The a-and b-parameters are larger for the iron compounds than the nickel, in accordance with the expected ionic radius and bond lengths but the a-parameter is also slightly larger for btd compounds than the pym due to the small distortion in the edge-sharing M Cl 2 bridge. The b-parameter is significantly larger for the btd compounds than the pym compounds (≈ 7%) due to the µ-1,3-ligand being a five-membered ring in btd and a six-membered ring in pym. The c-parameter is significantly larger in the btd compounds than the pym, as the larger btd separates the layers. The M-Cl-M bond angle is a key parameter in predicting J Cl , and is approximately 94 • in these compounds: 93.5 • for FeCl 2 (pym), 93.9 • for FeCl 2 (btd), 93.6 • for NiCl 2 (pym) and 94.9 • for NiCl 2 (btd). We see a decrease in the angle for FeCl 2 (pym) in the high temperature phase to 91.6 • , suggesting perhaps J Cl also changes, though we find no evidence of this in our bulk magnetic data. These angles are broadly consistent with the binary halides FeCl 2 (92.2 • 52 ) and NiCl 2 (91.6 ), which also have nearest-neighbour ferromagnetic superexchange. Our neutron diffraction measurements, in combination with the bulk magnetometry allow us to ascertain the magnetic ground state (Fig. ). We find that in all cases the moments are ferromagnetically correlated along the MCl 2 chains, which is consistent with the only magnetic structure of Ni(II) or Fe(II) MCl 2 L analogues, NiCl 2 (4,4 ′ -bipyridine) , and as predicted by the Goodenough-Kamenari-Anderson rules. Our PND measurements are sensitive to the canting angle γ, which are 19.6(5) • and 25.2(3) • for FeCl 2 (pym) and FeCl 2 (btd) (Tab. 2). For the Ni(II) compounds the small moment size means that we were only able to measure the most intense magnetic peaks, and so our neutron measurements instead put an effective ceiling on the canting angle. These values can be directly compared with those determined from the remnant magnetisation, and are broadly consistent. The size of the canting angles for FeCl 2 (pym) and FeCl 2 (btd) is very large : and are comparable with some of the largest known canting angles. This noncollinear magnetic order implies the presence of multiple competing interactions (as discussed below). The magnetic neutron diffraction also clearly establishes that although in all cases there is a (potential) net moment within the layers, only NiCl 2 (btd) has ferromagnetic order, as the layers in FeCl 2 (btd), FeCl 2 (pym) and NiCl 2 (pym) are all antiferromagnetically coupled.