【Nat.Chem.】北京大学窦锦虎|调控配体聚集斩获1792 S cm⁻¹超高导电性：解锁范德华金属有机框架堆叠新纪元
文章标题：Programming stacking order in conducting van der Waals metal–organic frameworks through ligand aggregation
通讯作者：Jin-Hu Dou
文章概要
引言
范德华材料的物理性质高度依赖于其层间堆叠顺序，如何精准且简便地构建具有特定层间堆叠模式的层状材料一直是一项重大挑战。近年来，导电范德华金属有机框架（vdW-MOFs）因其优异的导电性和丰富的电子态成为研究热点，但由于缺乏精准的单晶合成控制方法，其晶格堆叠序列与电荷传输行为之间的深层构效关系此前仍不为人知。为了打破这一瓶颈，研究团队提出了一种全新的“聚集继承”概念并开发了聚集继承法（AIM）。该策略通过利用不同溶剂环境调控共轭配体的可调亚稳态聚集行为，随后通过金属-配体配位将其稳定并完美“继承”到最终的骨架晶体中，成功在二维和三维范德华金属有机框架单晶中实现了对堆叠序列的理性设计与可控调节。
Fig. 1: Examples of stacking control in vdW materials.
a, Novel quantum states (for example, superconductivity) in twisted bilayer realized by tear-and-stack method with a small twisted angle. b, Higher mobility achieved in organic vdW material by molecular engineering. c, Different stackings presented in vdW-MOFs accomplished by controlling the metastable state of ligand. d, Schematic illustration for precise and predictable stacking control in 2D and 3D vdW-MOFs by tuning ligand aggregation.
主要实验及结论
研究人员首先在经典的二维范德华金属有机框架体系 中实施了聚集继承法。通过调节DMF与水的溶剂比例，成功操纵了共轭配体HHTP在溶液中的超分子聚集状态。原位同步辐射广角与小角X射线散射（WAXS/SAXS）技术实时揭示了铜离子与预组织配体之间极快的配位动力学过程，这种瞬时配位锁定了配体的初始溶液聚集态，从而成功催化生长出具有两种截然不同堆叠序列的单晶相：交替堆叠的A相和单向倾斜堆叠的U相。高分辨低温电子显微镜（cryo-EM）和微晶电子衍射（micro-ED）清晰解析了这两者的原子级结构差异，A相展现出具有强 相互作用的滑移平行堆叠，而U相层间则发生更大程度的错位。密度泛函理论（DFT）计算和单晶器件变温电导率测试表明，堆叠几何的微小改变剧烈地影响了其电子能带结构，层间错位较小的A相展现出更优异的垂直面外方向电导率。
Fig. 2: Controlled stacking sequences of polymorphic vdW-MOFs by the AIM, and crystal details of two polymorphs.
a,c, Schematics for the syntheses of phases A (a) and U (c). b, Normalized UV–vis absorption spectra of HHTP dispersed in H2O/DMF (10−5 M) solutions. Inset: optical image of HHTP dispersed in different solutions with different ratios of H2O/DMF ranging from 10:0 to 0:10. d,e, Single-crystal structure details, cryo-EM images (scale bars: 2 nm) and 3D reciprocal lattices of phases A (d) and U (e) (inset: real-space image; scale bars: 1 μm).
Fig. 3: Study on the mechanism of polymerization between Cu2+ and HHTP.
a,c, In situ synchrotron WAXS of phases A (a) and U (c). t, time; q, magnitude of the scattering vector. b,d, In situ synchrotron SAXS of phases A (b) and U (d). e–h, Single-crystal structure of H2OHHTP obtained from H2O (e), intermediate phase of HHTP obtained from aqueous solution (f; denoted as H2OI-HHTP), precursor of Cu3(HHTP)2 composed of one Cu2+ and two HHTP molecules (g; denoted as Cu–2HHTP dimer) and DMFHHTP obtained from DMF (h), comparing structures of phases A and U. i, MD simulation of HHTP dimers (extracted from H2OI-HHTP) in H2O (similar to H2OHHTP) and DMF (similar to DMFHHTP). Upon dispersing H2OI-HHTP in H2O and DMF, the addition of Cu2+ leads to the formation of phase A and phase U Cu3(HHTP)2, respectively. j, Cryo-EM images of Cu3(HHTP)2 with disordered stacking. Scale bar: 20 nm (left), 5 nm (right). k, Potential energy surface of Cu3(HHTP)2 with varied shift lengths along the a and b axes. l, Schematic of stacking inheritance principle from ligand to MOF.
为了进一步验证该策略的通用性，研究团队将聚集继承法拓展至更具挑战性的三维范德华金属有机框架 系统中。非平面配体DBC在水和DMF中由于氢键强度差异而表现出不同的构象扭曲角。通过引入铜离子发生快速配位锁定制备，单晶结构分析首次揭示了导电框架中两种具有独特相互贯穿网络的三维同质异形体。在水中配体展现出较大的扭曲角，继承形成了五重复步贯穿结构；而在DMF中配体更趋于平面化，诱导形成了堆叠更紧密的四重复步贯穿结构。单晶器件电学表征显示，五重贯穿相表现出常规的半导体传输特性，而结构更致密、主链共轭与电荷离域更强的四重贯穿相则斩获了1792 S cm⁻¹的超高室温导电率。令人惊叹的是，该单晶器件在150至300开尔文的区间内展现出罕见的金属键传输行为，其电导率随温度降低而持续飙升，完美实现了多孔性与金属性的共存。
Fig. 4: Single-crystal structures of Cu2DBC with fivefold and fourfold interpenetration topology.
a,b, Double 3D networks illustrating the fivefold (a) and fourfold (b) interpenetrated frameworks viewed along the a axis. c,d, Individual 3D network extracted from the fivefold (c) and fourfold (d) frameworks viewed along the b axis. e,g, Individual 3D network extracted from the fivefold (e) and fourfold (g) frameworks. f,h, Fivefold (f) and fourfold (h) interpenetration topology viewed along the b axis. i,l, Cryo-EM images of the fivefold (i) and fourfold (l) Cu2DBC. Insets: fast Fourier transform images; scale bars: 5 nm−1. j,k, 3D reciprocal lattices of Cu2DBC with fivefold (j) and fourfold (k) interpenetration. Insets: real-space images; scale bars: 1 μm.
Fig. 5: DFT calculations of Cu3(HHTP)2 and electrical properties of synthesized polymorphic vdW-MOFs based on single-crystal devices.
a, Schematic of simulated slipped crystal structure. b, Calculated band structure and density of states (DOS) of a. c, Calculated band structure and DOS of two phases of Cu3(HHTP)2. _E_g, bandgap energy. d,e, Room-temperature two-probe and four-probe electrical measurement of phase A (d) and phase U (e). Insets show optical images of fabricated single-crystal devices. Scale bar: 5 μm; I, current; V, voltage. f, Variable-temperature direct-current four-probe conductivity (σ) measurements on single-crystal device of phases A and U under argon atmosphere (150–295 K). g, Room-temperature four-probe electrical measurement of Cu2DBC with fivefold and fourfold interpenetration. Insets show optical images of fabricated single-crystal devices (top left, fourfold; bottom right, fivefold). Scale bars: 5 μm. h, Variable-temperature a.c. four-probe conductivity measurements on single-crystal device of Cu2DBC with fivefold and fourfold interpenetration under argon atmosphere (150–300 K). _E_a, activation energy. i, Conductivity statistics of porous MOFs. Data of conductivity values and the corresponding references are listed in the Supplementary Information.
总结及展望
这项研究成功建立了聚集继承法这一极具预测性的概念框架与合成策略，桥连了液相配体超分子聚集与固相框架拓扑之间的鸿沟。通过调控液相环境，该方法不仅成功在二维和三维范德华金属有机框架中实现了纳米级晶格堆叠秩序的精准编程，还实现了从半导体到罕见多孔金属传输机制的颠覆性调控。这一成果不仅打破了多孔导电材料的导电率纪录，更为未来通过拓扑工程理性设计与构筑具有定制电子性质的新一代前沿功能材料开辟了广阔的道路。