Often alkali metal hydrides react with metal halides. Illustrative storage compounds are hydrocarbons, boron hydrides, ammonia, and alane etc. It oxidizes chemicals such as hydrides, alkali metals, and some alkaline earth metals. With hydrogen, alkali metals form saline hydrides that hydrolyse in water. Aluminium chloride reacts with calcium and magnesium hydrides in tetrahydrofuran forming tetrahydroaluminates. Ytterbium reacts with hydrogen to form various non-stoichiometric hydrides. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile. Treatment of aromatic nitro compounds with metal hydrides gives good yields of azo compounds. A large number of anionic boron hydrides are known, e.g. [BH]. Pnictogens can react with hydrogen to form pnictogen hydrides such as ammonia. Transition metal hydrides include compounds that can be classified as "covalent hydrides". Metal complexes containing terminal hydrides are common. Both additives are able to oxidize the ruthenium hydrides which may explain their behavior. Hydrogen is more electronegative than silicon hence the naming convention of silyl "hydrides". Hydrogen can also be made by chemical reduction using chemical hydrides or aluminum.