Heteroleptic Dipyrrinato Complexes Containing 5‑Ferrocenyldipyrromethene and Dithiocarbamates as Coligands: Selective Chromogenic and Redox Probes

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 (Ka) 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.

本研究合成了6种异配型二吡咯亚甲基配合物，分别为[Ni(fcdpm)(dedtc)]（1）、[Ni(fcdpm)(dipdtc)]（2）、[Ni(fcdpm)(dbdtc)]（3）、[Pd(fcdpm)(dedtc)]（4）、[Pd(fcdpm)(dipdtc)]（5）及[Pd(fcdpm)(dbdtc)]（6）。其中fcdpm为5-二茂铁基二吡咯亚甲基（5-ferrocenyldipyrromethene），dedtc为二乙基二硫代氨基甲酸酯（diethyldithiocarbamate），dipdtc为二异丙基二硫代氨基甲酸酯（diisopropyldithiocarbamate），dbdtc为二丁基二硫代氨基甲酸酯（dibutyldithiocarbamate）。所有配合物均通过元素分析、光谱测试（电喷雾电离质谱（ESI-MS）、红外光谱（IR）、氢核磁共振谱（¹H NMR）、碳核磁共振谱（¹³C NMR）及紫外-可见吸收光谱（UV–vis））与电化学测试完成表征。配合物1、2、4和5的晶体结构经X射线单晶衍射分析确证。镍基配合物1~3对Hg²+与Pb²+离子表现出选择性比色及氧化还原传感性能，而钯基配合物4~6仅对Hg²+具备选择性比色与氧化还原传感能力。电子吸收光谱、ESI-MS及电化学研究表明，1~3与Hg²+、Pb²+的传感作用源于二者通过配位二硫代氨基甲酸酯的硫原子发生的相互作用；而4~6与Hg²+的传感作用则来源于fcdpm的吡咯氮原子及二硫代氨基甲酸酯的硫原子。镍基与钯基配合物间不同的结合模式进一步得到了理论计算研究的佐证。通过贝奈西-希尔德布兰德法（Benesi–Hildebrand method）与Job作图法（Job’s plot analysis），可估算得到受体-阳离子结合常数（Ka）以及探针与Hg²+、Pb²+间的化学计量比。测试结果显示，1~3对Hg²+、Pb²+以及4~6对Hg²+的检测限均处于合理的较高水平。