Cocrystals, solids composed of molecular and/or ionic compounds connected by noncovalent interactions, are objects of interest in crystal engineering. Theobromine, as an active pharmaceutical ingredient, was used in cocrystallization with dihydroxybenzoic acids.

In this work, benzene-1,3,5-tricarboxylic (trimesic acid, TMSA) and benzene-1,2,3-tricarboxylic acid (hemimellitic acid, HMLA) were used as coformers for cocrystal synthesis with chosen purine alkaloids. Theobromine (TBR) forms cocrystals TBR• TMSA and TBR•HMLA with these acids. Theophylline (TPH) forms cocrystals TPH•TMSA and TPH•HMLA, the cocrystal hydrate TPH•TMSA•2H 2 O and the salt hydrate (TPH) + •(HMLA) − •2H 2 O. Caffeine (CAF) forms the cocrystal CAF•TMSA and the cocrystal hydrate CAF•HMLA•H 2 O. The purine alkaloid derivatives were obtained by solution crystallization and by neat or liquid-assisted grinding. The powder X-ray diffraction method was used to confirm the synthesis of the novel substances. All of these solids were structurally characterized, and all synthons formed by purine alkaloids and carboxylic acids were recognized using a single-crystal X-ray diffraction method. The Cambridge Structural Database was used to determine the frequency of occurrence of analyzed supramolecular synthons, which is essential at the crystal structure design stage. Determining the influence of structural causes on the various synthon formations and molecular arrangements in the crystal lattice was possible using structurally similar purine alkaloids and two isomers of benzenetricarboxylic acid. Additionally, UV− vis measurements were made to determine the effect of cocrystallization on purine alkaloid solubility.

Theobromine, a compound from the purine alkaloid group, is much less soluble in polar solvents than its analogues, i.e. caffeine and theophylline, that is why it was used as an active pharmaceutical ingredient (API) model in cocrystal preparation.

A wide range of functionalized pyridine ligands have been employed to synthesize a variety of Pd(II) complexes of the general formulas [Pd L 4 ](NO 3 ) 2 and [Pd L 2 Y 2 ], where L = 4-X-py and Y = Cl – or NO 3 – . Their structures have been unambiguously established via analytical and spectroscopic methods in solution (NMR spectroscopy and mass spectrometry) as well as in the solid state (X-ray diffraction). This in-depth characterization has shown that the functionalization of ligand molecules with groups of either electron-withdrawing or -donating nature (EWG and EDG) results in significant changes in the physicochemical properties of the desired coordination compounds. Downfield shifts of signals in the 1 H NMR spectra were observed upon coordination within and across the complex families, clearly indicating the relationship between NMR chemical shifts and the ligand basicity as estimated from p K a values. A detailed crystallographic study has revealed the operation of a variety of weak interactions, which may be factors explaining aspects of the solution chemistry of the complexes. The Pd(II) complexes have been found to be efficient and versatile precatalysts in Suzuki–Miyaura and Heck cross-coupling reactions within a scope of structurally distinct substrates, and factors have been identified that have contributed to efficiency improvement in both processes.