We report a comparative neutron single crystal diffraction study of the structural and magnetic properties of layered halides CrCl₃ and α-RuCl₃, which host a honeycomb arrangement of transition metal ions with distinct electronic configurations and undergo a first-order structural transition between high-temperature C2/m and low-temperature R3̄. Both compounds show a step-like change in the c-lattice, consistent with an expected stacking rearrangement. In contrast, the in-plane lattice response is quite different: α-RuCl₃ exhibits an abrupt hysteretic change across the transition accompanied by progressive crystalline degradation upon thermal cycling, whereas CrCl₃ shows a smooth in-plane lattice evolution and remains structurally robust. Magnetically, CrCl₃ orders into an A-type antiferromagnetic structure at T_N=14 K and exhibits pronounced diffuse magnetic scattering extending up to about 40 K. α-RuCl₃ shows no observable magnetic diffuse scattering above its zig-zag antiferromagnetic ordering temperature T_N=7.6 K. These results suggest that the contrasting structural and magnetic behaviors arise from an interplay between interlayer sliding energetics and the fundamentally different electronic configurations of the two compounds.