When the crucible contributes: serendipitous formation, flux reactivity, and crystal and electronic structures of two aluminium-bearing mixed-metal oxides, Ba 2.1 Pb 0.9 Al 8.8 In 2.2 O 20 and BaAl 1.6 Ga 0.4 O 4

Two Al-bearing mixed-metal oxides, Ba 2.11(1) Pb 0.89 Al 8.78(1) In 2.22 O 20 , ( 1 ), and BaAl 1.57(2) Ga 0.43 O 4 , ( 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 C 2/ 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 Pb 3 GeAl 10 O 20 structure type. The structure contains mixed octahedrally coordinated Al/In sites and a split Ba/Pb position analogous to the Ba/Bi disorder in Ba 2 BiGa 11 O 20 . Compound ( 2 ) crystallizes in the hexagonal space group P 6 3 [ a = 9.0981 (3) and c = 8.7909 (4) Å], adopting a superstructure related to the BaAl 2 O 4 /SrAl 2 O 4 /BaZnGeO 4 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 ).