Synthesis, spectroscopic characterization, single crystal X-ray analysis and DFT calculation of isomeric Cu(MR)2(β/γ-pic)2 complexes: First transition metal complexes of methyl red

Abstract

Two transition metal complexes containing copper (II) ion, dye methyl red (H-MR) and nitrogen donor ligands β/γ-picoline (β/γ-pic) have been synthesized for the first time using appropriate starting materials in methanol-water (4:1 v/v) as solvent and characterized by spectroscopic methods (UV–Vis, FT-IR) and thermogravimetric analyses. The crystal structures of both complexes have been unambiguously determined by single crystal X-ray analysis as [Cu(MR)2 (β-pic)2] for 1 and [Cu(MR)2 (γ-pic)2 (MeOH)0.5(H2O)0.5]∙0.5MeOH∙1.5H2O for 2. Whereas in complex 1 Cu(II) coordinated by carboxylate oxygen atoms of two MR and nitrogen atoms of two β-pic molecules adopts an almost ideal square planar geometry, in complex 2 Cu(II) additionally coordinated by methanol/water exhibits a distorted square pyramidal structure. Both complexes are packed in layers stabilized by intermolecular C/OH⋯O hydrogen bonds. DFT calculations provided insight into the existence of the six possible relevant complexes. The relative stabilities are in the order Cu(MR)2 (γ-pic)2(H2O) 2w ≈ Cu(MR)2 (β-pic)2(H2O) 1w > Cu(MR)2 (γ-pic)2 (MeOH) 2m ≈ Cu(MR)2 (β-pic)2 (MeOH) 1m » Cu(MR)2 (γ-pic)22b ≈ Cu(MR)2 (β-pic)21, suggesting the significant role of solvent's coordination in enhancing the thermodynamic stability of metal coordination complexes.