A one-dimensional polymeric pyridinium chlorocuprate (HPy) 2[Cu3Cl8(H2O)2], an intermediate between (HPy)CuCl3 and CuCl2·2H 2O, has been synthesized and characterized by X-ray analysis [monoclinic, P21/c, a = 7.8950(10), b = 14.144(2), c = 9.921(10) Å, β = 99.20(2)°]. The structure contains [Cu3Cl 8(H2O)2]n2n- chains in which both square-pyramidal and octahedral CuII exist. The chains are composed of linked [Cu2Cl6]2- dimers and CuCl 2(H2O)2 monomeric units. On being heated in the solid state the compound undergoes dehydration followed by dehydrohalogenation to produce a pyridine complex of CuII: [Cu 3Py2Cl6]. Other compounds, (HPy) 2[CuCl4], CuPyCl2 and CuPy2Cl 2, and CuPy2Cl2, also produce [Cu 3Py2Cl6] as an intermediate on thermal analysis. Magnetic studies reveal ferromagnetic coupling within the chains with an intradimer exchange coupling of 12.1 cm-1 and a dimermonomer exchange coupling of 1.34 cm-1. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.