. Band structure calculations predict semiconducting properties for all synthesized compounds. Diffuse reflectance UV-vis spectroscopy indicates that Eu₂P₇I is a direct bandgap semiconductor with E_g of 1.7 eV.