Abstract: The synthesis and crystal structure of 4,N,N'- triethylbenzamidinium benzoate is reported in which the benzoate anion and the (E,E)-configured amidinium group are linked through two hydrogen bonds (with an N...O distance of 2.723 Angstrom). Since an amidine (E,E) isomer was also observed for chloroform solutions of the complex, the binding mode in the crystal and in solution was analogous to that reported for unsubstituted amidines. The strong basicity of the N,N'-diethyl-substituted benzamidine (pK(a) 11.99 +/- 0.02 in water-dioxane, 1:1) was evident from potentiometric titrations. (C) 2002 Elsevier Science Ltd. All rights reserved