Synthesis and Investigation of Solid‐ and Solution‐State Structures of Nickel(II) Complexes with 1,3‐Dimethyl‐5‐(arylazo)‐6‐aminouracil

The nickel(II)-arylazo-6-aminouracil derivatives, [NiII(DMA3U)2], where HDMA3U (1-3) = 1,3-dimethyl-5-(arylazo)-6-aminouracil [arylazo- => phenylazo (1), p-Me-phenylazo (2), and p-Cl-phenylazo (3)] have been synthesized and isolated in crystalline forms. Single-crystal X-ray diffraction study of [Ni(1)2] reveals that in the complex the metal center has square planar environment. The intramolecular N-H/π and C-H/π interactions hold in the solid state as well as in poor-HBA (H-bonds acceptor) solvents, but are disrupted in good HBA solvents. Crystal structure analysis further shows that the -NH groups of the coordinated ligands are not available for H-bonding interactions in the solid state which have been corroborated by DFT calculations. Complexes exhibit multiple absorption bands in the UV-vis region and TDDFT study was performed to understand the origin of the ground state electronic absorptions. The complexes are found to be highly radiative in poor HBA solvents rather than in good HBA solvents. The complex-HBA solvents association constant (Kasso) values were determined UV-vis spectrophotometrically, which range from 1.18 - 2.51 M-1.