Humidity-sensing and DNA-binding ability of bis(4-benzylpiperazine-1-carbodithioato-k² S,S′)nickel(II)

Bis(4-benzylpiperazine-1-carbodithioato-k² S,S′)nickel(II), 1, was prepared by metathesis of sodium salt of 4-benzylpiperazine-1-carbodithioate with nickel(II) chloride in 2: 1 ratio. Complex 1 was characterized by analytical techniques including elemental analysis, FT-IR, UV-visible spectroscopy, and X-ray single-crystal analysis. The latter technique confirmed square-planar geometry around Ni with the formation of NiS₄ core with two shorter and two longer Ni-S bonds. The packing diagram revealed a supramolecular chain structure mediated by unconventional HH dihydrogen bonds that resulted in a chair and a ladder-like structure when viewed along the a-axis and c-axis, respectively. The thin-film coating resulted in a microporous film with a band gap of 1.69 eV. Complex 1-based sensor was fabricated to check the humidity-sensing properties of the material. Resistance of the device decreased by two orders of magnitude and capacitance was enhanced with the increase of relative humidity. The DNA binding study proved 1 to be a good DNA binder with binding constant value of 1.4 × 10⁴ M^-1.