Synthesis and structure of 1,3-dimethyl-5-(p-sulfonamidephenylazo)-6-aminouracil and its Ni(II) complex: Topological insights and investigation for noncovalent interactions

The azo-derivative, 1,3-dimethyl-5-(p-sulfonamide-phenylazo)-6-aminouracil (HL) containing 6-aminouracil (a biomolecule) and sulfonamide functionality (commonly found in sulfa-drugs), and its Ni(II) complex, (NiL2)-L-II were synthesized. Single-crystal X-ray diffraction studies show that the ligand (HL) consists of an E conformation about the azo-linkage with a nearly planar geometry and the complex possesses distorted square planar geometry. The H-bonded underlying networks of HL and (NiL2)-L-II were topologically classified revealing distinct topological types, namely tts and hxl, respectively. Moreover, topology of molecular packings in HL and (NiL2)-L-II has also been discussed. Density functional theory (DFT) calculations, at the M06-2X/def2TZVP level of theory, are employed to characterize a great variety of non-covalent interactions that explicitly show the importance of antiparallel stacking interactions established by pi(-)-pi(+) interactions and H-bonds in the self-assembled dimmers in HL and 1p-pi/C-H...pi interactions in (NiL2)-L-II. The results of NMR and UV-vis spectroscopies evidence that the ligand exists in hydrazone-imine-keto (B) tautomeric form in solution. The ligand absorption bands consist of the overlapping bands of pi ->pi* and n ->pi* transitions. The complex experiences electronic transitions that consist of basically ILCT in character with some sort of participation of the atomic d-orbitals of the nickel. The pKa value of the ligand is found to be 4.09. (C) 2017 Elsevier B.V. All rights reserved.