Bis(5-chloro-8-hydroxyquinolinium) tetrachloridopalladate(II), (C(9)H(7)ClNO)(2)[PdCl(4)], (I), catena-poly[dimethylammonium [[dichloridopalladate(II)]-μ-chlorido]], {(C(2)H(8)N)[PdCl(3)]}(n), (II), ethylenediammonium bis(5-chloroquinolin-8-olate), C(2)H(10)N(2)(2+)·2C(9)H(5)ClNO(-), (III), and 5-chloro-8-hydroxyquinolinium chloride, C(9)H(7)ClNO(+)·Cl(-), (IV), were synthesized with the aim of preparing biologically active complexes of Pd(II) and Ni(II) with 5-chloroquinolin-8-ol (ClQ). Compounds (I) and (II) contain Pd(II) atoms which are coordinated in a square-planar manner by four chloride ligands. In the structure of (I), there is an isolated [PdCl(4)](2-) anion, while in the structure of (II) the anion consists of Pd(II) atoms, lying on centres of inversion, bonded to a combination of two terminal and two bridging Cl(-) ligands, lying on twofold rotation axes, forming an infinite [-μ(2)-Cl-PdCl(2)-](n) chain. The negative charges of these anions are balanced by two crystallographically independent protonated HClQ(+) cations in (I) and by dimethylammonium cations in (II), with the N atoms lying on twofold rotation axes. The structure of (III) consists of ClQ(-) anions, with the hydroxy groups deprotonated, and centrosymmetric ethylenediammonium cations. On the other hand, the structure of (IV) consists of a protonated HClQ(+) cation with the positive charge balanced by a chloride anion. All four structures are stabilized by systems of hydrogen bonds which occur between the anions and cations. π-π interactions were observed between the HClQ(+) cations in the structures of (I) and (IV).