Syntheses and crystal structures of copper(II) and copper(I) dpp complexes, [Cu(dpp)Br₂] and [Cu(dpp)₂][CuBr₂] (dpp = 2,9-diphenyl-1,10-phenanthroline)

The complexes [Cu(dpp)Br₂] (1) and [Cu(dpp)₂] [CuBr₂] (2) (dpp = 2,9-diphenyl-1,10-phenanthroline) were synthesized and characterized by single-crystal X-ray diffraction methods. Reaction of copper(II) bromide with the dpp ligand in dichloromethane at room temperature afforded 1, which is a rare example of non-square planar four-coordinate copper(II) complexes. Complex 1 crystallizes in the monoclinic space group C2/c with a = 15.352(3), b = 13.192(3), c = 11.358(2) Å, β= 120.61(3)°, V= 1979.6(7) ų, Z = 4, D_calc = 1.865 g cm^-3. The coordination geometry about the copper center is distorted about halfway between square planar and tetrahedral. The Cu-N distance is 2.032(2) Åand the Cu-Br distance 2.3521(5) Å. Heating a CH ₂Cl₂ or acetone solution of 1 resulted in complex 2, which consists of a slightly distorted tetrahedral [Cu(dpp)₂]⁺ cation and a linear two-coordinate [CuBr₂]^- anion. 2 crystallizes in the triclinic space group P1̄ with a = 10.445(2), b = 11.009(2), c = 18.458(4) Å, a = 104.72(3), β= 94.71(3), γ= 103.50(3)°, V = 1973.3(7) ų, Z = 2, D_calc = 1.602 g cm^-3. The four Cu(I)-N distances are between 2.042(3) and 2.067(3) Å, the distance of Cu(2)-Br(1) 2.2268(8) Å, and the disordered Cu(3)-Br(2) distances are 2.139(7) and 2.237(4) Å, respectively. Complex 2 could also be prepared by directly reacting CuBr with dpp in CH₂Cl₂.