Anion-Dependent Structure and Luminescence Diversity in ZnII-LnIII Heterometallic Architectures Supported by a Salicylamide-Imine Ligand

• Published in: Inorganic chemistry Vol. 60; no. 22; pp. 17051 - 17062
• Main Authors: Song, Fu-Qiang, Cheng, Hao, Zhao, Na-Na, Song, Xue-Qin, Wang, Li
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15.11.2021
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.1c02228

To advance the structural development and fully explore the application potential, it is highly desirable but challenging to elucidate the relationship between the structures and properties of ZnII-LnIII heterometallic species. Herein, three types of ZnII-LnIII heterometallic compounds (LnIII = GdIII, TbIII) formulated as [Zn16Ln4L12(μ3-O)4(NO3)12]·8CH3CN (ZnLn-1), [Zn2Ln2L2(NO3)6(H2O)2]·3CH3CN (ZnLn-2), and [Zn4Ln2L8(OAc)12]·xCH3CN (ZnLn-3: for Ln = Gd, x = 5; for Ln = Tb, x = 4) were dictated by common inorganic anions, NO3 – and OAc–, with the aid of the multidentate ligand H 2 L with propane as the central skeleton and 3-methoxysalicylamide and 3-methoxysalicylaldimine as terminal groups. ZnLn-1 features cubic cages with four {Zn4L3} tetrahedral subunits and four Ln3+ centers positioned at the eight vertices alternately when NO3 – was introduced into the reaction system exclusively. An attempt to replace NO3 – in ZnLn-1 with OAc– partially led to the formation of {Zn2Ln2L2} heterometallic wheels. Meanwhile, ZnLn-3 featuring double-hairpin-like {Zn4Ln2L4} hemicycles that are orthogonal to each other assisted by intermolecular hydrogen bonds was constructed when NO3 – in ZnLn-1 was completely replaced by OAc–. Their structural integrity in solution were ascertained by both emission and 1H NMR spectroscopy. Ascribed to the different Zn2+-containing antenna, ZnTb-2 possesses a relatively strong emission characteristic of Tb3+; ZnTb-1 has moderate Tb3+ luminescence, yet an absence of Tb3+ emission is found in ZnTb-3. Such an emission difference could be mainly attributed to the antenna effect directed by distinct structural characteristics induced by anions. The anion-dictated self-assembly strategy presented herein not only offers a facile approach to regulate the coordination mode of H 2 L to such an extent to obtain diverse structures of ZnII-LnIII heterometallic species but also provides an understanding of how common inorganic anions tune coordination-driven self-assemblies as well as the subsequent luminescence properties.