Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India.
Dalton Trans. 2013 Feb 7;42(5):1848-61. doi: 10.1039/c2dt30347g. Epub 2012 Nov 21.
Four tetranuclear complexes involving both homo- and hetero-metal combinations, viz. [Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Zn(II)(2)(hfac)(2)] (1), [Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Cd(II)(2)(hfac)(2)] (2), [Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)] (3), and [Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)] (4) have been prepared following a single-pot synthesis protocol using N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine (H(2)L) as a primary ligand. Both benzoate and hexafluoroacetylacetonate (hfac(-)), used here as ancillary ligands, play crucial roles in generating a tetranuclear core with high thermodynamic stability. Oxygen atoms of each carboxylate moiety bind all the four metal centers together in a rare η(2):η(2):μ(4)-bridging mode as confirmed by X-ray crystallography. In the homo-metallic complexes (1 and 2), the metal centers are all lying in a square plane, each occupying a corner, and remain connected together by oxygen bridges forming octagonal metallacrowns. These structures remain intact in solution as confirmed by (1)H NMR spectroscopy and photoluminescent studies. In the hetero-metal complexes (3 and 4), the metal centers are arrayed in alternate positions of the tetranuclear core. The Tb(III) centers have eight coordinate bi-capped trigonal prismatic coordination environments with different degrees of distortions. The all oxygen O(8) core surrounding each Tb(III) center is devoid of solvent molecules that make fluorescent emission from these molecules (3 and 4) quite interesting. The hfac(-)-based (1)(π-π*) emissions observed in 1 and 2 are quenched in 3 and 4. These sensitized Tb(III) emissions [(5)D(4)→(7)F(j); j = 6, 5, 4, and 3] are influenced by the local environments surrounding the 4f-metal center. The lifetime for the luminescence decay of 3 ((5)D(4)→(7)F(5) transition) is about 1.5 times longer than that of 4 in all the solvents studied at 298 K.
四种涉及同核和异核组合的四核配合物，即[Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Zn(II)(2)(hfac)(2)]（1）、[Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Cd(II)(2)(hfac)(2)]（2）、[Zn(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)]（3）和[Cd(II)(2)L(2)(μ(4)-PhCOO)(2)Tb(III)(2)(hfac)(4)]（4），是通过使用 N,N'-二甲基-N,N'-双(2-羟基-3,5-二甲基苄基)乙二胺（H(2)L）作为主要配体的单一锅合成方案制备的。这里使用的苯甲酸盐和六氟乙酰丙酮（hfac(-)）作为辅助配体，在生成具有高热力学稳定性的四核核心方面发挥着至关重要的作用。每个羧酸盐部分的氧原子以罕见的η(2):η(2):μ(4)-桥接模式将所有四个金属中心结合在一起，这一点通过 X 射线晶体学得到了证实。在同核配合物（1 和 2）中，金属中心都位于一个正方形平面内，每个金属中心占据一个角，并通过氧桥连接在一起，形成八元金属冠。这些结构在溶液中保持完整，这一点通过（1）H NMR 光谱和荧光研究得到了证实。在异核配合物（3 和 4）中，金属中心在四核核心的交替位置排列。Tb(III)中心具有不同程度扭曲的八配位双帽三角棱柱配位环境。每个 Tb(III)中心周围的全氧 O(8)核心没有溶剂分子，这使得这些分子（3 和 4）的荧光发射非常有趣。在 1 和 2 中观察到的基于 hfac(-)的（1）（π-π*）发射在 3 和 4 中被猝灭。这些敏化的 Tb(III)发射[(5)D(4)→(7)F(j)；j=6、5、4 和 3]受到 4f-金属中心周围局部环境的影响。在 298 K 下研究的所有溶剂中，3（(5)D(4)→(7)F(5)跃迁）的荧光衰减寿命比 4 长约 1.5 倍。
