Promoting the formation of metal-carboxylate coordination to modulate the dimensionality of ultrastable lead halide hybrids

Abstract

Crystal engineering of metal halide hybrids is critical to investigate their structure-property relationship and advance their photophysical applications, but there have been limited efforts to employ coordination chemistry to precisely control the dimensionality of metal halide sublattices. Herein, we present a coordination-assembly synthetic strategy developed for the rational modulation of lead halide dimensionality, realizing the transition from 2D to 3D architectures. This manipulation is achieved by utilizing three organocarboxylates featuring the identical cyclohexane backbone unit. Specifically, the 1,4-cyclohexanedicarboxylate and 1,2,4,5-cyclohexanetetracarboxylate ligands facilitate the formation of quasi-2D layered structures, characterized by weakly corrugated and strongly corrugated lead halide layers, respectively. Importantly, the introduction of the 1,2,3,4,5,6-cyclohexanehexacarboxylate ligand results in coordination architectures featuring 3D lead chloride/bromide sublattices. The formation of the 3D coordination architectures templated by the 1,2,3,4,5,6-cyclohexanehexacarboxylate ligand affords extended wavelength coverage and superior carrier transport properties compared to their quasi-2D layered analogues. Importantly, both the 2D and 3D lead halide-based coordination polymers exhibit high aqueous stability over a wide pH range, outperforming the conventional ionic-bound lead halides. Notably, the chemically stable 3D lead bromide exhibits efficient photocatalytic ethylbenzene oxidation with the conversion rate of 498 μmol g^-1 h^-1, substantially higher than its 2D lead bromide counterparts. This work highlights the important role of coordination chemistry in the rational design of metal halide hybrids, which is crucial for advancing their photophysical properties and applications.

Fig. 1. Synthetic scheme of TJU-10(Cl), TJU-11(Br), TJU-13(Cl), TJU-13(Br), TJU-14(Cl) and TJU-15(Br) and their templating organocarboxylate ligands. (a, b) Crystallographic view of weakly corrugated 2D [Pb₂X₂]²⁺ (X = Cl⁻/Br⁻) layers in TJU-10(Cl) (a) and TJU-11(Br) (b). (c, d) Crystallographic view of strongly corrugated 2D [Pb₃X₂]⁴⁺ (X = Cl⁻/Br⁻) layers in TJU-13(Cl) (c) and TJU-14(Br) (d). (e, f) Crystallographic view of 3D [Pb₁₂Cl₁₇(OH)]⁶⁺ lattice in TJU-14(Cl) (e) and 3D [Pb₁₅Br₂₄]⁶⁺ lattice TJU-15(Br) (f), chc ligands are omitted for clarity. The coordination geometry of Pb²⁺ centers is shown in the polyhedron. The green polyhedra represent lead chloride units and the blue polyhedra represent lead bromide units.

Fig. 2. (a,b) PXRD of TJU-14(Cl) (a) and TJU-15(Br) (b) before and after thermal and chemical treatment. (c) UV-vis diffuse reflectance spectroscopy of 2D-TJU-13(Cl) and 3D-TJU-14(Cl). (d) UV-vis diffuse reflectance spectroscopy of 2D-TJU-13(Br) and 3D-TJU-15(Br). (e) Calculated band structures and DOS of TJU-14(Cl). (f) Calculated band structures and DOS of TJU-15(Br).

Fig. 3. (a) Normalized PL spectra of TJU-13(Br) and TJU-15(Br). (b) Photoluminescence decay curve and fitting plot of TJU-13(Br) and TJU-15(Br), respectively. (c) Two-dimensional pseudo-color TA plot of TJU-15(Br). (d) TA kinetics of TJU-15(Br). (e) Nyquist plots of TJU-13(Br) and TJU-15(Br). (f) Transient photocurrent densities of TJU-13(Br) and TJU-15(Br) under light irradiation.

Fig. 4. Photocatalytic ethylbenzene oxidation performances of PbBr₂, Pt@TJU-11(Br), Pt@TJU-13(Br), Pt@TJU-15(Br) (a) and photocatalytic ethylbenzene oxidation performances of Pt_0.44@TJU-15(Br), Pt_0.66@TJU-15(Br), Pt_0.84@TJU-15(Br) (b). Conditions: photocatalyst (0.02 g), 2 mL ethylbenzene and 1 mL CH₃CN, 1 atm O₂, 293 K, AM1.5G simulated light irradiation, reaction time: 4 h. Conversion rate of ethylbenzene and the formation rate of acetophenone are shown in the figures. (c) Time dependence of photocatalytic oxidation of ethylbenzene over Pt_0.66@TJU-15(Br). (d) Recyclable catalysis studies of Pt_0.66@TJU-15(Br) over five consecutive runs. (e) Ethylbenzene oxidation rates with or without various radical scavengers. (f) The DMPO spin-trapping ESR spectra of Pt_0.66@TJU-15(Br) for ˙O₂⁻ under different visible-light irradiation times.