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 [2.930Å(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 P, 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 P, 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.