Structure of the compounds La3AlGe5O16, La3GaGe5O16 and Ce3GaGe5O16

Hydrothermal synthesis in the systems LaCl3 (CeCl3)–Al(OH)3 (Ga2O3)–GeO2 yielded crystals of composition La3AlGe5O16, La3GaGe5O16 and Ce3GaGe5O16, respectively. The syntheses were carried out at temperatures of 1023 K–1073 K under pressures of 1000 bar. The space group of the three substances was determined as P[unk] with the pseudosymmetry P21/c. All compounds are isostructural. The lattice parameters are a = 4.794(4) Å, b = 8.102(8) Å, c = 15.722(8) Å, α = 90.42(3)°, β = 94.46(2)°, γ = 89.91(2)° for La3AlGe5O16, a = 4.827(4) Å, b = 8.090(4) Å, c = 15.707(6) Å, α = 90.76(5)°, β = 94.01(7)°, γ = 90.01(7)° for La3GaGe5O16 and a = 4.768(7) Å, b = 8.088(5) Å, c = 15.600(2) Å, α = 90.55(4)°, β = 94.46(4)°, γ = 89.63(4)° for Ce3AlGe5O16. There are two formula units in the unit cell.