Complexes exhibiting trans(Cl)-RuCl2(dmso-S)2 geometry with methyl-picolinate-type neutral N,O-ligands: Synthesis, structural characterization, and chemical behavior analysis in aqueous solutions

• Synthesized Ru(II) complexes with Mepic and Hpic in MeOH and water solutions. • Complexes showed nearly identical trans (Cl)-RuCl 2 (dmso- S ) 2 geometries. • Water crucial for Hpic in 2 ·H 2 O to retain H + during crystallization. • 1 ·0·25H 2 O unstable in DMSO; 2 ·H 2 O stable because Hpic becomes a negative bidentate ligand, pic – . • 1 ·0·25H 2 O thermally unstable in water, forming MeOH, although free Mepic stable. Methyl picolinate (Mepic) is a starting material in the synthesis of several organic materials and enzymes. Notably, Mepic-ligand-based complexes with metals such as Zn(II), Cd(II), Ru(II), and Rh(III) have garnered attention for catalysis; however, Ru(II)–Mepic complexes remain structurally unexplored. In this study, trans (Cl)-[RuCl 2 (dmso- S ) 2 (Mepic)]·0·25H 2 O ( 1 ·0·25H 2 O, dmso = dimethyl sulfoxide) was produced in a satisfactory yield (80%) via the reaction of trans (Cl)-[RuCl 2 (dmso- S ) 4 ] with neutral N,O -ligand Mepic in methanol (MeOH) at room temperature. The use of picolinic acid (Hpic) instead of Mepic in H 2 O-ethanol (EtOH) produced the corresponding complex— trans (Cl)-[RuCl 2 (dmso- S ) 2 (Hpic)]·H 2 O ( 2 ·H 2 O)—with a slightly higher yield (82%). Crystal structure analysis of 1 ·0·25H 2 O and 2 ·H 2 O revealed that each chelating ligand coordinated to Ru 2+ via pyridyl- N and carbonyl- O atoms and Hpic acted as a neutral bidentate ligand in 2 . In DMSO, 1 was labile and released Mepic to form [RuCl 2 (dmso) 4 ], owing to the hemilability of N,O -ligand Mepic. In contrast, 2 was inert in DMSO because H + was released from Hpic in solution, forming the anionic mono(pic)Ru complex— trans (Cl)-[RuCl 2 (dmso- S ) 2 (pic- κ 2 N,O – )] − . 1 H NMR and UV–Vis spectroscopic studies showed that 2 also generated the anionic mono(pic)Ru complex in aqueous solutions. Although free Mepic is inert in water, 1 underwent thermal hydrolysis in water to produce free MeOH. The dissociation of monodentate ligands was also observed in the thermal hydrolysis of 1 . Thus, it was a complicated reaction. The reaction of 1 with equimolar OH − in water quickly and selectively yielded the same complex and a MeOH molecule. Our study will assist in assessing the catalytic potential of this complex and related systems.