Chapter 9 Structural chemistry of ionic compounds 9.1 The ionic radii ratio and the coordination polyhedra of ions Interstices octahedral holes tetrahedral holes hole size is 0.414R hole size is 0.225R CN:6 CN:4Chapter 9 Structural chemistry of ionic compounds 9.1 The ionic radii ratio and the coordination polyhedra of ions octahedral holes hole size is 0.414R CN: 6 tetrahedral holes hole size is 0.225R CN: 4 Interstices