Electronic properties and stereochemistry of the bis(diethylenetriamine)-copper(II) cation. Part 1. A fluxional elongated CuN6 chromophore

Abstract

The X-ray crystal structures of [Cu(dien)₂]Cl₂·H₂O, [Cu(dien)₂]Cl[ClO₄], [Zn(dien)₂]Cl[ClO₄], and 38% copper-doped [Zn(dien)₂]Cl[ClO₄], have been determined by photographic data for the first three complexes and diffractometer data for the doped system. All four complexes crystallise in the monoclinic space group P2₁/c with Z= 4; the structures were solved by heavy-atom techniques and successive Fourier syntheses. The two copper(II) complexes involve elongated rhombic-octahedral [Cu(dien)₂]²⁺ cations with the elongation along the N(1)–Cu–N(3) bond direction with a small but significant difference in the observed tetragonalities (0.853 and 0.835 respectively). The stereochemistry of the zinc(II) complex involves a compressed rhombic-octahedral ZnN₆ chromophore with the compression along the N(2)–Zn–N(5) bond direction. The structure of the 38% copper-doped [Zn(dien)₂]Cl[ClO₄] was analysed as an average CuN₆/ZnN₆ chromophore and an attempt was made to solve this structure as disordered CuN₆ and ZnN₆ chromophores. The axes of the CuN₆ chromophore in [Cu(dien)₂]Cl₂·H₂O are aligned parallel, while those of [Cu(dien)₂]Cl[ClO₄] are misaligned. The polycrystalline e.s.r. spectra of a series of copper-doped [Zn(dien)₂]XY complexes are reported at both room and liquid-nitrogen temperature; all the spectra are consistent with an elongated rhombic-octahedral CuN₆ environment and the g_∥ and A_∥ factors show marked temperature dependence, with ΔA_∥ varying from 8.9 to 36.0%. The temperature variation of the e.s.r. spectra of the copper-doped [Zn(dien)₂]XY systems have been confirmed by single-crystal rotation e.s.r. data, consistent with the monoclinic space groups involved, and the directions of the g and A factors are shown to be temperature invariant. A correlation is established betwen the ΔA_∥ values in the doped systems and the observed tetragonalities of the pure copper(II) complexes. The electronic reflectance spectra of the dilute and concentrated systems are shown to be independent of copper concentration and the polarised single-crystal electronic spectra of the doped system are assigned in a manner comparable to that of the pure copper(II) complex. The temperature-variable data are interpreted in terms of a fluxional model for the copper-doped [Zn(dien)₂]XY systems and the data extrapolated to the concentrated copper(II) complex.