Our bulk magnetic measurements show strong evidence of long-range ordered magnetic ground states in all four compounds and so to determine the magnetic structure and correlations in their ground states, we carried out PND measurements using the HB-2A diffractometer at HFIR (ORNL). The magnetic structures were determined by refinement against data from which background and nuclear Bragg peaks were removed by subtraction of high temperature data in the paramagnetic regime. The magnetic Bragg peaks were indexed to determine the magnetic propagation vector and the possible irreducible representations (irreps) were determined using symmetry-mode analysis in the ISODISTORT software suite are denoted below in Miller and Love's notation. Our Rietveld refinement of nuclear structures gave us the scale factor, which we then fixed for our Rietveld refinement of the magnetic structure using each irrep against the temperature subtracted dataset. Having determined the magnetic structure using temperature-subtracted data, we were then able to carry out a joint magnetic and nuclear refinement for FeCl 2 (pym) and FeCl 2 (btd) (Tab. S5).