text: Agostic interactions are best demonstrated by crystallography. Neutron diffraction data have shown that C−H and M┄H bond distances are 5-20% longer than expected for isolated metal hydride and hydrocarbons. The distance between the metal and the hydrogen is typically 1.8–2.3 Å, and the M┄H−C angle is in the range of 90°–140°. The presence of a H NMR signal that is shifted upfield from that of a normal aryl or alkane, often to the region normally assigned to hydride ligands. The coupling constant J is typically lowered to 70–100 Hz versus the 125 Hz expected for a normal sp carbon–hydrogen bond.