Asymmetric and symmetric cobalt(III) dioximates with pyrazinecarboxamide: Synthesis and crystal structure

Abstract

461Pyrazinecarboxamide (Pzca) has four electron donating centers and thus can act, depending on the conditions of the synthesis and the complexing metal, as a ligand with different dentate numbers to form mono , di , and polynuclear complexes. Analysis of the Cambridge Crystallographic Data has showed that Pzca in many copper, manganese, vanadyl, mercury, and silver complexes [1-8] is coordinated to the cen tral metal atom through only one N atom of the het erocycle, although its structure contains several elec tron donating centers. However, in terbium, neody mium, and cobalt complexes, as well as in some copper complexes, this organic molecule acts as a bidentate ligand coordinated to the metal atom through the N atom of the heterocycle and the car bamoyl O atom to give mononuclear complexes [9][10][11][12][13][14][15][16]. Pyrazinecarboxamide derivatives additionally functionalized with СONH 2 or СОО -always act as bidentate ligands coordinated either through the same pair of N, O atoms (as, e.g., in copper and nickel com plexes [17][18][19]) or through the electron donating atom of the substituent [20]. Mononuclear complexes of transition metals with Pzca can have the metal : Pzca ratios of 1 : 1 [1, 6, 17, 19] and 1 : 2 [2, 3, 5, 7, 11-16], regardless of the mono or bidentate coordi nation of Pzca. In Nd and Tb complexes, three such ligands are coordinated in a bidentate fashion to one metal atom, through more than two electron donating centers. Pyrazinecarboxamide acts as a bridging ligand in copper and silver complexes using a set of N,N,O atoms to form a polynuclear structure. One Pzca ligand can be coordinated to two metal atoms [21][22][23] (being bidentate with respect to one and monodentate with respect to the other) or to three metal atoms in a monodentate fashion as in a silver complex [24].When analyzing the Cambridge Crystallographic Data, we have found several crystallographic studies of metal complexes combining Pzca and other organic ligands [4,8,16,22]. However, data on complexes of transition metal dioximates with Pzca are lacking. To reveal the way in which Pzca is coordinated to the cen tral metal ion, the specific features of the coordination polyhedron of Co(III), and the relative positions and crystal packing of the complexes, we obtained four dif ferent complexes all combining dioxime (DioxH) resi due and Pzca. Three of the complexes were identified by X ray diffraction:[CoCl(NioxH) 2 (Pzca)] (II), and [CoCl(DmgH)(NioxH)(Pzca)] ⋅ 0.5C 2 H 5 OH ⋅ 0.5Н 2 О (III), where DmgH, DfgH, and NioxH are the monoanions of dimethylglyoxime, diphenylglyoxime, and cyclohexane 1,2 dione dioxime, respectively. Complexes I and II contain only one type of the dioxime (DfgH or NioxH), while asymmetric com plex III contains the residues of different dioximes (DmgH and NioxH). We also obtained a symmetric Co(III) complex with DmgH and Pzca, viz., [CoCl(DmgH) 2 (Pzса)] (IV). Complexes I-IV were examined by elemental analysis and IR spectroscopy. Abstract-A number of novel complexes of cobalt(III) trans dioxim...