In the complex ion [Cu(NH3)4]2+, the ammonia molecules act as

  • A. ligands, donating a lone pair of electrons to the central metal ion
  • B. reducing agents
  • C. counter ions balancing the charge
  • D. solvent molecules with no bonding role

Explanation

A ligand is a species with at least one lone pair that forms a dative covalent bond to the central metal ion, and here each nitrogen donates its lone pair, giving copper a coordination number of four. Water, chloride and cyanide act in the same way. The deep blue colour of this complex is the standard test for copper two ions.

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