Cu2FeGeSe4 is Stannite structured and crystallizes in the tetragonal I-42m space group. Fe(1) is bonded to four equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with four equivalent Ge(1)Se4 tetrahedra and corners with eight equivalent Cu(1)Se4 tetrahedra. Cu(1) is bonded to four equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with four equivalent Fe(1)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and corners with four equivalent Ge(1)Se4 tetrahedra. Ge(1) is bonded to four equivalent Se(1) atoms to form GeSe4 tetrahedra that share corners with four equivalent Fe(1)Se4 tetrahedra and corners with eight equivalent Cu(1)Se4 tetrahedra. Se(1) is bonded to one Fe(1), two equivalent Cu(1), and one Ge(1) atom to form corner-sharing SeFeCu2Ge tetrahedra.
Cu2FeGeSe4 is Stannite structured and crystallizes in the tetragonal I-42m space group. Fe(1) is bonded to four equivalent Se(1) atoms to form FeSe4 tetrahedra that share corners with four equivalent Ge(1)Se4 tetrahedra and corners with eight equivalent Cu(1)Se4 tetrahedra. All Fe(1)-Se(1) bond lengths are 2.43 Å. Cu(1) is bonded to four equivalent Se(1) atoms to form CuSe4 tetrahedra that share corners with four equivalent Fe(1)Se4 tetrahedra, corners with four equivalent Cu(1)Se4 tetrahedra, and corners with four equivalent Ge(1)Se4 tetrahedra. All Cu(1)-Se(1) bond lengths are 2.41 Å. Ge(1) is bonded to four equivalent Se(1) atoms to form GeSe4 tetrahedra that share corners with four equivalent Fe(1)Se4 tetrahedra and corners with eight equivalent Cu(1)Se4 tetrahedra. All Ge(1)-Se(1) bond lengths are 2.49 Å. Se(1) is bonded to one Fe(1), two equivalent Cu(1), and one Ge(1) atom to form corner-sharing SeFeCu2Ge tetrahedra.