Helicity in Photocatalysis – Advantage or Obstacle? Studies on Silver Complexes – Synthesis, Structure, and Photocatalytic Activity

Abstract

Much attention has been focused recently on the improvement of the photocatalytic efficiencies of known degradation catalysts and the design of new ones. As silver(I) compounds are of high interest in the field of photodegradation owing to their good optical and electron properties concerning their HOMO-LUMO (HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) band gaps, we have synthesized two new complexes with a Schiff base type ligand (L) of formulas [AgL(OTf )] (OTf = triflate) and [Ag 2 L 2 ][PF 6 ] 2 (monomeric and helical, respectively). In this [a]

Co(II/III) Complexes with Benzoxazole and Benzothiazole Ligands as Efficient Heterogenous Photocatalysts for Organic Dyes Degradation

“…Three Schiff base type ligands HL 1 , L 2 , and L 3 comprising three-donor-binding-units ( Figure 2) were synthesized in a two-step protocol via (i) nucleophilic substitution of 2-chlorobenzothiazole (HL 1 and L 2 ) or 2-chlorobenzoxazole (L 3 ) with excess of 1-methylhydrazine and (ii) condensation of thus obtained products with salicylaldehyde (HL 1 ) [29] or 2-pyridinecarboxaldehyde (L 2 and L 3 ) [28,30]. The selected ligands exhibit different coordination motifs (NNO in HL 1 vs. NNN in L 2 /L 3 ).…”

“…Complex 1 has a "closed" coordination sphere filled with two organic ligands HL 1 which makes it less active as a photocatalysts in comparison to the complexes 2 and 3. The lack of labile coordination sites impedes the photocatalytic action because of the hindrance of active center of photocatalyst which is the metal ion [28]. This can also be affected by the quasi-reversible redox processes related to the metallic center of complex 1.…”

“…By using Co(II) ions instead of Ag(I) we were able to lower the energy gap from the level of ca. 2.7 eV [28] and potentially utilize the visible light more efficiently. It stays in a good agreement with the photocatalytic measurements which showed that complex 1 and 3 are not active when irradiated with the UV light.…”

“…Ligands HL 1 -L 3 (Figure 2) were prepared according to the synthetic procedures reported previously, HL 1 [29], L 2 [28], and L 3 [30].…”

“…Because of the previous research in our group [28], we decided to check the photocatalytic activity of complexes 1-3 based on Co(II/III) metal ions with the following model textile and food dyes: Reactive Blue 21 (RB21) and Acid Red 18 (AR18) ( Figure 1). Also electrochemical measurements for all complexes and ligands were investigated.…”