The metal-chelating ability of 2-pyrrolylthiones is described. The readily available ligands di-2-pyrrolyl thione (6), 2-thioncetylpyrrole (10), and 2-thiobenzoylpyrrole (11) constitute examples of monoanionic ligands with N,S-donor atom sets, although di-2-pyrrolyl thione (6) could theoretically also achieve chelation through an N,N-donor set. A square planar Ni(II)) complex, 14, an octahedral Co(III) complex, 18, and a tetrahedral Hg(II) complex, 17, with the di-2-pyrrolyl thionato chelate have been prepared, and their structures have been characterized by H-1 NMR, UV-vis, MS, IR, elemental analysis, and single-crystal X-ray difraction. Crystal data for 14: C18H14N4N4-NiS2.0.28H(2)O, NiS2.0.28H(2)O, trigonal, R (3) over bar, a 18.467(1) Angstrom, b = 18.467(1) Angstrom, c = 26.404(2) Angstrom, V = 7797(1) Angstrom (3); Z = 18, R = 3.2%. Crystal data for 18-mer: C27H21CoN6S3.C3H6O (acetone), monoclinic, P2(1)/n, a = 9.569(1) Angstrom, b = 23.152(1) Angstrom, C = 13.659(1) Angstrom, beta = 100.882(8)degrees, V = 2971.6(5) Angstrom (3), Z = 4, R = 4.3%. Crystal data for 17: C18H14HgN4S2 triclinic, P (1) over bar, a = 8.443(2), b = 14.278(1) Angstrom, c = 7.445(1) Angstrom, alpha = 90.561(9)degrees, beta = 97.63(1)0, gamma = 104.250(9)degrees V = 861.3(2) Angstrom (3), Z = 2, R = 4.2%. The bond lengths and angles of these metal complexes are comparable to those of known N,S-chelates. A comparison of the structural parameters of the ligand in the metal complexes with those for the free ligand 6 demonstrates the preorganization of the free ligand for complexation and demonstrates the spectator role of the noncoordinating pyrrolic unit. Chelation of Ni(II) by 2-thioacetylpyrrole (10) and 2-thiobenzoylpyrrole (11) to provide complexes 12 and 13 with structures analogous to complex 14 is also described.