The tetrel elements (group 14) have the capacity to act as electrophilic sites and participate in structure-directing noncovalent tetrel bonds. We establish here the experimental response of several NMR interaction tensors to tetrel bonding via a range of 119Sn and 35Cl solid-state NMR experiments carried out in applied magnetic fields ranging from 4.7 to 21.1 T. Experimentally measured isotropic 1 J(119Sn, 35Cl) coupling constants and 35Cl nuclear quadrupolar coupling constants (C Q) in a series of cocrystals of triphenyltin chloride, wherein tin acts as the tetrel bond donor atom, correlate with the experimental Sn···O tetrel bond length. Remarkably, the formation of moderately strong tetrel bonds to Ph3SnCl results in substantial reductions in 1 J(119Sn, 35Cl) and C Q by 27–45 and 20–36%, respectively. The experimental findings are reproduced by periodic gauge-including projector-augmented wave density functional theory (DFT) calculations as well as spin–orbit relativistic zeroth-order regular approximation DFT calculations. The trend established here in J couplings parallels that for hydrogen bond donors, providing experimental evidence for the analogy between the two classes of interactions. Tin chemical shift tensors and computed magnetic shielding tensors correlate less well with structure, suggesting that these are less suitable measures of tetrel bond strength. These results contribute to the elucidation of important analogies and differences between tetrel bonds and related classes of noncovalent interactions such as hydrogen bonds and halogen bonds. This work provides new insights, which should prove to be useful in future studies of related crystalline or amorphous systems featuring tetrel bonds and/or tetrel–halogen moieties such as halide perovskites and related photovoltaic and optoelectronic materials.

Three novel chalcogen-bonded cocrystals featuring 3,4-dicyano-1,2,5-selenodiazole (C4N4Se) or 3,4-dicyano-1,2,5-tellurodiazole (C4N4Te) as chalcogen-bond donors and hydroquinone (C6H6O2), tetraphenylphosphonium chloride (C24H20P+·Cl−) or tetraethylphosphonium chloride (C8H20P+·Cl−) as chalcogen-bond acceptors have been prepared and characterized by single-crystal X-ray diffraction (XRD), powder X-ray diffraction and 77Se/125Te magic-angle spinning solid-state NMR spectroscopy. The single-crystal XRD results show that the chalcogenodiazole molecules interact with the electron donors through two σ-holes on each of the chalcogen atoms, which results in highly directional and moderately strong chalcogen bonds. Powder XRD confirms that the crystalline phases are preserved upon moderate grinding of the samples for solid-state NMR experiments. Measurement of 77Se and 125Te chemical shift tensors via magic-angle spinning solid-state NMR spectroscopy confirms the number of magnetically unique chalcogen sites in each asymmetric unit and reveals the impact of chalcogen-bond formation on the local electronic structure. These NMR data are further assessed in the context of analogous data for a wider range of crystalline chalcogen-bonded systems.

The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the P21/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the P1- space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine-nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 Å3) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. 1H → 13C and 19F → 13C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds.

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