Ligand backbone influenced luminescent properties of mononuclear Zn(II)-N3Py2 compounds: Synthesis, structures and nitroaromatics detection

Abstract

Mononuclear Zn(II) compounds, [Zn(L sup(1))](ClO sub(4))sub(2) (1) and [Zn(L sup(2))](ClO sub(4))sub(2) (2), embedded with ligands, L sup(1)=N sup(1)-(pyridin-2-ylmethyl)-N sup(2)-(2-((pyridin-2-ylmethyl)amino)ethyl)ethane-1,2-diamine and L sup(2)=N sup(1)-(pyridin-2-ylmethyl)-N sup(3)-(3-((pyridin-2-ylmethyl)amino)propyl)propane-1,3-diamine are synthesized. Compound 1 is revisited, and structure-function relation is compared with new compound 2. Single crystal X-ray analysis revealed that compound 1 crystallizes in the tetragonal non-centrosymmetric P4 sub(1) space group while 2 crystallizes in a centrosymmetric monoclinic space group P2 sub(1)/c. The asymmetric unit consists of a crystallographically independent [Zn(L sup(1))] sup(2+)cation in 1 while [Zn(L sup(2))] sup(2+)cation in 2 and two unique perchlorate anions in both. IR spectra of 1 and 2 confirmed the vibrations due to organic ligands and tetrahedral perchlorates. PXRD confirmed the phase purity of powdered samples compared with theoretical PXRD patterns obtained from single-crystal X-ray diffraction data. NMR and ESI-MS data suggested the phase purity and stability of compounds 1 and 2 in solution. Photoluminescence properties of compounds 1 and 2 have been investigated, considering their application in sensing explosive nitroaromatic compounds. Our results suggest that compound 1 is very selective in the chemical sensing of trinitrophenol (TNP) and dinitrophenol (DNP) in an aqueous medium compared to the reactivity of compound 2. The existence of spectral overlap in the absorption spectra of 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP) with the emission spectrum of 1 or 2 indicates the operation of the resonance electron transfer (RET) mechanism.