Ammonium and Isopropylammonium Salts of the Fumaric Acid Dianion

The crystal structures of diammonium fumarate, 2NH₄⁺.C₄H₂O₄²⁻, (I) and bis(isopropylammonium) fumarate, 2C₃H₇NH₃⁺.C₄H₂O₄²⁻, (II), have been determined. The intermolecular N-H...O hydrogen bonds form a three-dimensional network in (I), whereas two-dimensional sheets are formed in (II) and separated by layers of isopropyl groups. The N...O distances are 2.790 (1)–2.903 (1) Å in (I) and 2.747 (1)–2.807 (1) Å in (II). Differences between the solid-state photoreactivities of the fumaric acid ions in (I) and (II) are rationalized based on the crystal structures.

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