Mixed base pyridine (py)/triphenylphosphine adducts of the copper(1) halides, CuX, have been synthesized for 1 : 1 : 1 stoichiometry for X = chloride and iodide; single-crystal X-ray structure determinations of these show them to be isomorphous and isostructural with that of the bromide recorded elsewhere, being 嬵'- dihalo-bridged dimers , [(PPh3)( py )CuX2Cu( py )(PPh3)], monoclinic, C2/c, a 蠲6.2, b 蠱4.3, c 蠱1 .2 Š, ߠ蠹5, Z = 4 dimers. The bromide has been isolated as a new monoclinic C 2/m polymorph, a 11 .279(8), b 14.268(6), c 13.858(4) Ŭ ߠ109.33(6)ꬠZ=4 dimers, and details of its structure are also recorded. The structures of their pyridine-4-carbonitrile (pycn) analogues have also been determined and found to be also binuclear, with no cyano-copper interactions; these also are an isomorphous, isostructural series, monoclinic P21/n, a 蠱5.4, b 蠸.1, c 蠱7.9 Š, ߠ蠱01 ꬠZ = 2 dimers. In each series of dimers, one half of the dimer is crystallographically independent, the generators of the other half being twofold rotor (C2/c phase), mirror (C2/m phase) and inversion centre (P21/n phase) respectively.