Identifying and characterizing intermolecular forces (IMFs) in the condensed phase is crucial for understanding macroscopic properties of solids. Insight into these interactions enables a holistic comprehension of bulk properties, such as thermal expansion, with direct implications on supramolecular design. However, even modest changes to IMFs can create unpredictable changes to solid-state structures and dynamics. For example, while copper(II) acetylacetonate (Cu(C5H7O2)2) and copper(II) hexafluoroacetylacetonate (Cu(C5HF6O2)2) exhibit similar molecular conformations, subtle differences between the methyl and trifluoromethyl groups produce distinct sets of IMFs in the solid state. These discrepancies produce staggeringly different structural arrangements of the molecules in the solids. In this work, terahertz, mid-infrared, and Raman spectroscopy measure the vibrational dynamics and underlying IMFs that exist in each system. Additionally, theoretical quantum mechanical simulations quantify the IMFs and underlying electronic factors that are inherent to each system. Overall, this work provides fundamental insight into the origins of supramolecular structural effects in crystals.

Understanding the intermolecular forces that drive supramolecular crystal formation

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