Crystal structures of zinc(II) coordination complexes with iso-quinoline N-oxide.

The reaction of one equivalent of zinc(II) halide salts with two equivalents of iso-quinoline N-oxide (iQNO; C9H7NO) in methanol yields compounds of the general formula [ZnX 2(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)2 X 2 for X = NO3 - (V). Complexes (I), (II) and (III), namely di-chlorido-bis-(iso-quinoline N-oxide-κO)zinc(II) [ZnCl2(C9H7NO)2], di-bromido-bis-(iso-quinoline N-oxide-κO)zinc(II) [ZnBr2(C9H7NO)2], and di-iodido-bis-(iso-quinoline N-oxide-κO)zinc(II) [ZnI2(C9H7NO)2], each exhibit a distorted tetra-hedral 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 tetra-hedral distortion. In complex (IV), hexa-kis-(iso-quinoline 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 octa-hedrally 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-octa-hedral geometry; penta-aqua-(iso-quinoline N-oxide-κO)zinc(II) dinitrate-iso-quinoline N-oxide (1/2), [Zn(C9H7NO)(H2O)5](NO3)2·2(C9H7NO). The nitrate ions and non-coordin-ated iQNO mol-ecules engage in π-stacking and hydrogen-bonding inter-actions with the coordinated water mol-ecules. The iQNO-Zn-O equatorial bond angles range from 88.98 (9) to 94.90 (9)°, with the largest deviation from a perfect octa-hedral angle attributed to the influence of a weak C-H⋯O (from water) inter-action (2.287 Å) involving the bound iQNO ligand.