anion CN+ polyhedron hexahedron 0.732 octahedron 0.414 tetrahedron 8—6-4—3 0.225 trigonal 0.155anion polyhedron CN＋ ( )min hexahedron 8 0.732 octahedron 6 0.414 tetrahedron 4 0.225 trigonal 3 0.155 − + r r