[Cu(NH3)4]2+

[Cu(NH3)4]²⁺, known as a tetraamminecopper(II) complex, is a chemical where a copper ion (Cu²⁺) is surrounded by four ammonia molecules (NH₃). These ammonia molecules act as ligands, meaning they form coordinate bonds with the copper ion, stabilizing it. The entire structure carries a charge of +2. This complex shows vibrant blue color due to the way it absorbs and reflects light, which is common for copper complexes. Such compounds are used in various applications, including catalysis, chemical synthesis, and as part of colorimetric tests.