Structural studies of N-2-(6-picolyl)-N′-tolylthioureas

Reaction of 2-amino-6-picoline with 2-, 3-, and 4-tolyl isothiocyanates produces the three N-2-(6-picolyl)-N'-tolylthioureas, 6PicTu2T, 6PicTu3T, and 6PicTu4T. 6PicTu2T is mono-clinic, space group P2(1)/n with a = 8.1700(3) Angstrom, b = 25.5840(6) Angstrom, c = 12.6840(5) Angstrom, beta = 98.8750(16)degrees, and V = 2619.5(2) Angstrom(3) with Z = 8, for d(calc) = 1.305 g/cm(3). 6PicTu3T is monoclinic, space group C2/c with a = 23.879(3) Angstrom, b = 6.744(3) Angstrom, c = 17.116(10) Angstrom, beta = 99.26(4)degrees, and V = 2720(3) Angstrom(3) with Z = 8, for d(calc) = 1.257 g/cm(3). 6PicTu4T is triclinic, space group P-1 with a = 8.829(6) Angstrom, b = 8.8950(15) Angstrom, c = 10.495(3) Angstrom, alpha = 68.63(3)degrees, beta = 72.19(4)degrees, gamma = 63.06(4)degrees, and V = 681.2(5) Angstrom(3) with Z = 2, for d(c)alc = 1.255 g/cm(3). Intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen and the planarity of the thiourea are affected by the position of substitution on the aryl ring. H-1 NMR studies in CDCl3 show the NH' hydrogen resonance considerably downfield from other signals in the spectrum of each thiourea. The enthalpies of fusion of the present thioureas reflect the extent of intermolecular hydrogen bonding and are compared to other heterocyclic thioureas.