When the crucible contributes: serendipitous formation, flux reactivity, and crystal and electronic structures of two aluminium-bearing mixed-metal oxides, Ba2.1Pb0.9Al8.8In2.2O20 and BaAl1.6Ga0.4O4.

Two Al-bearing mixed-metal oxides, Ba2.11(1)Pb0.89Al8.78(1)In2.22O20, (1), and BaAl1.57(2)Ga0.43O4, (2), were obtained serendipitously from Pb-flux reactions carried out in alumina crucibles. Single-crystal X-ray diffraction analysis determined that (1) crystallizes in the monoclinic space group C2/m [a = 15.9491 (11), b = 11.5929 (8), c = 5.1241 (3) Å and β = 108.644 (2)°] and can be viewed as a disordered derivative of the Pb3GeAl10O20 structure type. The structure contains mixed octahedrally coordinated Al/In sites and a split Ba/Pb position analogous to the Ba/Bi disorder in Ba2BiGa11O20. Compound (2) crystallizes in the hexagonal space group P63 [a = 9.0981 (3) and c = 8.7909 (4) Å], adopting a superstructure related to the BaAl2O4/SrAl2O4/BaZnGeO4 families of oxide materials. Its structure contains mixed Al/Ga tetrahedral sites and positional disorder of bridging O atoms. Electronic structure calculations based on ordered structural models indicate wide-bandgap semiconducting behavior, with a calculated bandgap of 3.63 eV for (1) and 3.80 eV for (2).