Investigation on the physicochemical properties of bis[4-(2-aminoethyl) morpholine-K² N, N’] diaquanickel (II) dichloride NLO-single crystal

A novel ultramarine blue single crystal of bis[4-(2-aminoethyl) morpholine-K² N, N′] diaquanickel(II) dichloride (AEMNC) was synthesized using a slow-evaporation solution-growth technique. Single-crystal X-ray diffraction analysis (XRD) confirmed the monoclinic structure, with unit-cell parameters of a = 8.6495 Å, b = 8.6593 Å, c = 13.1882 Å, and β = 107.415°. The molecular structure consists of one Ni²⁺ ion coordinated with two 4-(2-aminoethyl) morpholine ligands and two water molecules. The FTIR analysis verified the presence of key functional groups, while UV–Vis studies revealed a cutoff wavelength of 249 nm and an optical band gap of 4.5 eV, highlighting its potential for optical applications. Thermal analysis indicated that AEMNC is stable up to 115 °C, and the Vickers hardness number of 113.3 kg/mm² confirmed its mechanical robustness. Dielectric studies showed a high dielectric constant at low frequencies, decreasing with frequency, indicating space-charge polarization. Most notably, Z-scan measurements demonstrated a significant third-order nonlinear optical susceptibility (χ³) of 6.54 × 10⁻¹¹ esu, surpassing that of well-known materials like potassium hydrogen phosphate (KDP). These findings establish AEMNC as a promising candidate for nonlinear optical applications, with superior mechanical and optical properties.