Salts of the edge-sharing bitetrahedral anion [M2Cl6](2-) with M = Mn, Fe, and Co were prepared in high yields by reaction of MCl2 with 1 equiv of chloride ion. The anion [Fe2Cl6](2-) was isolated with five different cations, namely, [PPh4](+) (1), [Et4N](+) (2), [ppn](+) (3), [AsPh4](+) (4), and [H-TMPP](+) (5) ([H-TMPP](+) = tris(2,4,6-trimethoxyphenyl)phosphonium; [ppn](+) = bis(triphenylphosphonium)iminium chloride). The Mn and Co compounds were isolated as [ppn](+) salts, [ppn](2)[Co2Cl6] (6) and [ppn](2)[Mn2Cl6] (7). The compounds were characterized by single-crystal X-ray analysis and subjected to variable-temperature and field-dependent magnetic measurements. These magnetic data were analyzed from a spin Hamiltonian that contains an isotropic exchange term supplemented by a zero-field-splitting term to account for the single-ion anisotropy of the interacting spins. By using this approach, the [Fe2Cl6](2-) salts (1-5) were shown to exhibit magnetic behavior dominated by single-ion anisotropy of the spin S = 2 of the tetrahedral Fe(II) ions (D similar to 5 cm(-1)). The Co(II) compound (6) was found to exhibit considerable single-ion anisotropy of the spin S = 3/2 tetrahedral Co(II) centers (D = 29 cm(-1)) and stronger antiferromagnetic coupling than the Fe compounds. In the absence of complicating factors such as ZFS effects, as is the case for the Mn(II) derivative (7) it was possible to discern weak intermolecular as well as intramolecular antiferromagnetic interactions. Reactions between 2,2'-bipyrimidine (2,2'-bpym) and salts of [Fe2Cl6](2-) yielded two neutral compounds, namely, Fe2Cl4(2,2'-bpym)(3) (8) and [Et4N]Cl .[Fe2Cl4(MeOH)(4)(mu-2,2'-bpym)] (9). In contrast to the previously described Fe(LI) compounds, the Fe(II) center is octahedral in 8 and 9. The electronic ground state of this ion is orbitally degenerate and therefore highly anisotropic. An analysis of the magnetic data confirmed these predictions and revealed that the bridging ligand mediates antiferromagnetic exchange of similar to 1 cm(-1) and that the D parameter is large and negative (D similar to -17 cm(-1)).