A series of six-coordinate [Cu(L)L-1][BF4](2) (L-1 = 2,6-bis{1-oxyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-2-yl}pyridine) complexes are reported. Ferromagnetic coupling between the Cu and L-1 ligand spins is enhanced by an L coligand with distal methyl substituents, which is attributed to a sterically induced suppression of its Jahn-Teller distortion.