Detailed spectrophotometric study of the copper(II) halides in anhydrous methanol

Abstract

A spectrophotometric study of the copper(I1) chlorides and the copper(I1) bromides in anhydrous methanol was carried out at 25 "C and at constant ionic strength (1 mo1.L-I). A matrix rank treatment of the experimental data followed by the testing of different theoretical models confirmed the presence of four mononuclear complexes for both systems, viz. C u X ' , CuX2, CuX3-, and CuXz-. Overall stability constants calculated for the chlorocuprates are PI = 2.8 X lo2, b2 = 1.6 X IO4, 8, = 2.3 X los, and P4 = 4.5 X lo5 and for the bromocuprates are PI = 5.2 X lo', P2 = 3.9 X IO5, P3 = 2.0 X lo6, and b4 = 2.1 X lo6. Individual electronic spectra of all species in methanol are reported for the first time. In this solvent the tetracoordinated chloro complex exhibits a calculated absorption maximum in the near-IR region consistent with a square-planar structure, in contrast to the structure in the solid state, while for the tetrabromocuprate the structure of a flattened tetrahedron is confirmed. IntroductionThe copper( 11) chlorides have been extensively studied in aqueous and nonaqueous solutions, as have the bromide complexes, although to a lesser extent. The results of studies carried out at constant ionic strength are definitely divergent, and few allusions have been made to the more highly substituted halide complexes.

Ultrafast Photochemistry of Copper(II) Monochlorocomplexes in Methanol and Acetonitrile by Broadband Deep-UV-to-Near-IR Femtosecond Transient Absorption Spectroscopy

“…These copper(II) chlorocomplexes have the characteristic electronic absorption spectra with the spectral shape depending on the number of the chloride ligands 57−59 and the nature of the solvent. For methanol and acetonitrile solutions, the absorption spectra of the individual complexes and their overall stability constants are known, 57,60 Under these conditions, using the known stability constants, we calculated with the help of "Medusa" software that more than 93% of copper(II) exist as a mixture of the pure solvatocomplexes and monochlorocomplexes, with a small contribution from the dichlorocomplexes (Figure 2) 4 Cl solution in acetonitrile can be fitted to a sum of the absorption spectra of the pure copper(II) solvatocomplexes, monochlorocomplexes, and dichlorocomplexes ( Figure 2). In these fits, the known molecular extinction coefficients were held constant and the concentrations of these complexes were varied.…”

Photochemistry of Monochloro Complexes of Copper(II) in Methanol Probed by Ultrafast Transient Absorption Spectroscopy

“…EXAFS studies showed that copper(I) cations in solution form tetrahedral [Cu I (solvent) 4 ] + complexes with solvents such as acetonitrile, dimethylsulfoxide, pyridine, and tetrahydrothiophene 18. Similarly, copper(I) solvated complexes are expected to adopt the tetrahedral [Cu I (MeOH) 4 ] + Steady-state absorption spectra of individual chloro complexes of copper(II) in methanol, [Cu II (MeOH) 6-n Cl n ] 2-n , where n = 0À4, taken from the literature 32.…”

“…The best-fit spectrum obtained using the known ε values of the individual copper(II) complexes as the parameters and their fractional concentrations as the variables is shown by a dashed line. The distribution of chloro complexes of copper(II) as function of concentration of chloride ions was also calculated by Medusa software (inset) using the following overall stability constants β 1 = 2.8 Â 10 2 , β 2 = 1.6 Â 10 4 , β 3 = 2.3 Â 10 5 , and β 4 = 4.5 Â 10 5 32.…”

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

“…Stern−Volmer analysis of the decay lifetimes in the CH 3 CN−H 2 O mixtures suggests dynamic quenching by water with a quenching rate constant of 1.06 × 10 11 M −1 s −1 , which is typical for diffusion-limited reactions. We conclude that the water molecule diffuses to the 2 To conclude, our measurements of the solvent medium effects on nonradiative relaxation dynamics of the 2 A 1 state of CuCl 4 2− reveal the unexpected physical quenching of this LFexcited state by water and fill an existing gap in studying solvent effects on nonradiative relaxation dynamics of low-lying metalcentered excited states.…”