Comparative Studies on the Structural, Optical, and Electrical Properties of Two [Co(II) and Ni(II)] Complexes: Insights through Theoretical Analysis

Two new complexes, [Co(N3L)2](NO3)2·6H2O (complex 1) and [Ni(N3L)2](NO3)2·6H2O (complex 2), have been synthesized using the organic heterocyclic chelating ligand N3L [4-(1-methylimidazole)-2,6-di(pyrazinyl)pyridine] and characterized primarily by single-crystal X-ray diffraction. In addition to detailing the crystal structures of these complexes, we highlight their distorted octahedral geometries and diverse supramolecular interactions, including π···π stacking, anion···π interactions, and hydrogen bonding. These interactions play a crucial role in shaping the distinct 1D, 2D, and 3D supramolecular architectures of both complexes. Notably, noncoordinated water molecules assemble into hexameric water clusters (H2O)6, which are key stabilizing factors for the 3D structures in the solid state. To gain deeper insight into these noncovalent interactions, we performed density functional theory (DFT) calculations combined with quantum theory of atoms in molecules (QTAIM) and noncovalent interaction plot (NCIplot) analyses. These studies allowed us to explore the nature of anion···π interactions and hydrogen bonding within the water clusters. Additionally, the electronic properties of the complexes were investigated through electrical characterization of as-fabricated Schottky diodes, revealing their potential applications in Schottky-diode-based electronic devices. Notably, in the Schottky device structure, complex 1 demonstrated superior electrical transport properties compared to complex 2 followed by its lower bandgap, better conductivity, and lower Schottky barrier height. Furthermore, we analyzed the optical properties of the Co complex (complex 1) as a model system using band structure analysis, density of states (DOS), and projected density of states (PDOS) calculations. The superior performance of complex 1 has also been explained with proper theoretical justification.本研究以有机杂环螯合配体N3L[4-(1-甲基咪唑)-2,6-二(吡嗪基)吡啶]为原料，合成了两种新型配合物[Co(N3L)₂](NO₃)₂·6H₂O（配合物1）与[Ni(N3L)₂](NO₃)₂·6H₂O（配合物2），并主要通过单晶X射线衍射完成结构表征。除详细阐述这两种配合物的晶体结构外，本研究还重点剖析了它们的畸变八面体几何构型，以及丰富的超分子相互作用，包括π···π堆积、阴离子···π相互作用与氢键作用。上述相互作用在构建两种配合物独特的一维、二维及三维超分子架构的过程中发挥了关键作用。值得注意的是，未配位水分子会自发组装为六聚水团簇(H₂O)₆，该团簇是固态下配合物三维结构的核心稳定因素。为深入探究这些非共价相互作用的本质，本研究开展了密度泛函理论（density functional theory, DFT）计算，并结合分子中原子量子理论（quantum theory of atoms in molecules, QTAIM）与非共价相互作用图（noncovalent interaction plot, NCIplot）开展分析。通过上述研究，我们得以阐明阴离子···π相互作用与水团簇内氢键作用的本质。此外，本研究还通过对制备得到的肖特基二极管（Schottky diode）进行电学表征，探究了配合物的电子性质，揭示了其在基于肖特基二极管的电子器件中的潜在应用价值。值得一提的是，在肖特基器件结构中，配合物1展现出优于配合物2的电学传输性能，这源于其更窄的带隙、更高的电导率以及更低的肖特基势垒高度。进一步地，本研究以钴基配合物（配合物1）为模型体系，通过能带结构分析、态密度（density of states, DOS）与投影态密度（projected density of states, PDOS）计算，分析了其光学性质，并为配合物1的优异性能提供了合理的理论解释。