Development of a novel Cd(ii) metal complex for solvent-sensitive detection of Zn(ii) and Mg(ii) with the formation of Cd(ii)–Zn(ii)/Cd(ii)–Mg(ii) complexes and their application in effective Schottky devices

The novel mononuclear Cd(II) metalloreceptor Cd[LH2I2] (complex 1), derived by the reaction of the Schiff base ligand 6,6′-(1E,1′E)(ethane-1,2 diylbis(azaneylidene))bis(methaneylylidene)bis(2-ethoxyphenol) (H2L) and CdI2, was successfully used to detect Zn(II) and Mg(II) in semi-aqueous and aqueous media, respectively, among several competitive cations. The single crystal data analysis revealed that the asymmetric unit of complex 1 consists of one ligand, H2L, and two I-ions, compensating the +2 oxidation state of Cd. The optically monitored sensing of Zn(II) and Mg(II) by complex 1 was further assessed by utilizing UV and fluorescence spectroscopic techniques. The remarkable enhancement of the fluorescence intensity of complex 1-Zn(II) and complex 1-Mg(II) in the presence of CH3COO− and SO4= indicated that a heteronuclear bridging complex could be obtained if two separate reactions of complex 1 with (CH3COO)2Zn and MgSO4 could be carried out. Interestingly, two different single crystals of Cd–Zn (complex 2) and Cd–Mg (complex 3) were obtained after conducting two separate reactions of complex 1 with Zn(II) and Mg(II). Single crystal data analysis showed that complex 2 is an octanuclear Zn(II)/Cd(II) complex with the presence of acetate and an hydroxy group, and both metal centers are in the +2 oxidation state. The IR and NMR spectra results confirmed the formation of complexes 2 and 3. The SPX and EDX studies confirmed the presence of Zn(II) and Mg(II) in complex 2 and complex 3, respectively. The limit of detection for sensing of both was measured in the nanomolar range. Although it is well-known that mononuclear Cd complexes are effective Schottky devices, there have been few reports of investigation of heteronuclear Cd(II) complexes as candidates for effective Schottky devices, or determination of the values of device performance, conductivity, and device parameters with heteronuclear Cd complexes 2 and 3. Surprisingly, all the results indicated that a potential Schottky device could be produced due to the efficacy of complex 2 with respect to complex 3. The effectiveness of the device would be satisfactory because of the lower band gap value and the presence of weak intramolecular π–π stacking interactions in complex 2.