The Carbonyl⋅⋅⋅Tellurazole Chalcogen Bond as a Molecular Recognition Unit: From Model Studies to Supramolecular Organic Frameworks

Abstract In the last years, chalcogen bonding, the noncovalent interaction involving chalcogen centers, has emerged as interesting alternative to the ubiquitous hydrogen bonding in many research areas. Here, we could show by means of high‐level quantum chemical calculations that the carbonyl⋅⋅⋅tellurazole chalcogen bond is at least as strong as conventional hydrogen bonds. Using the carbonyl⋅⋅⋅tellurazole binding motif, we were able to design complex supramolecular networks in solid phase starting from tellurazole‐substituted cyclic peptides. X‐ray analyses reveal that the rigid structure of the cyclic peptides is caused by hydrogen bonds, whereas the supramolecular network is held together by chalcogen bonding. The type of the supramolecular network depends on peptide used; both linear wires and a honeycomb‐like supramolecular organic framework (SOF) were observed. The unique structure of the SOF shows two channels filled with different types of solvent mixtures that are either locked or freely movable.


Investigation of the Structures of 16 and 17 in Solution
The NMR spectra ( 1 H, 13 C) for the cyclic peptides 16 and 17 indicate that in solution, they are C2-and C3-symmetric, respectively. The doublets of the amide NH resonances in 17 are shifted about δ = 0.5 to 1.5 ppm further downfield than those in 16, suggesting that the interaction between the lone pairs of the imidazole nitrogen and the hydrogen of the secondary amides are probably stronger in 17 than in 16 (Table S3). The vicinal coupling constant ( 3 JNHCH) for the amide NH resonance in 17 is 9.0 to 9.3 Hz and corresponds to NHαCH dihedral angles of 153° < | | < 156° in solution (Table S3). [1] The dihedral angles found for 17 in solid state amounts to 156°. Thus, the structure of the peptidic skeleton in solid state corresponds to that in solution.
In the case of the cyclic peptide 16, the vicinal coupling constants are measured to be 7.8 to 10.7 Hz (Table S3). Accordingly, dihedral angles between 144° and 174° are expected. In solid state the NHαCH dihedral angles amount to -145°, -151°, -157° and -163°, which agree with the values determined by 1 H NMR spectroscopy. The low dependence of the vicinal coupling constants on the solvent shows that the geometry of the macrocycles 16 and 17 is essential the same in all solvents. Overall, the NMR data of the cycles 16 and 17 resemble that of similar peptides lacking benzotellurazole units. [2][3] This allows the conclusion that the benzotellurazole units have no impact on the solution structure of the cyclopeptides. ---b ---b 8.577 ---b ---b 9.27 a not determinable. b no signals due to a rapid H/D exchange.

Computational Details
All calculations were performed by using the program package Gaussian 16 [13] . The geometrical parameters of all stationary points were optimized by means of the density functional B3LYP [9][10][11] and the double-hybrid density functional approximation B2PLYP [12] . In both cases the additional dispersion correction with Becke-Johnson damping [13] (D3BJ) were used. For all structures C1 symmetry was applied. Frequency calculations were carried out at each of the stationary points to verify the nature of the stationary point. It turned out that all stationary states have none imaginary frequency. As basis set TZVP was employed for the light elements C, H, N, O, S and Se, whereas aug-cc-pVTZ-PP was used for tellurium. Furthermore, single point calculations on the B2PLYP-optimized structures were performed using B2PLYP, CCSD [14] and CCSD(T) [15] .

Treatment of hydrogen atoms
Riding model on idealized geometries with the 1.2 fold isotropic displacement parameters of the equivalent Uij of the corresponding carbon atom.

Twinning
Refined as a 2-component inversion twin.

Disorder
The Te bicyclic residues are disordered over two position. The residues were realted by noncrystallographic symmetry restraints. The corresponding bond lengths of the disordered parts were restrained to be equal (SADI) and to lie on a mutual plane (FLAT). RIGU restraints were applied to all adp and the ISOR restraints to those of the disordered light atoms. The adp of the disordered light atoms were additionally restrained to be similar (SIMU). To the adp of C2_2 an additional more strict ISOR restraint (sigma= 0.01) was applied to avoid a non positive definite.
Due to the vast use of restraints quantitative results may be of limited validity.

Absolute structure
Considering

Treatment of hydrogen atoms
Riding model on idealized geometries with the 1.2 fold isotropic displacement parameters of the equivalent Uij of the corresponding carbon atom. The methyl groups are idealized with tetrahedral angles in a combined rotating and rigid group refinement with the 1.5 fold isotropic displacement parameters of the equivalent Uij of the corresponding carbon atom. The hydrogen atoms of the water molecules could not be identified but were included in the sum formula.

Disorder
One of the water molecules is disordered over two position.

SQUEEZE
The structure contains highly disordered solvent -possibly EtOAc or methanol. The final refinement was done with a solvent free dataset from a PLATON/SQUEEZE run. For details see: A. L. Spek, Acta Cryst. A 1990, 46, 194-201. Since the nature and amount of the solvent is not clear it was not included in the sum formula.

Possible twinning by inversion
The starting material was enantiopure and a racemization of all four stereo centers is highly unlikely thus the possible twinning by inversion suggested by the Flack-parameter was ignored.
The deviation from zero likely results from the low data quality.

Weak diffraction data
The intensities at resolutions > 1 Å were very weak and a high percentage < 2σ(I).
Consequently, the model should be carefully interpreted and any conclusions draw from it supported by other means. Quantitative results may be unreliable.

S43
Crystal Structure Data of 17

Treatment of hydrogen atoms
Riding model on idealized geometries with the 1.2 fold isotropic displacement parameters of the equivalent Uij of the corresponding carbon atom. The methyl groups are idealized with tetrahedral angles in a combined rotating and rigid group refinement with the 1.5 fold isotropic displacement parameters of the equivalent Uij of the corresponding carbon atom. The NH hydrogen was refined freely with its NH bond lengths restrained to be equal to 0.85 Å (DFIX).

Disordered solvent
The structure contains a THF molecule disordered over a three-fold rotational axis. A second one is partly occupied and sharing its location with a dichloromethane molecule. All corresponding 1,2 and 1,3 distances of the THF were restrained to be equal (SADI). The C-O bond lengths were restrained to be equal to 1.43 Å (DFIX). The bond angle of the dichloromethane was restrained to the tetrahedral angle and its bond lengths to be equal (SADI, DFIX). RIGU restraints were applied to all solvents adp. All solvent molecules are highly disordered and amount and nature of the solvent should not be taken for granted.

Absolute structure
The absolute structure could be determined reliably.