Two N,N-dimethylbiguanidium salts displaying double hydrogen bonds to the counter-ions.

The crystal structures of N,N-dimethylbiguanidium oxalate monohydrate, C₄H₁₃N₅²⁺·C₂O₄^2-·H₂O, (I), and N,N-dimethylbiguanidium sulfate monohydrate, C₄H₁₃N₅²⁺·SO₄^2-·H₂O, (II), show that both compounds contain the same N,Ndimethylbiguanidium 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. [ABSTRACT FROM AUTHOR]