Experimental and Computational Investigation of Salophen–Zn Gas Phase Complexes with Cations: A Source of Possible Interference in Anionic Recognition

We
explore the possibility that protonated molecular ions might
be an unexpected source of interference in the recognition process
of anions and neutral species by Zn–salophen receptors. Zn–salophen
complexes are known to bind anions and neutral molecules in solution.
We present here evidence (from computational work and IRMPD spectroscopy)
that these complexes can also be the binding site for protonated pyridine
or quinuclidine. The resulting binding pattern does not involve the
Zn ion, but one of the oxygen atoms directly attached to it. The resulting
complex therefore turns out to have a positive charge adjacent to
the Zn–salophen binding site. This finding seems to point to
the existence of an interfering factor in the quantification of the
experimental data about the association constant.