Isothiocyanato and azido coordination induced structural diversity in zinc(ii) complexes with Schiff base containing tetrahydrofuran group: synthesis, characterization, crystal structure and fluorescence study

Abstract

Isothiocyanato and azido coordination induced structural diversity in zinc(II) complexes with Schiff base containing tetrahydrofuran group: synthesis, characterization, crystal structure and fluorescence study † Haridas Mandal, Sukanta Chakrabartty and Debashis Ray * Three new structurally diverse zinc(II) complexes of formula [H 3 O][ZnL 2 ]ClO 4 (1), [Zn 2 (m-L) 2 (NCS) 2 ] (2) and [Zn 3 (m-L) 2 (m-N 3 ) 4 ] n (3) have been synthesized using the same furan-based tridentate ONO-donor Schiff base ligand HL (2-hydroxybenzyl-2-tetrahydrofurylmethyl)imine and characterized by X-ray structural analysis. Complex 1 is mononuclear, whereas 2 is a double phenoxido-bridged dinuclear compound. The novel polymeric compound 3 from azido coordination driven aggregation possesses a very rare 1D structure in which the dinuclear ligand-bound Zn 2 L 2 fragments are bridged by four ligand-free m 1,1 -azido bridging Zn(N 3 ) 4 2À units resulting in a zigzag arrangement of repeating triangular Zn 3 motifs with structural similarity to the P1 nuclease. Solid state mixing and grinding processes were applied for the ligand exchange reaction and core conversion. In mechanochemical solvent free synthetic routes 1 reacts with isothiocyanato and azido ions to provide 2 and 3 in pure form. The ligand HL serves as sensitive fluorescent probe for Zn 2+ , and complex 1 for SCN À and N 3 À ions in MeOH medium. Coordination induced fluorescence enhancement due to intraligand p / p* transition in the presence of Zn 2+ of HL and quenching of emission intensities of 1 with SCN À and N 3 À anions are accounted for by the formation of hitherto unknown complexes [Zn(L)(X)] (where X ¼ ClO 4 À , SCN À and N 3 À ). HL shows chelation-enhanced fluorescence response from strong metal ion coordination and binding of isothiocyanato and azido anions with an appreciable lifetime of the fluorophore signals. Excitation at 380 nm of MeOH solutions of all three complexes in air exhibit excited state life-time spanning from 2.5-4.8 ns.

The Role of Zinc(II) Ion in Fluorescence Tuning of Tridentate Pincers: A Review

“…Tridentate furan-containing half-salen-type ligands were published by Debashis Ray and coworkers in 2014 [22] (Figure 8). Participation of the furan oxygen group in coordination is scarcely reported.…”

“…Finally, the aggregate nature of materials consisting of fluorophores frozen into polymeric chains or networks give rise to noticeable changes in the energetic levels of the ligands. The assembly of emissive pincers by zinc coordination produces the most varied polymeric structures: coordination polymers (CPs) obtained by zinc bridges [22][23][24][25], metallated polymers obtained by coordination with pre-formed chains [26,27], and polymeric networks obtained by interlacing of flexible zinc-crossed fluorophores [28][29][30]. Owing to both the restrictions imposed to fluorophore and the efficient electron hopping in the tight structure, relevant emission tuning with respect to the free ligands and to mononuclear structures is envisaged.…”

(E)-N-(Pyridine-2-ylmethylene)arylamine as an Assembling Ligand for Zn(II)/Cd(II) Complexes: Aryl Substitution and Anion Effects on the Dimensionality and Luminescence Properties of the Supramolecular Metal–Organic Frameworks

“…The most obvious observation is that the lifetime of Cd2 (τ = 8.17 μs) is 1.92-fold compared to the corresponding ligand L 2 (τ = 4.25 μs) in acetonitrile solution. This is attributed to the more stable structure and interaction upon coordination . Meanwhile, the luminescence lifetimes of the ligand and corresponding complexes in the solid state (τ = 5.50–7.71 μs for L 1 – L 5 ; τ = 7.08–9.92 μs for Zn­(II)/Cd­(II) complexes) are longer than those in acetonitrile solution (τ = 4.25–5.58 μs for L 1 – L 5 ; τ = 5.94–8.17 μs for Zn­(II)/Cd­(II) complexes), which might be explained by the fact that there is a less polar nature in the solid-state environment …”

“…This is attributed to the more stable structure and interaction upon coordination. 63 Meanwhile, the luminescence lifetimes of the ligand and corresponding complexes in the solid state (τ = 5. L 1 −L 5 ; τ = 5.94−8.17 μs for Zn(II)/Cd(II) complexes), which might be explained by the fact that there is a less polar nature in the solid-state environment.…”

Study of the ZnIIComplexes of 1,1′‐Binaphthyl‐Based Schiff Bases: Fluorescent Detection of Thiocyanate

“…SCN – . It is proposed that upon coordination of SCN – to 3 , the dimeric [2+3] structure should remain intact and two SCN – might displace two hydroxyl groups off two of the zinc centers to form complex 4 …”