The crystalline solvates of the divalent group 12 metal ions with the soft sulfur donor N,N-dimethylthioformamide display an unusual variation in coordination number and geometry with two, four, and six ligands attached to the mercury(ll), zinc(II), and cadmium(II), ions, respectively. Bis(N,N-dimethylthioformamide)mercury(II) perchlorate precipitates from acetonitrile solution when adding less than 2 equiv of N,N-dimethylthioformamide, while the zinc and cadmium solvates crystallize from saturated N,N-dimerhylthioformamide solutions. The disolvate [Hg-(SCHN(CH3)(2))(2)](ClO4)(2) crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 6.208(1) Angstrom, b = 15.239(7) Angstrom, c = 8.681(2) Angstrom, beta = 99.30(3)degrees, and Z = 2. Centrosymmetric mercury(II) complexes with strong collinear bonds to two N,N-dimethylthioformamide molecules, Hg-S 2.350(2) Angstrom, are joined by double bridges of perchlorate ions in chains along the a-axis by four weak interactions between the mercury and the perchlorate oxygen atoms, mean Hg-O distance 2.84 Angstrom. Tetrakis(N,N-dimethylthioformamide)zinc trifluoromethanesulfonate, [Zn(SCHN(CH3)(2))(4)](CF3SO3)(2), crystallizes in the triclinic space group P (1) over bar (No. 2) with a = 10.487(3) Angstrom, b = 13.489(5) Angstrom, c = 68.800(4)degrees, beta = 69.260(4)degrees, gamma = 74.05(1)degrees, and Z = 2, with the zinc ions tetrahedrally surrounded by four N,N-dimethylthioformamide ligands, mean Zn-S distance 2.34 Angstrom. Also the cadmium solvate of corresponding composition, [Cd(SCHN(CH3)(2))(4)(CF3SO3)(2)], crystallizes in the space group P (1) over bar, with a = 8.670(1) Angstrom, b = 9.529(1) Angstrom, c = 10.685(1) Angstrom, alpha = 75.20(1)degrees, beta = 66.97(1)degrees gamma = 65.31(1)degrees, and Z = 1, although the structure comprises centrosymmetric tetrakis(N, N-dimethylthioformamide)bis(trifluoromethanesulfonato)cadmium(II) complexes in which four Cd-S bonds (mean 2.65 Angstrom) and two weaker Cd-O bonds at 2.470(2) Angstrom to the trifluoromethanesulfonate ions give rise to a pseudo-octahedral coordination around the cadmium ion. When using perchlorate instead as counterion, hexakis(N, N-dimethylthioformamide)cadmium perchlorate, [Cd(SCHN(CH3)(2))(6)](ClO4)(2), crystallizes in the space group P2(1)/n with a 12.757(1) Angstrom, b = 7.4681-(6) Angstrom, c = 19.732(2) Angstrom, beta = 96.31(1)degrees, and Z = 2. The mean Cd-S bond distance increases to 2.715 Angstrom in the fully solvated cadmium ion with almost regular octahedral coordination geometry to its six centrosymmetrically related ligands. The effect of the weak internal hydrogen bonding occuring between the hydrogen atom of a -CHS group and the sulfur atom of neighboring N,N-dimethylthioformamide ligands is discussed.