Static–dynamic distortions of the tris(1,2-diaminoethane)copper(II) cation [Cu(en)3]2+. Crystal structures of the salts [Cu(en)3][SO4] at 120 K and of [Cu(en)3]Cl2·0.75 en at 298 K

Abstract

The structure of [Cu(en)₃]Cl₂·0.75 en at room temperature and of [Cu(en)₃][SO₄] at ca. 120 K have been determined by X-ray analysis using diffractometric data. The crystals of [Cu(en)₃]Cl₂·0.75 en are monoclinic, space group C2/c, with a= 33.774(6), b= 8.756(2), c= 23.972(5)Å, β= 99.96(4)°, and Z= 16. The structure has been refined to a conventional R factor of 0.062 over 1 465 independent reflections. It consists of [Cu(en)₃]²⁺ cations, Cl^– anions, and interposing 1,2-diaminoethane (en) molecules. The cell contains two independent [Cu(en)₃]²⁺ cations, one of which shows disorder in the co-ordination polyhedron due to two different positions of the nitrogen atoms. All of these polyhedra can be described as tetragonally elongated octahedra. The crystals of [Cu(en)₃][SO₄] are triclinic, space group P, with a= 8.814(3), b= 8.896(3), c= 9.588(3), α= 90.34(4), β= 89.37(4), γ= 119.80(4)°, and Z= 2. The structure has been refined to an R factor of 0.063 over 1 044 independent reflections. It consists of [Cu(en)₃]²⁺ cations and of [SO₄]^2– anions, the cations being compressed octahedra. The nitrogen atoms of the three en molecules, however, have surprisingly high temperature factors in comparison with those found for the room-temperature structure. Single-crystal e.s.r. spectra have shown one and three signals for the chloride and sulphate respectively. In the former compound spin exchange over the whole crystal accounts for the observed g values and for the shape of the signals, whereas for the latter a three-domain structure is proposed. The possibility that in each domain elongated chromophores are coupled in an antiferrodistortive manner is discussed.