Two Highly Stable Proton Conductive Cobalt(II)–Organic Frameworks as Impedance Sensors for Formic Acid

Abstract

Metal-organic frameworks (MOFs) have been extensively exploreda sa dvanced chemical sensors in recent years. However,t here are few studies on MOFs as acidic gas sensors, especiallyp rotonc onductive MOFs.I nt his work, two new proton-conducting 3D MOFs,{ [Co 3 (p-CPhHIDC) 2 (4,4'-bipy)(H 2 O)]·2H 2 O} n (1)( p-CPhH 4 IDC = 2-(4-carboxylphenyl)-1 H-imidazole-4,5-dicarboxylic acid;4 ,4'-bipy = 4,4'-bipyridine) and {[Co 3 (p-CPhHIDC) 2 (bpe)(H 2 O)]·3H 2 O} n (2) (bpe = trans-1,2-bis(4-pyridyl)ethylene) have been solvothermally prepared and investigated their formic acid sensing properties. Both MOFs 1 and 2 show temperature-and humidity-dependent protonc onductive properties and exhibit optimizedp roton conductivities of 1.04 10 À3 and 7.02 10 À4 Scma t9 8% relative humidity (RH) and 100 8C, respectively.T he large number of uncoordinated carboxylic acid sites, free and coordination water molecules, andh ydrogen-bondingn etworks inside the frameworks are favorable to the proton transfer.B ym easuringt he impedance values after exposure to formic acid vapor at 98 %o r6 8% RH and 25 8C, both MOFs indicater eproducibly high sensitivity to the analyte. The detection limit of formic acid vapor is as low as 35 ppm for 1 and 70 ppm for 2.M eanwhile, both MOFs also show commendable selectivity towards formic acid among interfering solutions. The proton conducting and formic acid sensingm echanismsh ave been suggested according to the structural analysis, E a calculations, N 2 and water vapor absorptions, PXRD and SEM measurements. This work will open an ew avenue for proton-conductive MOFbased impedance sensors and promote the potentiala pplication of these MOFs fori ndirectly monitoring the concentrationsofformic acid vapors.[a] R.

Synthesis, Structures and Magnetic Properties of CuII and CoII Compounds Based on Asymmetric 5‐(1H‐Imidazole‐1‐yl)‐3‐pyridine Carboxylic Acid

“…The H ··· O distances (bond angles) are 2.77(19) Å (168°) for O1–H1B ··· O5 and 2.674(16) Å (163°) for O1–H1A ··· O4 which agrees well with those reported in the literatures (Table S2) . The adjacent linear chains are further outspread to form a 2D supramolecular structure (Figure b) through weak π ··· π interactions between the adjacent benzene rings (interplanar separation: 3.435 Å; centroid‐centroid separation: 3.695 Å) . Both these interactions stabilize the supramolecular structure and further result in a 3D supramolecular structure (Figure c).…”

“…The adjacent 2D layers are further extended to form a 3D supramolecular structure via some weak edge‐to‐face CH/π interactions: one is 3.105 Å (dihedral angle 101.49°, H/π‐plane separation: 3.11 Å) between two adjacent imidazole rings, the other is 3.114 Å (dihedral angle 105.5°, H/π‐plane separation: 3.13 Å) between two adjacent imidazole and pyridine rings, respectively, which are longer than the average distance (ca. 2.86 Å) of the sp 2 ‐CH ··· π . Both the above interactions extend the 2D layers into 3D supramolecular structure.…”

“…2.86 Å) of the sp 2 -CH•••π. [39][40][41][42][43][44][45] Both the above interactions extend the 2D layers into 3D supramolecular structure. For achieving further insight into the structure of 1, both Cu1 and Cu2 ions can be abstracted as a 5-connected node which links five impcligands.…”

“…[51][52][53][54] The adjacent linear chains are further outspread to form a 2D supramolecular structure ( Figure 4b) through weak π•••π interactions between the adjacent benzene rings (interplanar separation: 3.435 Å; centroid-centroid separation: 3.695 Å). [39][40][41][42][43][44][45] Both these interactions stabilize the supramolecular structure and further result in a 3D supramolecular structure (Figure 4c). The variable-temperature magnetic susceptibilities of 1 and 2 have been performed, and shown as M and M T vs. T plots ( M is the molar magnetic susceptibility per Cu 2 unit for 1 and 2) ( Figure 5), the magnetization (M vs. H) has been measured at 2 K. The bulk purity of 1 and 2 is confirmed by comparing its experimental powder X-ray diffraction (PXRD) pattern to that simulated based on the single crystal structure ( Figure S1).…”

Berlin Green Framework-Based Gas Sensor for Room-Temperature and High-Selectivity Detection of Ammonia

“…Additionally, a Janus nanostructure of Au@ ZnO@ ZIF-8 has been prepared and shows fast response to formaldehyde at room temperature [20]. Li et al have prepared various kinds of MOFs which show outstanding gas performance to formic acid as well as ammonia and ammines [23][24][25]. Specially, a 2D copper-organic framework and a 3D cadmium-organic framework both show perfect selectivity to ammonia [24,25], whereas the identification is based on impedance spectroscopy which is not suitable for device minimization.…”