Cadmium(ii) complexes containing N,N′-dimethylviolurate as ligand or counteranion: synthesis, characterization, crystal structures and DFT study

Abstract

N,N′-dimethylvioluric acid mono hydrate (HDMV) (1·H₂O) and two cadmium(II) complexes with N-donor ligands of formula [Cd(DMV)₂(benzim)₂]·2H₂O (2) (benzim = benzimidazole) and [Cd(H₂O)₄(py)₂](DMV)₂ (3) (py = pyridine) have been synthesized. Free N,N′-dimethyl violuric acid mono hydrate (HDMV) and the complexes have been fully characterized by elemental analysis, IR, ¹H and ¹³C NMR spectral methods, fluorescence spectroscopy, TGA and structural X-ray crystallography. HDMV (1·H₂O) which remains in keto-oxime form in the solid state transforms to the nitroso-enolato form in the complexes [(2) and (3)]. A typical R₁²(6) motif with a bifurcating hydrogen bond is observed in all three structures. Dimethylviolurate anion acts as a bidentate ligand in (2), whereas in (3) it is present as a counter-ion, outside the coordination sphere. In addition, DFT-D3 calculations have been performed to study interesting noncovalent interactions observed in the solid states of (1) and (2) with special interest in the lone pair (lp)–π interactions and their interplay with π–π interactions.