Studies on cobalt(II) complexes with N,N,N′,N′-tetraethylpyridine-2,6-dicarboxamide(L1) containing PF6-,BF4-,ClO4- and NO3- anions: X-ray crystal structures of [Co(L1)2(CH3CN)](PF6)2 and [Co(L1)2(H2O)2](X)2·H2O(X=PF6-,ClO4-)

The ligand N,N,N′,N′-tetraethylpyridine-2,6-dicarboxamide (L1 and abbreviated as deap) reacts with CoX2(X=PF6-,BF4-,ClO4-andNO3-) salts to give the octahedral complexes, [Co(L1)2(CH3CN)](PF6)2 (1) and [Co(L1)2(H2O)2](X)2·H2O(X=PF6-(2),BF4-(3),ClO4-(4)andNO3-(5). The compounds have been characterised by elemental analysis, IR spectroscopy and X-ray crystallography. The composition of the product is dependant upon the nature of the reaction medium. Compound 1 contains ON and ONO bonded deap ligands in bidentate and tridentate coordinating modes, in which the coordination sphere of the Co2+ ion is completed by attachment of an acetonitrile molecule. Compounds 2 and 4 have identical cationic species [Co(L1)2(H2O)]2+ in which Co2+ is bonded by deap ligands in a bidentate ON mode. As deap is coordinating in a bidentate mode, the two coordinating water molecules are placed cis to each other in the octahedral arrangement.The similarity of the molecular structure of compounds 2 and 4 is, interestingly, also reflected in their crystal structures, both are structurally similar with a C2/c space group in the monoclinic crystal system. In the crystal lattice, due to the symmetrical disposition of the complex on a twofold axis, there is an interesting chain of molecules formed through hydrogen bonding. The lattice water has a crucial role in the formation of this chain, in fact it acts as a connecting link between the complex molecules running almost perpendicular to the ‘ac’ plane.

Graphical abstractOctahedral cobalt(II) complexes [Co(L1)2(CH3CN)](PF6)2 (1) and [Co(L1)2(H2O)2](X)2(X = PF6- (2), BF4- (3), ClO4-, (4), NO3- (5)) have been prepared; the composition of the product is dependent upon the reaction medium. The ligands use either ONO or ON donor atoms depending upon the steric demands. Compounds 2 and 4 are structurally similar and the lattice water is involved in the formation of chains by hydrogen bonding between different structural units.Figure optionsDownload full-size imageDownload as PowerPoint slide