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The reaction of one equivalent of zinc(II) halide salts with two equivalents of iso­quinoline N-oxide (iQNO; C9H7NO) in methanol yields compounds of the general formula [ZnX2(iQNO)2], with X = Cl− (I), Br− (II) and I− (III). However, starting with zinc(II) perchlorate or nitrate leads to the formation of complex ions with the compositions [Zn(iQNO)6](X)2 for X = ClO4− (IV), and [Zn(iQNO)(H2O)5](iQNO)2X2 for X = NO3− (V). Complexes (I), (II) and (III), namely di­chlorido­bis­(iso­quinoline N-oxide-κO)zinc(II) [ZnCl2(C9H7NO)2], di­bromido­bis­(iso­quinoline N-oxide-κO)zinc(II) [ZnBr2(C9H7NO)2], and di­iodido­bis­(iso­quinoline N-oxide-κO)zinc(II) [ZnI2(C9H7NO)2], each exhibit a distorted tetra­hedral coordination geometry around the zinc(II) ion coordinated by two iQNO ligands bound through the oxygen atom and two halide ions. The zinc ion lies on a crystallographic twofold axis in the bromo complex. The X—Zn—X bond angles are approximately 15–17° larger than the O—Zn—O bond angles resulting in the observed tetra­hedral distortion. In complex (IV), hexa­kis­(iso­quinoline N-oxide-κO)zinc(II) bis­(perchlorate), [Zn(C9H7NO)6](ClO4)2, the zinc(II) ion occupies a special position with 3 site symmetry and is octa­hedrally coordinated by six iQNO ligands, albeit with slight distortions evidenced by a spread of cis bond angles from 85.82 (4) to 94.18 (4)°. The chlorine atom of the perchlorate anion lies on a crystallographic threefold axis. Finally, complex (V) crystallizes with a pseudo-octa­hedral geometry; penta­aqua­(iso­quinoline N-oxide-κO)zinc(II) dinitrate–iso­quinoline N-oxide (1/2), [Zn(C9H7NO)(H2O)5](NO3)2·2(C9H7NO). The nitrate ions and non-coordin­ated iQNO mol­ecules engage in π-stacking and hydrogen-bonding inter­actions with the coordinated water mol­ecules. The iQNO—Zn—O equatorial bond angles range from 88.98 (9) to 94.90 (9)°, with the largest deviation from a perfect octa­hedral angle attributed to the influence of a weak C—H⋯O (from water) inter­action (2.287 Å) involving the bound iQNO ligand. [ABSTRACT FROM AUTHOR]