To confirm that the ground state was indeed long-range mag- netic antiferromagnetic order, we carried constant wavelength powder neutron diffraction measurements on the high-intensity medium resolution D1B diffractometer at ILL, Grenoble. The incident wavelength was λ = 2.52 Å and the scattering was measured over an angular range of 2 < 2θ < 128 • . We measured high quality long-acquisition time diffraction patterns at 10 K and 2 K, supplemented by shorter measurements at intermediate temperatures of 5, 4.5, 4, 3.5, 3 and 2.5 K. By subtracting the 10 K dataset from the lower temperature data we were able to confirm that additional magnetic Bragg peaks emerged between 4 and 4.5 K, demonstrating that the cusp identified in bulk magnetic susceptibility was due to antiferromagnetic order. We first refined the structural model against the previously determined room temperature structure of Cr[Bi(SCN) 6 ] • H 2 O to determine the overall scale and unit cell parameters using the Rietveld method and the FullProf software suite. We began our determination of the magnetic structure by indexing the additional magnetic reflections with reference to the pseudocubic Fm 3m √ 2 × √ 2 × 1 supercell, because the magnetic lattice has near-cubic metrical symmetry: sinβ = 5×10 -6 , a/V ). This will correspond, for a simple collinear antiferromagnet, to ferromagnetically correlated close packed {111} cubic planes coupled antiferromagnetically. However, accounting for the true monoclinic P2 1 /n symmetry splits this pseudocubic propagation vector into two inequivalent propagation vectors: (0 1 2 1 2 ) and ( 1 2 0 1 2 ), the E and Y points on the Brillouin zone boundary, respectively. This reflects the fact the {111} cubic -type close-packed planes are symmetryand chemically-distinct in this material. Using the k-search program program program included in the FullProf suite to quan- Using the ISODISTORT tool from the ISOTROPY software suite, we were able to identify the three distinct possible irreducible representations (irreps) consistent with this family of propagation vectors that produce a non-zero magnetic moment: mE 1 + E 2 , mY 1 and mY 2 (Miller and Love notation). These three models correspond to the magnetic spaces groups P S 1 (mE 1 + E 2 ) and P c 2 1 /n (mY 1 , mY 2 ). We were able to achieve a good Rietveld refinement fit to models for all three of these structures, in each case leading to structure consisting approximately of ferromagnetically correlated {111} cubic antiferromagnetically coupled. These structures are nearly collinear with moments lying nearly within the {111} cubic plane with small tilts of the moments away from the primary axis (ca. 6 • ), though the high degree of pseudosymmetry meant our determination of the relative angles of the moment is not completely unambiguous. We were able to refine the magnitude of the Cr 3+ giving M = 2.45(20) µ B , which is approximately 80% of the anticipated spin-only value. This small deviation is likely explained by the combination of some covalency and comparatively high scaled measurement temperature (T /T N = 0.5). The main difference between the models was which of the four {111} cubic type planes the spins ordered ferromagnetically within: the mY models ordered in the (1 11) cubic or (10 1) planes and the mE 1 + E 2 model ordered in the (11 1) cubic or (01 1) planes. We found that the mY 1 model fitted the data best and as the mE 1 + E 2 is in addition a lower symmetry triclinic structure with two symmetry independent moments, we therefore think the mY 1 model is likely to be correct structure. Single crystal neutron diffraction data would allow for completely unambiguous deter- mination of the magnetic structure but as yet single crystals of sufficient size are unavailable.