First hyperpolarizability of Ru-half-sandwich complexes: The effect of halogen atom substitution on the ancillary ligand

•β of Ru-complexes with single halogen substituted 2-mercaptobenzothiazole ligand.•Doubling of β in going from F to Br substitution.•Manifestation of both resonance and inductive effects of halogen atom on β.

The first hyperpolarizability (β) of a series of half-sandwich Ru complexes with a mercaptobenzothiazole ligand bearing a halogen atom substitution in the para-position has been investigated by hyper-Rayleigh scattering and quantum chemical calculations. The heterocyclic ligand with a bromine atom in the para position makes it a very good donor and charge flows to the Ru center enhancing the β value of the complex by a factor of 2 compared to the complex with the ligand without the halogen substitution. The resonance (+R) and the inductive (-I) effects exerted by the halogen atom in the para position push electrons in opposing directions in the complex. For the Br and Cl atoms the resonance effect dominates which enables the ligand to donate electrons to the metal center thereby increasing the hyperpolarizability whereas for the fluorine atom, the inductive effect is dominant which reduces the charge flow to the metal and the hyperpolarizability drops even below that of the unsubstituted ligand. This unprecedented halogen atom effect on β of metal complexes is reported.

Graphical abstractFirst hyperpolarizability (β) of Ru-complexes with single halogen substituted 2-mercaptobenzothiazole ligand doubles in going from F to Br substitution.Figure optionsDownload full-size imageDownload as PowerPoint slide