The dinuclear alkyne copper(I)-halide complexes [CuX(tmtch)](2) [tmtch = 3,3,6,6-tetramethyl-l-thiacyclohept-4-yne; X = Cl (2a), X = Br (2b), X = I (2c)] react with the N containing Lewis bases ammonia, aniline, pyridine, and diethylamine to form the mononuclear compounds [CuX(N-base)(tmtch)] (5a: X = Cl, base = ammonia; 5b: X = Cl, base = aniline; 5c: X = Cl, base = pyridine; 5d: X = Cl, base = diethylamine; 5e: X = Br, base = diethylamine; 5f: X = I, base = diethylamine). X-ray diffraction studies on all compounds (except 5b) reveal trigonal-planar coordinated mononuclear Cu(I) complexes with the C drop C triple bond (123.7 pm) in the coordination plane. A strong Cu(I) alkyne interaction with two slightly different Cu-C bond lengths is found: a shorter distance (194.0 pm) to the carbon atom in trans position to the N base and a longer one (195.7 pm) to the carbon atom in trans position to the halide ligand.