Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N‐Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X‐ray Spectroscopic and Crystallographic Investigation

Abstract

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole-and pyridine-based ligands were examined by 1 H, 13 C and 15 N NMR spectroscopy. The magnitude of the 15 N imine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained CuÀ N imine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperaturedependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.

Conformationally dynamic copper coordination complexes

“…The Cu–N pyridine bond distances experience a slight contraction upon metal oxidation, consistent with chelating pyridine arms bound to Cu. 10,23,28,29 The Cu I –N aniline bond distance of >2.4 Å is well above the sum of the covalent radii. Therefore, in the solid-state, there appears to be no bond between the Cu I ion and aniline (dashed bond in Fig.…”

Self-assembly induced tunable multiple fluorescence output from a white light-emitting functionalized single π-conjugated molecule and implication in VOC sensing applications

“…These results undoubtedly proved the involvement of the imine (CQN) nitrogen and imidazole proton in inter/intramolecular H-bonding, which was interrupted by the increase in the temperature. 60,61 We also recorded the concentrationdependent FT-IR spectrum of L1 and L2 in solution (ranging from 0.5-2.5 mg mL À1 ) (Fig. S17 and S18, ESI †).…”

Quantification of Linker Defects in UiO-Type Metal–Organic Frameworks

“…The first MOF was commercially purchased by PROFMOF A/S and was synthesized using 10% 2,2′-bipyridine-5,5′-dicarboxylic acid, denoted UiO-67-BIPY-BA. The second multivariate UiO-67 sample was synthesized using an already published procedure 33 and contains 20% 2,2′-diamino-[1,1′-biphenyl]-4,4′-dicarboxylic acid and is denoted UiO-67-NH 2 −BA.…”