We have explored the structural and energetic properties of a series of RMX3–NH3 (M=Si, Ge; X=F, Cl; R=CH3, C6H5) complexes using density functional theory and low-temperature infrared spectroscopy. In the minimum-energy structures, the NH3 binds axially to a halogen, while the organic group resides in equatorial site about the metal. Remarkably, the primary mode of interaction in several of these systems seems to be hydrogen bonding (C-H–N), rather than a tetrel N-M interaction. This is particularly clear for the RMCl3–NH3 complexes, and analyses of the charge distributions of the acid fragment corroborate this assessment. We also identified a set of metastable geometries in which the ammonia binds axial to the organic substituent. Acid fragment charge analysis also provide a clear rationale as to why these configurations are less stable than their R-equatorial counterparts. In matrix-IR experiments, we see clear evidence of the minimum-energy form of CH3SiCl3–NH3, but analogous results for CH3GeCl3–NH3 are less conclusive. Computational scans of the M-N distance potentials for CH3SiCl3–NH3 and CH3GeCl3–NH3, both in the gas phase and bulk dielectric media reveal a great deal of anharmonicity, and a propensity for condensed-phase structural change.