EPR and X-ray structural study of some tetrahalocuprates CuX 42- (X  Cl, Br) of protonated ammines with thermochromic properties

Abstract

The EPR spectra of the tetrachlorocuprates(II) of a group of protonated ammines (n-propyl, isopropyl, n-butyl, isobutyl, octyl, lauryl-ammine, pyridine and piperidine) have been studied and the crystal structures of bis(isopropylammonium)tetrabromocuprate(II) ( 1) and of bis(piperidinium)tetrachlorocuprate(II) ( 2) have been studied by X-ray diffraction in single crystals. Compound 1 is monoclinic, space group P2 1/ n, with unit cell parameters of 10.8137(3), 14.6227(5), 14.2048(5) Å, 106.918(2)°, D x 1.816 g cm -3 and one independent formula unit. The final Rfactor, for the 3455 observed reflections recorded with Cu Kα radiation, was 0.052. Compound 2 is also monoclinic space group P2 1/ c, unit cell parameters of 8.2221(2), 16.9179(7), 12.1725(3) Å, 100.542(2)°, D x 1.507 g cm -3 and one independent formula unit. Final R factor is 0.055 for the 2506 observed reflections, recorded with Cu Kα radiation. In both cases the anions, [CuBr 4] 2- and [CuCl 4] 2-, have a squashed tetrahedron structure with a range of distances Cu-Br of 2.372(1)- 22.405(1) Å and Cu-Cl of 2.226(1)–2.261(I) Å, and angles, at the Cu atom, of two types, [96.74(5)103.40(5)°] and [130.62(5)–136.50(5)°] these for both compounds. In each case the anions are involved in a network of hydrogen interactions that have as donor atoms the charged tetrahedral nitrogens of the organic cations.