The crystal structure of ribociclib hydrogen succinate (commonly referred to as ribociclib succinate) has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Ribociclib hydrogen succinate crystallizes in space group P-1 (#2) with a = 6.52215(4), b = 12.67120(16), c = 18.16978(33) Å, α = 74.0855(8), β = 82.0814(4), γ = 88.6943(1)°, V = 1430.112(6) Å3, and Z = 2 at 295 K. The crystal structure consists of alternating layers of cations and anions parallel to the ab-plane. The protonated N in each ribociclib cation acts as a donor in two strong N–H⋯O hydrogen bonds to two different succinate anions. Strong O–H⋯O hydrogen bonds link the hydrogen succinate anions into chains parallel to the a-axis. N–H⋯N hydrogen bonds link the cations into dimers, with a graph set R2,2(8). The result is a three-dimensional hydrogen bond network. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®)
