The structure of phthalocyanine is shown below: H2PcThe complex fCu(Pc)l is an important c...

The structure of phthalocyanine is shown below:

H2Pc

The complex fCu(Pc)l is an important commercial pigment and its electronic absorption spectrum is shown in Fig. 20.40. The absoiption spectrum represented by the green line in Fig. 20.40 arises from another metal(ll) phthalocyanine complex, [M(Pc)]. (a) Suggest how the ligand H2Pc binds Cu2+, and draw the structure of [Cu(Pc)]. Comment on its formation in terms of the chelate effect, (b) What colour is the [Cu(Pc)J pigment? Rationalize your answer, (c) The absoiptions around 600- 650 nm in Fig. 20.40 arise from 7r*-— tt transitions. Explain what this notation means and the origins of the orbitals involved, (d) Explain how the absorption spectrum of [M(Pc)J gives rise to a green pigment, (e) When Cu2-1 forms a complex with the perchlorinated analogue of H2Pc, there is a red shift in the lowest energy absorption band compared to that in the spectrum of [Cu(Pc)J. How does this affect the colour of the pigment? (f) Inkjet printing dyes based on [Cu(Pc)] contain sulfonate substituents. Suggest a reason for this.

Fig. 20.40 The electronic absorption spectrum of copper(ll) phthalocyanine, |Cu(Pc)J, (red trace) and an absoiption spectrum of a different metal(ll) phthalocyanine, |M(Pc)] (green trace). [Based on Figure 4 in: P. Gregory in Comprehensive Coordination Chemistry II. 2004, Elsevier, Chapter 9.12, p. 549.1.