Syntheses and crystal structures of 4-(4-meth­oxy­phen­yl)piperazin-1-ium 4-methyl­benzoate monohydrate and bis­[4-(4-meth­oxy­phen­yl)piperazin-1-ium] benzene-1,2-di­carboxyl­ate

Co-crystallization of N-(4-meth­oxy­phen­yl)piperazine with 4-methyl­benzoic acid and with benzene-1,2-di­carb­oxy­lic acid yields the salts 4-(4-meth­oxy­phen­yl)piperazin-1-ium 4-methyl­benzoate monohydrate, C(11)H(17)N(2)O(+)·C(8)H(7)O(2) (−)·H(2)O (I), and bis­[4-(4-meth­oxy­phen­yl)piperazin-1-ium] benzene-1,2-di­carboxyl­ate, 2C(11)H(17)N(2)O(+)·C(8)H(4)O(4) (2−) (II). These salts both crystallize with Z′ = 2, in space groups P [Image: see text] and Pna2(1), 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 mol­ecules 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.