The First Observation of Heteronuclear Two-Bond <i>J</i>-Coupling in the Solid State: Crystal Structure and Solid-State NMR Spectroscopy of Rb₄(NbO)₂(Si₈O₂₁)

High-temperature, high-pressure hydrothermal synthesis of the title compound and its 93Nb and 29Si MAS NMR spectra are reported. The 29Si MAS NMR spectrum shows four signals corresponding to the four distinct Si sites in the structure. Three signals show multiplet patterns which arise from 93Nb(spin-9/2)−29Si J-coupling. This is the first example of two-bond J-coupling between a quadrupolar nucleus and a spin-1/2 nucleus in the solid state. A combination of 93Nb and 29Si solid-state NMR and X-ray diffraction data has provided a correlation between NMR interaction parameters and local structure. This work opens a new opportunity to examine the relationship between 2J-coupling and structural parameters in the solid state.