Vibrational and structural studies of new Cu2+ and Co2+ complexes based on croconate ion and 5,5 '-dimethyl-2,2 '-dipiridyl ligands

This work deals with the synthesis and spectroscopic characterization of novel complexes involving the coordination of croconate (C5O5)2- and 5,5′-dimethyl-2,2′-bipyridyl (DmBpy) ligands to the transition metal ions Co2+ and Cu2+. Two complexes involving the croconate species with the DmBpy ligand were obtained. The complex [Cu(C5O5)(DmBpy)(H2O)].H2O (1) crystallizes in a monoclinic system, belonging to the P21/c space group and Z equal to four, whereas[Co(C5O5)(DmBpy)(H2O)2] (2) crystallizes in a triclinic system and belonging to the P-1 space group and Z equal to four. The Cu(II) complex presents a slightly distorted square base pyramid geometry, presenting a water molecule at the vertical position, whereas Co(II) compound shows an octahedral geometry with two water molecules at the vertices. In both compounds croconate ions act as a building block, and the nitrogenous ligand is the spacer agent, giving rise to the 3D structure. The vibrational analysis (Raman and infrared) supports the crystallographic data, and several band markers are identified in order to understand the supramolecular interactions, such as the stretching modes νCC/νCN at 1600 and 1498 cm−1, respectively, shifted by the coordination to higher wavenumbers in both compounds (1604 and 1507 cm−1, and 1604 and 1508 cm−1, for (1) and (2) respectively), thus strongly corroborating the coordination of the ligand to the metal site through the nitrogen atoms present in the pyridine moiety. On the other hand, the band at 1718 cm−1, assigned to the (CO) stretching mode from croconate ion, can be used as the main band marker, due to the observed shift caused by the coordination to the metal center.