Supramolecular architectures of metal complexes containing 4-sulfobenzoate dianion and 1,2-bis(4-pyridyl)ethane

In this work, synthesis, spectroscopic properties (infrared and Raman) and crystal structures of four new supramolecular arrangement named [Mn(Hbpa)2(H2O)2(4-sb)2]·2H2O (1), [Co(Hbpa)2(H2O)4](4-sb)2 (2), [Ni(Hbpa)2(H2O)4](4-sb)2 (3) and [Zn(Hbpa)2(H2O)4](4-sb)2 (4) have been reported, where bpa is 1,2-bis(4-pyridyl)ethane, Hbpa is the protonated bpa species and 4-sb2− is the sulfobenzoate diânion. All compounds crystallize in a triclinic system with space group P1¯; however, only for the complex 1 it was observed the coordination between the metal site and the building block 4-sb2−, being possible to assign the metal hardness. Despite this observed differentiation, the supramolecular arrangement exhibited a similar disposition of planes present in all structures (distinction of 4-sb2− ligand), showing supramolecular interactions such as hydrogen bonding, π-stacking, C–H⋯π and electrostatics interactions, all of them responsible for the stability of the synthesized compounds. The vibrational spectra of all the compounds are very similar, in agreement with the crystal data. The Raman spectra have showed important bands to confirm the compound formation at 1637 and 1617 cm−1, assigned ν(−O–CO) and ν(CC)/ν(CN) of the 4-sb2− and Hbpa building blocks, respectively, in addition to the disappearance of a major band in the synthesized compounds at 801 cm−1, related to the δ(COOH) mode. Other very important vibrational markers for the bpa ligand can be seen at ca. 1020 cm−1, all of them assigned to the ν(ring) for compounds 1 to 4, respectively. The lower value for the ν(ring) was observed for compound 1, then suggesting that the coordination by the 4-sb2− building block is important for the weakness of this vibrational mode.

Graphical abstractFour Mn(II), Co(II), Ni(II) and Zn(II) complexes with multidentate organic acid and nitrogen ligand have been obtained. For the manganese complex was observed a different coordination, where only the 4-sulfobenzoate ions are bonded, whereas for all the other compounds the 1,2-bis-(4-pyridyl)ethane is also coordinated. For all the compounds, hydrogen bonds, C–H⋯π and π-stacking are the major forces driving the solid state arrangement.Figure optionsDownload full-size imageDownload as PowerPoint slide