Abstract: | The crystal structures of N,N‐dimethylbiguanidium oxalate monohydrate, C4H13N52+·C2O42?·H2O, (I), and N,N‐dimethylbiguanidium sulfate monohydrate, C4H13N52+·SO42?·H2O, (II), show that both compounds contain the same N,N‐dimethylbiguanidium dication. In (I), two independent oxalate ions lie about inversion centres. Strong double hydrogen bonds, with D?A distances of 2.658 (2) and 2.830 (3) Å in (I), and 2.722 (3) and 2.815 (3) Å in (II), are present between N atoms of the N,N‐dimethylbiguanidium moieties and either the carboxylate group of the oxalate anion or the sulfate anion. |