Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide – Acetanilide

Hydrogen bond formation in the triphenylphosphine oxide (TPPO), acetanilide (ACN) supramolecular heterosynton system, named [TPPO0.5·ACN0.5], has been studied by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques. In toluene solution, Isothermal Titration Calorimetry (ITC) presented a 1:1 stoichiometry and indicated that the complexation process is driven by entropy, with low enthalpy contribution. X-ray structure determination showed the existence of a three-dimensional network of hydrogen bonds, allowing also the confirmation of the existence of a 1:1 crystalline molecular complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complex are relatively weaker than those found in pure precursors, leading to a higher positronium formation probability at [TPPO0.5·ACN0.5]. These weak interactions in the complex enhance the possibility of the n- and π-electrons to interact with positrons and consequently, the probability of positronium formation is higher. Through the present work is shown that PALS is a sensible powerful tool to investigate intermolecular interactions in solid heterosynton supramolecular systems.

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► [TPPO(1−X)·ACNX] was studied by thermodynamic, spectroscopic and structural techniques.
► By PALS, TPPO and ACN have the same positronium formation probability.
► The [TPPO0.5·ACN0.5] complex showed a higher positronium formation probability.
► Weak interactions in [TPPO0.5·ACN0.5] complex affect the positronium formation.
► The lifetime of positronium proved to be sensitive to complex formation.