Rationalization of Lattice Thermal Expansion for Beta-Blocker Organic Crystals

Paola Paoli,Stella Milazzo,Andrea Ienco,Patrizia Rossi

doi:10.3390/cryst10050350

Abstract

Anisotropic lattice expansion could be a source of misunderstanding in powder pattern recognitions, especially in the case of organic crystals where for the interpretation of room temperature patterns single crystal data at low temperature are usually used. Trying to rationalize the thermal lattice expansion, we studied two close related β-blocker molecules with similar packing in the solid state but with different thermal behavior. Solid state calculations, using the fast and accurate HF-3c method and the quasi harmonic approximation for the simulation of the lattice expansion, were able to reproduce the experimental trends with good accuracy. The complete analysis of the calculated thermal expansion of the two structures, as well as of other structures with similar packing found in a database survey, revealed the primary role of the hydrogen bonds. Secondary non-covalent interactions in the plane perpendicular to the hydrogen bond system could also play a role.

Highlights

IntroductionA volume enlargement is observed with the same change of all cell axes, but in other cases one axis could change at a different rate with respect to the other two
As discussed by Stephenson [4], an unrecognized anisotropic thermal expansion could cause the wrong assignment of room temperature powder pattern recognitions, given that some peaks are unexpectedly more shifted with respect to those in the patterns simulated using single crystal data, usually obtained at low temperatures
We have analyzed, using the Quasi Harmonic Approximation, the thermal behavior of a series of β-blocker drugs with similar solid structures characterized by a particular type of hydrogen bond columns

Summary

Introduction

A volume enlargement is observed with the same change of all cell axes, but in other cases one axis could change at a different rate with respect to the other two. This phenomenon is called anisotropic thermal expansion. As discussed by Stephenson [4], an unrecognized anisotropic thermal expansion could cause the wrong assignment of room temperature powder pattern recognitions, given that some peaks are unexpectedly more shifted with respect to those in the patterns simulated using single crystal data, usually obtained at low temperatures. The variation in 2θ is significant in the diffraction patterns of crystal samples having unit cell axis dimension smaller than 10 Å [4]

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