Crystal engineering of Pb(II)-salen coordination polymer enforced for the selective fluorescence NACs sensing activity in a dispersed aqueous medium: A combined experimental and theoretical DFT monologue

Abstract

A new 1D coordination polymer (CP), [(SCN)Cd(L1)Pb(NCS)]n (1) was synthesized using N2O4-based Scaffold (H2L1 = N, N’-bis(3-methoxysalicylidenimino)-1,3-diaminopropane) and structurally characterized using various analytical instruments. X-ray structure disclosed complex (1) crystallize in the Orthorhombic space group P212121 with Z=4. The crystal structure contains heteronuclear units of [(SCN)Cd(L1)Pb(NCS)]n, linked by a μ1,1,3 thiocyanate (SCN−) bridging. Here weak S···S chalcogen, Pb···S tetrel bonding with two C-H···π(SCN) and one C-H···π(arene) like interactions are vividly observed. The QTAIM/NCI diagram successfully explains the nature of these contacts. Hirshfeld surface (HS) and 2D fingerprint plots analysis has described the non-covalent supramolecular features. The H…H interactions dominate the solid-state crystal structure. The complex fluorescence behaviour is eventually quenched in the presence of explosive nitroaromatic compounds. Complex (1) retained high fluorescence sensitivity and selectivity only for organo-toxin trinitrophenol (TNP). The Stern-Volmer equation evaluated the enhancement of the fluorescence mechanism, the limit of detection (LOD), and the quenching constant (KSV), which for TNP is 6.92 × 104 M−1. The turn-off fluorescence sensing mechanism is explained by (a) AIM/RDG surface interactions energy, (b) Charge-transfer complex, (b) Photo-induced electron transfer (PET) through the HOMO-LUMO approach, (c) Fluorescence resonance energy transfer (FRET), and (d) 1H NMR titration. Notably, the active dynamic sensing is due to a decrease in fluorescence lifetime after the successive addition of TNP with the polymer. Finally, the title complex (1) is employed as a quenched fluorescence response sensor for detecting TNP in a dispersed aqueous medium.