Complexation of triangular silver(i) or copper(i) nitropyrazolates with dibenzothiophenes having potential use in adsorptive desulfurization

Abstract

Triangular silver(I) and copper(I) 3,5-diethyl-4-nitropyrazolates (abbreviated as [Ag(denpz)]₃ or Ag₃pz₃, and [Cu(denpz)]₃ or Cu₃pz₃), as well as their adducts with dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT) and benzothiophene (BT), have been prepared and characterized by a series of techniques. X-ray analyses show that these adducts are stabilized by M⋯S, M⋯C contacts and π⋯π stacking interactions. NMR measurements and theoretical calculations indicate that the intensity of interaction between the metal complexes and dibenzothiophenes follows the trend: Ag₃pz₃–DMDBT > Ag₃pz₃–DBT > Cu₃pz₃–DMDBT > Cu₃pz₃–DBT, which can be understood on the basis of a weak interaction between π-acid (Ag₃pz₃ or Cu₃pz₃) and π-base (DBT/DMDBT). Both complexes show good adsorptive ability and reusability toward the removal of DBT and DMDBT from model oil (n-octane), with the maximum adsorption capacity at room temperature being 39 mg S (DMDBT) per g Cu₃pz₃, 34 mg S (DMDBT) per g Ag₃pz₃, 40 mg S (DBT) per g Cu₃pz₃, 36 mg S (DBT) per g Ag₃pz₃, respectively. Compared to Ag₃pz₃, Cu₃pz₃ exhibits higher adsorptive capacities for DBT/DMDBT, which has been attributed to its lower molecular mass.