Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium–Nitrate Example

• Published in: Journal of the American Chemical Society Vol. 139; no. 49; pp. 18003 - 18008
• Main Authors: Jin, Geng Bang, Lin, Jian, Estes, Shanna L, Skanthakumar, S, Soderholm, L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.12.2017; American Chemical Society (ACS)
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.7b09363

The influence of countercations (A n+) in directing the composition of monomeric metal–ligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of A n+ in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A+ hydration enthalpies found for two related series of thorium (Th)–nitrate molecular compounds obtained by evaporating acidic aqueous Th–nitrate solutions in the presence of A+ counterions. Analyses of their chemical composition and solid-state structures demonstrate that A+ not only affects the overall solid-state packing of the Th–nitrato complexes but also influences the composition of the Th–nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A+ hydration enthalpies, such that the A+ with smaller hydration enthalpies associate with less hydrated and more anionic Th–nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of A n+, opens a new avenue for the design and synthesis of targeted metal–ligand complexes.