Sr3Ga2P4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent P(2) and four equivalent P(1) atoms. In the second Sr site, Sr(2) is bonded to two equivalent P(1) and four equivalent P(2) atoms to form distorted SrP6 octahedra that share corners with four equivalent Ga(1)P4 tetrahedra, edges with two equivalent Sr(2)P6 octahedra, and edges with four equivalent Ga(1)P4 tetrahedra. Ga(1) is bonded to two equivalent P(1) and two equivalent P(2) atoms to form distorted GaP4 tetrahedra that share corners with two equivalent Sr(2)P6 octahedra, corners with two equivalent Ga(1)P4 tetrahedra, edges with two equivalent Sr(2)P6 octahedra, and  an edgeedge with one Ga(1)P4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-55°. There are two inequivalent P sites. In the first P site, P(1) is bonded in a 7-coordinate geometry to one Sr(2), four equivalent Sr(1), and two equivalent Ga(1) atoms. In the second P site, P(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ga(1) atoms to form a mixture of distorted corner and edge-sharing PSr4Ga2 pentagonal pyramids.
Sr3Ga2P4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent P(2) and four equivalent P(1) atoms. There is one shorter (3.01 Å) and one longer (3.03 Å) Sr(1)-P(2) bond length. There are a spread of Sr(1)-P(1) bond distances ranging from 3.13-3.47 Å. In the second Sr site, Sr(2) is bonded to two equivalent P(1) and four equivalent P(2) atoms to form distorted SrP6 octahedra that share corners with four equivalent Ga(1)P4 tetrahedra, edges with two equivalent Sr(2)P6 octahedra, and edges with four equivalent Ga(1)P4 tetrahedra. Both Sr(2)-P(1) bond lengths are 3.16 Å. There are two shorter (3.01 Å) and two longer (3.04 Å) Sr(2)-P(2) bond lengths. Ga(1) is bonded to two equivalent P(1) and two equivalent P(2) atoms to form distorted GaP4 tetrahedra that share corners with two equivalent Sr(2)P6 octahedra, corners with two equivalent Ga(1)P4 tetrahedra, edges with two equivalent Sr(2)P6 octahedra, and  an edgeedge with one Ga(1)P4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-55°. There is one shorter (2.43 Å) and one longer (2.46 Å) Ga(1)-P(1) bond length. There is one shorter (2.38 Å) and one longer (2.40 Å) Ga(1)-P(2) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded in a 7-coordinate geometry to one Sr(2), four equivalent Sr(1), and two equivalent Ga(1) atoms. In the second P site, P(2) is bonded to two equivalent Sr(1), two equivalent Sr(2), and two equivalent Ga(1) atoms to form a mixture of distorted corner and edge-sharing PSr4Ga2 pentagonal pyramids.