On cooling below T C we find magnetic Bragg peaks for FeCl 2 (pym) (T N = 10.5(5) K), FeCl 2 (btd) (T N = 3.8(2) K), NiCl 2 (pym) (T N = 15.8(7) K) and NiCl 2 (btd) (T C = 17.5(5) K). In the subtracted datasets we were able to isolate and index the magnetic Bragg peaks with propagation vectors, with the three antiferromagnets having a propagation vector k = 00 2 and the ferromagnetic NiCl 2 (btd) having k = 000, confirming its ferromagnetic ground state (Fig. , Tab. 2). We identified the possible irreps in each case and carried out Rietveld refinement of the magnetic structures using every irrep for each material. We found that only one irrep was consistent with the experimental data for each material: mB + 1 for both FeCl 2 (pym) and FeCl 2 (btd); mZ - 1 for NiCl 2 (pym); and mΓ + 2 for NiCl 2 (btd). We note that the observed magnetic structure for FeCl 2 (pym) would require two different magnetic irreps were the high temperature orthorhombic phase used as the parent paramagnetic phase rather than the correct monoclinic phase (ESI Sec. S).