Dd2 500

Solution ¹H NMR spectroscopy was performed on digested crystalline and glassy ZIF samples with Bruker DPX-300, DPX 500 or Agilent DD2 500 spectrometers. The solid samples were digested before the measurement using DMSO-d₆ (0.5 mL) and DCl/D₂O (35 wt%, one drop, <0.1 mL) as solvents. The data were processed with the MestReNova (v14.2.0) software. Data were referenced to the residual proton signal of DMSO and chemical shifts are given relative to tetramethylsilane.

All commercially available starting materials and solvents were purchased from commercial vendors and used without further purification. Reactions were monitored using analytical thin-layer chromatography (TLC) on precoated silica gel GF254 plates (Qingdao Haiyang Chemical Plant, Qingdao, China) and visualized under ultraviolet light (254 nm and 365 nm). Column chromatography was performed on silica gel (200–300 mesh). Melting points were determined on a Mitamura-Riken micro-hot stage and uncorrected. ¹H and ¹³C NMR spectra were recorded on the Broker AVANCE NEO and Agilent DD2 500 with 400 or 500 MHz for proton (¹H NMR) and 100 or 125 MHz for carbon (¹³C NMR), respectively. The chemical shifts (δ) were expressed in parts per million (ppm) downfield, and the coupling constant (J) values were described as hertz. High-resolution (ESI) MS spectra were recorded using a QTOF-2 Micromass spectrometer. The purity of the final compounds for biological evaluation was higher than 95% by analytical HPLC analysis with the Primaide 1210 system.
Compounds 1–4, 16–19 and 20–23 were prepared according to the procedure published by Dong et al., and the spectroscopic data for the intermediates were identical to those described in the literature [30 (link)].

Tetrahydrofuran (THF) was distillated with Na in the presence of benzophenone under argon atmosphere. Dichloromethane was distillated by molecular sieve. Dimethyl sulfoxide (DMSO) was distillated with t-BuOK. All other materials and solvents were obtained from commercial sources and used without further purification. Thin-layer chromatography (TLC) was performed on precoated E. Merck silica-gel 60 F254 plates. Column chromatography was performed on silica gel (200–300 mesh, Qingdao, China). Melting points were determined on a Mitamura-Riken micro-hot stage without correction. ¹H and ¹³C NMR spectra were recorded on the Broker AVANCE NEO and Agilent DD2 500 with 500 or 600 MHz for proton (¹H NMR) and 125 or 150 MHz for carbon (¹³C NMR) with tetramethylsilane (Me₄Si) as internal standard, respectively. The chemical shifts (δ) were expressed in parts per million (ppm) downfield, and the coupling constant (J) values were described as hertz. High-resolution (ESI) MS spectra were recorded using a Q TOF-2 Micromass spectrometer.
The general procedures for the synthesis of important intermediates 4a–4e, 5a–5e and 6a–6c can be seen in Supplementary Materials.

An aliquot of various samples obtained by the procedure described in previous Section 4.5. was evaporated to dryness and redissolved in deuterated methanol (CD3OD). On an Agilent DD2 500 (500.1 MHz for 1H-NMR) spectrometer, at 295 K in CD3OD, 1H NMR was measured.

For the Job plots 3 mM stock solutions of each component in deuterated buffer were mixed in different ratios with an interval of 10% or 20%. Spectra were recorded on a DD2 500 (Agilent) or a DD2 600 (Agilent) spectrometer. Small amounts of DMSO (83 nM) were used as reference (δ = 2.62 ppm). Variable temperature ¹H NMR of a(CFC)₂ was recorded in pure D₂O.
Deuterated buffer was prepared by the following procedure. Regular non-deuterated NaHPO₄·2H₂O (156 mg, 1 mmol) was dissolved in D₂O (1 mL) and afterwards dried in vacuo. This step was repeated for a total number of three times. The salt was dissolved again in D₂O (10 mL) and the pD was adjusted with NaOD (40 wt % in D₂O) using a pH-calibrated glass electrode and the following relation [26 (link)].

Electrochemical tests were performed in a two-compartment H-cell. A proton exchange membrane (Nafion 117) was used. The electrolyte was 30 mL of 0.1 M KHCO₃ solution saturated with CO₂ gas in the cathode part for at least 30 min prior to the CO₂ reduction test. Platinum was used as the counter electrode and Ag/AgCl as the reference electrode (saturated with 3.0 M KCl, BASi). The glassy carbon electrode loaded with the catalyst served as the working electrode. Liner sweep voltammetry (LSV) with a scan rate of 50 mV/s was conducted first. The gas products were detected using a gas chromatograph (GC, PerkinElmer Clarus 600) equipped with a thermal conductivity detector (TCD) for hydrogen (H₂) quantification and a flame ionization detector (FID) for methane (CH₄) and ethylene (C₂H₄). Liquid products were quantified using ¹H nuclear magnetic resonance (NMR, Agilent DD2 500). The NMR samples were prepared by mixing 0.5 mL of electrolyte with 0.1 mL of deuterated water (D₂O), and 0.02 μL of dimethyl sulfoxide (DMSO) was added as an internal standard. Potential E was converted to the RHE reference electrode using: $$E\left(\mathrm{versus}\mathrm{RHE}\right)=E\left(\mathrm{versus}\mathrm{Ag∕AgCl}\right)+0.197\mathrm{V}+0.059\mathrm{V}\times \mathrm{pH}.$$

¹H, ¹³C and 2D NMR experiments were recorded at 295 K in CD₃OD using an Agilent DD2 500 (500.1 MHz for ¹H-NMR and 125.5 MHz ¹³C-NMR) spectrometer. COSY, HSQC and HMBC were performed using standard Varian microprograms. Column chromatography (CC) was performed on Sephadex LH-20 (MilliporeSigma, Burlington, MA, USA) and Amberlite XAD7HP resin (Supelco, Merck, Darmstadt, Germany) with the solvent mixtures indicated in each case; TLC analyses were carried out using aluminum-coated silica gel plates 60 F₂₅₄ (Merck, Art. 5554). Detection was carried out using UV-light and vanillin/sulfuric acid reagent.