Any of a wide range of ionic compounds that have negative ions containing boron and oxygen (see formulae). Lithium borate, for example, contains the simple anion B(OH)4−. Most borates, however, are inorganic polymers with rings, chains, or other networks based on the planar BO3 group or the tetrahedral BO3(OH) group. ‘Hydrated’ borates are ones containing –OH groups; many examples occur naturally. Anhydrous borates, which contain BO3 groups, can be made by melting together boric acid and metal oxides.