Neutron and X-Ray Diffraction Study of Ca3Al2(O4D4)3, a Garnetoid

Deuterated hydrogrossular, Ca₃Al₂(O₄D₄)₃, has been prepared in order to investigate, by neutron and x‐ray diffraction, the isomorphic substitution of (O₄H₄)⁴⁻ for (SiO₄)^4 −. A polycrystalline specimen yielded the cubic‐cell edge, 12.5755 ± 0.0009 Å (28°C) and oxygen parameters $\text{x\hspace{0.17em}=\hspace{0.17em}0.0303(3); y\hspace{0.17em}=\hspace{0.17em}0.0547(4); z\hspace{0.17em}=\hspace{0.17em}0.6430(3)}$ . Diffraction experiments show no phase change from 301° to 77°K, although deuterium atoms shift to more symmetrically located general positions at the lower temperature. Deuterium parameters are $\text{x\hspace{0.17em}=\hspace{0.17em}0.149(1); y\hspace{0.17em}=\hspace{0.17em}0.086(1); z\hspace{0.17em}=\hspace{0.17em}0.792(1)}$ at 301°K and 0.148(2); 0.087(2); and 0.798(2) at 77°K. The shortest O–D distance is 0.95 Å at 301°K and 0.94 Å at 77°K, indicating hydroxyl bonding.