 Ionic crystals may contain a mixture of covalent and ionic species, as for example salts of complex acids such as sodium cyanide, NaCN.X-ray diffraction shows that in NaCN, for example, the bonds between sodium cations (Na+) and the cyanide anions (CN−) are "ionic", with no sodium ion associated with any particular cyanide.However, the bonds between C and N atoms in cyanide are of the "covalent" type, so that each carbon is strongly bound to "just one" nitrogen, to which it is physically much closer than it is to other carbons or nitrogens in a sodium cyanide crystal.