Heteroleptic dipyrrinato complexes containing 5-ferrocenyldipyrromethene and dithiocarbamates as coligands: selective chromogenic and redox probes

Abstract

Six heteroleptic dipyrrinato complexes [Ni(fcdpm)(dedtc)] (1), [Ni(fcdpm)(dipdtc)] (2), [Ni(fcdpm)(dbdtc)] (3), [Pd(fcdpm)(dedtc)] (4), [Pd(fcdpm)(dipdtc)] (5), and [Pd(fcdpm)(dbdtc)] (6) (fcdpm = 5-ferrocenyldipyrromethene; dedtc = diethyldithiocarbamate; dipdtc = diisopropyldithiocarbamate; dbdtc = dibutyldithiocarbamate) have been synthesized and characterized by elemental analyses and spectral (ESI-MS, IR, ¹H, ¹³C NMR, UV–vis) and electrochemical studies. Crystal structures of 1, 2, 4, and 5 have been authenticated by X-ray single-crystal analyses. Nickel-based complexes 1–3 display selective chromogenic and redox sensing for Hg²⁺ and Pb²⁺ions, while palladium complexes 4–6 display selective chromogenic and redox sensing only for Hg²⁺. Electronic absorption, ESI-MS, and electrochemical studies indicated that sensing arises from interaction between 1–3 and Hg²⁺/Pb²⁺ through sulfur of the coordinated dithiocarbamates, while it arises from the pyrrolic nitrogen of fcdpm and dithiocarbamate sulfur from 4–6 and Hg²⁺. Different modes of binding between Ni and Pd complexes have further been supported by theoretical studies. The receptor–cation binding constants (K_a) and stoichiometry between probes and Hg²⁺/Pb²⁺ have been estimated by the Benesi–Hildebrand method and Job’s plot analysis. Detection limits for 1–3 toward Hg²⁺/Pb²⁺ and 4–6 for Hg²⁺ have been found to be reasonably high.