Lewis-base adducts of Group 1B metal(I) compounds. Part 2. Synthesis and structure of CuIL2 complexes (L = nitrogen base)

Abstract

The crystal structures of five complexes CuIL₂, L = 2-methylpyridine (1), 2-ethylpyridine (2), quinoline (as its solvate)(3), 3,5-dimethylpyridine (4), and 2,6-dimethylpyridine (5), have been determined by single-crystal X-ray diffraction methods at 295 K. Crystals of (1) are triclinic, space group P, with a= 10.662(5), b= 9.552(6), c= 7.936(6)Å, α= 112.35(4), β= 96.20(4), γ= 104.66(4)°, and Z= 2; R= 0.037 for 1 060 ‘observed’ reflections. Crystals of (2) are tetragonal, space group I4₁/acd, with a= 14.826(5), c= 27.980(8)Å, and Z= 16; R= 0.035 for 1 000 ‘observed’ reflections. Crystals of (3) are triclinic, space group P, with a= 15.85(1), b= 10.24(1), c= 7.696(7)Å, α= 105.72(7), β= 92.64(7), γ= 99.51(7)°, and Z= 2; R= 0.033 for 2 694 ‘observed’ reflections. Crystals of (4) are monoclinic, space group C2/m, with a= 13.435(5), b= 16.127(5), c= 9.313(4)Å, β= 127.69(3)°, and Z= 2; R= 0.036 for 1 330 ‘observed’ reflections. In each case, the complex is dimeric and of the form L₂Cul₂CuL₂; the asymmetric unit is the monomer in (1) and (3) and the half monomer in (2) and (4). The dimer in (1) and (3) includes a crystallographic inversion centre, while compounds (2) and (4) have 222 and 2/m symmetry respectively. In all four complexes, each copper atom is pseudo-tetrahedrally co-ordinated by two nitrogen atoms, one from each base, and two bridging iodine atoms. Complex (5) crystallizes in two distinct monoclinic phases, both with space group C2/c and Z= 4. For the α phase, a= 8.431(4), b= 14.018(8), c= 13.019(7)Å, and β= 96.19(5)°; R= 0.036 for 1 127 ‘observed’ reflections. For the β phase, a= 16.060(22), b= 7.394(4), c= 14.715(10)Å, and β= 119.70(4)°; R= 0.026 for 1 679 reflections. The two phases differ in their mode of packing of discrete monomeric [Cul(2,6Me₂-py)₂] molecules; the copper atom is three-co-ordinate in each case with a planar environment. In the α phase, Cu–N,I are 1.984(5) and 2.682(2)Å respectively with N–Cu–I,N 105.2(1) and 149.6(2)°; in the β phase Cu–N,I are 1.984(4) and 2.642(2)Å and N–Cu–I,N 108.26(8) and 143.5(1)°. The adoption of the unusual three-cordination about the copper is ascribed to the steric crowding caused by the substituents in both the 2 positions of the base.