Electrochemical synthesis and structural characterization of homoleptic and heteroleptic cobalt, nickel, copper, zinc and cadmium compounds with the 2-hydroxy-1,4-naphthoquinone ligandDedicated to the memory of Professor Antonio Sousa.Electronic supplementary information (ESI) available: Table S1 shows the hydrogen bonding parameters for compounds 16. Table S2 shows OC&z.dbd;O interactions for compounds 1 and 2. Table S3 shows ,-stacking interactions for compounds 16. Table S4 shows CH interacti

• Main Authors: Casanova, Isabel, Sousa-Pedrares, Antonio, Viqueira, Joaquin, Durn, Mara L, Romero, Jaime, Sousa, Antonio, Garca-Vzquez, Jos A
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c3nj00227f

The electrochemical oxidation of anodic metals (cobalt, nickel, copper, zinc or cadmium) in an acetone solution of the ligand 2-hydroxy-1,4-naphthoquinone (HL) afforded homoleptic [ML 2 ] compounds. The addition to the cell of co-ligands (L) such as 2,2-bipyridine (bipy), 1,10-phenanthroline (phen) or 1-methylimidazole ( N -MeIm) allowed the one-step synthesis of heteroleptic [ML 2 L n ] compounds. The crystal structures of [CoL 2 (H 2 O) 2 ]MeOH ( 1 ), [CoL 2 (H 2 O)(MeOH)] ( 2 ), [CuL 2 ( N -MeIm) 2 ] ( 3 ), [CoL 2 (bipy)] ( 4 ), [ZnL 2 (bipy)] ( 5 ) and [CdL 2 (bipy)] ( 6 ) have been determined by X-ray diffraction techniques. In compounds 1 and 2 the metal is in a distorted octahedral [CoO 6 ] geometry with the quinone acting as a monoanionic bidentate ligand. In both complexes, classical OHO-type intermolecular interactions dominate the crystal packing behavior. In 1 this gives rise to tetrameric supramolecular units that are connected through coordinated water molecules. In 2 dimers are formed and these are grouped in layers, which are held together by coordinated water molecules. In 3 the copper atom is in a regular square planar [CuO 2 N 2 ] environment with the ligand acting in a monodentate manner. In this case the crystal packing involves non-classical CHO and -stacking interactions. Complexes 4 , 5 and 6 are six coordinated [MO 4 N 2 ] systems with a distorted octahedral geometry for 4 and 5 and a trigonal prismatic geometry for 6 . This difference in molecular geometry is reflected in the crystal packing of the compounds. Thus, in 4 and 5 the non-classical CHO intermolecular interactions responsible for the crystal packing involve the CH groups in positions 6 and 6 of the 2,2-bipyridine and the oxygens of the two phenolate groups, which give rise to ribbons of molecules. In 6 these interactions involve the CH groups in positions 5 and 5 of the 2,2-bipyridine, which give rise to molecular layers. All compounds were characterized by microanalysis, IR, UV-visible (Co, Ni and Cu complexes) and 1 H NMR spectroscopy (Zn and Cd complexes) and FAB mass spectrometry. One-pot electrochemical synthesis of metal complexes containing 2-hydroxy-1,4-naphthoquinone is reported.