Syntheses and crystal structures of 4-(4-meth-oxy-phen-yl)piperazin-1-ium 4-methyl-benzoate monohydrate and bis-[4-(4-meth-oxy-phen-yl)piperazin-1-ium] benzene-1,2-di-carboxyl-ate.

Co-crystallization of N-(4-meth-oxy-phen-yl)piperazine with 4-methyl-benzoic acid and with benzene-1,2-di-carb-oxy-lic acid yields the salts 4-(4-meth-oxy-phen-yl)piperazin-1-ium 4-methyl-benzoate monohydrate, C11H17N2O+·C8H7O2 -·H2O (I), and bis-[4-(4-meth-oxy-phen-yl)piperazin-1-ium] benzene-1,2-di-carboxyl-ate, 2C11H17N2O+·C8H4O4 2- (II). These salts both crystallize with Z' = 2, in space groups P and Pna21, respectively. In compound (I), a combination of four O-H⋯O, four N-H⋯O, one C-H⋯O and one C-H⋯π(arene) hydrogen bonds link the six independent components into complex sheets, within which the two piperazine rings, the two anions, and the two water mol-ecules are related by an approximate, non-crystallographic translation along the b-axis direction. In compound (II), sheets containing R 4 4(18) and R 10 12(38) rings are formed by the combined action of eight independent N-H⋯O hydrogen bonds. Comparisons are made with the structures of some related compounds.