Among a large series of monoanions, dihydrogen phosphate gives an anion-specific reaction with ZnII-salphen complexes based on a proton transfer to the chromophore. Detailed NMR and UV/Vis spectroscopic studies and mass spectrometric analyses point to initial activation of the phosphate anion upon coordination, followed by protonation of the phenolic positions of a second ZnII-salphen structure as supported by kinetic investigations. For a bis(ZnII-salphen) chromophore this process is accompanied by a considerable colour change.
![Dimetallic activation of dihydrogen phosphate by Zn(salphen) chromophores](https://www.iciq.org/wp-content/uploads/2014/03/Dimetallic-activation_4611.jpg)