Synthesis, Structural, and Quantum Chemical Analysis of Neutral and Cationic Ruthenium(II) Complexes with Nicotinate-Polyethylene Glycol Ester Ligands

Ruthenium(II/III)-based compounds have gained significant interest due to the biocompatibility of ruthenium, its similarity to iron, and the possibility for structural diversification through the choice of ligands. In this contribution, two novel ligands, (2-(2-methoxyethoxy)ethyl nicotinate hydrochloride) and (2-[2-(2-methoxyethoxy)ethoxy]ethyl nicotinate hydrochloride) (pyCOO(CH2CH2O)nCH3: L2, n = 2; L3, n = 3), were synthesized and characterized via ESI-HRMS, as well as IR and NMR spectroscopies. Their structures were optimized at the B3LYP/6-311++G(d,p) level of theory, and NMR chemical shifts were predicted, along with the most important intramolecular interactions. Additionally, two neutral complexes of the general formula [RuCl2(eta 6-p-cym) (L-kappa N)] (L = L2: 2; L3: 3) and two cationic complexes of the general formula [RuCl(eta 6-p-cym)(L-kappa N)2][PF6] (L = L1: 4; L2: 5) were obtained and characterized. The optimization of the structures was performed at the B3LYP/6-31+G(d,p)(H,C,N,O,Cl)/LanL2DZ(Ru) level of theory. Structural features were described, and intramolecular stabilization interactions were outlined.