Transition metal complex directed lead bromides with tunable structures and visible light driven photocatalytic properties

Abstract

With similar transition metal (TM) complex cations as structural directing agents (SDAs), six new hybrid lead bromides were synthesized and structurally characterized as [Co(2,2-bipy)₃]₂{[Co(2,2-bipy)]₃Pb₇Br₂₄} (1), [Co(2,2-bipy)₂Br]PbBr₃ (2), [TM(phen)₃]Pb₂Br₆ (TM = Co (3) and Ni (4)), [Co(2,2-bipy)₃]Pb₃Br₉ (5) and [Co(2,2-bipy)₃]Pb₅Br₁₃·CH₃CN (6) with distinct structural types from zero-dimensional (0D) unit, one-dimensional (1D) chain to two-dimensional (2D) layer. Compound 1 contains the 0D {[Co(bipy)]₃Pb₇Br₂₄}⁴⁻ units built from the [Pb₇Br₂₄] ring attached by three unsaturated [Co(2,2-bipy)]²⁺ complexes via Co–Br bonds. Under the direction actions of different SDAs, compounds 2 and 3–4 contain two different types of [Pb₂Br₆]⁴⁻ chains based on the same octahedral [PbBr₆] units but with distinct connecting manners, respectively. Using the same [Co(2,2-bipy)₃]³⁺ as SDA, compound 5 reveals a 1D [Pb₃Br₉]³⁻ double chain, whereas compound 6 features a 2D complex [Pb₅Br₁₃]³⁻ layer. The UV/vis diffuse-reflectance measurements reveal that the title compounds feature tunable band gaps of 1.70–2.29 eV. Under the visible light irradiation, sample 6 exhibits efficient and stable photocatalytic degradation activities over organic pollutants, which mainly originates from the multi-electronic effects of the TM complex cations. A possible photocatalytic mechanism is also proposed based on the radical trapping experiments and electronic band structural calculations.