HSAB principle and nickel(II) ion reactivity towards 1-methyhydantoin

1-Methylhydantoin and its novel nickel(II) complex [Ni(H2O)4(1-mhyd)2] were prepared and identified, by elemental analysis, single crystal X-ray determination and MS methods. In addition, the complex was characterized by spectroscopic (IR, UV–Vis), magnetic and thermal techniques. The ligand reveals an interesting supramolecular architecture with both classical and non-conventional extended HB bonding networks. All rings and chains formed due to this HB bonding are embedded into the undulated pattern. A single crystal X-ray diffraction analysis of the complex shows that the nickel ion is coordinated by deprotonated hydantoin and water ligands in a N2O4 tetragonal arrangement. In the [Ni(H2O)4(1-mhyd)2] structure both inter and intramolecular hydrogen bonds are created with the participation of water molecules.The ESI-MS method confirmed mono-nuclearity of the complex while electronic spectroscopy proved the tetragonal and pseudooctahedral geometries around the metal ion in the solid state and solution, respectively. By application of the “average environment rule”, 10Dq parameters were obtained for the hypothetical, hexa-coordinate [Ni(1-mhyd)6] approximation or rather more realistic [Ni(1-mhyd)3] chelate. Based on this the mhyd ligand was ranked in the spectrochemical series close to ammonia. The general consideration of the structure of the hydantoin complexes as a function of the metal ion hardness within the framework of the HSAB theory has been provided. Both the ligand and the complex were found to be non-toxic agents against breast (MCF-7), lung carcinoma epithelial (A549) and mouse fibroblasts (Balb/3T3) cancer cell lines.

Graphical abstractThis paper contains the structural characterization of 1-methylhydantoin and its Ni(II) mononuclear complex: [Ni(H2O)4(1-mhyd)2] (1). The structure determination of (1) revealed tetragonally distorted coordination polyhedron around the metal ion involving two N(3) atoms, one from each 1-methylhydantoinate anion and the O atoms of four water molecules. The crystal field strength of 1-mhyd was determined on the basis of the electronic spectra analysis with two levels of approximation. The mode of hydantoins binding to the metal ion was found to correlate with the position of the latter in the frame of the HSAB theory.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The mode of hydantoin derivatives coordination related to metal hardness. ► The level of symmetry approximation important in the analysis of CF. ► The 1-mhyd ligand reveals an interesting supramolecular architecture. ► The ligand positioned in the spectrochemical scale. ► Both the ligand and complex are not cytotoxic.