Abstract

This contribution presents a previously unreported
example and comparative study of a binary
crystalline adduct that exhibits concomitant salt and cocrystal
forms. Specifically, three new polymorphs (α, β, γ) of a novel
2:1 cocrystal of bis(isonicotinamide) citric acid are reported,
and the route to isolating each polymorph from aqueous
solution is presented and the crystal chemistry of the system is
characterized. In addition, the metastable 2:1 salt (ionic
adduct) isolated as a transient (overlapping) phase under
crystallization conditions identical to the polymorphs is also
presented. As far as the authors can ascertain, this may be the
first reported example of a salt−cocrystal−polymorphic
concomitant system. A comparative study of the solid form
landscape is presented, wherein mapping reveals the unique structural complexity of this multiple form salt−cocrystal
concomitant system. The α and β forms are structurally very similar, where comparisons of packing behavior are shown to only
be different outside the glide plane. The γ form is very different in structure, where supramolecular chirality is present. In
addition, further characterization of the isolated solid-state forms includes thermal, spectroscopic, and computational analysis,
all of which are employed to further verify the solid form landscape of the isonicotinamide−citric acid adduct and were found to
have an order of stability of β, α, γ, salt, the salt being the metastable form.