Described herein are crystalline fumarate salts having a Formula I, pharmaceutical formulations comprising the same, methods for their production, and uses thereof, Formula I comprising:




wherein each R1 is independently selected from protium and deuterium; each R2 is independently selected from protium and deuterium; each R3 is independently selected from protium and deuterium; and each R4 is independently selected from protium and deuterium; and wherein the compound has a PXRD pattern comprising characteristic peaks at 19.2±0.2 and 24.7±0.2 degrees 2-theta.