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⋯OC 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 (λ_ex = 369 nm). The transesterification catalysis showed significant halogen effects in the order [Zn₃I₆L(MeOH)₃] > [Zn₃Cl ₆L(MeOH)₃] > [Zn₃Br₆L(MeOH) ₃] in methanol, whereas in a mixture of methanol and acetonitrile, the order was [Zn₃I₆L(MeOH)₃] > [Zn ₃Br₆L(MeOH)₃] > [Zn₃Cl ₆L(MeOH)₃]. Such notable different effects among the three complexes might be explained by the halogens' electronic effects and dissociation properties.