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The crystal structure of famotidine form B has been solved directly from powder diffraction data by the application of simulated annealing. The molecule crystallizes in the monoclinic space group P21/c with refined unit‐cell dimensions a = 17.6547 (4), b = 5.2932 (1), c = 18.2590 (3) Å and β = 123.558 (1)° at T = 130 K. The core of this work is a systematic investigation of the influence of algorithmic, crystallographic and molecular factors on the structure solution process. With an appropriate choice of annealing schedule, molecular description and diffraction data range, the overall number of successes in solving the crystal structure is close to 100%. Other factors, including crystallographic search space restrictions and parameter sampling method, have little effect on the structure solution process. The basic principles elucidated here have been factored into the design of the DASH structure solution program.

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Remacemide [2-amino-N-(1-methyl-1,2-diphenylethyl)-acetamide] was developed as a potential antagonist for epilepsy, Parkinsonism, and Huntington's disease. This paper investigates hydrophilic and hydrophobic intermolecular interactions that occur within the series of crystal structures comprising remacemide 1 and six of its salts [2 ) chloride; 3 ) nitrate; 4 ) acetate (C 2 H 3 O 2 -); 5 ) hydrogenfumarate (C 4 H 3 O 4 -); 6 ) naphthalene-2-sulfonate (napsilate, C 10 H 7 O 3 S -); 7 ) 1-hydroxynaphthalene-2-carboxylate (xinafoate, C 11 H 7 O 3 -)]. The hydrophilic interactions are described through graph set analyses of the hydrogen bond motifs and networks. The lattice of 1 comprises unidirectional, one-dimensional chains of molecules parallel to the c-axis.In 2, the cation-anion hydrogen bonding imposes a well-defined hydrophilic stratum structure on the lattice. As the cation itself is amphiphilic, a natural consequence of this is the creation of two-dimensional stacked layers with alternating hydrophilic and hydrophobic character (lattice bilayers). This tendency to form bilayers within the lattice is also observed in structures 3-5 (polar anions) and structures 6-7 (amphiphilic anions). Relatively few well-directed intermolecular interactions are observed between aromatic rings, either in 1 or in the hydrophobic layers of 2-7. Therefore, it is concluded that it is the hydrophilic hydrogen bond interactions that dominate the crystal packing and drive the segregation into lattice bilayers in the salt crystal structures.