Macrocycle 2. Dihydrazide 10 (500 mg, 2 mmol) was suspended in ethanol (100 mL) and heated with a heat gun until a slightly hazy solution was obtained. This solution was then allowed to cool to 35°C and added in one portion to a vigorously stirred mixture of phthalaldehyde (267 mg, 2 mmol) and tetrabutylammonium dihydrogenphosphate (339 mg, 1 mmol) in ethanol (100 mL). After stirring overnight a precipitate had formed which was filtered off on a sintered glass funnel, washed thoroughly with ethanol (8x 15 mL) and dried in high vacuum to yield the desired macrocycle as a white powder (397 mg, 57 %). Mp: Decomposition > 230°C. H NMR (400 MHz, DMSO-d6) δ 12.19 (s, 4H), 8.97 (s, 4H), 8.38 (t, J = 1.5 Hz, 2H), 8.19 (d, J = 1.5 Hz, 4H), 7.93 (dd, J = 5.8, 3.4 Hz, 4H), 7.58 (dd, J = 5.9, 3.3 Hz, 4H), 1.41 (s, 18H). (15). To a stirred solution of N-hydroxyphthalamide (926 mg, 5.68 mmol) and 1,2-bis(bromomethyl)-4,5-diethoxybenzene 13 (1 g, 2.8 mmol) in dry DMF (15 mL) under argon was added DBU (1 mL, 6.8 mmol) over 5 minutes. Following complete addition, the mixture was left to stir for 25 minutes after which HCl (1N aq. solution, 20 mL) was added and the resulting precipitate filtered on a sintered glass funnel followed by washing with water (3x 10 mL). The wet solid was suspended in toluene for azeotropic removal of water twice over after which the resulting solid was dried in high vacuum to obtain the desired compound as a white solid (1.4 g, 95 %). Mp: Decomposition > 220°C. H NMR (400 MHz, DMSO-d6) δ 7.88 -7.80 (m, 8H), 7.12 (s, 2H), 5.41 (s, 4H), 4.01 (q, J = 7.0 Hz, 4H), 1.27 (t, J = 7.0 Hz, 6H). (16). To a solution of protected hydroxylamine 15 (400 mg, 774 µmol) in ethanol (5 mL) was added hydrazine hydrate (85 µL, 1.7 mmol) and the resulting mixture stirred overnight at room temperature. The mixture was evaporated onto celite for purification by FCC using 5% MeOH/DCM as the eluent to yield the desired bis(hydroxylamine) as a white solid (180 mg, 90%) Mp: 104-106°C. H NMR (400 MHz, DMSO-d6) δ 6.89 (s, 2H), 5.97 (s, 2H), 4.55 (s, 4H), 4.01 (q, J = 7.0 Hz, 4H), 1.31 (t, J = 7.0 Hz, 6H). Macrocycle 3. To a stirred solution of tetrabutyl ammonium chloride (108 mg, 390 µmol) and triethylamine (20 µL, 156 µmol) in dry DCM (5 mL) under an argon atmosphere was added solutions of 5-(tert-butyl)isophthaloyl dichloride 17 (10.11 mg, 5 mM in dry DCM) and bis(hydroxylamine) 16 (10 mg, 5 mM in dry DCM) dropwise over the course of 30 minutes. The solution was left to stir overnight after which it was evaporated onto celite for purification by FCC using 25 % acetonitrile/toluene to yield the desired macrocycle as a white solid (9.5 mg, 55 %). Mp: Decomposition > 260°C. H NMR (400 MHz, DMSO-d6) δ 12.11 (s, 4H), 8.24 (t, J = 1.6 Hz, 2H), 8.06 (d, J = 1.6 Hz, 4H), 6.97 (s, 4H), 5.07 (s, 8H), 3.92 (q, J = 7.0 Hz, 8H), 1.37 (s, 18H), 1.21 (t, J = 7.0 Hz, 12H). General procedures for 1 H-NMR titrations. All titrations were carried out at 1 mM macrocycle concentration in DMSO-d6 with 0.5% H2O. Stock solutions of guests were prepared using the host solution to ensure that no dilution of the host takes place over the course of the titration. TBA salts were dried under high vacuum prior to the preparation of stock solutions with concentrations in the range of 20-200 mM depending on the titration. Aliquots of guest stock solution were added sequentially to an NMR tube with the free host and a proton spectrum acquired for each addition. The chemical shift of NH protons and other relevant signals were fitted to a 1:1 binding model using Bindfit. General procedures for UV-Vis titrations. Titrations were carried out at concentration ranges of 5-15 µM in DMSO. Stock solutions of guests were prepared using the host solution to ensure that no dilution of the host takes place over the course of the titration. TBA salts were dried under high vacuum prior to the preparation of stock solutions with concentrations in the range of 0.5-100 mM. Aliquots of guest stock solution were added sequentially to a cuvette with the free host and a UV-Vis absorption spectrum acquired for each addition on a Shimadzu UV-3600 UV-Vis spectrometer at 25°C. The change of absorption at relevant wavelengths were fitted to an appropriate binding model (1:1 or 1:2 host to guest models) using Bindfit (Nelder-Mead fit method). Molecular modelling. Initial modelling was done by Monte Carlo multiple minimum (MCMM) conformational searches (100 steps per torsion angle, maximum 1000 steps in total), performed in Schrödinger Release 2019-1, using the OPL3e force field without implicit solvation in Maestro MacroModel (version 11.9.011). The structure obtained after this first run of Molecular Mechanics geometry optimization runs were further minimized using the semi-empirical MOPAC2016 package (Version: 22.110W, James J. P. Stewart) using the PM7 Hamiltonian (full coordinates geometry optimization, MM correction to CONH barrier, convergence for gradient norm below 0,10). X-ray crystallography. Generally, single crystals were grown from 1-4 ml solutions of macrocycle (1-3 mM). Single crystals of 2•Cl -were grown by slow evaporation of a dioxane solution of 2 in the presence of excess TBACl. Single crystals of 2•H2PO4 -were obtained by slow evaporation of a DMSO/acetone solution of 2 in the presence of excess TBAH2PO4. Single crystals of 2•H2P2O7 2-were obtained by slow evaporation of a chloroform solution of 2 in the presence of excess TBA2H2P2O7. Single crystals of 2 with malonate were obtained by slow evaporation of a dioxane solution of 2 in the presence of excess TBA2C3H2O4. Single crystals of 1•Cl -were grown by slow evaporation of a chloroform solution of 1 in the presence of excess TBACl. Single crystals of 3 were obtained by slow evaporation of a dioxane solution of 3. Diffraction data were collected using the Oxford Diffraction Gemini R Ultra diffractometer (Cu Kα, multilayer mirror, Ruby CCD area detector) at 100(2) K except 2•H2PO4 - was collected at 295(2) K. Data collection, unit cells determination and data reduction were carried out using Crys-Alis PRO software package 59 using Olex2 60 and shelXle , the structure was solved with the SHELXT 2015 structure solution program by Intrinsic Phasing methods and refined by full-matrix least squares on |F| 2 using SHELXL-2018/3. 60 Non-hydrogen atoms were refined anisotropically, while C-H hydrogen atoms were placed in geometrically calculated positions using a riding model. Additional details of the refinement are given in the SI. CCDC deposition numbers are 2311610-2311615.