M (H) increases linearly in the low field region with near constant susceptibility as expected for an antiferromagnet (Fig. &). A sharp metamagnetic transition then occurs, H c1 = 0.2(1) T for FeCl 2 (pym) and H c1 = 3.8(4)T for NiCl 2 (pym). Finally a high field transition, likely to be a field polarised state, occurs at H c2 = 1.2(2) T for FeCl 2 (pym) and H c2 = 6.8(2) T for NiCl 2 (pym) (Fig. e & S11c-e). There is considerable hysteresis in these transitions and the transition back to the antiferromagnetic state H c1 does not occur, leading to significant remnant magnetisation: M r = 0.28(1)µ B for FeCl 2 (pym) and M r = 0.127(5)µ B for NiCl 2 (pym). This metamagnetic state has a considereable coercive field, H C = 0.2(1) T for FeCl 2 (pym) and H C = 1.8(1) T for NiCl 2 (pym) (Tab. 1, Fig. , Fig. &). FeCl 2 (btd) shares the initial metamagnetic transition H c1 = 0.04(1) and high field transition H c2 = 0.8(1) T, which are accompanied by discontinuities in dM dH (H) (Fig. ). However, we were not able to measure any hysteresis associated with either transition. As such, there is no remnant magnetisation or coercive field, and the antiferromagnetic state can be easily reached by removing the applied field.