Nickel(II) based homo- vs heterometallic 1D coordination polymers derived from a novel 6-aminouracil building block : structures, topologies, non-covalent interactions, magnetism, and antibacterial activity

• Main Authors: Purkayastha, Atanu, Debnath, Diptanu, Majumder, Moumita, Ortega-Castro, Joaquín, Kirillov, Alexander M., Ganguly, Rakesh, Klak, Julia, Frontera, Antonio, Misra, Tarun Kumar
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2020
• Subjects: Science::Chemistry; Coordination Polymer; Crystal Structure
• Online Access: https://hdl.handle.net/10356/139638
• Institution: Nanyang Technological University

A new azo-ligand, 1,3-dimethyl-5-(p-carboxy-phenylazo)-6-aminouracil (H3L) containing 6-aminouracil (a biomolecule) and a carboxylic function (a potential linker) was synthesized. This ligand was then employed for complexation with Ni(II), resulting in the Ni(II)/Na(I) heterometallic {[NiNa2(μ-HL)2(μ-H2O)2(H2O)6]·6H2O}n (1) and Ni(II) homometallic {[Ni2(μ-HL)2(H2O)4]·5·.5H2O}n (2) 1D coordination polymers. These were obtained from similar reaction mixtures and conditions, except the type of the base (NaOH for 1 or KOH/Et3N for 2). Compounds 1 and 2 were characterized by single-crystal X-ray diffraction, UV-vis, NMR, and IR spectroscopy. Both the coordination polymers 1 and 2 show resembling zigzag chains that are topologically classified as 2-connected underlying nets with the 2C1 topology. In 1, the 1D metal-organic chains are further extended by intermolecular H-bonds, giving rise to a 3D H-bonded net; it is topologically described as a uninodal 6-connected net with the pcu topology. In solution, the 1D polymeric structures of both compounds disaggregate into monomeric Ni(II)-square-planar complex units [Ni(HL)2]2−, as evidenced by NMR and UV-vis spectroscopy studies. The magnetic properties of 2 were also investigated, indicating a dominant zero field splitting parameter D of the Ni(II) center. The type of the base is important for tuning the selective formation of the desired product 1 or 2. Density functional theory (DFT) study justifies the experimental findings for a base-assisted selectivity between the compounds 1 or 2 by optimizing their structures at the PBE-D/DNP level of theory. The existence of agostic interactions between the C–H bonds of the methyl groups of the coordinated HL2− moieties and the Ni centers in both structures is suggested by natural bond orbital (NBO) calculations at the M06-2X/6-31 + G∗ level of theory. The compound 1 proves to be a potential inhibitor of a bacterial virulence factor, pyocyanin.