Isotopic polymorphism in pyridine

Not so simple: It is normally assumed that deuteration has only a minor effect on the stabilities of crystal structures. This assumption is wrong for pyridine. A low-temperature polymorph exists for [D₅]pyridine, but not for [H₅]pyridine, which adds a further twist to the already unusual structural chemistry of one of the simplest and most familiar laboratory chemicals. (Figure Presented).