Spectroscopy, molecular structure, and electropolymerization of Ni() and Cu() complexes containing a thiophene-appending fluorinated Schiff base ligand

In this contribution, we describe the preparation, characterization, and electrochemical behavior of a series of four new mononuclear M( ii ) complexes featuring a symmetric substituted N 2 O 2 -tetradentate Schiff base ligand, bearing either trifluoromethyl and p -bromophenyl (M = Ni, 3 ; Cu, 4 ) or trifluoromethyl and the π-extended p -(2-thienyl)phenylene (M = Ni, 5 ; Cu, 6 ) substituents. Complexes 3 and 4 were readily synthesized by reacting the diprotic fluorinated Schiff base proligand 2 with the appropriate hydrated metal(II) acetates, whereas 5 and 6 were obtained upon Stille cross-coupling reaction of 3 and 4 with 2-(tributylstannyl)-thiophene, respectively. Compounds 3-6 were isolated as neutral, air, and thermally stable-coloured solids, with yields ranging from 60 to 80%. The four complexes, the diimine precursor 1 and its trifluoroacetylated derivative 2 , were identified using analytical (EA, ESI-MS), spectroscopic (IR, 1 H, 13 C, and 19 F NMR), and X-ray crystallographic methods. X-ray crystal structure determination of complexes 3-5 revealed that both four-coordinate Ni( ii ) and Cu( ii ) metal ions adopt a square planar geometry. The magnetic properties of powdered samples of the Cu( ii ) derivatives 4 and 6 have been investigated (2-300 K) and found consistent in both cases with a single isolated copper( ii ) ion ( s = 1/2). DFT calculations were used to examine the optimal geometries of complexes 5 and 6 , allowing for a consistent perspective of their structure and characteristics. The primary aspects of the UV-vis spectra were interpreted using TD-DFT computations. Finally, electrochemical data indicate that complexes 5 and 6 polymerize at high anodic potentials in acetonitrile (greater than 2.0 V vs. Ag/AgCl). Cyclic voltammetry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM-EDS) analyses were used to characterize the obtained films poly- 5 and poly- 6 . Electropolymerization of the title compounds yields golden-colored deposits, with the Cu( ii ) monomer enabling the formation of thicker coatings with increased conductivity in both CV and chronoamperometry voltammetric profiles.