Vario micro cube analyzer

Ground plants sections and soil samples (see Section 4.3) were air-dried in an electrical oven for 48 h. We dried plants sections at 70 °C and soil at 40 °C, respectively. Dried soil was sieved through a 2 mm mesh. We manually removed root residues or soil organisms. Plant sections and soil were ground with a ball mill for 30 s with 30 Hz (MM400, Retsch GmbH) in order to homogenize the sample and reduce the particle size to 100 µm or less. We dried for 2 h the plant and soil samples at 70 °C and 40 °C, respectively. We weighed the dried and ground samples into tin boats (Elementar Analysensysteme GmbH) with the following dimensions: 4 × 4 × 11 mm for plants and 6 × 6 × 12 mm for soil. For soil we added a standard of WO₃ (Elementar Analysensysteme GmbH) in a 1:1 weight ratio sample/standard. We weighed the samples (10–15 mg for plants, 40–50 mg for soil) with a microbalance (Cubis MSA Sartorius AG), tightly folded the tin boat with the sample and compressed it with a press into a tight pellet. We weighed the final pellets and stored them in a desiccator until measurement. We quantified elemental nitrogen using a Vario MICRO cube analyzer (Elementar Analysensysteme GmbH). We analyzed the samples following the manufacturer’s protocol.

All commercial reagents and solvents were used as received without further purification unless otherwise indicated. Synthetic compounds 3a–d and 4a–l were directly used for reaction without further purification and characterization. Melting points were recorded on an SGW X-4 microscope melting point apparatus (Shanghai Tech Instrument Co., Ltd., Shanghai, China). Infrared spectra (IR) were performed on NICOLET iS10 sepectrometer (Shimazu Co., Ltd., Kyoto, Japan). NMR spectra were recorded on a Bruker Avance 500MHz spectrometer (Bruker Co., Ltd., Zurich, Switzerland) at room temperature with tetramethylsilane (TMS) as an internal standard and CDCl₃ or DMSO-d₆ as solvents. Mass spectra (MS) were obtained by LCMS-IT-TOF spectrometer (Shimadzu Co., Ltd., Kyoto, Japan) or TSQ Quantum Ultra (Thermo Scientific Co., Ltd., Madison, WI, USA). Elemental analysis for C, H, O, and N were carried out with Elementar VarioMICRO Cube analyzer (Elementar, Frankfurt, Germany).

All manipulations were conducted under a nitrogen atmosphere using standard Schlenk techniques. All reagents were purchased from commercial vendors: benzamidine (L^NN-H) (Sigma-Aldrich), ZnEt₂ (ABCR). Solvents were purified and dried using MBraun Solvent Purification System (SPS). The ¹H and ¹³C NMR spectra were acquired on Varian Mercury (400 MHz) spectrometer. FTIR spectra were recorded on a Bruker-Tensor II spectrometer. Powder X-ray diffraction (PXRD) measurements were performed using a PANalytical Empyrean diffractometer equipped with Ni-filtered Cu Kα radiation (40 kV, 40 mA). The sample for the PXRD analysis was sealed between two layers of Kapton foil and measured in transmission geometry. Elemental analyses were performed on an Elementar VarioMicro Cube analyzer. TGA-differential scanning calorimetry (DSC) analyses were performed under argon with a heating rate of 5 °C min⁻¹ using a TA Instruments Q600 apparatus. Volumetric N₂ sorption studies were undertaken using a Micromeritics ASAP 2020 system. Approximately 150 mg of 1^LT and dried under vacuum at −10 °C for 5 h. Helium was used for the free space determination after sorption analysis. Adsorption isotherms were measured at 77 K in liquid nitrogen.