Sensing Synthon Architectures with Hyperfine-Resolved Rotational Spectroscopy

Supramolecular synthons that engage in noncovalent carbon bonding offer promising routes toward programmable molecular architectures, yet experimental strategies capable of unambiguously resolving their docking geometries remain limited. Here, we show that electric field gradients at nitrogen nuclei─accessed through nuclear quadrupole splittings─provide a uniquely sensitive probe of supramolecular topology. Using hyperfine-resolved broadband rotational spectroscopy in a supersonic jet expansion combined with quantum-chemical calculations, we investigate tetracyanocyclopropane (TCCP), a synthetically accessible synthon bearing four cyano groups that act as local sensors of the electronic environment. Complexes formed between TCCP derivatives and tetrahydrofuran are observed in the jet expansion and shown to dock through a tetrel bond between an sp3-hybridized carbon center and the oxygen lone pair of tetrahydrofuran. While the rotational constants alone struggle to discriminate between candidate docking geometries, the nitrogen nuclear quadrupole coupling constants encode the orientational fingerprint of the complex through their electric field gradients. By exploiting symmetry relationships among the four nitrogen sites and implementing a tailored spectral fitting strategy to disentangle the dense hyperfine manifold, we extract precise rotational parameters that uniquely define the docking arrangements of two TCCP derivatives with different symmetries. These results demonstrate nitrogen electric field gradients as powerful structural sensors of noncovalent interactions and position hyperfine-resolved rotational spectroscopy as a configuration-sensitive approach for identifying supramolecular synthon motifs and guiding the design of nitrogen-rich supramolecular materials.