Structural Diversity in Luminescent MOFs Containing a Bent Electron‐rich Dicarboxylate Linker and a Flexible Capping Ligand: Selective Detection of 4‐Nitroaniline in Water

Abstract

Ac ombination of ab ent bis(naphthalene) and hydroxy-basedd icarboxylate linker and af lexible bis(tridentate)polypyridyl ligand has been employed to self-assemble with two different d 10 metal centers, Zn II and Cd II ,t of orm structurally diversifiedl uminescent metal-organic frameworks, [Zn 2 (tpbn)(mbhna) 2 (H 2 O) 2 ]·4 H 2 O·1.5DMF (1)a nd {[Cd 2 (tpbn)(mbhna) 2 ]·2DMF} n (2), respectively (where, tpbn = N,N',N'',N'''-tetrakis(pyridine-2-ylmethyl)butane-1,4-diamine and H 2 mbhna = 4,4'-methylene-bis[3-hydroxy-2-naphthalene carboxylic acid]). Both 1 and 2 are characterizeda nd analyzed by various analytical techniques includings ingle-crys-tal X-ray diffractometry.T heire xcellent emissive nature is studied in different solvents andf urtheru tilized to selectively detect aromatica mines,p articularly 4-nitroaniline in water with detection limits at sub-ppm level. The difference in sensing activity of 1 and 2 toward 4-NA is corroborated well with their structures. The mechanism of action has been established through Stern-Volmer plot, spectral overlap, timeresolved lifetime studies and HOMO-LUMO energy calculations. In addition, 1 and 2 are found to be recyclable and display good stability after sensing experiments.[a] Dr.Figure 4. Effect of solvents on the emissionspectra of 1 (a) and 2 (b).

Luminescent, Helical and Highly Stable Zn(II) and Cd(II) Coordination Polymers: Structural Diversity and Selective Sensing of 4‐Nitroaniline in Water

“…These are close to other reported Zn(II) based compounds with mbhna as the linker. [29,[38][39][40][41][42] In this case, the linker adopts a trans conformation which is also observed in the other reported architectures based on mbhna. [40] The dihedral angle between two naphthyl moieties in mbhna is found to be 79.87°(Figure S6).…”

“…The CdÀ O distances range from 2.207(4) to 2.555(7) Å, which are close to other reported Cd(II) based compounds with mbhna. [29,[41][42][43] Similar to 1, here also the linker adopts trans conformation with a dihedral angle of 83.79°b etween the naphthyl moieties of mbhna (Figure S6). Unlike 1, the bpma ligand binds to the Cd center in a meridional fashion (values of N alkyl À ZnÀ N py and N py À ZnÀ N py angles are 72.2°and 71.0°, and 143.04°, respectively).…”

“…Notably, these values are comparable to those of reported frameworks. [23][24][25][26][27][29][30][31][32]45] Also, the detection limits of 4-NA are calculated and found to be 7.15 ppm, 1.33 ppm, 1.94 ppm and 4.5 ppm in 1-4, respectively (Figures S46-S49). These values are found to be better (or comparable to) than other reported MOFs (Table S5), specifically, {[Zn 4 (μ 3 -OH) 2 (L)(H 2 O) 2 ] • 2DMF} n (where L = [1,1'; 4',1'']terphenyl-3,5,2',5',3'',5''-hexacarboxylic acid) (4 ppm), [23] and {[Zn 2 (oba) 2 (4-bpdb)] • 2DMF} n (where H 2 oba = 4,4'-oxybisbenzoic acid and 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) (6.9 ppm), [25] {[Cd(5-asba)(bimb)]} n (where, H 2 5-asba = 2-amino-5-sulfobenzoic acid and bimb = 1,4-bis(1H-imidazol-1yl)butane) (0.52 ppm), [31] and [Cd(H 2 BDDA)] n (where, H 4 BDDA = 4,4-([2,2'-bipyridine]-6,6'-diylbis(oxy) diphthalicacid) (0.68 ppm).…”

“…On the basis of no spectral overlap, it can be stated that the quenching of 1-4 has less contribution due to the energy transfer process. [46] In our previous work [29] with the mbhna linker, it has been shown that the LUMO of 4-NA is lower in energy compared to that of mbhna, facilitating an electron transfer process. On the other hand, the polar hydroxyl moieties on the linker provide H-bonding interactions with the NH 2 group of 4-NA and thus the quenching of emission intensity can be correlated to it as well.…”

“…[20] Considering the good electron acceptor properties of various analytes including 4-NA and 2,6-DCNA, target LCPs and LMOFs with electron rich π-conjugated systems have recently been reported. [21][22][23][24][25][26][27][28][29][30][31][32] However, examples of LCPs and MOFs for sensing of 4-NA and 2,6-DCNA in water are rare in the literature, as most of the sensing have been performed in organic solvents. It should be noted that LCPs and LMOFs should exhibit high stability in water for their application in such environmental concerns.…”