Solvent effects on colors and stability are often attributable to changes in the second coordination sphere. Such effects can be pronounced in complexes where the ligands in the first coordination sphere are strong hydrogen-bond donors and acceptors, e.g. respectively [Co(NH)] and [[Ferricyanide|[Fe(CN)]]].  Crown-ethers bind to polyamine complexes through their second coordination sphere.  Polyammonium cations bind to the nitrogen centres of cyanometallates.