Photoconductive Coordination Polymer with a Lead–Sulfur Two-Dimensional Coordination Sheet Structure

Abstract

Coordination polymers with metal−sulfur (M−S) bonds in their nodes have interesting optical properties and can be used as photocatalysts for water splitting. A wide range of inorganic−organic hybrid materials with M−S bonds have been prepared in recent years. However, there is a dearth of structural information because of their low crystallinity, which has hampered the understanding of their underlying chemistry and physics. Thus, we conducted a structural study of a novel, highly crystalline coordination polymer with M−S bonds. Theoretical calculations were performed to elucidate its photoconductivity mechanism. The photoconductive, three-dimensional coordination polymer [Pb(tadt)] n (denoted as KGF-9; tadt = 1,3,4-thiadiazole-2,5-dithiolate) was synthesized and confirmed to have a three-dimensional structure containing a two-dimensional Pb−S framework by singlecrystal X-ray diffraction. We also performed diffuse-reflectance ultraviolet−visible−near-infrared spectroscopy, time-resolved microwave conductivity, and photoelectron yield spectroscopy measurements on the bulk powder samples, as well as first-principles calculations. Additionally, direct-current photoconductivity measurements were conducted on a single-crystal sample.

Selective CO2-to-Formate Conversion Driven by Visible Light over a Precious-Metal-Free Nonporous Coordination Polymer

“…The PXRD pattern for the obtained sample was in good agreement with a simulated pattern calculated based on the crystal structure of KGF-9 (Figure S1). The as-synthesized KGF-9 has clear visible-light absorption even without any postmodification, which would be ascribed to the high energy level sulfur atom orbitals (Figure b) …”

“…The results showed that this CP could reduce CO 2 to HCOO − under visible-light irradiation with a high AQY (∼2.6% at 400 nm and ∼12.4% at 365 nm) and selectivity (>99%) in the presence of BIH as an electron donor, as supported by isotope tracer experiments. KGF-9 could theoretically reduce CO 2 to CO, MeOH, and CH 4 because the position of conduction band minimum of KGF-9 versus vacuum was located at −3.12 52 and the potentials to reduce CO 2 to HCOOH, CO, HCOH, MeOH, and CH 4 lied at −3.62, −3.76, −3.80, −3.88, and −4.03 eV, respectively. 58 Nevertheless, KGF-9 was a photocatalyst that selectively produced formate as the sole CO 2 reduction product.…”

“…Here, we report an exceptional example of the CO 2 photoreduction of nonporous CP, a photocatalyst containing (−Pb–S−) n infinite structure, [Pb­(tadt)] n (denoted as KGF-9; H 2 tadt = 1,3,4-thiadiazole-2,5-dithiol, see Figure a). KGF-9 has previously been reported to be a photoconductive S–CP, which exhibits moderate photocatalytic activity for half-cell H 2 evolution upon visible light with the aid of a Pt cocatalyst . As mentioned, CO 2 reduction is obviously more challenging than proton reduction.…”

“…KGF-9 has previously been reported to be a photoconductive S−CP, which exhibits moderate photocatalytic activity for half-cell H 2 evolution upon visible light with the aid of a Pt cocatalyst. 52 As mentioned, CO 2 reduction is obviously more challenging than proton reduction. However, surprisingly, KGF-9, without cocatalyst loading, was found to photoreduce CO 2 to HCOO − with a relatively high apparent quantum yield (AQY) of 2.6% at 400 nm and with high selectivity (>99%), as confirmed by a tracer experiment using 13 ■ RESULTS AND DISCUSSION KGF-9 powder was prepared by solvothermal reaction of Pb(NO 3 ) 2 and H 2 tadt in a mixture of water and acetone, and the obtained powder was analyzed by powder X-ray diffraction (PXRD).…”

“…The as-synthesized KGF-9 has clear visible-light absorption even without any postmodification, which would be ascribed to the high energy level sulfur atom orbitals (Figure 1b). 52 Sorption isotherms for KGF-9 were recorded at 77 K to evaluate its specific surface area via the Brunauer−Emmett− Teller (BET) method (Figure 2a). 53 The isotherms show a very small amount of adsorbed N 2 , indicating that KGF-9 has neither pores nor voids in its structure.…”