Dithiomalonamide (HL = Hdtma) and diphenyldithiomalonamide (HL = Hdpma) form diamagnetic planar complexes Ni(dtma)₂, Ni(dpma)₂, Ni(Hdtma)₂X₂(X = Cl, Br, I, or ClO₄) and Ni(Hdpma)₂X₂(X = I or ClO₄) and paramagnetic octahedral complexes Ni(Hdpma)₃X₂(X = Cl, Br, or ClO₄). NiL₂ complexes are non-electrolytes: their electronic spectra in solution and their i.r. spectra in the solid state, both very similar to those of bis(dithioacetylacetonato) nickel(II), the increase in ν(CN), the decrease in ν(CS), and the ν(NiS) frequencies are consistent with a [NiS₄] co-ordination. NiL₂ form adducts NiL₂,nA (nA = 2 MCS, 2 DMF for Hdtma and DMF, 4 DMF, 2 HAc for Hdpma). The splitting orbital parameter Δ₁ indicates that these anion ligands assume an intermediate position in the spectrochemical series of sulphur donors. Ni(HL)₂X₂ and Ni(HL)₃X₂ are S,N-co-ordinated, as shown by the splitting of the ν(CN) and ν(CS), by their ν(NiN) and ν(NiS) i.r. bands and by the Δ₁ values, greater for the Ni(HL)₂X₂(21 000 cm^–1) than for the NiL₂(18 000cm^–1) complexes. The Δ₁ parameters for the Ni(HL)₂X₂ six-membered ring complexes indicate a ligand strength stronger than in the analogous five-membered ring S,N-co-ordinated complexes of the dithio-oxamides. The distorted octahedral Ni(HL)₃X₂ complexes have Dq and B values characteristic of [NiS₃N₃] chromophores.