The crystal structures and s3.s5Cu NOR spectra are reported of the two-co-ordinated complex cations formed between Cu' and hindered pyridine homologues, [CuLJX [L = 2,6-dimethylpyridine, X = BF,-1, PF,-2 or CI0,-( a phase) 3, (p phase) 4, (y phase) 5; L = 2,4,6-trimethylpyridine, X = BF,-6 or CuCI,-71. All complexes have essentially linear N-CU-N fragments, but whereas for 1, 2, 4 and 6 the copper atom is located on a two-fold axis and the two pyridine rings have dihedral angles of 60.4, 56.0, 58.1 and 51.3" respectively, 3, 5 and 7 have essentially planar structures with dihedral angles of 0, 3.0 and 0" respectively. In agreement with a previous study of the planar complex 3, the CU-N bond is significantly longer than in the non-planar conformation, and the corresponding 63,65Cu NOR resonance frequencies are less.