Thin films of crystalline solids with substantial free volume from organic chromophores and metal secondary building units (SBUs) are promising for engineering new optoelectronic properties through control of interchromophore coupling. Zn-based SBUs are especially relevant in this case because they avoid quenching the chromophore’s luminescence. We find that layer-by-layer spin-coating using Zn acetate dihydrate and benzene-1,4-dicarboxylic acid (H2BDC) and biphenyl-4,4’-dicarboxylic acid (H2BPDC) linkers easily produces crystalline thin films. However, analysis of the grazing-incidence wide-angle X-ray scattering (GIWAXS) data reveals the structures of these films vary significantly with the linker, and metal-to-linker molar ratio used for fabrication. Under equimolar conditions, H2BPDC creates a type of structure like that proposed for SURMOF-2, whereas H2BDC generates a different metal-hydroxide-organic framework. Large excess of Zn2+ ions causes the growth of layered zinc hydroxides, irrespective of the linker used. Density functional theory (DFT) calculations provide structural models with minimum total energy that are consistent with the experimentally observed diffractograms. In the broader sense, this work illustrates the importance in this field of careful structural determination, e.g., by utilizing GIWAXS and DFT simulations to determine the structure of the obtained crystalline metal-organic thin films, so properties can be rationally engineered and explained.

中文翻译：

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确定逐层旋涂二羧酸锌基金属有机薄膜的结构

具有来自有机发色团和金属二级结构单元（SBU）的大量自由体积的结晶固体薄膜有望通过控制发色团间耦合来设计新的光电特性。锌基 SBU 在这种情况下尤其重要，因为它们可以避免猝灭发色团的发光。我们发现，使用二水合乙酸锌和苯-1,4-二甲酸（H2BDC）和联苯-4,4'-二甲酸（H2BPDC）连接剂的逐层旋涂很容易产生结晶薄膜。然而，对掠入射广角 X 射线散射 (GIWAXS) 数据的分析表明，这些薄膜的结构随连接体以及用于制造的金属与连接体摩尔比的不同而显着变化。在等摩尔条件下，H2BPDC 产生一种类似于 SURMOF-2 的结构，而 H2BDC 产生不同的金属-氢氧化物-有机框架。无论使用何种连接剂，大量过量的 Zn2+ 离子都会导致层状氢氧化锌的生长。密度泛函理论 (DFT) 计算提供了具有最小总能量的结构模型，与实验观察到的衍射图一致。从更广泛的意义上讲，这项工作说明了在这一领域中仔细确定结构的重要性，例如，通过利用 GIWAXS 和 DFT 模拟来确定所获得的晶体金属有机薄膜的结构，从而可以合理地设计和解释性能。