Lewis-base adducts of Group 1B metal(I) compounds. Part 1. Synthesis and structure of CuIL_n complexes (L = nitrogen base, n ≤ 1.5)

Crystallization of copper(I) iodide from triethylamine-acetone yields a white crystalline solid of novel stoicheiometry [Cu₄I₄(NEt₃)₃]; its structure determination by single-crystal X-ray diffraction shows trigonal symmetry [space group P3, a = 19.46(2), c = 7.119(7) Å, and Z = 3] and polymeric strings of Cu₄I₄ 'cubane' units, oriented with one body diagonal of each unit along c and linked to the next unit generated by the unit c translation by a copper-iodine interunit bond [2.93₀ Å (mean)]. There are three independent such polymeric strings in the unit cell. R was 0.074 for 2 942 'observed' reflections. The structures of the 1: 1 complexes of copper(I) iodide with 2-methylpyridine, (2Me-py) (2), 2,2,6,6-tetramethylpiperidine, (tmpip) (3), and acridine, (4), have also been determined. Each crystallizes in a structural form determined by the steric properties of the ligand. Crystals of (2) are tetragonal, space group I4cm, with a = 20.10(2) and c = 15.94(1) Å; R = 0.055 for 782 independent observed reflections. The structure is a 'cubane'-type tetramer, [Cu₄I₄(2Me-py)₄], with Z = 8. Crystals of (3) are orthorhombic, space group Cmca, with a = 12.43(2), b = 9.964(7), and c = 19.30(3) Å; R = 0.071 for 278 independent observed reflections. The structure is a di-μ-iodo-bridged dimer [Cu₂I₂(tmpip)₂], with four molecules in the unit cell. Crystals of (4) are triclinic, space group P1̄, with a = 14.381(4), b = 9.888(3), c = 4.117(1) Å, α = 83.96(2), β = 81.57(2), and γ = 86.03(2)°; R = 0.078 for 2 649 observed reflections. The structure is a 'split stair' polymer, (-CuL-I-)_∞. The structures of (3) and (4) are unsymmetrical as a consequence of ligand steric effects. The synthesis and structure determination at 295 K of [Cu₄I₄(2Me-py)₆] are also reported. Crystals are triclinic, space group P1̄, with a = 12.856(8), b = 9.736(7), c = 9.472(7), Å, α = 105.38(5), β = 98.68(5), γ = 104.90(5)°, and Z = 1; 4 010 observed reflections were refined to a residual of 0.034. The molecule is centrosymmetric and based on the 'step' structure well known for Cu₄I₄L₄ species; however, the copper atoms at the periphery of the chair are co-ordinated by a pair of ligands, giving rise to the first known examples of 1: 1: 1.5 Cu: halide: base stoicheiometry observed in nitrogen-base systems, and the first example of this stoicheiometry based on the 'step' array.