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EuSi2 is hexagonal omega structure structured and crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Eu is bonded to twelve equivalent Si atoms to form a mixture of edge and face-sharing EuSi12 cuboctahedra. All Eu–Si bond lengths are 3.17 Å. Si is bonded in a 9-coordinate geometry to six equivalent Eu and three equivalent Si atoms. All Si–Si bond lengths are 2.36 Å.
EuSi2O2N2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Eu2+ sites. In the first Eu2+ site, Eu2+ is bonded in a 7-coordinate geometry to one N3- and six O2- atoms. The Eu–N bond length is 2.84 Å. There are a spread of Eu–O bond distances ranging from 2.53–2.69 Å. In the second Eu2+ site, Eu2+ is bonded in a 7-coordinate geometry to one N3- and six O2- atoms. The Eu–N bond length is 2.96 Å. There are a spread of Eu–O bond distances ranging from 2.49–2.74 Å. In the third Eu2+ site, Eu2+ is bonded in a 7-coordinate geometry to one N3- and six O2- atoms. The Eu–N bond length is 2.83 Å. There are a spread of Eu–O bond distances ranging from 2.51–2.68 Å. In the fourth Eu2+ site, Eu2+ is bonded in a 7-coordinate geometry to one N3- and six O2- atoms. The Eu–N bond length is 2.95 Å. There are a spread of Eu–O bond distances ranging from 2.50–2.74 Å. There are eight inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.73–1.77 Å. The Si–O bond length is 1.63 Å. In the second Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There is two shorter (1.75 Å) and one longer (1.76 Å) Si–N bond length. The Si–O bond length is 1.64 Å. In the third Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There is two shorter (1.75 Å) and one longer (1.76 Å) Si–N bond length. The Si–O bond length is 1.63 Å. In the fourth Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.74–1.77 Å. The Si–O bond length is 1.64 Å. In the fifth Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.73–1.76 Å. The Si–O bond length is 1.63 Å. In the sixth Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. All Si–N bond lengths are 1.75 Å. The Si–O bond length is 1.63 Å. In the seventh Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There is two shorter (1.75 Å) and one longer (1.76 Å) Si–N bond length. The Si–O bond length is 1.63 Å. In the eighth Si4+ site, Si4+ is bonded to three N3- and one O2- atom to form corner-sharing SiN3O tetrahedra. There are a spread of Si–N bond distances ranging from 1.74–1.77 Å. The Si–O bond length is 1.63 Å. There are eight inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted trigonal planar geometry to one Eu2+ and three Si4+ atoms. In the second N3- site, N3- is bonded in a trigonal planar geometry to three Si4+ atoms. In the third N3- site, N3- is bonded in a distorted trigonal planar geometry to one Eu2+ and three Si4+ atoms. In the fourth N3- site, N3- is bonded in a trigonal planar geometry to one Eu2+ and three Si4+ atoms. In the fifth N3- site, N3- is bonded in a distorted trigonal planar geometry to one Eu2+ and three Si4+ atoms. In the sixth N3- site, N3- is bonded in a trigonal planar geometry to three Si4+ atoms. In the seventh N3- site, N3- is bonded in a trigonal planar geometry to three Si4+ atoms. In the eighth N3- site, N3- is bonded in a trigonal planar geometry to three Si4+ atoms. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to three Eu2+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to three Eu2+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 1-coordinate geometry to three Eu2+ and one Si4+ atom.