Structure of L-phenylalanine L-phenylalaninium formate

C9H11NO2.C9H12NO2+.CHO2-, M(r) = 376.41, monoclinic, P2(1), a = 11.507 (6), b = 5.638 (3), c = 14.610 (5) A, beta = 100.65 (4) degrees, V = 932 (1) A3, Z = 2, Dx = 1.342 g cm-3, lambda(Mo K alpha) = 0.7107 A, mu = 0.94 cm-1, F(000) = 400, T = 295 K, final R = 0.047 for 2693 observed reflections. The phenylalanine zwitterion and the phenylalanine cation form a Speakman-salt-type hydrogen bond [O ... O = 2.496 (3) A]. Aromatic side chains constitute a thick hydrophobic layer with edge-to-face interactions between the phenyl rings.