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

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)].2H(2)O (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, H-1 and C-13 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 R-1(2)(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)-pi interactions and their interplay with pi-pi interactions.