Crystallization of copper(i) iodide from triethylamine-acetone yields a white crystalline solid of novel stoicheiometry [Cu,l,( NEt,),] ; its structure determination by single-crystal X-ray diffraction shows trigonal symmetry [space group P3, a = 19.46(2), c = 7.1 19(7) A, and Z = 31 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 A (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 14cm, with a = 20.10(2) and c = 15.94(1) A; R = 0.055 for 782 independent observed reflections. The structure is a ' cubane '-type tetramer, [Cu414(2Me-py),], 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) A; R = 0.071 for 278 independent observed reflections. The structure is a di-p-iodo-bridged dimer [ C ~ ~ I ~ ( t m p i p ) ~ ] , with four molecules in the unit cell. Crystals of (4) are triclinic, space group P7, with a = 14.381 (4), b = 9.888(3), c = 4.117(1) A, a = 83.96(2), /3 = 81.57(2), and y = 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 [Cu,14(2Me-py) group PT, with a = 12.856(8), b = 9.736(7), c = 9.472(7), A, x = 105.38(5), p = 98.68(5), y = 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.