The reaction of Pd(cod)Cl-2 (cod = cycloocta-1,5-diene) with 1 and 2 equiv. of rac-diphenyl[2.2]paracyclophanylphosphine, rac-PPh2(C16H15), affords the dimer [Pd{PPh2(C16H15)}Cl-2](2) (1) and the square-planar complex trans-Pd{PPh2(C16H15)}(2)Cl-2 (2), respectively. In solution the dimer undergoes a fluxional process which has been probed by NMR and involves isomerisation between pseudo-trans- and cis-conformations. The structures of trans -[Pd{Ph-2(C16H15)}Cl-2](2) (1a) and 2 have been established by single crystal X-ray diffraction; the structure of the dimer is severely disordered. In addition, co-crystals containing both these complexes and solvate molecules have been isolated and their structures established by single crystal X-ray diffraction. The structure of the monomer in the homonuclear and co-crystals are not too dissimilar whereas the structure the dimer has a significantly different structure in the homonuclear and co-crystals. In the homonuclear crystal the central Pd2Cl2 unit has a dihedral angle of 26.5degrees between the two planes whereas the Pd2Cl2 unit in the co-crystals is planar. (C) 2003 Elsevier B.V. All rights reserved.