Ligand-Substitution-Induced Single-Crystal to Single-Crystal Transformations in a Redox-Versatile Cu(II) MOF toward Smartphone-Based Colorimetric Detection of Iodide

Fabrication
of a new three-dimensional Cu(II) metal–organic
framework, {[Cu4(4,4′-bipy)3(OH)2(mal)3]·4H2O}n (1a; 4,4′-bipy = 4,4′-bipyridine,
H2mal = malonic acid; P21/m), that undergoes an unprecedented redox-versatile ligand-substitution-induced
single-crystal to single-crystal transformation, for smartphone-based
detection of iodide was studied. The Cu-MOF 1a has been
effortlessly synthesized by the microwave-heating technique. Phase
formation of the Cu-MOF 1a depended on counter-anions.
The transformations can be triggered by halides to corresponding coordination
polymers through both non-redox and redox-associated pathways. The
changes in the local structure and oxidation state of copper during
the transformation were studied by ex situ and in situ synchrotron
X-ray absorption spectroscopies. The selectivity of the halide-triggered
transformation was investigated. A study on smartphone-based colorimetric
detection of iodide was found to be linearly proportional to the iodide
concentration in the range 10–1500 mg/L with a limit of detection
of 5 mg/L and good precision relative standard deviation of 1.9% (n = 11), possibly to construct the iodide test kit.

本研究针对用于智能手机基碘离子检测的新型三维Cu(II)金属有机框架（Metal-Organic Framework, MOF）{[Cu₄(4,4′-联吡啶)₃(OH)₂(丙二酸根)₃]·4H₂O}ₙ（命名为1a；其中配体4,4′-联吡啶（4,4′-bipyridine, 4,4′-bipy）、丙二酸（malonic acid, H₂mal），该MOF的空间群为P2₁/m）展开，该框架可发生前所未有的、兼具氧化还原多样性的配体取代诱导单晶到单晶转变。该Cu基MOF 1a可通过微波加热法简便合成。该Cu-MOF 1a的晶相形成过程依赖于抗衡阴离子。该转变过程可由卤化物触发，通过非氧化还原与氧化还原关联两条路径得到相应的配位聚合物。研究人员借助非原位与原位同步辐射X射线吸收光谱，对转变过程中铜的局部结构与氧化态变化进行了表征分析。同时探究了卤化物触发该转变的选择性。针对智能手机基比色法检测碘离子的研究表明，该方法在10~1500 mg/L浓度范围内响应与碘离子浓度呈良好线性关系，检出限为5 mg/L，相对标准偏差为1.9%（n=11），具备构建碘离子检测试剂盒的应用潜力。