Thixotropic Hydrogel Derived from a Product of an Organic Solid-State Synthesis: Properties and Densities of Metal−Organic Nanoparticles

Metallogels form from Cu(II) ions and tetratopic ligand rctt-1,2-bis(3-pyridyl)-3,4-bis(4-pyridyl)cyclobutane. The tetrapyridyl cyclobutane has been synthesized in the organic solid state. The gel forms with a variety of counteranions and gels water. The hydrogel is thixotropic and is composed of nanoscale metal−organic particles (NMOPs), a high surface area of which likely accounts for the gelation of the polar aqueous medium. A shear stress profile of the thixotropic hydrogel gave a yield value of 8.33 Pa. A novel combination of atomic force microscopy (AFM) and scanning transmission X-ray microscopy (STXM) is used to assess the densities of individual NMOPs. A density of 1.37 g/cm3 has been determined. A single-crystal X-ray diffraction study demonstrates the ability of the unsymmetrical cyclobutane 3,4′-tpcb to self-assemble with Cu(II) ions in [Cu2(hfac)4(3,4′-tpcb)]∞ (where hfac is hexafluoroacetylacetonate) to form a solvated 1D coordination polymer.

金属凝胶由Cu(II)离子与四位点配体rctt-1,2-双(3-吡啶基)-3,4-双(4-吡啶基)环丁烷自组装形成。该四吡啶基环丁烷已在有机固态体系中合成得到。该凝胶可在多种抗衡阴离子存在下形成，并可胶凝水介质。该水凝胶具有触变性，其组分为纳米尺度金属有机颗粒（NMOPs），其极高的比表面积极有可能是该极性水介质发生胶凝作用的原因。针对该触变性水凝胶的剪切应力分布测试显示，其屈服值为8.33 Pa。研究采用原子力显微镜（AFM）与扫描透射X射线显微镜（STXM）的联用新技术，对单个NMOP的密度进行了表征。最终测得其密度为1.37 g/cm³。单晶X射线衍射研究表明，不对称环丁烷3,4′-tpcb可与Cu(II)离子自组装形成溶剂化一维配位聚合物[Cu₂(hfac)₄(3,4′-tpcb)]∞（其中hfac为六氟乙酰丙酮根）。