Mechanism of Formation of Copper(II) Chloro Complexes Revealed by Transient Absorption Spectroscopy and DFT/TDDFT Calculations

Abstract

Copper(II) complexes are extremely labile with typical ligand exchange rate constants on the order of 10 6 −10 9 M −1 s −1 . As a result, it is often difficult to identify the actual formation mechanism of these complexes. In this work, using UV−vis transient absorption when probing in a broad time range (20 ps to 8 μs) in conjunction with DFT/TDDFT calculations, we studied the dynamics and underlying reaction mechanisms of the formation of extremely labile copper(II) CuCl 4 2− chloro complexes from copper(II) CuCl 3 − trichloro complexes and chloride ions. These two species, produced via photochemical dissociation of CuCl 4 2− upon 420 nm excitation into the ligand-to-metal-charge-transfer electronic state, are found to recombine into parent complexes with bimolecular rate constants of (9.0 ± 0.1) × 10 7 and (5.3 ± 0.4) × 10 8 M −1 s −1 in acetonitrile and dichloromethane, respectively. In dichloromethane, recombination occurs via a simple one-step addition. In acetonitrile, where [CuCl 3 ]− reacts with the solvent to form a [CuCl 3 CH 3 CN] − complex in less than 20 ps, recombination takes place via ligand exchange described by the associative interchange mechanism that involves a [CuCl 4 CH 3 CN] 2− intermediate. In both solvents, the recombination reaction is potential energy controlled.

Tuning Dynamic Mechanical Response in Metallopolymer Networks through Simultaneous Control of Structural and Temporal Properties of the Networks

“…Ligand substitution in transition metal complexes is influenced by their electronic configuration and coordination number of the metal centers. The ligand exchange in four-coordinate tetrahedral complexes, such as Zn­(Imz) 4 2+ and Cu­(Imz) 4 2+ , proceeds mainly through an associative mechanism for which the rate of exchange increases as the concentration of free ligand increases. ,− For both L-ICP–Cu and L-ICP–Zn, at high L/M ratio (i.e., low metal ion content) the cross-linked junctions can rapidly exchange due to the relatively high concentration of uncoordinated imidazole moieties on the polymer chains. Accordingly, an uncoordinated imidazole moiety is not merely a dangling chain with no contribution to the mechanical properties.…”

Solvent Effects on Nonradiative Relaxation Dynamics of Low-Energy Ligand-Field Excited States: A CuCl42– Complex

“…Furthermore, the lower-lying 2 B 1 and 2 E LF excited states can also be ruled out as the product states because the absorption from the 2 B 1 and 2 E states is different from the observed ΔA spectra. 18,26 We note that spectral narrowing, accompanied by a slight blue-shift of the ΔA bands, is noticeable at the delay times shorter than 0.8 ps. This spectral evolution is typical of vibrational relaxation of small polyatomic molecules 29 and can be attributed to vibrational relaxation of the CuCl 4 2− complex in the 2 A 1 excited state.…”

Ultrafast Excited-State Dynamics of CuBr3–Complex Studied with Sub-20 fs Resolution

“…The geometries of the copper­(II) complexes were optimized at the DFT level of theory using B3LYP, BP86, and PBE0 density functionals, − which were successfully applied in a previous study for the calculation of copper­(II) complexes. The 6-31G­(d) and aug-cc-pvdz basis sets were implemented for geometry optimization.…”