Abstract
A Curie–Weiss-type paramagnetic δ′-(BEDT-TTF)₂ClC₂H₄SO₃·H₂O with θ/2 = j = −45.4 K has a phase transition at 160 K, below which the salt has a δ′-type 2D donor arrangement with 1D Heisenberg antiferromagnetic behavior with j = −121.6 K. Further cooling below 140 K induces a weak dimerization in the donor layers leading to a spin ladder system.