section_path: Compounds/Coordination chemistry
section_name: Coordination chemistry
paragraph_text: Coordination chemistry
  
  Copper forms coordination complexes with ligands. In aqueous solution, copper(II) exists as. This complex exhibits the fastest water exchange rate (speed of water ligands attaching and detaching) for any transition metal aquo complex. Adding aqueous sodium hydroxide causes the precipitation of light blue solid copper(II) hydroxide. A simplified equation is:
  
  Aqueous ammonia results in the same precipitate. Upon adding excess ammonia, the precipitate dissolves, forming tetraamminecopper(II):
  
  Many other oxyanions form complexes; these include copper(II) acetate, copper(II) nitrate, and copper(II) carbonate. Copper(II) sulfate forms a blue crystalline penta hydrate, the most familiar copper compound in the laboratory. It is used in a fungicide called the Bordeaux mixture.
  
  Polyols, compounds containing more than one alcohol functional group, generally interact with cupric salts. For example, copper salts are used to test for reducing sugars. Specifically, using Benedict's reagent and Fehling's solution the presence of the sugar is signaled by a color change from blue Cu(II) to reddish copper(I) oxide. Schweizer's reagent and related complexes with ethylenediamine and other amines dissolve cellulose. Amino acids such as cystine form very stable chelate complexes with copper(II) including in the form of metal-organic biohybrids (MOBs). Many wet-chemical tests for copper ions exist, one involving potassium ferricyanide, which gives a red-brown precipitate with copper(II) salts.