# Methods for Detecting Picric Acid--A Review of Recent Progress
## 3 Sensors for Detecting and Measuring PA
### Metal-Organic Frameworks Sensor
#### 3.1.2 Lanthanide-MOFs
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Metal-Organic Framework** & **Structure 1** & **Solvent** & **LOD** & **K\({}_{\bf{SV}}\) 2** [M-1]** & **Ref.** \\ \hline \([Eu_{2}L_{3}(DMF)(H_{2}O)_{3}]\cdot x(solvent)\) & 3 DP & DMF & 5 \(\times\) 10\({}^{-6}\) M & 2912 & [69] \\ Eu\({}_{2}\)L\({}_{2}\) 3 & 2 DL / 3 DF & DMF & 1 \(\times\)10\({}^{-5}\) M & 1359 & [70] \\ Tb\({}_{2}\)L\({}_{2}\) 3 & 2 DL / 3 DF & DMF & 5 \(\times\) 10\({}^{-6}\) M & 4995 & [70] \\ \([Dy(\mu_{2}-FcDCA)1.5(MeOH)-(H_{2}O)]\cdot 0.5H_{2}O]_{n}\) & 2 DL & H\({}_{2}\)O & 7.1 \(\times\) 10\({}^{-7}\) M & 8550 & [71] \\ ([Eu\({}_{2}\)L\({}_{1.5}\)(H_{2}O)_{2} EtOH)\cdot\)DMF\(n\) & 3 DP & DMF & 1\(\times\)10\({}^{-5}\) & 2001 & [72] \\ \((C_{2}H_{6}NH_{2})_{2}[Tb_{2}(ptptpc)_{2}(DMF)(H_{2}O)]\cdot DMF\cdot 6H_{2}O\) & 2 DL / 3 DF & methanol & 1 \(\times\) 10\({}^{-7}\) & 38,910 & [73] \\ Eu(naphthalenedicarboxylic acid) & n/a & H\({}_{2}\)O & 1.64 \(\times\) 10\({}^{-7}\) & 3220 & [74] \\ \(Tb(tfba)_{1.5}(phen)(H_{2}O)]_{n}\) & 3 DH & H\({}_{2}\)O & 1.02 \(\times\) 10\({}^{-5}\) & 5890 & [75] \\ Eu-MOF & MP & DMF & n/a & 1500 & [76] \\ \([Tb(1,3,5-benzetricarboxylate)]\) & Nanowire & Ethanol & 8.1 \(\times\) 10\({}^{-8}\) & 3410 & [77] \\ TbL\({}^{4}\) & n/a & Tris-HCl buffer & 1.1 \(\times\) 10\({}^{-7}\) M & 1.6 \(\times\) 10\({}^{5}\) & [78] \\ Tb\({}_{0.01}\)Gd\({}_{0.99}\)L\({}^{4}\) & n/a & Tris-HCl buffer & 4.1 \(\times\) 10\({}^{-7}\) M & 4.42 \(\times\) 10\({}^{4}\) & [78] \\ GdL\({}^{4}\) & n/a & Tris-HCl buffer & 4.0 \(\times\) 10\({}^{-7}\) M & 4.48\(\times\)10\({}^{4}\) & [78] \\ \hline \hline \end{tabular}  
* \({}^{1}\) 3 DP = 3D porous, 3 DH = 3D polyhedron, 3 DF = 3D framework, 2 DL = 2D layered, MP = microporous, n/a = No information was provided; 2 Fluorescence quenching constant; 3 The compounds have the form of Ln\({}_{2}\)L\({}_{2}\) = [Ln\({}_{2}\)L\({}_{2}\)(DMF)(H\({}_{2}\)O)\({}_{3}\)(\(\mu_{3}\)-O)]+H\({}_{2}\)O\({}_{n}\), where L = 4,4\({}^{\prime}\)-(carbonylbis(azanedily))dibenzoic acid, DMF = N,N-dimethylformamide, Ln = Eu (EuL) or Tb (TbL); 4 The compounds have the form of LnL = [Ln\({}_{2}\)L\({}_{5}\)(NMP)\({}_{2}\)L\({}_{n}\), where L = [1,1\({}^{\prime}\)4\({}^{\prime}\),1\({}^{\prime}\)-terphenyl]-2\({}^{\prime}\),4\({}^{\prime}\),5\({}^{\prime}\)-tetracarboxylic acid, NMP = N-methyl-2-pyrrolidone, Ln = Tb (TbL), Gd (GdL) or a 1:99 mixture of Tb and Gd (Tb\({}_{0.01}\)Gd\({}_{0.99}\)L);  
\end{table} 
Table 3: Summary of lanthanide-based metal-organic frameworks used to detect picric acid. Figure 3: Structures of selected Ln-MOF compounds: (**1**) Coordination environment of Eu\({}^{3+}\). Reprinted with permission from [69]. Copyright 2020, American Chemical Society; (**2**) Ball-and-stick representation of the asymmetric unit in the crystal structure of Eu-MOF. Reprinted with permission of John Wiley & Sons, Inc. from [76]; (**3**) Molecular structure of [Dy(\(\mu_{2}\)-FcDCA)1.5(MeOH)-(H\({}_{2}\)O)]\(\cdot\)0.5H\({}_{2}\)O]n showing the coordination environment around the Dy(III) metal ion. Reprinted with permission from [71]. Copyright 2019, American Chemical Society; (**4**) Coordination environments of Tb1 and Tb2 in complex (C\({}_{2}\)H\({}_{6}\)NH\({}_{2}\))\({}_{2}\)[Tb\({}_{2}\)(ptptc)\({}_{2}\)(DMF)(H\({}_{2}\)O)]-DMF\(\cdot\)6H\({}_{2}\)O, guests and hydrogen atoms are omitted for clarity. Reprinted with permission of the Royal Society of Chemistry from [73]. Copyright 2018, permission conveyed through Copyright Clearance Center, Inc.