Energetically significant anti-parallel π-stacking and unconventional anion-π interactions in phenanthroline based Ni(II) and Cu(II) coordination compounds: Antiproliferative evaluation and theoretical studies

Two new coordination compounds of Ni(II) and Cu(II), viz. [Ni(phen)(2)Cl(H2O)] 4-NO(2)bz center dot 3H(2)O (1) and [Cu(phen)(2)Cl]Cl center dot 5H(2)O (2) (phen = 1,10-phenanthroline, 4-NO(2)bz = 4-nitrobenzoate) have been synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, electronic spectroscopy, TGA and EPR. The detailed crystal structure analysis of the Werner Type Clathrate 1 reveals the self-assembled unconventional enclathration of 4-NO(2)bz moieties in supramolecular Ni(II) hosts. In addition to the conventional discrete (H2O)(n) clusters in the crystal structure of 2, the layered architecture involves enclathration of single guest water molecules in the Cu(II) supramolecular hosts. We have theoretically analysed the biologically relevant anti-parallel pi-stacking interactions in compound 1 and two types of anion center dot center dot center dot pi interactions involving coordinated and uncoordinated chloride ions in compound 2. MEP surface analysis and DFT calculations reveal that the anti-parallel pi-stacking interaction in 1 is energetically significant and enhanced upon complexation of the ligands to the Ni(II) centre. Remarkably, studies also reveal that in addition to the conventional anion-ac interaction involving the chloride anion in the lattice, the unusual Cl(chlorido)center dot center dot center dot pi interaction observed in the crystal assembly of 2 is also energetically significant. The antiproliferative potential of the compounds 1 and 2 have been studied in Dalton's Lymphoma (DL) malignant cancer cell lines considering MIT cell viability and apoptosis assays. The compounds 1 and 2 exhibited significant concentration dependent increase in cell cytotoxicity and apoptosis in DL cells with negligible cytotoxicity in normal (PBMC) cells.

Automated summary

Two new coordination compounds of Ni(II) and Cu(II) have been synthesized and characterized by various methods. Compound 1 showed unconventional enclathration of 4-nitrobenzoate moieties, while compound 2 exhibited layered architecture involving enclathration of single guest water molecules.