The two cationic palladium(II) complexes, [Pd(L_en)₂][OTf]₂ (4) and [Pd(L_phen)₂][OTf]₂ (5), were synthesized by treatment of bis(benzonitrile)dichloropalladium(II) with [H₂L_en][OTf]₂ (2) or [H₂L_phen][OTf]₂ (3), respectively, in the presence of a weak base. The pro-ligands 2 and 3 were synthesized by melt reactions between N-methyl-4-chloropyridinium triflate (1) and the amines ethylenediamine or phenylenediamine, respectively. The water-soluble compounds 2–5 were fully characterized, including by single-crystal X-ray crystal structure determinations for 2–4. UV-Vis and fluorescence spectroscopy were used to study the binding interactions of 2–5 with CT-DNA. The spectroscopic data suggested the presence of intercalative and groove binding modes and this was supported by molecular docking studies. The in vitro cytotoxicity studies (IC₅₀ values) showed that the human breast cancer cell lines MCF-7 and T47D were more sensitive towards 3, 4 and 5 than cisplatin. The cytotoxicity of the new compounds decreased in the order 5 > 4 > 3 > 2. Furthermore, the annexin V-FITC staining method strongly suggested the presence of phosphatidylserine (PS) on the outer membrane of the treated cells, which is a hallmark of apoptosis.

Aiming to design economical metal-based medications to replace platinum-based drugs in the treatment of a variety of cancers, this article presents four new Zn(II) and Cd(II) complexes namely [Zn(L^m _Me)(OTf)₂] (C1), [Cd(L^m _Me)(Cl)(OAc)] (C2), [Zn(L^m _Bn)(Cl)₂] (C3) and [Cd(L^m _Bn)(Cl)(OAc)] (C4), where L^m _Me = pyridine-2,6-dicarbonyl)bis((1-methylpyridin-1-ium-3-yl)amide and L^m _Bn = pyridine-2,6-dicarbonyl)bis((1-benzylpyridin-1-ium-3-yl)amide, and their anticancer potential. These mesoionic ligands were derived in situ from their respective pro-ligands, H₂L^m _Me(OTf)₂ and H₂L^m _Bn(Cl)₂ in the presence of 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) as a base during complex formation reactions. Elemental analysis, FT-IR and NMR (¹H & ¹³C) spectroscopy were employed to systematically characterize the complexes and single crystal X-ray crystallography was used to confirm the structures. X-ray structural analysis of C3 and C4 revealed that the ligands coordinated to the metal centre in a NNN tridentate fashion, forming two five membered chelate rings. Intermolecular interactions within the crystal structure of C3 and C4 were examined by Hirshfeld surface analysis. Electronic spectroscopy, viscosity measurements and cyclic voltammetry were used to examine the mechanism of interaction of the compounds with CT-DNA. All inspected compounds showed strong affinity toward CT-DNA via non-covalent nature with intrinsic binding constant values in the range of 5.8 × 10³–9.0 × 10⁴ M⁻¹. The MTT assay was executed to test the compound's ability to inhibit the proliferation of two human cancer cell lines (MCF-7 and T47D) along with a normal cell line (Vero). The in vitro anticancer studies showed that the complexes are more efficacious towards MCF-7 and T47D in the following order C4 > C3 > C2 > C1 and the results are consistent with the DNA binding potential. Moreover, the IC₅₀ value of complex C4 in the T47D cell line (21.00 ± 1.41 μM) was comparable to that of cisplatin (25.10 ± 1.09 μM).

• Synthesis of series of novel Pd(II) complexes with NNO-donor ligands. • Subtle variations of electronics and hydrophobicity on ligand arms of complexes. • Pd(II) complex with impressive inhibitory effects against breast cancer cell lines (MDA-MB-231 and MCF-7) • Cancerous cells showed Apoptotic mode of cell death. • Molecular docking studies of most active palladium complex with tyrosine kinases—an integral target in cancer research.

This manuscript provides a comprehensive overview of the synthesis, characterization, and photophysical and electrochemical properties of terpyridine-based metal complexes (C₁–C₂₀). The synthesis of these terpyridine (TPY) complexes involves the coordination of TPY ligands (L₁–L₁₁) with transition metal ions, leading to a variety of novel structural and electronic configurations. The characterization of TPY ligands and their complexes is carried out using various techniques, including UV-Vis spectroscopy, NMR, FTIR and mass spectrometry. To the best of our knowledge, for the first time, we comprehensively investigate the photophysical, solvatochromic, electrochemical, and computational properties of an extensive series of TPY-based metal complexes (C₁–C₂₀) within a single framework. The solvatochromic behavior of the synthesized complexes (C₁–C₂₀) is explored, revealing their sensitivity to solvent polarity, which is a key factor influencing their photophysical properties. The TPY-based complexes (C₁–C₂₀) exhibited solvent-dependent fluorescence behavior, with distinct ILCT and MLCT mechanisms, and enhanced fluorescence in specific solvents, particularly for Zn(II) and Cu(II) complexes. The absorption and emission characteristics of the complexes are studied in dilute solutions to explore their structure–property relationships. Additionally, the electrochemical properties of the TPY-based metal complexes (C₁–C₂₀) are investigated, highlighting their redox activity and potential for use in energy storage and conversion applications. Density functional theory (DFT) calculations are employed to provide detailed insights into the electronic structure and reactivity of these complexes, supporting the experimental observations. The correlation of electronic band gaps with photophysical and electrochemical behaviors showed compounds as promising candidates with efficient charge transfer and strong fluorescence. The integrated analyses reveal the exceptional potential of this scaffold for advanced materials applications, highlighting its versatility and significance in cutting-edge research.

The conversion of CO₂ into CO as a substitute for processing fossil fuels to produce hydrocarbons is a sustainable, carbon neutral energy technology. However, the electrochemical reduction of CO₂ into a synthesis gas (CO and H₂) at a commercial scale requires an efficient electrocatalyst. In this perspective, a series of six new palladium complexes with the general formula [Pd(L)(Y)]Y, where L is a donor-flexible PYA, N²,N⁶-bis(1-ethylpyridin-4(1H)-ylidene)pyridine-2,6-dicarboxamide, N²,N⁶-bis(1-butylpyridin-4(1H)-ylidene)pyridine-2,6-dicarboxamide, or N²,N⁶-bis(1-benzylpyridin-4(1H)-ylidene)pyridine-2,6-dicarboxamide, and Y = OAc or Cl⁻, were utilized as active electrocatalysts for the conversion of CO₂ into a synthesis gas. These palladium(II) pincer complexes were synthesized from their respective H-PYA proligands using 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) or sodium acetate as a base. All the compounds were successfully characterized by various physical methods of analysis, such as proton and carbon NMR, FTIR, CHN, and single-crystal XRD. The redox chemistry of palladium complexes toward carbon dioxide activation suggested an evident CO₂ interaction with each Pd(II) catalyst. [Pd(N²,N⁶-bis(1-ethylpyridin-4(1H)-ylidene)pyridine-2,6-dicarboxamide)(Cl)]Cl showed the best electrocatalytic activity for CO₂ reduction into a synthesis gas under the acidic condition of trifluoracetic acid (TFA) with a minimum overpotential of 0.40 V, a maximum turnover frequency (TOF) of 101 s⁻¹, and 58% FE of CO. This pincer scaffold could be stereochemically tuned with the exploration of earth abundant first row transition metals for further improvements in the CO₂ reduction chemistry.