Template Synthesis, Spectral, Thermal and Glucose Sensing of Pr³⁺ Complexes of Metformin Schiff-Bases

Schiff-bases of metformin with each of salicylaldehyde (HL¹); 2,3-dihydroxybenzaldehyde (H₂L²); 2,4-dihydroxybenzaldehyde (H₂L³); 2,5-dihydroxybenzaldehyde (H₂L⁴); 3,4-dihydroxybenzaldehyde (H₂L⁵) and 2-hydroxynaphthaldehyde (HL⁶) and their complexes with Pr(III) were synthesized by template reaction. The complexes were characterized through elemental analysis, conductivity and magnetic moment measurements, IR, UV-Vis., fluorescence, GC-MS and XRD spectroscopy. The complexes exhibit a series of characteristic emission bands for Pr³⁺ ion in the 481-472 and 590-580 nm range with a 318-332 nm excitation source. The complexes have eight coordinated structure with the formulae [PrL^1-4,6(NO₃)₂(H₂O)₃].nH₂O where n = 1, 1½, 3, 4, 4 and [PrL⁵(NO₃)(H₂O)₅].2H₂O. The suggested stereochemistry was confirmed using TGA, DTG and DTA analysis and a mechanism for thermal decomposition was proposed. Coates-Redfern equation was used to calculate kinetic and thermodynamic parameters of the main decomposition step. The utility of the complexes towards the detection of glucose at physiologically relevant pH in phosphate buffer using UV-Vis and fluorescence spectroscopy as well as viscosity measurements are tried where the association constants were calculated. Graphical Abstract ᅟ.