text: Metal ions can be described as consisting of series of two concentric coordination spheres, the first and second. More distant from the second coordination sphere, the solvent molecules behave more like "bulk solvent."  Simulation of the second coordination sphere is of interest in computational chemistry. The second coordination sphere can consist of ions (especially in charged complexes), molecules (especially those that hydrogen bond to ligands in the first coordination sphere) and portions of a ligand backbone. Compared to the first coordination sphere, the second coordination sphere has a less direct influence on the reactivity and chemical properties of the metal complex.  Nonetheless the second coordination sphere is relevant to understanding reactions of the metal complex, including the mechanisms of ligand exchange and catalysis.