Selective recognition of Fe3+ and CrO42− ions using a Zn(ii) metallacycle and a Cd(ii) coordination polymer and their heterogeneous catalytic application

Abstract

We report the syntheses and structural characterization of a Zn(II) metallacycle [Zn₂{(L)₂(DMF)₂(NO₃)₂}]·(NO₃)₂ (1) along with a Cd(II) coordination polymer [{Cd₁(L)₂(DMF)₂}·(NO₃)₂]_n (2) (where L = N,N′-bis-(3-pyridyl)terephthalamide; DMF = dimethylformamide) and their utilization as fluorescent probes for highly selective recognition (turn-off) of Fe³⁺ and CrO₄²⁻ ions. Compounds 1 and 2 were prepared by utilizing ligand L and the nitrate salt of zinc and cadmium, respectively. Single crystal X-ray analysis reveals that 1 adopts an overall Zn(II) metallacycle architecture, whereas 2 displays a one-dimensional (1D) polymeric structure. Both 1 and 2 showed high fluorescence stability in aqueous solution and selectively detected Fe³⁺ and CrO₄²⁻ ions with high quenching constants and low detection limits of 2.34 × 10⁶ M⁻¹ and 0.153 μM for Fe³⁺, 6.72 × 10⁵ and 0.205 μM for CrO₄²⁻ (for 1); 3.25 × 10⁶ and 0.193 μM for Fe³⁺, 6.94 × 10⁵ and 0.155 μM for CrO₄²⁻ (for 2). Notably, ligand L itself did not display any type of recognition for any ions in DMF as well as in aqueous media. Moreover, 1 and 2 were also employed as heterogeneous catalysts for the ring-opening reaction (ROR) of epoxides with various assorted amines and up to 95% yield (TON, 47.5 and TOF, 11.9 h⁻¹) was observed with perfect regioselectivity in the case of styrene oxide.