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

Two transition metal complexes containing copper (II) ion, dye methyl red (H-MR) and nitrogen donor ligands beta/gamma-picoline (beta/gamma-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, FTIR) and thermogravimetric analyses. The crystal structures of both complexes have been unambiguously determined by single crystal X-ray analysis as [Cu(MR)(2) (beta-pic)(2)] for 1 and [Cu(MR)(2) (gamma-pic)(2) (MeOH)(0.5)(H2O)(0.5)]center dot 0.5MeOH center dot 1.5H(2)O for 2. Whereas in complex 1 Cu(II) coordinated by carboxylate oxygen atoms of two MR and nitrogen atoms of two beta-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/O-H center dot center dot center dot 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) (gamma-Pic)(2)(H2O) 2w approximate to Cu(MR)(2) (beta-pic)(2)(H2O) 1w > cu(MR)(2) (gamma-pic)(2) (MeOH) 2m approximate to Cu(MR)(2) (beta-pic)(2) (MeOH) 1m >> Cu(MR)(2) (beta-pic)(2) 2b approximate to Cu(MR)(2) (beta-pic)(2) 1, suggesting the significant role of solvent's coordination in enhancing the thermodynamic stability of metal coordination complexes. (C) 2018 Elsevier B.V. All rights reserved.