A new polypyridyl ligand 4โ(4โnitrophenoxy)โN,Nโbis (pyridinโ2โylmethyl)aniline (L1) and its three ruthenium (II/III) complexes, [Ru (Cl)3L1] (C1), [Ru(L1)2]Cl (C2), and [RuCl (dpa)L1] (C3) where dpaโ=โ2,2โdipyridylamine, have been successfully synthesized and characterized using Fourierโtransform infrared spectroscopy (FTIR), elemental analysis, proton nuclear magnetic resonance (1H NMR), highโresolution electrospray ionization mass spectrometry (HRโESIโMS), thermal analysis (thermogravimetric analysis [TGA] and differential scanning calorimetry [DSC]), UV/Vis absorption, and magnetic susceptibility. The structures of the ligand and the complexes were optimized, and the structural characteristics were determined by density functional theory (DFT) using the B3LYPโGD3/6โ311G++(d,p) method. Optimized FTIR vibrational frequencies and 1H NMR chemical shifts agreed well with the corresponding experimental FTIR and 1H NMR data. In vitro cytotoxicity of the ligand and the complexes were evaluated against the MCFโ7 breast cancer cell line. Ligand L1 was the most potent with an IC50 of 38.45โฮผM, followed by C2 with an IC50 of 45.23โฮผM. However, the ligand and the complexes showed low antiproliferative activity compared to cisplatin, which had an IC50 of 9.67โฮผM. To predict the reactivity trend of L1 and the complexes, frontier molecular orbital (FMO) analysis was performed. The FMO energy gap (Egโ=โELUMOโโโEHOMO) for C2 was found to be 1.675โeV, which was the lowest among all the complexes or L1. In addition, molecular docking studies were carried out so as to predict the binding capacity of L1 and the complexes to estrogen receptor alpha (ERโฮฑ). The results showed that C2 has the most negative binding energy score (โ9.63โkcal/mol), which indicates more stable adducts with the key amino acid residues at the active sites of ERโฮฑ. Furthermore, C2 displayed the lowest inhibition constant (Ki) of 0.09โฮผM compared to all the complexes or L1. These results are very promising and show that the novel complex C2 may help in the development of anticancer drugs.