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BaAl2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ba is bonded in a 12-coordinate geometry to twelve equivalent Al atoms. All Ba–Al bond lengths are 3.54 Å. Al is bonded to six equivalent Ba and six equivalent Al atoms to form a mixture of corner, edge, and face-sharing AlBa6Al6 cuboctahedra. All Al–Al bond lengths are 3.02 Å.
BaAl2Si2O8 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ba2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ba–O bond distances ranging from 2.68–3.24 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.75–1.78 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.75–1.77 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four AlO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.65 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four AlO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.65 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Ba2+, one Al3+, and one Si4+ atom.
BaAl2Si2O8 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ba2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ba–O bond distances ranging from 2.78–2.90 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.75–1.78 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.74–1.78 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four AlO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.65 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four AlO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.62–1.65 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ba2+, one Al3+, and one Si4+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Ba2+, one Al3+, and one Si4+ atom.