Halogen effects on photoluminescence and catalytic properties: a series of spatially arranged trimetallic zinc(II) complexes.

Self-assembly of ZnX2 (X = Cl, Br, and I) with N,N',N''-tris(2-pyridinylethyl)-1,3,5-benzenetricarboxamide (L) as a tridentate N-donor ligand yields discrete C3-symmetric trimetallic zinc(II) complexes, [Zn3X6L(MeOH)3]. These form, via π∙∙∙π interactions and NH∙∙∙∙O=C hydrogen-bonds, an ensemble constituting a unique columnar stacking structure in an abab staggered fashion. For this series of complexes, the halogen effects on the photoluminescence, catalysis, and thermal properties were investigated. For [Zn3Cl6L(MeOH)3], a blue luminescence was observed at 462 nm (λex = 369 nm). The transesterification catalysis showed significant halogen effects in the order [Zn3I6L(MeOH)3] > [Zn3Cl6L(MeOH)3] > [Zn3Br6L(MeOH)3] in methanol, whereas in a mixture of methanol and acetonitrile, the order was [Zn3I6L(MeOH)3] > [Zn3Br6L(MeOH)3] > [Zn3Cl6L(MeOH)3]. Such notable different effects among the three complexes might be explained by the halogens' electronic effects and dissociation properties.