Synthesis and crystal structures of a copper(ii) dinuclear complex and zinc(ii) coordination polymers as materials for efficient oxidative desulfurization of dibenzothiophene

Abstract

The synthesis, structure and physical properties of a dinuclear copper(II) complex [Cu₂(BAc)₄(QX)₂], and 2D zinc(II) coordination polymers, [Zn(TDPA)₂(TMPy)₂]_n (where HBAc = 4-hydroxyl benzoic acid; QX = quinoxaline; HTDPA = 3,3-thiodipropionic acid; TMPy = 4,4-trimethylenedipyridine) are presented. The complexes were characterised by elemental analysis, FT-IR, electronic spectroscopy and thermogravimetric analysis. The structures of all the complexes were determined by single crystal X-ray diffraction studies. The geometry around the Cu(II) of [Cu₂(BAc)₄(QX)₂] is slightly distorted square pyramidal, with four oxygen atoms of the carboxylate occupying the trans orientation and one quinoxaline molecule occupying the axial position. [Zn(TDPA)₂(TMPy)₂]_n coordination polymers are linked by two (μ-N)₂ coordination TMPy and two (μ-O)₂ (halves) from (TDPA)⁻. [Zn(TDPA)₂(TMPy)₂]_n stacks in layers with disordered water molecules in the voids. This work further investigated [Cu₂(BAc)₄(QX)₂] catalysed oxidation of dibenzothiophene (DBT) followed by the adsorption of the resulting dibenzothiophene sulfoxide (DBTO) over [Zn(TDPA)₂(TMPy)₂]_n. The theoretical strength of adsorption is in the order of DBTO-[Zn(TDPA)₂(TMPy)₂]_n (binding energy of −53.10 kJ mol⁻¹) > DBT-[Zn(TDPA)₂(TMPy)₂]_n (binding energy of −38.53 kJ mol⁻¹) suggesting that the presence of oxygen influences the adsorption process. The use of [Cu₂(BAc)₄(QX)₂] and [Zn(TDPA)₂(TMPy)₂]_n in model fuel resulted in 97% oxidation of DBT with an adsorption capacity of 35.5 mg g⁻¹, respectively.