The synthesis and structure of C2H7N4O.ZnPO4 (guanylurea zinc phosphate) are reported, The cationic [C2H7N4O](+) template was prepared in situ by the slow hydrolysis of the neutral 2-cyanoguanidine starting material. The resulting structure contains an unusual, unprotonated, zincophosphate layer topology as well as N-H...O template-to-template hydrogen bonds which help to stabilize a "double sandwich" of templating cations between the inorganic sheets. Crystal data: C2H7N4O.ZnPO4, Mr = 263.48, monoclinic, P2(1)/c, a = 13.6453(9), b = 5.0716(3), c = 10.6005(7) Angstrom, beta = 95.918(2)degrees, Z = 4, V = 729.7(1) Angstrom(3), R(F) = 0.034, omegaR(F) = 0.034. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.