In chemistry, a complex, also called a "coordination compound" or "metal complex", is a structure consisting of a central atom or molecule connected to surrounding atoms or molecules. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. As applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong. Copper is a transition metal, which in the zero oxidation state has an electron configuration of [Ar]4s24p63d9. Copper is found in three different oxidation states: Cu(I), Cu(II), and Cu(III). Copper (I) atoms have 10 d electrons. Cu(I) complexes being d10 have no Jahn-Teller distortion. Cu (I) complexes are diamagnetic and typically colorless. If a Cu(I) complex is colored, the color is a result of a charge transfer band or an internal transition in a ligand. In the copper(II) oxidation state, the metal has 9 d electrons. Jahn- Teller distortion causes a splitting of eg and t2g orbitals. Most Cu(II) complexes are square planar for this reason. Usually observed in the electronic spectra of Cu(II) complexes is a single broad, poorly resolved band envelope. This envelope is typical of Cu(II) complexes in tetragonal complexes. These complexes are generally blue or green because of an absorption band in the 600-900 nm region of the spectrum. Reproducing complex biological reactivity within a simple synthetic molecule is a challenging endeavor with both intellectual and aesthetic goals. The sequence of examining biological reactivity, creating similar chemical architectures, and determining functional reaction conditions for model systems is a process that allows the biological code of reactivity to be deciphered. In the past years the report on the crystal structures of type 3 copper enzymes (e.g. catechol oxidase, hemocyanins, and tyrosinase), as too type 2 - type 3 copper enzymes (e.g. ascorbate oxida.