Eu2NbGaO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share edges with two equivalent Eu(1)O8 hexagonal bipyramids, edges with four equivalent Eu(2)O8 hexagonal bipyramids, edges with two equivalent Ga(1)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. In the second Eu site, Eu(2) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share edges with two equivalent Eu(2)O8 hexagonal bipyramids, edges with four equivalent Eu(1)O8 hexagonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Ga(1)O6 octahedra. Nb(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Ga(1)O6 octahedra, edges with two equivalent Eu(2)O8 hexagonal bipyramids, and edges with four equivalent Eu(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 46-47°. Ga(1) is bonded to two equivalent O(3) and four equivalent O(4) atoms to form GaO6 octahedra that share corners with two equivalent Ga(1)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Eu(1)O8 hexagonal bipyramids, and edges with four equivalent Eu(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 47-50°. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with two equivalent O(3)Eu2Ga2 tetrahedra, corners with two equivalent O(2)Eu2Nb2 tetrahedra, corners with four equivalent O(1)Eu4 tetrahedra,  an edgeedge with one O(3)Eu2Ga2 tetrahedra, and  an edgeedge with one O(2)Eu2Nb2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Eu(1) and two equivalent Nb(1) atoms to form distorted OEu2Nb2 tetrahedra that share corners with two equivalent O(1)Eu4 tetrahedra, corners with four equivalent O(2)Eu2Nb2 tetrahedra, and  an edgeedge with one O(1)Eu4 tetrahedra. In the third O site, O(3) is bonded to two equivalent Eu(2) and two equivalent Ga(1) atoms to form distorted OEu2Ga2 tetrahedra that share corners with two equivalent O(1)Eu4 tetrahedra, corners with four equivalent O(3)Eu2Ga2 tetrahedra, and  an edgeedge with one O(1)Eu4 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Eu(1), one Eu(2), one Nb(1), and one Ga(1) atom.
Eu2NbGaO7 crystallizes in the orthorhombic Imma space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to two equivalent O(1), two equivalent O(2), and four equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share edges with two equivalent Eu(1)O8 hexagonal bipyramids, edges with four equivalent Eu(2)O8 hexagonal bipyramids, edges with two equivalent Ga(1)O6 octahedra, and edges with four equivalent Nb(1)O6 octahedra. Both Eu(1)-O(1) bond lengths are 2.25 Å. Both Eu(1)-O(2) bond lengths are 2.58 Å. All Eu(1)-O(4) bond lengths are 2.61 Å. In the second Eu site, Eu(2) is bonded to two equivalent O(1), two equivalent O(3), and four equivalent O(4) atoms to form distorted EuO8 hexagonal bipyramids that share edges with two equivalent Eu(2)O8 hexagonal bipyramids, edges with four equivalent Eu(1)O8 hexagonal bipyramids, edges with two equivalent Nb(1)O6 octahedra, and edges with four equivalent Ga(1)O6 octahedra. Both Eu(2)-O(1) bond lengths are 2.28 Å. Both Eu(2)-O(3) bond lengths are 2.58 Å. All Eu(2)-O(4) bond lengths are 2.57 Å. Nb(1) is bonded to two equivalent O(2) and four equivalent O(4) atoms to form NbO6 octahedra that share corners with two equivalent Nb(1)O6 octahedra, corners with four equivalent Ga(1)O6 octahedra, edges with two equivalent Eu(2)O8 hexagonal bipyramids, and edges with four equivalent Eu(1)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 46-47°. Both Nb(1)-O(2) bond lengths are 2.03 Å. All Nb(1)-O(4) bond lengths are 2.00 Å. Ga(1) is bonded to two equivalent O(3) and four equivalent O(4) atoms to form GaO6 octahedra that share corners with two equivalent Ga(1)O6 octahedra, corners with four equivalent Nb(1)O6 octahedra, edges with two equivalent Eu(1)O8 hexagonal bipyramids, and edges with four equivalent Eu(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 47-50°. Both Ga(1)-O(3) bond lengths are 2.01 Å. All Ga(1)-O(4) bond lengths are 2.03 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Eu(1) and two equivalent Eu(2) atoms to form OEu4 tetrahedra that share corners with two equivalent O(3)Eu2Ga2 tetrahedra, corners with two equivalent O(2)Eu2Nb2 tetrahedra, corners with four equivalent O(1)Eu4 tetrahedra,  an edgeedge with one O(3)Eu2Ga2 tetrahedra, and  an edgeedge with one O(2)Eu2Nb2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Eu(1) and two equivalent Nb(1) atoms to form distorted OEu2Nb2 tetrahedra that share corners with two equivalent O(1)Eu4 tetrahedra, corners with four equivalent O(2)Eu2Nb2 tetrahedra, and  an edgeedge with one O(1)Eu4 tetrahedra. In the third O site, O(3) is bonded to two equivalent Eu(2) and two equivalent Ga(1) atoms to form distorted OEu2Ga2 tetrahedra that share corners with two equivalent O(1)Eu4 tetrahedra, corners with four equivalent O(3)Eu2Ga2 tetrahedra, and  an edgeedge with one O(1)Eu4 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Eu(1), one Eu(2), one Nb(1), and one Ga(1) atom.