Elucidating the properties of a novel [Ni(SCN)4] complex

The structure and properties of a new crystalline compound, having the empirical formula (C₆H₈N₂)₂Ni(SCN)₄·2(C₆H₉N₂) were characterized using several techniques. The synthesized compound contained discrete coordination entities in which Ni²⁺ ions from one end of the coordination sphere are coordinated to four thiocyanate ligands through nitrogen atoms, as well as two 2-amino-4-methylpyridine molecules to form trans-NiN₆ octahedra that have a distorted geometry. These discrete complexes form linear chains, which are held together by hydrogen bonding involving N − H···N and N − H···S interactions between adjacent chains, resulting in a three-dimensional supramolecular framework. The linear chains run parallel to the crystallographic c-axis direction of the crystal growth. The successful synthesis and structural integrity of the compound were confirmed by both single-crystal and powder X-ray diffraction. Additionally, the optical and vibrational properties were investigated through UV-Vis and FT-IR spectroscopy. Two-dimensional fingerprint plots and Hirshfeld surface maps allowed for the identification of the primary intermolecular interactions that lead to the formation of the crystal structure. The compound demonstrates semiconducting behavior with a narrow energy gap of 1.2 eV. This is attributed to the synergistic effect of intramolecular SCN-to-Ni charge transfer and the formation of extended intermolecular stacking pathways. The specific orientation of the molecules within the crystal lattice facilitates π-orbital overlap, enabling efficient charge carrier hopping between adjacent units. Thermogravimetric analysis identified that the compound is thermally stable up to approximately 550 K, where degradation of the organic moiety begins, although a phase transition is observed at 435 K. In addition, in a series of calculations utilizing gas-phase DFT methods, the electron distribution within the trans-NiN₆ complex was determined to be similar to that of previously characterized compounds. Finally, in an effort to evaluate the potential biological value of the compound, a molecular docking study was performed with peroxiredoxin 5, revealing moderate affinity for the antioxidant compound Trolox.